AudioCircle
Industry Circles => Tortuga Audio => Topic started by: tortugaranger on 18 Jun 2022, 03:10 pm
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Hi All,
Development work is progressing on the new ePot.V4 series attenuator/controller. The V4 builds on the V3 keeping the core LDR control scheme the same (closed loop LDR current control), and same physical size, but with interesting changes & options that will hopefully keep costs down while delivering overall improved performance.
This is plenty to keep me busy and since I'm no longer designing/building finished preamps, I now have more time to focus on core components which is what I enjoy the most.
Here's an outline of coming attractions..
Input Switching - The V4 moves on from using analog switches (integrated circuit chips) and instead employs conventional miniature electro-mechanical relays. The analog switches worked well for the V3 but under certain circumstances would exhibit leak-thru behavior which oddly enough I could never duplicate here in my development rig no matter what I tried. Since the analog switch I was using is yet another semiconductor chip available only from one manufacturer, I decided that the V4 would use more conventional switching hardware while eliminating another often hard to find chip whose price has doubled. The downside to this decision is I could only squeeze 4 relays on the same real estate as the 6 analog switches. Sure, I could have made the board a little longer to accommodate 6 but few people really need/want 6 input channels and I wanted to keep the board dimensions identical to the V3 so retrofitting/upgrading would be easy.
Firmware Updating Port - The V3 uses a UART serial port for firmware updating. This worked fine, but to interface the V3 with a PC or MAC required an extra USB-to-UART conversion board or special cable which is frankly a PITA for both designers and users. The earlier V25 used a simpler direct USB port but when I designed the V3, I needed to eliminate the external crystal clock to free up some real estate for other things. But without the accuracy of a crystal clock, USB was no longer an option. With the V4, the crystal clock is back and so is the USB port.
PWM vs DAC - The V3 uses a 4-channel 16 bit DAC chip to generate the voltage setpoint to the 4 LDR (light dependent resistors) attenuator closed-loop current controllers. Over the past 2 years the cost of this chip has almost tripled and has become difficult to source reliably. Time to jettison yet another chip. Instead, the V4 employs 16 bit PWM (pulse width modulation) which is generated directly by the microcontroller together with external first order filters to smooth out the pulses. This change is arguably the biggest departure from earlier designs but should prove to be highly effective. I've yet to fully test this out but expect to be able to within the next month or so.
Plug-in Buffer Module - I've redesigned the stand alone SSPB.V2 Solid State Buffer board into a plug-in buffer module (board). It plugs right into the LDR module socket of the new V4 board. The LDR module then plugs into the buffer board. The buffer board essentially converts the V4 from a passive attenuator into a very compact solid state active attenuator that sounds just as great as the passive but with a touch more authority and punch. The new buffer module has its own built-in split voltage switch mode power supply that needs an external source of nominally 12 VDC power. When plugged into the new ePot.V4 board, the buffer module also powers the V4. But there are alternative power supply options as well. More on that in the next section.
Power Supply Options - There are several power options. First, like the V3, the V4 can be powered by a small split-voltage switching power board located on the underside of the main board that needs an external source of 12 VDC. Secondly, when a buffer module is plugged into the V4, the V4 is powered directly from the buffer board's split-voltage switching power supply which is a higher quality power source. A third option is a new stand-alone linear power supply board that is the same size as the V4 board and is powered from AC mains (120VAC or 240VAC - set by jumpers). Typically, the linear power supply board will sit next to the V4 board and there's a short 5 wire power cable that connects from the linear power supply to either the V4 by itself, or to the buffer board when present. When a V4 or buffer board is powered by the linear power supply, the V4/buffer board's own power supply components are excluded from the build. The advantage of the new linear power supply is the complete elimination of any high frequency noise/artifacts associated with switching power supplies resulting in the cleanest possible source of power for the V4 and buffer module.
Cheers,
Morten
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The first pic shows the layout of the ePot.V4 attenuator/controller prototype currently in development. The V4 is the V3 evolved.
The second pic shows the layout of the SSBM.V4 Solid State Buffer Module prototype also currently in development. The Solid State Buffer Module is a piggy-back board that plugs directly into the ePot.V4 converting the V4 from a passive to a solid state active attenuator built around the same op-amp buffer input stage and a discrete, direct coupled, JFET buffer output stage used in our earlier SSPB.V2 stand-alone buffer board.
The third pic attempts to show the solid state buffer module superimposed on top of the V4 attenuator/controller as it would appear when plugged into the V4. The LDR attenuation module would then plug into the buffer module resulting in a compact triple layer V4->Buffer->LDR sandwich. This is awkward to show 2 dimensionally but will be quite clear once I have actual boards/hardware.
Prototypes of these boards are on order. I hope to have working prototypes of both by the end of July.
(https://tortugaaudio.com/images/ePot_V4_proto1.jpg)
(https://tortugaaudio.com/images/SSBuffModule_prototype_RevA.jpg)
(https://tortugaaudio.com/images/ePot_V4_with_SSBuffer_proto1.jpg)
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Looks good. I am hoping to roll one of these into my pre!
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Looks good. I am hoping to roll one of these into my pre!
Prototype boards are in. Now I have to set aside some time to populate them and run through initial testing to assess operation and performance. Probably another week before I'm there.
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Hi All,
It's been about a month since my last update. I've had some time in the barrel with the V4 prototype board. Something is shorting out so clearly I need to resolve that before I can draw any conclusions sonically. While working through that, it became apparent that the existing V3 firmware code could use some tightening up prior to adapting it to the V4 hardware. That sent me down a 3 week rabbit hole during which I ended up re-writing an entire section of the code involving soft timers (timers not implemented within the microcontroller hardware). The soft timers are now closely integrated with the real time operating system (RTOS) that runs on top of the bare metal microcontroller.
