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Noisy Symetrix 501
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Guitarzan
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#1
17th June 2006
Old 17th June 2006
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Noisy Symetrix 501

I recently purchased an old looking symetrix 501 compressor. It has a fair amount of hiss. The output gain pot is a bit scratchy too. Would changing this pot quiet this thing down? Any other tips or suggestions?
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#2
21st June 2006
Old 21st June 2006
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You might be able to get by with just opening it up and spraying the pot. As for being noisey, maybe capacitors. I've got two of them and use them regularly for tracking because of their transparency.
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21st June 2006
Old 21st June 2006
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I am certainly sure that changing the potentiometer will not reduce that level of hiss. You can clean the pot to remove the scratchiness. I think replacing some capacitors in the power supply may improve things for you.
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21st June 2006
Old 21st June 2006
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It's also loaded with 4558 opamps, perhaps one of these has gone south. Pop in some sockets and test them.

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#5
23rd June 2006
Old 23rd June 2006
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After looking at the schematics, the first suspects for noise would be the electrolytic capacitors in the power supply section, followed by U1 and U4, which are the only opamps directly in the audio chain. They are 4560 opamps and could be replaced with either a 5532 or some other dual opamp that is quieter and has a better slew rate. The other opamps are in the circuit for controlling the VCA so they shouldn't be inducing any noise unless they are having major problems, at which point it won't be working right anyway. Hope that helps. You can download the schematic in Symetrix's tech support area of their website.

I did some more checking and found that not all 501's have 4560 opamps. My blackface one has all socketed LF353, National equivalent of a TL072, while the grey panel has the 4560's soldered in. I actually think the blackface one sounds a bit better.
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