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)