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LDR Volume/Preamp Controller with 256x64 OLED Display & Remote
LDR Volume/Preamp Controller with 256x64 OLED Display & Remote
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Old 26th May 2019, 05:01 PM   #1
CaptainWatt is offline CaptainWatt  United States
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Default LDR Volume/Preamp Controller with 256x64 OLED Display & Remote

Starting a new thread focused solely on our DIY preamp components with emphasis on our LDR preamp controller and related items for the DIYer.

Tortuga Audio's latest offering is the LDR.V25 Preamp Controller together with a 256x64 pixel white-on-black graphical OLED display module with encoder and apple remote. This is our 4th generation design. We use this same hardware in our commercial preamp product line.

The firmware is mature at this point with occasional minor bug fixes and/or tweaks but will remain proprietary hence we don't share the source code. The V25 runs on an ARM Cortex M3 microcontroller and is programmed in C. Updated hex code files can be downloaded from our website and uploaded into the controller by the end-user.

As a standalone passive preamp the V25 sounds great. You can also incorporate it into most any new or existing solid state or tube based active preamp with exceptional results.

Here are the highlights:

* 100 step volume control/attenuation over 60 dB range
* Muting with volume ramp-down and ramp-up
* Built-in self calibration of the LDRs - no LDR matching required
* LDRs are replaceable plug-in modules
* Can switch up to 6 stereo inputs with switching built into the board
* LDRs are also used for input switching in lieu of relays
* Mono/stereo mode controllable via remote
* Use a pair of V25 boards to handle balanced audio
* Fully remote controlled via any silver Apple remote with remote ID pairing (256 remote ID's possible)
* Adjustable input impedance between 1-99k ohms | up to 10 possible settings (#1 is 20k fixed default)
* Firmware can be updated via simple PC based bootloader program and USB cable
* Powered by most any DC source between 9 and 30 volts DC rated at 500 ma (actual demand is considerably less)
* 256 x 64 pixel graphical OLED display with interface board with mounted IR receiver module & encoder attachment point
* OLED attaches to the V25 board via a 14 pin ribbon cable which carries power, OLED, encoder and IR signals.
* Menu driven OLED display with numerous functions including
* Turn preamp off
* Control volume
* Adjust left/right channel balance
* Switch inputs
* Adjust display brightness
* Adjust display timeout (blanking)
* Change max initial volume on startup or input change
* Change units between steps & dB
* Show firmware version
* Adjust impedance & update calibration
* Reset (all impedance/calibration data)

When purchased together as a package, the LDR.V25 (equipped for 3 inputs) plus OLED display/encoder run $399.

With few exceptions, we ship most anywhere in the world.

Here's a link to the LDR.V25: LDR V25 Preamp Controller | Tortuga Audio

This pic of the V25 shows the Rev A version. We are now on Rev C that looks almost identical has a few parts moved around. The Rev C board switched to SPI communication with the OLED rather than the earlier 8 line parallel method.
Click the image to open in full size.

Click the image to open in full size.

The control menu has changed slightly from the one shown below. The Impedance and Calibration items have been merged into a single Imped-Cal menu item since these are so inextricably linked functionally.
Click the image to open in full size.
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Last edited by CaptainWatt; 26th May 2019 at 05:33 PM.
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Old 30th May 2019, 07:47 PM   #2
CaptainWatt is offline CaptainWatt  United States
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What you need to build a Tortuga Audio DIY passive preamp...

1) $399 - V25 Preamp Controller Board (3 inputs expandable to 6) with OLED display and Encoder
2) $15 - USB port/cable (for updating firmware)
3) $25 - Apple remote
4) $?? - A set of RCA jacks (at least 4 for 1 input & 1 output)
5) $?? - An enclosure of your choice or making
6) $?? - A knob for the encoder
7) $?? - A 12 VDC 0.5A power supply

Already have an active preamp that could use some updating? You can probably skip items 4) through 7).

What are you waiting for, just go do it!

DIY Preamp Components Archives | Tortuga Audio
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Old 17th March 2020, 08:24 AM   #3
nautibuoy is offline nautibuoy  United Kingdom
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Hello Morten.

Any news on your LDRPot development?

Cheers
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Old 17th March 2020, 01:55 PM   #4
CaptainWatt is offline CaptainWatt  United States
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Quote:
Originally Posted by nautibuoy View Post
Hello Morten.

Any news on your LDRPot development?

Cheers
The following summarizes our current development roadmap on what we are now more broadly calling the ePot.

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, all designed around our LDR (light dependent resistor) attenuation technology. 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.
Click the image to open in full size.
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Old 17th March 2020, 06:54 PM   #5
nautibuoy is offline nautibuoy  United Kingdom
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Thanks for the information, some interesting looking developements - I'm interested in your ePot mini for an amp project I'm currently working on - just one input so no need for anything more complex and limited space available anyway - shame you can't give any clues on timescale or prices.

If there is sufficient interest might this be a prospect for a group buy?
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Old 8th April 2020, 09:44 PM   #6
CaptainWatt is offline CaptainWatt  United States
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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 ( the smaller Mini board is 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

Click the image to open in full size.
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Old 20th April 2020, 11:03 AM   #7
CaptainWatt is offline CaptainWatt  United States
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Here's a cool backlit pic of the plug-in discrete attenuator board for the new ePot.V3 Stepped Attenuator and Preamp Controller.
  • 127 smooth as silk volume steps (~0.5 dB/step)
  • 63 dB range
  • Low noise nickel-chrome thin film resistors
  • No step change artifacts - no clicks, dropouts etc.
  • 60k impedance
  • 10 dB +/- channel balance adjustment range in 0.5 dB increments
  • Totally independent stereo channels
  • Manual and remote controlled
  • Switchable 6 stereo inputs
  • Can swap out discrete module for LDR attenuation module
  • Optional OLED display
  • Available later in May

Click the image to open in full size.
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Old 20th April 2020, 11:21 AM   #8
nautibuoy is offline nautibuoy  United Kingdom
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Stackable for balanced signals?
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Old 20th April 2020, 12:17 PM   #9
CaptainWatt is offline CaptainWatt  United States
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Quote:
Originally Posted by nautibuoy View Post
Stackable for balanced signals?
A pair of ePot.V3 boards are required for balanced signals. They could be stacked to save space. The right channel board serves as the primary controller and connects to secondary board via a 2 wire serial data link.

Keep in mind that the pic in the last post is only of the plug-in discrete attenuator board and is not the ePot.V3 board itself. It plugs into the V3 and each V3 would need one of these plug-ins.
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Old 20th April 2020, 06:08 PM   #10
nautibuoy is offline nautibuoy  United Kingdom
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Quote:
Originally Posted by CaptainWatt View Post
A pair of ePot.V3 boards are required for balanced signals.
Sounds expensive. I imagined that the LDR/switch boards would be stackable on a single e-pot controller
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