For those curious about these things, using an RTOS allows various parts of the code to be segregated into separate tasks (threads) where each task executes kind of like a standalone program. Only one task runs at any point in time but the hand-offs of control from one task to the next happen so fast that it appears as though they are all running at the same time when in reality each runs for only 1-10 milliseconds before handing off control to the next task. This approach makes for a much smoother real-time interactive controller.
I will be gone for part of September on family business up north, so probably won't have any updates on the V4 prototype board for another 2-3 weeks.
I also got the new linear power supply prototype board up and running and it appears to be fine as is although I'll likely end up changing the interconnections between it and the V4 board as this work progresses.
Cheers, :thumb:
Morten
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Thanks for the update.
Wayne in Oregon.
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best wishes to you Morten through this weather! Keep us posted with your return to your shop,
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best wishes to you Morten through this weather! Keep us posted with your return to your shop,
Power is back as is the internet. I'm going to limit my comments on hurricane Ian and related matters to this one thread already started before the storm hit....https://www.audiocircle.com/index.php?topic=183359.0
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Have you been able to make any progress on V.4? I'm especially interested in the LPS.
Thanks,
Wayne in Oregon
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Have you been able to make any progress on V.4? I'm especially interested in the LPS.
Thanks,
Wayne in Oregon
I wish the answer was yes but the V4 has been sidelined since hurricane Ian. Between hurricane recovery and general ongoing support, the V4 has been on the back burner. Also, in preparation for evolving the V3 firmware for use in the V4 hardware, I've been doing substantial refactoring of the existing firmware code to improve stability and longer term maintainability. That is going well.
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Cool, Thank You so much. I thought that was the case with hurricane Ian but thought I would ask.
I will wait a few more months, I don't want to get V.3 then upgrade to V.4 a few months later.
Thank You,
Wayne in Oregon
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While I have a lot on my plate at the moment with our upcoming move to Oregon, I continue to chip away and evolve the V4 design. I'm really pleased with its evolution and in many ways I believe the V4 will ultimately benefit from a slower and more deliberate development cycle. That said, I've put together an article updating the status of the V4's development including information on both the buffer board and linear power supply that are being developed in parallel with the V4.
Here's a link to an V4 info article that I just posted: https://tortugaaudio.com/epot-v4-ldr-preamp-controller-stepped-attenuator-with-optional-plug-in-solid-state-buffer-linear-power-supply/ (https://tortugaaudio.com/epot-v4-ldr-preamp-controller-stepped-attenuator-with-optional-plug-in-solid-state-buffer-linear-power-supply/)
The pics below are PCB CAD layout snapshots of the V4, the plug-in solid state buffer board and the linear power supply. These are obviously not to scale. The buffer board is the same height as the 2.7 inch V4 but not as long. The linear power supply board is currently the exact same size as the V4 although that might change.
(https://tortugaaudio.com/images/V4_PCB_layout_1.jpg)
(https://tortugaaudio.com/images/SSBM_V4_PCB_layout1.jpg)
(https://tortugaaudio.com/images/LPS_V4_PCB_layout1.jpg)
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Thank You for the update, very cool :thumb:
I am going to get a cheap/used preamp for now and will wait for the V.4 to be available next year.
Thanks again
Wayne in Oregon
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I have been looking to upgrade from my V2.5, and I am very impressed with the V4 design, I can't wait to order it!
I especially like the relays, I am curious what relays will you use? It would be cool if you could use the ones that are powered only when switching, then stay in the position without having to be always powered on. (But it's not that essential really, rather finish the design sooner so that we can finally order!)
I am also curious about the buffer, I really like the idea to be able to use my own opamp! Especially good that it can be all packed into one neat assembly! 😊
Thank you and I can't wait to see the news!
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I have been looking to upgrade from my V2.5, and I am very impressed with the V4 design, I can't wait to order it!
I especially like the relays, I am curious what relays will you use? It would be cool if you could use the ones that are powered only when switching, then stay in the position without having to be always powered on. (But it's not that essential really, rather finish the design sooner so that we can finally order!)
I am also curious about the buffer, I really like the idea to be able to use my own opamp! Especially good that it can be all packed into one neat assembly! 😊
Thank you and I can't wait to see the news!
The relays used in the V4 design are 5 volt non-latching miniature low level signal relays. So yes, they are normally-open powered-closed relays. To make them latching requires 2 control signals to each relay and while it's possible to do so the price is a bigger board, a bigger chip, more signals, more components, more cost etc. I've been using these relays in various products for the past 10 years and have yet to note any degradation in the audio signals when the relays are powered on/closed. My guess is the EM field of the relay coil in these very small relays is sufficiently weak as to not matter. I concluded the extra cost/complexity of going with larger latching versions isn't justified. Please note that that is my personal view and not a statement of absolute truth regarding the virtues of latching relays. I've reached an age where anyone who wishes to argue with me is automatically right and I am happily wrong - have fun! :thumb:
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I've reached an age where anyone who wishes to argue with me is automatically right and I am happily wrong - have fun! :thumb:
Yep its just easier that way and then do whatever you were going to do :thumb:
Wayne in Oregon
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Thanks for the explanation Morten. Considering the compromises, I fully understand sticking to the non-latching and I am very excited to see the V4 coming to life ASAP!
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(https://tortugaaudio.com/images/EpotPi_V4_Pico.jpg)
Hi All,
Thought I'd share some updates on the evolution of the ePot.V4 Preamp Controller/Stepped Attenuator. There are 2 significant changes to the design since my last update.
