In article ,
harrogate wrote:
After doing some frequency and phase sweeps on the 33 I built
replacement amp boards usinf TL074 bi-fet op-amps. The effect was
noticable. They went from a response of 50Hz-18KHz at -1dB to
22Hz-243KHz!

Quad *deliberately* restricted the frequency response to within the audio
band. BC 109s are quite capable of going above 100kHz. But this makes any
circuit more open to interference.

Did you increase the supply rail? IMHO, the 12 volt rail was the biggest
shortcoming of the 33, when used on the high gain pickup setting.

--
*Why isn't 11 pronounced onety one? *

Dave Plowman London SW 12
RIP Acorn