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big muff pi - how to clean up noise?


 
5/28/1999 2:06 PM
f capo
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big muff pi - how to clean up noise?
I have a NOS big muff pi. It has been  
unused for many years. (I suspect that it  
was not sold because of the noise.)  
It is quite noisy (uniform rushhhhing noise)  
when vol up towards max. Is this normal?  
Where would I start in replacing components  
or improving circuit dress/paths to attempt  
to minimize the noise while maintaining effect  
performance. thanks
 
5/28/1999 5:11 PM
R.G.
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First, remelt every solder joint on the board, touching each joint with just a smidgen of fresh rosin core solder.  
 
Second, replace every electrolytic cap in it. The thing is old enough to need it. Just make a list of the values of each polarized capacitor and replace them.  
 
Third, if the first two haven't fixed it, replace the transistors with 2N5088 devices, being careful to get the right lead in the right place. Start with the input transistor, as all of its noise gets amplified by the rest of the circuit.  
 
If that doesn't help, start replacing resistors with same-value metal film ones, starting with the input resistor and the collector resistor of the first stage.  
 
One of those will get it if it's a "normal" fault. Some abnormal faults could be a non-electro cap or diode getting noisy, but that's unlikely.
 
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