The first change involves the choice of microcontroller.
I've been using ARM type micros made by STM for several years now and was planning on going with a newer STM chip for the V4 design which would minimize firmware changes. I'm still going with an ARM micro but not an STM. I've decided to go with an ARM based chip made by non other than the Raspberry Pi folks who introduced the world to super cheap single board computers that run on the Linux operating system. In fact, I'm adopting an entire Raspberry Pi Pico W board that plugs into the V4 board. The Pico uses the RP2040 ARM chip developed by Raspberry Pi. The Pico board has WiFi and Bluetooth on board which advances the possibility of going beyond only using an infrared remote. And given the competitive price point of the Pico, there are too many advantages to not go with it. As a result the V4 has shrunk in length from 4.4 to 4.1 inches. Firmware updating to the V4 will be simplified as well. When placed into firmware update mode, the entire V4 will act like any thumb drive. With it plugged into the USB port of a PC or a MAC, you'll just have to move a firmware update file on to the ePotPi "drive" to update its programming.
Adopting the Raspberry Pi Pico as a piggy-back micro board will drive a slight name change going forward. The ePot.V4 will now be known as the ePotPi.V4!! Get it? PotPi!! :thumb:
The second design change involves balanced audio.
With both the V25 and the V3, balanced audio configurations used a pair of controller boards with one designated as the primary (right channel) and the secondary acting as the left channel. Both boards were physically identical with each running on its own microcontroller. In hindsight, this created significant challenges keeping the secondary micro perfectly in sync with the primary. Basically two brains when only one is really necessary.
Going forward, the V4 design is adopting a special purpose balanced audio expansion board. The expansion board duplicates much of the hardware on the primary V4 board but it will not have its own microcontroller. A 14 pin ribbon cable will connect the V4 board to the expansion board allowing the primary V4 to control everything on the balanced expansion board. This will greatly simplify the software needed for balanced audio configurations.
Cheers,
Morten
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The news about balanced audio configuration is most welcome to me given what I have found with the V3 in balanced configuration.
So, 2024 looks really good to me!
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Interesting development Morten, I can't wait to see the V4 come to life, but I am curious about two implications of this new design change. Pico's onboard ADC is 12 bit, does this mean you are giving up on the idea of having 16bit ADC in V4? Also, is there a threat of potential RF interference from the Pico's onboard wireless and bluetooth chips?
Thanks!
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Interesting development Morten, I can't wait to see the V4 come to life, but I am curious about two implications of this new design change. Pico's onboard ADC is 12 bit, does this mean you are giving up on the idea of having 16bit ADC in V4? Also, is there a threat of potential RF interference from the Pico's onboard wireless and bluetooth chips?
Thanks!
The V4 will not be using the PICO's 12 bit ADC. The V4 has a separate dedicated 4 channel 16 bit ADC chip used only for calibration plus a 4 channel 12 bit DAC chip used for both LDR calibration and LDR control during normal operation. The V3 had the opposite - a 12 bit ADC and a 16 bit DAC. In hindsight, I believe accurate measurement is more important than more granular control provided the 12 bit DAC control is monotonic and repeatable which is it. I'm tweaking the LDR calibration algorithm somewhat as well to further optimize around the 12 bit DAC while taking full advantage of 16 bit ADC.
In the event using the PICO's WiFi or Bluetooth creates any problems, I simply won't use them. Initially they'll both be dormant until such time as I've come up with remote control solution that warrants their use.
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Hi All,
I just published the first working draft of the V4 Hardware Manual which is now available online in our online documents section via this link: https://tortugaaudio.com/docs/epotv4-max-hardware-manual/ (https://tortugaaudio.com/docs/epotv4-max-hardware-manual/)
As the V4 remains under active development, there will likely be numerous changes to the manual over the next several weeks until the V4 is finally released. But those curious about the details of the V4, it's a fairly comprehensive description of the V4 Max hardware so far.
Cheers,
Morten
P.S. We are currently having snowmageddon here in Bend, Oregon with probably a foot or more white stuff by tomorrow.
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Hi All, P.S. We are currently having snowmageddon here in Bend, Oregon with probably a foot or more white stuff by tomorrow.
Central Oregon will do that, then the sun will come out melt it and then Slushageddon! It freezes at night so then its Iceageddon and so on. lol Lived in the Bend area for 10 years or so. Back in the valley now. LOL
Wayne in Oregon
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Looking forward to when the V4 comes out, when it comes out. I can do balanced without issues then.
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Hi All,
I've now published a draft manual for the new optional plug-in V4 Solid State Buffer Module (SSBM.V4) that mounts directly to the new V4 Max board. Treat it as a working draft since changes are inevitable.
https://tortugaaudio.com/docs/epotv4-max-hardware-manual-copy/ (https://tortugaaudio.com/docs/epotv4-max-hardware-manual-copy/)
The buffer module converts the V4 Max from a passive preamp/attenuator into an active version with optional gain (up to +12 dB) by simply pugging the buffer module into the same socket on the Max as the LDR Module. Then the LDR Module plugs into the buffer module such that you end up with a 3-layer board arrangement that looks roughly like the diagram below.
The buffer module design is an evolution of my earlier stand alone buffer board which has been in circulation for the past 3 years or so and has performed well.
(https://tortugaaudio.com/images/V4_boards_stacked.jpg)
(https://tortugaaudio.com/images/Screenshot_BufferBoard_RevA.jpg)
(https://tortugaaudio.com/images/JFET_buffer_scheme_with_LDRattenuator.jpg)
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A fair summary of the past 8 months...
