ePot.V3 Max & Mini Stepped Attenuators & Preamp Controllers

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tortugaranger

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I'm pleased to announce that Tortuga Audio is developing the LDRPot.V1 Stepped Attenuator. The LDRPot is intended as a LDR based drop-in replacement/alternative to stereo potentiometers and stepped attenuators.

The LDRPot is an active development and as such is subject to change as we go through the final stages of finalizing the design.

I've published a summary article on the LDRPot which can be found here: https://www.tortugaaudio.com/ldrpot-stepped-attenuator/

I'll provide more info on this as things evolve.

Comments and suggestions are always welcome.

The pic below shows the LDRPot main board with the smaller LDRPot LDR module shown both by itself and superimposed on the LDRPot main board. The main board is 2.9 inches long by 1.3 inches tall.

« Last Edit: 15 Jul 2020, 01:52 pm by tortugaranger »

WC

Re: LDRPot.V1 Stepped Attenuator
« Reply #1 on: 14 Nov 2018, 01:33 am »
Looks interesting. I might use this on a headphone amp instead of a pot.

happyrabbit

Re: LDRPot.V1 Stepped Attenuator
« Reply #2 on: 16 Nov 2018, 02:22 am »
thank you for sharing   :thumb:   

suggestion -   placement might be a bit easier if the encoder is cabled instead of mounted to the board..   just a thought.  ymmv

Dwight

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #3 on: 16 Nov 2018, 01:33 pm »
thank you for sharing   :thumb:   

suggestion -   placement might be a bit easier if the encoder is cabled instead of mounted to the board..   just a thought.  ymmv

Dwight

What you're describing is essentially our existing LDR.V25 (the "V25") Preamp Controller which has to be mounted on standoffs with a cable connection to a separate panel mounted encoder. The V25 has input switching (up to 6 inputs) and built-in LDR calibration which the LDRPot does not have.

The idea behind the LDRPot is a smaller, simpler, lower cost option that conveniently mounts directly in a front panel and thus doesn't require a mounting space footprint on the enclosure floor.

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #4 on: 27 Nov 2018, 03:46 pm »
We just got our first round of LDRPot prototype circuit boards. Here you see the smaller LDRPot Module board above the LDRPot Main board. The LDRPot Module board will plug into the LDRPot Main board. I included a US penny as a size reference (19 mm in diameter). The LDRPot Main board uses the same new design as our V3 Preamp Controller which is in parallel development. We'll be using a variation of the V3 as an in-house calibrator to calibrate the LDRPot Modules since the LDRPot Main board does not have its own built-in calibration.


WC

Re: LDRPot.V1 Stepped Attenuator
« Reply #5 on: 6 Dec 2018, 03:14 am »
So looking at the board, this looks like it is for unbalanced stereo connections only? Is there a way to use it with balanced connections?

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #6 on: 6 Dec 2018, 03:20 pm »
So looking at the board, this looks like it is for unbalanced stereo connections only? Is there a way to use it with balanced connections?

You are correct in that the LDRPot board as shown is for unbalanced stereo.

As with our current LDR.V25 Preamp Controller, to implement balanced volume control you need 4 channels, or 2 boards, with one board acting as the primary control interface which communicates to the secondary board to keep them both in sync.

I fully expect the final LDRPot design to be configurable for balanced audio. That will require a 2nd LDRPot main board with its own 2 channel LDR module be attached to the underside of the primary LDRPot main board. The secondary board will need 4 connections to the primary board; power, ground and a 2 wire serial data link. I'm hopeful those can be made with a direct board-to-board pin link but worst case you end up with a 4 wire square pin cable connecting the 2. Of course the secondary board will have its own screw terminal header for its own 2 channel balanced signal.

We have a few iterations to go through before the LDRPot is ready for release. We are developing the LDR.V3 Preamp Controller in parallel with the LDRPot where the LDRPot will be a simplified variant of the LDR.V3.

happyrabbit

Re: LDRPot.V1 Stepped Attenuator
« Reply #7 on: 22 Jan 2019, 05:57 pm »
Any updates ?  Also what are the dimensions for the encoder shaft / mounting hole ? 

Thanks

Dwight   

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #8 on: 22 Jan 2019, 07:52 pm »
Any updates ?  Also what are the dimensions for the encoder shaft / mounting hole ? 

