[sdiy] noise with vintage equipment

[Tom Wiltshire]

Firstly, are you sure it's not just a dodgy connection? I've had  
horrible noises coming out of old equipment that were just due to  
broken earth connections on the jack sockets or filthy sockets making  
a lousy connection.

After that, I'd replace the electrolytics, particularly in the power  
supply. This is simply a good idea to avoid frying the rest of the  
circuit in the future. Do the power supply first, and then see how  
you feel.

If you think the op-amps are rubbish, find a modern one with the same  
pinout and use that instead to avoid changing the circuit. I've  
replaced very old 741's like this and had a noticable (but not  
massive) improvement.

Replacing carbon composite resistors with modern metal film resistors  
would reduce noise, but is a sufficiently awkward job that I'd  
probably decide that that is part of the 'original character' and  
leave them in.

Transistors can also be a source of noise. If you look at many noise  
source schematics, you'll see a transistor with one leg unconnected.  
This can happen in a circuit with a dry joint. I've currently got  
this problem in an old 1970's Yamaha organ that I have. It's a top- 
octave/divider design, and the oscillator that generates all the "D"s  
is making a lot of noise. I've narrowed this down with the 'scope to  
one of transistors, but haven't got to fixing it yet.

Ultimately, if it's making a really hideous amount of noise, you're  
probably looking for something broken rather than something that is  
just old.

HTH,
T.


On 12 Jan 2010, at 10:52, mailing gigaspeeds wrote:

>
> Hi Guys,
>
> I have an almost restored eminent 310 string ensemble, on the front  
> is a stereo out, If I connect this to my amp I have terrible noise...
>
> How can I fix this while preserving the vintage sound...
>
> I know you have these 19" noise reducers, but I though as NOISE is  
> found in the whole spectrum this would alter my whole sound as well  
> I guess...
>
> I'm also willing o fix the root of this problem, probably worn/old  
> parts ?
>
> - carbon composite resistors
> - what about dried up caps ? (this would cause other problems I guess)
> - noisy opamp design ? (would be harder to fix, altering the  
> design...I have the schematisch though)
> - are there any other parts that would cause noise ?
>
> Do any of you own vintage equipment ? How did you *try* to fix this ?
>
>
> thx a lot for the advice
> Benjamin
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