July-Oct: Sort, cull & pack up everything while getting rid of 2 cars and a boat while recovering from a Cat 5 hurricane
Nov: Drive from Florida to Oregon and then stuff everything into a garage plus a storage shipping container next to the house
Dec: Holiday time with family
Jan: Unpack and set up Tortuga Audio operations
Feb: Get back to working on the ePotPi.V4 LDR Stepped Attenuator & Preamp Controller
And that's how you blow through 8 months moving from Florida to Oregon.
With all that behind me, I'm now focused again on completing development of the V4. The good news is over 90% of the firmware is directly portable from the V3 to the V4 hardware. The bad news is the I'm using a whole new development toolchain (collection of software applications) together with the new RP2040 based Raspberry Pi PICO microcontroller board which means an obligatory learning curve.
I can happily report that the initial firmware port is now basically done and is now ready for functional testing and refinement. I'm moving on to the 2nd gen V4 board prototype and with a little luck may only require 1 more iteration beyond that before it's ready for production. This means there's a chance of ordering production hardware as early as April with release/availability by May. And this could easily slip by 2-3 months because it can.
Meanwhile, back to work.
Cheers,
Morten
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Thanks for the update. Glad to here you are settled in.
(Im)patiently waiting and saving my pennies for the V4 lol
Wayne in Oregon
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Hi All,
I'm opening up the V4 stepped attenuator & preamp controller for pre-ordering. Here's how the pre-ordering is going to work.
1) You can pre-order a V4 starting today, March 25.
2) You don't have to pay in full when you place the pre-order BUT you do have to pay a $50 refundable deposit.
3) There is no firm/estimated release date yet - May/June is achievable and I'm working towards that but no promises
4) Orders will be shipped in the order they came in - so FIFO (first in, first out).
5) When it's time to ship your order, you'll receive an invoice for the remaining amount due.
6) If you change your mind, your order will be canceled and the $50 deposit will be refunded in full.
The V4 product page is set up so that the default scope is: 1) a V4 board, 2) an LDR module, 3) an OLED display assembly, and; 4) an Apple compatible remote. You can opt out of items 2, 3 and 4 if you already have these items but you will need them. The OLED display assembly includes infrared receiver and encoder plus cabling. A 5V power supply is NOT provided but minimally you can power the V4 from any Micro-USB cable.
Any existing quad LDR Module from your V3 board will work with the V4.
Most older OLED displays (Rev C or later) will also work with the V4.
An existing silver/metal Apple remote will work with the V4.
Here's the link to the V4 product page: https://tortugaaudio.com/products/diy-preamp-components/epotpi-v4-max-electronic-stepped-attenuator/ (https://tortugaaudio.com/products/diy-preamp-components/epotpi-v4-max-electronic-stepped-attenuator/)
Please PM or email (morten@tortugaaudio.com) me with any questions.
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The V4 pre-order web page had a glitch which I believe has now been corrected. If you run into any problems, please let me know.
//Cheers | Morten
Hi All,
I'm opening up the V4 stepped attenuator & preamp controller for pre-ordering. Here's how the pre-ordering is going to work.
1) You can pre-order a V4 starting today, March 25.
2) You don't have to pay in full when you place the pre-order BUT you do have to pay a $50 refundable deposit.
3) There is no firm/estimated release date yet - May/June is achievable and I'm working towards that but no promises
4) Orders will be shipped in the order they came in - so FIFO (first in, first out).
5) When it's time to ship your order, you'll receive an invoice for the remaining amount due.
6) If you change your mind, your order will be canceled and the $50 deposit will be refunded in full.
The V4 product page is set up so that the default scope is: 1) a V4 board, 2) an LDR module, 3) an OLED display assembly, and; 4) an Apple compatible remote. You can opt out of items 2, 3 and 4 if you already have these items but you will need them. The OLED display assembly includes infrared receiver and encoder plus cabling. A 5V power supply is NOT provided but minimally you can power the V4 from any Micro-USB cable.
Any existing quad LDR Module from your V3 board will work with the V4.
Most older OLED displays (Rev C or later) will also work with the V4.
An existing silver/metal Apple remote will work with the V4.
Here's the link to the V4 product page: https://tortugaaudio.com/products/diy-preamp-components/epotpi-v4-max-electronic-stepped-attenuator/ (https://tortugaaudio.com/products/diy-preamp-components/epotpi-v4-max-electronic-stepped-attenuator/)
Please PM or email (morten@tortugaaudio.com) me with any questions.
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Hi Morton. When will the stackable active v4 buffer and power supply be available?
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Hi Morton. When will the stackable active v4 buffer and power supply be available?
I expect both to be available soon after the V4 production boards are ready to ship. The plug-in buffer module and the PS are mostly done. Need to do final testing on both once the final V4 prototype has been proven out.
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:thumb:
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Pic of latest V4 prototype board without any parts installed. With some luck, this may be the next to last iteration. Have already made some minor mods to this layout. Will be building and testing out this board next week.
(https://tortugaaudio.com/images/v4_prototype_bare_PCB.jpg)
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One thing I've learned the hard way (over and over again) is that the road to hardware/firmware development takes many turns and you never really know how long it will take until you actually arrive.
One of my objectives with the V4 has been to get away from having to use a very expensive and sometimes hard to find 4-channel 16 bit DAC chip. The 16 bit requirement is driven by the inherent behavior of LDRs when trying to regulate their resistance level in the high 10k's of ohms upwards of 100k. At these higher resistance levels, a very small change in control current translates into a big change in resistance (i.e. their gain becomes very large). This requires finer higher resolution control - hence the 16 bits.
