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Wednesday, October 5, 2016

The Differential Power Amplifier - Part 2


A quick update on the differential (push pull) amps.

The first mono amp and it's power supply are completed and went through some bench tests. This is the 'naked' amp section:

Lot's of iron and absolutely no capacitor at all in the signal chassis! As can be clearly seen in this shot from the side:

Power output is a solid 15W.

The power supply section of course has some smoothing caps:

Filament supplies on the bottom and high voltage supply above.
Another photo of the signal section:

Once the second channel is complete listening will start. Measurements are promising. 15W of deep Class A sound. No capacitor colorations since there are simply none in the signal path!

Best regards



  1. Looks magnificent

  2. That looks great Thomas.. Would you mind sharing the models of the input phase splitting trafo, IT's, and OPT's you used in future installments of the build? Looks like Luhndal TOTL. Thank you.

  3. Hi Rick,
    Input transformer is the LL7903. IT is LL1660S. The OPT is a non standard model

  4. Really interesting. Can't wait for your listening impressions, especially combining with/without SE or differential line stages.

  5. Hi Thomas,
    Very interesting! How did you achieve differential output stage, as it needs a highish impedance in the cathodes(?) I remember you posted at diyaudio about using a choke in the common cathode circuit - did you do that?
    Cheers, Erik

    1. Hi Erik,
      these amps will not be offered as kits. Please understand that I will not share circuit details of these. I am sharing a lot of technical details, but need to keep some secrets as well ;-)


    2. Thanks for the reply Thomas,