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Push-Pull Amplifiers - 10-20W no feedback!


This projects born to explore the Push-Pull amps. world.

One of the problems of the push-pull amplifier is the phase plitter stage.
This stage should give two equal signals with opposite phase and there is not a very good solution.
In this project such a problem has been solved using a symmetric transformer to generate two signals opposite in phase.
The version 1.0 use this transformer also to get a gain voltage.

This projet will start with a simple but good version with a limited budget and go until a terrible version with electrical performance near to solid stade amplifiers.
In any case also the first version should give a sonic performances better than any commercial push-pull like Conrad-Johnson.


All the audio transformers used in this project are Lundahlproducts:

Lundahl is one of the world´s leading manufacturer of audio transformers used in many professional studio recording and radio stations so He have a very big experince and all these products use a custom audio C-core.

I am using a DACT stepper attenuator instead of the normal ALPS or NOBLE solution, because the the sound is clearer. A good review of these components can be found on the article published in Hi-Fi World.

The output tubes used are the new Sovtek SV6550WE.

but I have tested with this circuit many output tubes like the 8417 GE, KT88 Svetlana, KT90 EI..

About passive components types,  I don't leave many choices:  Allen Bradley or Caddock resistances on anode, Holco or Caddock resistances on cathode, ELNA Cerafine capacitors on cathode and power supply.
For all my new projects, I am using the very good ELNA Cerafine capacitors that I love and which can be find at good price by AUDIOKIT.
The ELNA Cerafine capacitors contain super fine ceramic particles which, through chemical reaction, improve the discharging speed between the anode and electrolyte with very low distortion.
Any other electrolytic or polypropylene capacitor give very lower sonic performances introducing some alteration. Only the Blackgate WKZ could give better sound, but I have not tested it and I know of some problems during startup phase.

About wire forget the teflon ! use only stranded tinned copper wire with pvc isulator and for loudspeakers I am testing the elevator cables (paralleled wire with a good section).

A very good quality stranded tinned copper wire could be buy directly from E-Z-HOOK that carries an extensive line of fine stranded and extra flexible wire.

The schematic

Sonic results
I don't like the sound of this amp.