Knowing this all too well, I still tried to get away with a low cost 12 bit DAC but was reminded all over again that the 16 bits used with the V3 build was indeed needed for a reason.
As a result I've opted to go with 16 bit pulse width modulation (PWM) instead of a 16 bit DAC. High resolution PWM doesn't require any special hardware and only requires 8 additional low cost passive resistors/capacitors for filtering. The PWM machinery runs as an independent peripheral within the microcontroller in parallel with with the firmware code.
Unfortunately, this requires yet another design/prototype iteration which means I have to wait until the first week of June to receive the updated boards that then have to be tested. So it goes.
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Hi All,
Time for a V4 update.
Here we are with June almost over and the V4 is still not ready for production/release. What gives?
Roughly 4 weeks ago, I came to the realization that there was no way to accomplish a key goal of the V4 design if I insisted on staying with the Raspberry Pi PICO/RP2040 microcontroller.
First, let's review a key design goal. To accommodate balanced audio requires 2 boards because balanced audio uses twice as many audio signals as single-ended. Prior designs (the V25 and V3) handled balanced audio by designating 1 of the 2 boards to be the primary (right channel) and the 2nd board as the secondary (left channel) board. Each board was otherwise identical with its own microcontroller running identical firmware. The primary handled all the controls and had to communicate what to do to the secondary board. In turn, the secondary board had to communicate key info back to the primary board. Simple conceptually but a bear to implement cleanly and reliably.
I decided that with the V4, there would be only a single microcontroller running everything on both boards for balanced audio. This meant that the secondary board would be physically different than the primary and that the primary would have to handle more input/output which translates into needing more pins on the microcontroller chip. The RP2040 has 56 total pins but only 40 are made available via the PICO board and not all of those 40 pins are for control signals.
So simply put, I realized late in the development process that I could not achieve this goal given the low pin count available with the RP2040. I quickly pivoted and decided to revert to using an STM32 microcontroller instead of the PICO. Both the V25 and V3 had used STM32 microcontrollers so I was very familiar with their quirks and challenges. I first tried a 64 pin STM32G4 chip only to realize it was still 1 or 2 pins shy of what was needed. So I bumped it up to an 80 pin model which handles everything with room to spare.
The good news is the code needed to run the STM32 is over 90% the same as the core code used in the V3 that had already been adapted for the V4 and the PICO/RP2040 chip. While switching from the PICO to the STM32 does not require reinventing the entire wheel, it does require a few additional weeks of concentrated work to adapt everything over. I've already put almost a month's effort into adapting the STM32G4 chip into the design. Work is progressing but it will be August by the time the V4 is ready for production. In short, this change has put me roughly 2 months behind my original schedule. :duh:
There are several advantages to this design evolution and a couple of drawbacks but the net benefits win out. It's a less complex design overall with fewer parts and arguably higher overall precision when it comes to LDR calibration and control. The V4 will now have 16 bit resolution on both the LDR current control circuit as well as the calibration measurement circuit. Prior designs used a mix of 12 and 16 bit resolution.
One unfortunate downside to this change is the elimination of built-in WiFi/Bluetooth communications. However, this feature can readily be added externally and linked with the V4 provided the necessary firmware is added to handle this - no small job but doable (future firmware upgrade would be needed).
So it goes.
Here's a screenshot of the updated V4 design with the STM32G4 microcontroller. Compared to the earlier design (shown below this pic), the updated design eliminates 3 complex external chips whose jobs are now all performed by the very capable STM32G4 microcontroller.
(https://tortugaaudio.com/images/V4_prototype_Screenshot-2024-06-25-104318-e1719337805275.png)
Below is a pic of the V4 with the earlier PICO/RP2040 microcontroller that proved too small for theapplication.
(https://tortugaaudio.com/images/Screenshot_V4_Max_Proto_RevB-1-e1719338027723.jpg)
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Thanks for this update. I eagerly await this new board so that I can go comfortably back to balanced operation.
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Any updates for an August release? Eager to get an upgrade to v4.
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(https://tortugaaudio.com/images/v4_prototype_making_sausage.jpg)
I’ve managed to chew up both July and August since my last update on the V4 so it’s due time for an update on the update.
Short version – the V4 is not ready yet.
Longer version. But it’s almost ready and I’m all but 100% certain that I will have production hardware in hand in October.
Elaborate version. As you may recall, I realized back in June that I would have to abandon using the Raspberry Pi Pico RP2040 microcontroller for the V4. Why? Because the Pico simply didn’t have enough pins for the job. Should I have known that going in? Perhaps. But development is a dynamic process and it teaches humility whether you like it or not.
Once I realized I had run out of micro real estate, I switched back to using an STM32 microcontroller albeit a newer and more powerful version that I had used in the V3. Fortunately, with the passage of time, the STM32 chips were finally widely available again after the Covid chip drought of 2020-2023.
With that decision made, I also made the decision to abandon the STM32 integrated development environment (IDE) software I’d used previously and adopt something that didn’t involve writing $1500 checks each year to a software company nor adopting a proprietary vendor toolset that would lock me into any particular vendor. Yes, that’s right, I was going rogue. And that meant an entire new IDE system for C/C++ embedded application development.
And that’s what I did for the entire month of July. I sorted through several free-to-low-cost IDE options, tried them out, cursed them out, flailed around a lot, cursed some more, and finally settled on one that sucked the least. If you have had any exposure to the world of embedded microcontroller IDEs, you know what I’m talking about. IDE’s mostly suck. Except when they don’t and make it possible to code, compile, upload, and debug your software in real time on actual hardware. But until you get one to work properly it’s a special kind of hell getting up each day and breaking your pick on the same rock day after day only to realize you’ve burned up the whole month of July simply getting your tool to work. But I did get it to work…finally.