Thanks

Dwight

The encoder shaft will require a nominal 0.3 inch diameter panel hole (could be a bit larger if you like) and the shaft is standard 6 mm. The panel hole size could change but not likely. Shaft size is fixed.

Development of the LDRPot is running in parallel with the LDR.V3 Preamp Controller. The V3 will become the de facto LDR Module programmer for the LDRPot's LDR Module. Both the V3 and the LDRPot will use the same plug-in LDR Module board. Unlike the V3, the LDRPot will not have its own built-in LDR calibration and it won't have input switching. Another key difference between the V3 and the LDRPot is the V3 will have an isolated control system ground whereas the LDRPot will not. The V3 is in its 4th or 5th prototype iteration and is hopefully close to the end of its development cycle. Once that's basically done, the LDRPot will follow closely behind the V3 since it will be a stripped down version of the V3.

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #9 on: 13 Feb 2019, 04:50 pm »
I've been getting numerous inquiries regarding the status of the LDRPot so here's a short update.

The LDRPot and the V3 version of our preamp controller board are in parallel development. The LDRPot will effectively be a variant on the V3 with the key differences being: a) no built-in LDR calibration, b) no input switching, and; 3) an encoder mounted directly to the board itself. The LDRPot will be commensurately way smaller than the V3 board in keeping with its being mountable directly to a front panel just like a volume pot or conventional stepped attenuator.

The LDRPot and the V3 will share the same new plug-in 4-LDR module board. Thus the V3 will be the de facto calibrator board for the new 4-LDR module board used by the LDRPot.

We are several iterations deep on the V3 design (plus a couple deep on the LDRPot itself) with the latest V3 build board due back from fabricator later this month. Once the V3 design is complete it will be a short hop to finishing the LDRPot. Timing on all that is iffy but I'm thinking April/May is doable but I'm usually wrong when guessing on this stuff.

More info to follow as we  get closer to release.

Cheers,   :thumb:
Morten
« Last Edit: 21 Feb 2019, 09:21 pm by tortugaranger »

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #10 on: 6 Jun 2019, 09:04 pm »
Wow. Where did the time go!!?? This week we inch ever closer to the launch of the LDRPot but first things first which means we need to finalize the design details of the V3 preamp controller. The latest V3 prototype boards arrived this week and over the next few days we'll be building and testing the latest V3 design iteration. There's a key go-nogo aspect to the V3 design that we need to get past and the latest iteration should get us past this development milestone. I sure hope so. It's been several month longer than I'd anticipated but what else is new....things take twice as long (or longer) and cost twice as much (or more!). Keep in mind that the V3 will be the LDR calibration board for the 4-LDR plug-in LDR module used by both the V3 and the LDRPot. Hence the road to the LDRPot goes right through the V3. Road trip!!!  :thumb:

mrderrick

Re: LDRPot.V1 Stepped Attenuator
« Reply #11 on: 2 Sep 2019, 05:02 pm »
How's the progress going on the attenuator?

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #12 on: 3 Sep 2019, 12:56 pm »
How's the progress going on the attenuator?


July, August and Sept are being chewed up by our work on the new LDR3000T Tube Preamp. As soon as we release the LDR3000 in mid September we'll start turning our focus back on the V3/LDRPot development. We don't have  that much work left to do on the V3/LDRPot but rather than dilute our efforts we are concentrating on the tube preamp first.

mrderrick

Re: LDRPot.V1 Stepped Attenuator
« Reply #13 on: 31 Dec 2019, 10:16 pm »
Are we going to see this in 2020?

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #14 on: 2 Jan 2020, 02:11 pm »
Are we going to see this in 2020?

In a word...yes. We continue to actively work on this and related products. No small part of the delay  in getting this done is a series of decisions that include: a) moving to a new software development toolchain with a steep learning curve, b) converting the existing firmware over to running  within a real time embedded operating system (FreeRTOS), and c) selection of a new model microcontroller that will greatly simplify firmware updates including wireless over-the-air updating. Not surprisingly that slowed us down considerably but they were the right decisions to make longer term. Still not willing to commit to a date but a first quarter release date is possible.

