Oscillating Preamp?
I've got a preamp using 4 12au7 (ECC82) tubes.
When I use my preferred combination (RCA 12au7A's) there is a high pitched whining every so often. Must be above 16Khz as I can hear it but the old man can't!
If I use other (less good sounding) tubes it completely goes away.
If I use the same 12au7A's in other preamps they are silent in them too.
Are these particular tubes sending the preamp into oscillation? I can't really think of any other logical reason why they would do this and only in this particular preamp. The tubes are pretty much NOS and not microphonic at all.
It's really rather annoying as when they are not whining the sound is sublime, which is the reason I want to persevere with this combination rather than resorting to other tubes!
Cheers
Chris
System 1: - Amp - Musical Paradise MP-701 mk2 - Neurochrome 686
- Source: Audio Technica LP-5 - Custom 6V6 stage - Novafidelity X30 - Soekris 1421 (LPSU) - Custom TDA1541 C3G DAC -
- Speakers: Martin Logan Prodigy's - Subs: - REL T3's -
System 2 - Amp: Musical Paradise MP 303/Custom 300B SET - Custom 6SL7 Pre -
- Source: Pioneer N-30K - SONCOZ SGD1 -
- Speakers: Loth X BS1's - Sub: REL T3 -