In August I finally made actual progress bringing up the revised V4 board with the new STM32 chip. Except for one particular bug which seemed to defy gravity until I realized I had shot myself in the foot by installing too small a EEPROM memory chip that kept overwriting its data because there wasn’t enough memory space for what I was using it for. Only took 2 weeks to sort that out. More of that humility being taught again.
So what’s left to do? I’d like to believe it’s mostly just clean-up and fine tuning but we shall see. Most of the code is mature and stable at this point but the LDR calibration coding has been substantially revised and updated and needs further testing. I also believe the V4 hardware/board is only 1 iteration away from final with only minor tweaks needed between the current prototype and the production version.
If all goes well, I’ll be placing an initial order for production boards later in September and have the first batch of production boards in hand by October. If all goes well.
Oh, and the new optional linear power supply and optional active buffer boards are both pretty much done as well. Those both use 100% conventional analog parts with no microcontrollers – easy peasy – kind of.
Cheers,
Morten
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Hi All,
Just a quick note to say the V4 is in the home stretch. All major issues with the hardware have been resolved. The remaining work is mostly minor bugs and testing to identify/resolve surprise behavior. Two things are for sure at this point. #1 - the V4 sounds great! #2 - the V4 will be released before year end. Soon! Soon! :thumb:
Cheers,
Morten
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Pic of final prototype V4 build. Here the LDR Module has been unplugged from the V4 and is sitting next to the board. With the LDR Module removed you can see all the board parts normally hidden by the LDR Module. First batch of production boards are on order.
(https://tortugaaudio.com/images/V4_board_with_detached_LDRModule.jpg)
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The V4 board with installed LDR module with most of the components annotated
(https://tortugaaudio.com/images/V4_board_annotated.png)
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Still have a ways to go yet but the V4 hardware manual has just been substantially updated to reflect the final prototype.
The V4's manual is now fairly verbose and goes into more detail on the basis of design and fundamentals than earlier versions.
Here's the link to the ePot.V4 hardware manual: https://tortugaaudio.com/docs/epotv4-max-hardware-manual/ (https://tortugaaudio.com/docs/epotv4-max-hardware-manual/)
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Here are several photos of the V4 board with the Solid State Preamp Buffer module. The first photo is the buffer module by itself without the LDR module installed. All the rest show the buffer module installed on the V4 board with the LDR module included.
The buffer module is entirely optional but will convert the passive V4 into an active preamp volume/controller with adjustable gain from unity to +12 dB using plug-in gain modules. I'm still tweaking the buffer module design so it's likely the V4 will be released first with the buffer module to be released some time later.
(https://tortugaaudio.com/images/SSPB_V4_board.jpg)
(https://tortugaaudio.com/images/V4_board_with_SSPB_vertical.jpg)
(https://tortugaaudio.com/images/V4_board_with_SSPB_front_vertical.jpg)
(https://tortugaaudio.com/images/V4_board_with_SSPB_rear_vertical.jpg)
(https://tortugaaudio.com/images/V4_board_with_SSPB_right_horiz.jpg)
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The Tortuga Audio website has a new home page and is all about the new and soon to be released ePot.V4 LDR stepped attenuator & preamp controller. Check it out!
https://tortugaaudio.com/ (https://tortugaaudio.com/)
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Hi All,
Early Nov development update.
Overall things are finally coming together on the V4 development front and we are on track for releasing the V4 before year's end. But there's always something. I noticed that when I upped the gain to 12 dB on the buffer module, that there was a noticeable low level hum coming from the speakers. That started a search for the cause. After challenging every aspect of the buffer board design, and the V4 board itself, the ultimate cause of the noise was the OLED display. Essentially the same OLED display I've been using for several years now. Turns out the hum was always there but it wasn't until the buffer board amplified it that it became an audible issue. I'm actually a bit perplexed that I hadn't noticed this sooner.
So I took a deep dive into the OLED display itself and discovered that the OEM controller for the display, which runs off of 3.3 volts from the V4 board, has its own dc-dc switching boost converter that generates 12 volts used internally to refresh the OLED display screen. This converter is the cause of the 100-200 hertz noise. Turn off the OLED display and the noise goes away completely because this converter turns off as well. After evaluating corrective options, I'm going to add an isolated power converter to our OLED interface board. The isolated power converter converts 3.3 volts into 3.3 volts with its own independent ground separate from the V4 itself. This will prevent any OLED noise from traveling upstream into the V4 controller and the buffer board (if one is present).
This will require one more iteration on the OLED adapter board design which will likely take until mid-November before I have updated hardware on hand and am able to test out the fix.
Aside from this issue, the V4 board design is done and I have production blanks on hand already. I may tweak the buffer board and linear power supply board designs slightly and order updated blanks on those too while we wait on the OLED adapter updates.
Almost there,
Morten
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Hi All,
Mid'ish November development update.
I had been chasing a source of low frequency hum in the 100-200 Hz range which I'd traced to the OLED display as a source. However, I also determined that this noise only manifested when I had the optional active buffer board plugged into the V4 board. No such hum is present when using the V4 board alone as a passive attenuator. After numerous attempts to isolate and eliminate the active buffer hum, I finally arrived at a fix by isolating the split +/- 12 volt power and ground used by the buffer. Isolating the buffer ground from the power that runs the V4 board and the OLED board did the trick. No more sneaky ground loops. This fix is easily accomplished through the use of isolating switching DC-DC regulators.