CL418

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Re: LDRPot.V1 Stepped Attenuator
« Reply #15 on: 4 Jan 2020, 05:07 pm »
Thank you for the update...

My specific interest is to replace a motorized Blue Velvet volume control in my existing preamp.  You may have answered this already - will the necessary hardware fit into that kind of space?  I can mount a small board or ancillary device nearby, if it is on a cable connection.

Again, thanks for the update, CHRIS

tortugaranger

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Re: LDRPot.V1 Stepped Attenuator
« Reply #16 on: 23 Jan 2020, 03:49 pm »
Thank you for the update...

My specific interest is to replace a motorized Blue Velvet volume control in my existing preamp.  You may have answered this already - will the necessary hardware fit into that kind of space?  I can mount a small board or ancillary device nearby, if it is on a cable connection.

Again, thanks for the update, CHRIS

Hi Chris,

My tech just reminded me that we did not respond to your question so apologies for the delay in getting back to you.

The ePot (as we're calling it now) is approximately 2.9 inches long by 1.35 inches wide. At one end there's an encoder mounted to the board that  is pretty much flush with end of the board so the encoder/board would butt up against the face of any panel it's attached to. Like a pot, the encoder is threaded so the encoder/board is retained via a nut and washer in a panel. The board thickness is approximately 0.75 inches with the thickness due to the mother board having a plug-in LDR module daughter board.

It's conceivable that the final design may be a tad shorter than 2.9 inches but if so only by maybe 1 or 2 tenths of an inch.

The board does have a 2x7 pin header to which you could attach our optional OLED display which itself has a connection header for an external encoder. If you don't want to use an OLED display or can't fit/mount the board directly to the panel where your existing pot resides, you can connect an external encoder to the board via the same 2x7 header using only 2 wires instead of the full 14 pin OLED ribbon cable. This  way you could mount the board somewhere nearby. It does have  2 mounting holes in opposite corners for mounting via standoffs.

Cheers,
Morten

tortugaranger

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Re: ePot Max & Mini Stepped Attenuator & Preamp Controllers
« Reply #17 on: 10 Mar 2020, 10:45 pm »
Hi All,

Over a year ago I introduced the development of what we were calling the LDRPot, essentially an electronic potentiometer (volume control) that you can use instead of a pot or mechanical stepped attenuator. A year later this work has taken us down some rabbit holes and dead ends but with each iteration things have gotten more interesting and compelling.

The purpose of this post is to give you a brief update on this effort and give a sneek peek into what’s coming as a result. To the inevitable question of how soon and how much I’m going to disappoint and only say as soon as we’re ready.

More info will be forthcoming as we get closer to release. I apologize for the long development cycle on this stuff but we’ve gone through numerous iterations and have made big changes in both the hardware and the software along the way and all of that has taken an enormous amount of time and effort.

The drawing included below shows the relative sizes of the boards discussed herein.

Re-introducing The ePot – The LDRPot is now the new ePot and the ePot is more than the LDRPot. Bear with me as I elaborate on that. The ePot, as the name suggests, is effectively an electronic potentiometer that works in discrete steps (100 – 127) over a 60 dB range. More than just an alternative volume control device it can also serve as an overall preamp controller. 

The ePot MAX – The MAX is essentially the next generation iteration of our current V25 preamp controller board. It can serve as a stand alone passive preamp with input switching (up to 6 inputs), visual display  driver for an external (256x64) OLED display and provides both remote and manual control. Anyone familiar with our existing LDR.V25 preamp controller and preamps will recognize all this. The new ePot MAX will be the same width at the V25 but is 23% smaller at 4.4 inches long vs. 5.7 or roughly 1 inch longer than a deck of playing cards. There are 3 significant changes to the ePot Max compared to the current V25:  1) the use of analog switches instead of LDRs for input switching/isolation; 2) completely redesigned LDR control system using precision closed loop current control rather than open loop voltage control; and 3) ability to use either a plug-in LDR (light dependent resistor) attenuation module or a new 127 step discrete thin-film resistor attenuation module. The same MAX board will operate with either of these plug-in attenuation boards.

