I picked up a non-working Beta Bass several months ago and have now started to reapir it. The +-15V supply had an issue with one of the BJT/zener diode regulators and that was fixed and I also had to replace one of the level pots.
The unit now works but has a wonderful 1/f (white) noise issue. The drive input pot doesn't seem to increase the noise but the level pot does seems to increase the noise - it's the same on both channels. I could use an AC coupled probe with earphone to hunt this down but I'm wondering if anyone else has been there done that??? My guess is that it's the RC4558 on the output stage of the level circuit. Thanks for the help.........george
BTW - these amps seem to be very popular - based on what they sell for on ebay and craig's - is it the input switching, the funny inverter based soft clipper (i.e. drive control) or what?
Well... no, I ain't done it with a beta. They (betas) are kinda noisy to begin with - way too many gain stages between input and output.
The 4558 is the favorite of stompbox folks because (I think) it was used in the original tube screamer.
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Always seemed funny to me that a BJT op amp would be claimed to give a tube sound... but, if the truth be told, most people couldn't tell the difference between tube and transistors if their life depended on it... although they will claim to the grave that they can, prior to any real test of course. I
always think it is a good thing that their life
really doesn't depend on it. (
ok, not always... there are certain individuals 
)
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If there is no op amp socket, snip out the 4558 and install a socket. I've done this with way too many amps to count. I can't remember if sockets are used with the beta preamp.
Sometimes the 4558 is defective - it does happen, even (especially) with opamps. You may want to consider different dual op amp types - like a TL072 as an example.
Not really any different than swapping tubes...