That got me thinking about the linear power supply and after some last minute testing and research I made the decision to change the optional stand alone power supply board from a classically linear design to a hybrid switching-linear design. The hybrid PS can be powered either from 90-250 VAC 50/60Hz mains or your own external source of 5 volt DC power. AC mains power produces raw 5 VDC via a switching AC-DC converter. Regardless of the source, the raw 5 VDC drives 2 different isolated DC-DC boost converters with one producing split rail +15/-15 volt DC power and the other producing a single rail of +9 volt DC. All of these DC voltages are on an isolated ground. All three switching voltages are then run through separate second stage linear regulators resulting in clean low noise +12/-12 and 5 volt regulated DC power. The result is the best of both worlds with effectively zero low frequency ripple with no hum, and with most of the higher (above audible) frequency switching noise significantly suppressed by the linear regulators and bypass caps. An added benefit of the hybrid approach is significantly reduced weight and size.
Meanwhile I've started production of the main V4 boards and expect to begin shipping V4 product by early December. Finally! :thumb:
To clarify, only the V4 Max board, the OLED display, and the optional V4 buffer board will start shipping initially. A Mini version of the V4 will come later in 1Q25. The new hybrid PS board will lag the V4 by a few weeks since I'm still finalizing changes to its design per the above.
Cheers,
Morten
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Are you ready to begin taking orders for an upgrade to my LDR3000x.V3 at this time? I've been having issues with it intermittently shutting down and as of right now its just collecting dust so can ship to you at your convenience.
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Are you ready to begin taking orders for an upgrade to my LDR3000x.V3 at this time? I've been having issues with it intermittently shutting down and as of right now its just collecting dust so can ship to you at your convenience.
The short answer is yes eventually but not yet. Most 3000 series preamps are balanced. However, the left channel V4 board is a special expansion board rather another full V4 board. I have yet to finalize and finish testing of the V4 expansion board but that will get done in 1Q25. For those with single-ended Tortuga preamps, I will start taking orders for upgrading any of those to V4 soon after release of the V4 and getting the backlog of pre-orders out the door.
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Hi All,
Quick update for anyone interested in reading more about the new V4 preamp controller. I've just finished editing both the hardware and operating manuals for the V4.
You can find them via the links below.
Operations & Control Manual here: https://tortugaaudio.com/docs/epot-v4-operation-control-manual/ (https://tortugaaudio.com/docs/epot-v4-operation-control-manual/)
Hardware Manual here: https://tortugaaudio.com/docs/epotv4-max-hardware-manual/ (https://tortugaaudio.com/docs/epotv4-max-hardware-manual/)
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I am pleased to announce that the V4 LDR attenuator & preamp controller is now available and shipping has begun on our backlog of pre-orders.
Here's the link to the V4 product page: https://tortugaaudio.com/products/diy-preamp-components/epotpi-v4-max-electronic-stepped-attenuator/ (https://tortugaaudio.com/products/diy-preamp-components/epotpi-v4-max-electronic-stepped-attenuator/)
The V4 itself, the optional new solid state buffer board, the updated OLED display, and the new Function remote, are all available for order now.
The optional power supply for the buffer board plus the V4 expansion board for balanced audio applications will both be available early next year.
Cheers,
Morten
Photo of the V4 board with the optional buffer board installed.
(https://tortugaaudio.com/images/V4_board_with_SSPB_rear_vertical.jpg)
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Now that the V4 Max board has been released, I'm now close to finalizing the layout of the smaller V4 Mini.
THE big difference between the V3 vs. V4 Mini is that the V4 Mini retains full LDR calibration capabilities - same as the Max.
The key differences between the V4 Max and Mini are:
1) Mini is only a single input device (no input switching)
2) Mini is for single-ended audio only (no balanced audio)
3) Mini has built-in encoder - can be panel mounted same as a volume pot
4) Mini is 50% physically smaller (board area) than the Max
(https://tortugaaudio.com/images/V4_mini_proto_layout.png)
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Morten, check your email and voicemail. I’ve left you messages with no response.
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Morten, check your email and voicemail. I’ve left you messages with no response.
Apologies for letting this fall between the cracks. Check your PM later today.
Regards,
Morten
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Now that I'm almost caught up with V4 pre-orders and a handful of V4 upgrade projects with older version preamps, I was able to finally launch the V4 firmware updating manual in the V4 online documents. While I've tested this method and verified it works on my end, it remains untested by customers. I will be getting customer feedback next week from at least one person who I know will be trying this.
V4 firmware update manual: https://tortugaaudio.com/docs/epot-v4-firmware-updating/ (https://tortugaaudio.com/docs/epot-v4-firmware-updating/)
With any new model, there's always an initial flurry of mostly minor firmware updates/fixes over the first few weeks of release. The V4 has been no exception. So far, there's only one significant change in the firmware that warrants all early adopters update their V4 boards to firmware version 1.0.6 or later. Rev 1.0.6. adds watchdog timer safety feature that forces the controller to reset itself safely should the processor every freeze or encounter a fault. That feature was unfortunately left out of earlier versions.
I'm pleased that initial customer feedback on sonic performance has been all super positive. While I'm certainly biased, there's no doubt in my mind that the V4 is THE most satisfying LDR based attenuator/controller to listen to that I've ever designed/sold. :thumb:
Regards,Morten
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So I just got back my LDR3000x Active Tube upgraded to V4 and I have to say it sounds fantastic. Great work Morten! By the way, I swapped out the tubes with a pair of Amprex 7308s and am quite blown away. I know they are pricey and rare, so I will only use them on special occasions. I also have a pair of PHILIPS PCC88 (7DJ8) but unsure those are compatible with your preamp as your page doesn't reference them. Hoping I can get an answer on this, thanks!
