Investigating Balanced Tube Preamp

[roderickvd]

Hello!
See schematics in picture.

I have a hard time understanding this schematic. XLR pins 2 and 3 as well as the RCA got signal seem to be connected to… nothing? How should I read this?

 

[roderickvd]

Sorry for replying to myself. I asked the seller on AliExpress who turns out to be very responsive. Here it is:



Still interested to learn whether you ended up using the values on the schematic, or the ones from the components supplied!

 

[peteyp]

Audio board build and test.

Finished the audio board, bench tested and listened.

It tested very well with essentially flat frequency response from 15hz to 24khz. Didn’t bother going any further. Waveform very clean. Also did well with square waves with no ringing or overshoot/undershoot. Could not get it to clip or distort at any volume.

Listening test: Very quiet and clean. Fast. Maybe not as “tube” sounding as some might like. Drives my Class D monoblocks very well.

I hooked up the in and out connectors directly. Still need to build the input/output board.

Really happy with the results. Definitely a keeper.

Attached are shots from my (admittedly) crappy scope.

What's left to do.

Power supply.
Nothing

Audio board:
Upgrade coupling capacitors.
Upgrade volume control
Upgrade gain pots

Input output board:
Buy better signal switching relays
Buy better audio jacks
Build

Overall
Buy case and complete assembly.

Hi. Did you complete the build? If so, would you mind posting detailed photos of the remaining additions as I would like to build pretty much exactly the same thing. I would like to add a remote control for volume though, so would appreciate any guidance on what to buy and how to integrate it. Thanks.

 

[giubio]

Ciao, from Italy,
I am interested in building this preamplifier.
Last time you write it was june 2022...
After one year, which is your opinion on this kit?
Thanks for the suggestions.
Beppe