Sunn Coliseum 300 noise issue

[gbono]

Coliseum_300[1].pdf

I brought this amp back from being "air locked" but it seems to be very noisy. Not the 60/120 Hz kind of noise but more "white" or 1/f noise associated with semiconductors or resistors. All the active devices were replaced on the pre-amp board along with adding sockets. Power amp board also has new active devices as well. I haven't really been able to isolate the noise from either preamp or power amp since the power amp out is located before the CMOS limiter section and the preamp out "sounds" okay - hard to hear over the fan noise. Were these old (80's) Sunn amps just noisy?

[Enzo]

I would write it again here, but I have a headache. GO see what I wrote over at SS guitar and report back.

[gbono]

I checked the noise levels with a scope at C1 and the reading was 1-2 mV of random noise. I looked at the test point 9 (base of Q4) and the noise voltage was still around 2 mV. The noise signal jumps up to 10-11 mV at test point 12 (13 dB!) I get the same readings on test points on the other rail. I have replaced ALL the active devices on this board so I'm stumped - is this just the going noise level for this design?

[louloomis]

I don't know if this is helpful but I bought one of these new in the 1980s. I remember it being very noisy and that's one of the reasons I sold it (not that you should sell it, but I'm just talking about my state of mind then, you know?). It picked up a lot of radio signals, etc. Crazy, no?

LL