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Hi Hikmer. Morten if your reading this. Are you able to upgrade the LDR3000t with the new boards?
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So I just got back my LDR3000x Active Tube upgraded to V4 and I have to say it sounds fantastic. Great work Morten! By the way, I swapped out the tubes with a pair of Amprex 7308s and am quite blown away. I know they are pricey and rare, so I will only use them on special occasions. I also have a pair of PHILIPS PCC88 (7DJ8) but unsure those are compatible with your preamp as your page doesn't reference them. Hoping I can get an answer on this, thanks!
Hi. Sorry for the slow response. Just got back from 2 weeks in Scandinavia and am still in the process of adjusting. I do not care for those 12 hour flights and the 9 time zones.
Glad you're liking the V4 upgrade. Your LDR3000x was one of only a few that got built right before I stood down from building new preamps. As part up the V4 upgrade I did a redesign of the power supply board which I was never quite happy with earlier. I also had to do a minor update to the tube buffer board to fit with the V4 controller but made no basic design changes to the tube buffer circuitry. The combination sounded really sweet on my end. I was very pleased with the results.
Pretty much any of the 9 pin 7DJ8/6DJ8 family tubes will work including 6922, 7308 etc. I believe the 7DJ8 run a 7 volt heater rather than the more typical 6.3 volts which the LDR3000x uses for the 6H30P and most other such 9 pin tubes. Heater current is often a key limiting factor in swapping various 9 pin tubes around but since the 6H30's use a higher current than all those other tubes, the LDR3000x will run on them. Now whether they sound better or not than the 6H30 is open for debate since the tube circuit used in the LDR3000x runs at a very odd 30V "slack" plate voltage instead of the typical 300-600 volt range typical of most tubes. That this works at all is due to the linearity of the 6H30's at very low plate voltages and where the gain of the tube circuit is minimal. After all, the tube circuit in the LDR3000x is a 2 stage buffer with little to no gain so gobs of plate voltage simply aren't needed. You'll get pushback from tube people on this point but you've listened to it and it definitely does not suck! Not all otherwise compatible tubes will perform their best under similar off-spec plate voltage conditions compared to the 6930's but what rolling I did do back when didn't sound bad either.
Cheers,
Morten
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Hi Hikmer. Morten if your reading this. Are you able to upgrade the LDR3000t with the new boards?
The short answer is yes but not quite yet. The LDR3000T is designed for a mix of single-ended and balanced audio so it needs a balanced LDR attenuator/controller. The V4 will handle balanced but not yet because the special V4 expansion board is not ready yet because simply haven't finished the work yet. It's next on the primary to-do list. The balanced version of the V4 does not use 2 V4 boards like the earlier V3s and V25s. The V4 system uses only 1 primary V4 board that handles single-ended and also the 2 phases of the right channel. A secondary V4 expansion board handles the 2 phases of the left channel. The primary V4 has a single microcontroller that handles everything while the expansion board has none is fully controlled by the primary board. I expect to finish out the design and testing of the V4 expansion board this month and have it ready in April.
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Here's the PCB layout for the V4 expansion board which is used together with primary V4 board for balanced audio applications. The expansion board has essentially the same layout and key control circuit as the primary board but is "headless" meaning it has no brain of its own. It's controlled entirely by the primary V4 board. In balanced audio applications the primary V4 board handles the right channel while the expansion board handles the left channel thus 4 total channels for balanced stereo attenuation.
The expansion board connects to the primary V4 board via a 14 pin ribbon cable. It's also 1 inch shorter but has the same width.
I'm waiting on blank boards from the fabricator which should be here in another week or so but what with all the tariffs and trade war noise there's a lot more uncertainty in shipment timing.
(https://tortugaaudio.com/images/V4_expansion_screenshot_1.png)
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Heh All,
I've been iterating on the design of the HPS.V4 Hybrid Power Supply and believe I'm all but done with the development work and am waiting on latest boards back from the fabricator. Meanwhile I took a few simple Input/Output readings to indicate overall performance. In this specific instance, the input to the HPS.V4 is from a typical 5 volt USB switching charger. Not the worst I've seen but not the best either. I'm showing the before/after (input/output) taken at both 1 ms (1000 Hz) and 100 us (10 kHz). Clearly there's more high frequency noise but this is to be expected with switching power supplies. This info was taken using a common LM1117 5 volt linear voltage regulator. Better performance is possible with a super-regulator such as the one made by Sparkos Labs.
The vertical units are in millivolts and the horizontal units are time.
Here's the AC component of the raw 5 volt input to the HPS.V4 at 1000 Hz. Not terrible - a few millivolts.
(https://tortugaaudio.com/images/5volt_noise_before_1ms.png)
Here's the AC component of the 5 volt output from the HPS.V4 - at same 1000 Hz. Dead quiet at lower frequencies - well under a millivolt.
(https://tortugaaudio.com/images/5volt_noise_after_1ms.png)
Next we take the same before/after look but with the sampling set higher at 100 us or 10,000 Hz.
Here's the raw 5 volt input. Clearly more noise at the higher frequencies but in absolute terms not awful at around +/- 10 millivolts.
(https://tortugaaudio.com/images/5volt_noise_before_100us.png)
Below, you see what the HPS.V4 does to the above waveform. Roughly a 10:1 reduction in noise magnitude.
Overall a very decent noise profile for a nominal 5 volt DC supply.
(https://tortugaaudio.com/images/5volt_noise_after_100us.png)
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Morten, you have a PM from me.
Randy