Firebottle
30-11-2018, 11:32
I have very recently received an OTL headphone amplifier designed by Helmut Becker in the 1980's.
It uses four PCL805 valves plus an opamp for DC control. It is a very clever circuit that compensates for valve characteristic variations and tube ageing.
It was somewhat poorly (no output) so has had some remedial work done on it, particularly two new output capacitors as one was particularly leaky, putting 63V on the output without phones connected. The gain was particularly high so I have reduced that as well.
http://i67.tinypic.com/29wjrzs.jpg
It was the forerunner of the RKV headphone amps by Audio Valve, not cheap by any means :
https://positive-feedback.com/Issue15/images/rkv1.jpg
However its performance is exceptional, being valve based it can drive high impedance phones with aplomb. It sounds superb, the best headphone sound I have heard.
It's a keeper :D
It uses four PCL805 valves plus an opamp for DC control. It is a very clever circuit that compensates for valve characteristic variations and tube ageing.
It was somewhat poorly (no output) so has had some remedial work done on it, particularly two new output capacitors as one was particularly leaky, putting 63V on the output without phones connected. The gain was particularly high so I have reduced that as well.
http://i67.tinypic.com/29wjrzs.jpg
It was the forerunner of the RKV headphone amps by Audio Valve, not cheap by any means :
https://positive-feedback.com/Issue15/images/rkv1.jpg
However its performance is exceptional, being valve based it can drive high impedance phones with aplomb. It sounds superb, the best headphone sound I have heard.
It's a keeper :D