The ePot Mini – The Mini is a shrunken version of the MAX and at 1.35 x 2.9 inches is 1/3rd the size of the MAX or a bit smaller than a typical credit card. The key functional differences are that the Mini has no input switching and has a volume control encoder mounted directly to the board. Thus the ePot Mini can literally replace any existing panel mounted volume control pot or stepped attenuator. If you want to add remote control and a visual OLED display the Mini can do that too. And just like the MAX the Mini accepts either plug-in attenuation module types – LDR or discrete thin-film resistor. A final key difference from the MAX is the Mini can not re-calibrate the LDR module although you can take any LDR module already calibrated by a MAX and plug it into the Mini and go.

The LDR Attenuation Module – The LDR module is a small 0.75 x 1.55 inch board with 4 embedded LDRs that plugs into either the ePot MAX or Mini and provides 100 step 2 channel (stereo attenuation) over a 60 dB range.  It contains its own EEPROM memory chip that stores the calibration data of each LDR. You can use an ePot MAX to calibrate the LDR module if needed or you can purchase a discounted replacement LDR module from us provided you return the original module which we will then refurbish.

The Discrete Resistor Attenuation Module – The Discrete module is a 1.35 x 1.65 inch board that also plugs into either the ePot MAX or Mini. It provides 127 step 2 channel (stereo attenuation) over a 60 dB range. Unlike an LDR module it never requires calibration but its impedance is fixed. If you need a different impedance attenuator you’ll need a module built to that impedance spec.  This modules uses 28 discrete thin-film resistors that are switched using very low-noise analog switches.

In order of appearance from the top down, here are printed circuit board prototypes for the ePot MAX, the ePot Mini, the Discrete Module and the LDR Module.
« Last Edit: 11 Mar 2020, 05:46 pm by tortugaranger »

tortugaranger

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Hi All,

We just posted an article on the ePot.V3 & ePot.V3 Mini. Here's the link: https://www.tortugaaudio.com/new-epot-v3-to-be-released-soon/

As things stand now I  expect to release the V3 before the end of May (this year  :lol:)

Cheers,
Morten

tortugaranger

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Here is a side-by-side close-up view of the new ePot.V3 board with the plug-in LDR attenuation board on the left and the new plug-in discrete attenuation board on the right. Both plug-in modules plug into the same audio & control headers. Both will also plug into the smaller ePot Mini board. The larger/wider discrete attenuation board is the same width as the ePot Mini board ( Mini not shown here).

Note the single chip next to the 4 LDRs in the LDR attenuation module. This is the EEPROM memory chip which remembers the calibration data for each LDR that is used to normalize the behavior of each quad of LDRs (no pre-matching of LDRs required).

On the larger discrete attenuation module on the right, the big chip in the center is an I/O expander with serves as a control pin extension to the microcontroller in lieu of having to add 14 more pins/signals to the module header. This chip communicates with the microcontroller via a high speed SPI serial data link.  The 14 smaller chips are the low noise analog switches each with a total harmonic distortion spec of 0.004%. The rest of the hardware are the 30 nickel-chromium thin-film resistors that provide the dual 7 stage logarithmic attenuation ranging from 0.5 dB to 32 dB per stage for both the left and right channels for a total of 127 steps over a 0 to -63.5 dB attenuation range.

The plug-in LDR board is done and we already have production blank boards on hand for those. The discrete attenuation board is going through one more round of prototyping since we needed to rearrange the thin film resistors to run N-S rather the W-E (or left to right) as shown in the pic. Hopefully this will be the last round. The plug-in attenuation boards are turning out to be a nice concept and have proven easy to remove and replace even though there are 2 sets of pins on either end of the modules that plug into 2 different header sockets.

Although you can't see the whole ePot.V3 board itself in this pic, the board design is essentially done (can you spot the main board error workaround?)  but we have yet to order production boards in the event we stumble across some last minute issue but will probably be ordered soon. The very last thing we'll order is the smaller ePot.Mini board since it is effectively a subset of the full size ePot.V3 and we want to freeze the ePot.V3 first before finalizing the Mini.

On the software side of things, I'd like to think we're 95% done with that but that last 5% can sometimes be a bear. Despite all the changes going from the V25 to the V3, I'd say 90% of the software was a direct port over from the V25 so I think it's fair to say the V3 firmware will actually start off quite mature.

As things stand right now we remain on track for a May release but too soon to say early vs. late May.

Cheers,
Morten