Telefunken V72, Pleiades V0, V(-1), Electro-Voice 635a, Sony F-96

This is about finding out how the V72 sounds when generously driven.


The V72 was used ungrounded, it should have been grounded.


The capacitors were softly started to be reformed by sliding the V72 open and connecting 12V in series with 1.7MΩ to a positive power supply capacitor terminal. The voltage across the capacitor did not increase beyond 500mV indicating that either a bleeding shock protecting resistor exists in the circuit or capacitors are bad. Possibly the first is true. The reforming circuit had been left overnight. When mains was supplied it was only for split seconds and then waiting for minutes before re switching on. This gave opportunity to the electrolytic capacitors to reform. After a few hours of repeating the procedure with increasing turning on times and greater turn off periods the V72 was ready for audition.


What an amplifier!


Firstly it was directly connected to 635a.


Signal path, setup:


635a at 1-2in - V72 - Sennheiser HD580


The sound was very clean, beautiful sound, low volume since the V72 was under driven. There were some buzzing problems. Grounding has to be redone as the V72 is used with 2 external XLRs for input and output and perhaps pin 1 is not connected to the metal part of the connector as should be done on chassis XLRs, (see Jensen papers on pin 1 problem).


Next setup:


635a - Pleiades (-1) prepreamp - V72 - 20dB pad - Sennheiser HD580


Sound much louder. Very bright. No s problems. More buzzing problems.


By touching some metal part buzzing disappeared and it was possible to judge the interesting sound quality. The sound was very good quality but very bright.


Next setup:


635a - Canford step up transformer with 400mH primary inductance - Pleiades V0 prepreamp - V72 - 10dB pad - Sennheiser HD580


More full sound, a little bass heavy. Still buzzing . Excellent quality. No s problems. It seems the V72 can be driven more without problem. It's limits may be tried at a later experiment.


Next the Sony F-96 high Z version microphone was connected.


Setup, signal path:


Sony F-96 High at 1 inch - Plaides V0 - V72 - 10dB pad or no pad - Sennheiser HD580


The sound was very clear. Of less volume than 635a. More suitable for high pitched male vocals due to less bass heavy sound. No s problems. No buzzing problems at all.


Then the pad was removed.


Beautiful sound.


More experiments would be useful to find out how the V72 sounds when overdriven.


It is interesting that world class amplifiers do not exhibit any (s) sibilant problem.