[tortugaranger]

Hi Morten!

I'm still having problems with the impedance adjustment and my DAC and power amp are quite picky so I would really like to be able to switch between all 5 settings. Setting 1-3 is no problem but setting 4 seems to "erase" itself after finishing autocal so it goes back to 99.
Any ideas?     

Also, how come you advised me not to buy the internal PSU for my balanced configuration and now you are using it in the new amps or is it a different new PSU? http://www.audiocircle.com/index.php?topic=151395.0
 
Many thanks!
/ Simon

Hi Simon,

The issue with the impedance not sticking on #4 is a reported bug that's on the "to fix" list. A firmware update will take care of that once we get it resolved.

I advised against our internal PSU because I don't like to waste my customer's money on something they don't need or that I don't think will improve the performance of the preamp. We still use that PS in our LDRx and LDRxB models because that's how they were originally designed. When we eventually update/replace those models we won't be using that PS anymore and will be using an external 12 VDC wallwart instead. The V25 board is way less sensitive to power supply quality than the V2. There's a very specific reason for that because the V2 used the incoming power directly to drive a pair of op amps in the control circuit. The V25 has a 2 stage DC-DC converter with the 1st stage being a switch mode converter followed by a second stage linear regulator. A good $10-25 12V wallwart is all you need. Anything way better isn't likely going to give you better results.

Best,
Morten

[TheMonkey]

Thanks a lot for a fast and good reply! You are the best!! 
Good to hear that about the PSU, reassuring and thanks for not wasting our money on stuff we don't need! 

[WC]

Morten,

Does the current firmware support Uart control for the V2.5?

[tortugaranger]

Morten,

Does the current firmware support Uart control for the V2.5?

Yes it does although I've not yet published the commands and have not really thought through possible issues interfacing with devices that aren't also at same 3.3V level as the V25 processor. UART is how 2 V25s communicate in balanced audio scenario. It's a very simple system. Runs at 115k baud, 1 stop bit, no parity.

[WC]

The Arduino Due I was planning to use is a 3.3V Uart controller. So that is good. 

So any idea when you are going to publish the commands? On the website it mentions available upon request.

[tortugaranger]

The Arduino Due I was planning to use is a 3.3V Uart controller. So that is good. 

So any idea when you are going to publish the commands? On the website it mentions available upon request.

I'll move up the priority on the To Do list. 

[WC]

Hi Simon,

The issue with the impedance not sticking on #4 is a reported bug that's on the "to fix" list. A firmware update will take care of that once we get it resolved.

I advised against our internal PSU because I don't like to waste my customer's money on something they don't need or that I don't think will improve the performance of the preamp. We still use that PS in our LDRx and LDRxB models because that's how they were originally designed. When we eventually update/replace those models we won't be using that PS anymore and will be using an external 12 VDC wallwart instead. The V25 board is way less sensitive to power supply quality than the V2. There's a very specific reason for that because the V2 used the incoming power directly to drive a pair of op amps in the control circuit. The V25 has a 2 stage DC-DC converter with the 1st stage being a switch mode converter followed by a second stage linear regulator. A good $10-25 12V wallwart is all you need. Anything way better isn't likely going to give you better results.

Best,
Morten

So would a meanwell Switchmode PS like the IRM 12V work just fine. I was looking at using it to power the arduino and the V25 board(s), since neither seems to need a linear PS.

[tortugaranger]

So would a meanwell Switchmode PS like the IRM 12V work just fine. I was looking at using it to power the arduino and the V25 board(s), since neither seems to need a linear PS.

For the V25 I think it would work fine. The output hits another switching DC-DC regulator on the board and then a linear regulator. 

[WC]

Yes, with dual boards you can mix balanced and single-ended inputs.

It gets a bit messy to explain/show but with balanced signals the master board handles the + phase for both the right/left channels and similarly the slave board handles the - phase for both channels. This arrangement is necessary in order for the channel balance adjustment feature to work properly.

To add single-ended inputs you would would only connect inputs to the master board's right/left channels.

The output wiring follows the same approach as the inputs. When a balanced input is selected that attenuated signal would also be present on the RCA output jacks but only from a single phase so the volume would be reduced. When a single-ended input is selected the balanced output would have a signal present on only one phase.

V25 Balanced Wiring


V25 Single-Ended Wiring

I was thinking of this. Could I use the second slave board as a balanced board for 2-channel use and as a single ended for multichannel use? I would have a DAC and phono inputs for 2 channel input. Both could be balanced. I would have two multi-channel inputs which are only single ended for total of 6 channels. I would switch the outputs so that the right outputs get the correct signal to the amp and speaker.

[tortugaranger]

I was thinking of this. Could I use the second slave board as a balanced board for 2-channel use and as a single ended for multichannel use? I would have a DAC and phono inputs for 2 channel input. Both could be balanced. I would have two multi-channel inputs which are only single ended for total of 6 channels. I would switch the outputs so that the right outputs get the correct signal to the amp and speaker.

I'm probably not clear on the specific arrangement you described but will try to answer your question this way:

1) With dual boards you essentially have 4 independent channels that in theory you can use any way your want in terms of mixed balanced and single ended but with the constraints/limitations discussed in 2) below.

2) When you adjust channel balance towards the right or left you are raising the volume of one channel on a board with respect to the other channel on that same board. Withe dual boards this happens to both boards the same way at the same time. With balanced signals if we wired both phases to just a single board and then adjusted the channel balance all you'd accomplish was raising one phase with respect to the other on both left and right stereo channels - resulting in no channel balacne shift. The reason the balanced wiring is the way it is is in order for the channel balance adjustment feature to work properly. If you didn't care about channel balanced adjustment you could wire both balanced phases to either board rather than splitting the phases between both boards  (as shown in the diagram).

[WC]

I would run the positive phases to the master board and the negative phases to the slave board as a normal configuration for 2-channel. For multichannel, I would run single ended channels 1 and 2 on the master board, single ended channels 3 and 4 on the slave board. That seems possible based on what you said. Now I just have to switch the output signals so they go to right location.

[tortugaranger]

I would run the positive phases to the master board and the negative phases to the slave board as a normal configuration for 2-channel. For multichannel, I would run single ended channels 1 and 2 on the master board, single ended channels 3 and 4 on the slave board. That seems possible based on what you said. Now I just have to switch the output signals so they go to right location.

Yep, that should work!

[WC]

Can you stack the boards, if you are using multiple boards? If so, how much space is needed between boards?

[tortugaranger]

Can you stack the boards, if you are using multiple boards? If so, how much space is needed between boards?

I'm sure you can but having considered doing this myself I decided not to in order to ensure ease of access. I'd allow for 0.5 inch space below and 0.8 inch space above each board as a rough guide. The limiting item on the topside is the 5 V regulator with is about 0.75 inch tall. The bottom side has a 2x5 pin header used only for initial programming of the processor and also a pair of low profile relays active only during calibration. The version B of the V25 board in development will likely do away with both the relays and the pin header on the underside but that's not been verified yet.

P.S. Your board ships this week.

[tortugaranger]

It's been awhile since we highlighted the LDR.V25 Preamp Controller as the core part of any DIY passive preamp or new/modified existing active preamp so here's to all of you DIY'ers out there...draw near and take heed!

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.




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.

[walterslw]

Trying to connect to the Tortuga website and am receiving "www.tortugaaudio.com refused to connect."

[srb]

 

[tortugaranger]

Yes, am aware the website is down at the moment and am working on resolving it. Thanks for the heads up though. 

[tortugaranger]

Trying to connect to the Tortuga website and am receiving "www.tortugaaudio.com refused to connect."

Thanks for the notice. Took a bit of work but everything's up and running again.

[tortugaranger]

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!

https://www.tortugaaudio.com/product-category/diy-preamp-components/