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previous: Joel Ok, maybe another stupid question.<... -- 1/26/1998 10:12 AM View Thread

Re: Backround Noise

1/30/1998 9:14 AM
R.G.Re: Backround Noise
>Can a tube amp be made dead quiet at all volumes  
>(i.e., with no guitar playing into it)?  
Dead quiet? No. There will be some detectable hiss in any circuit. Effectively dead quiet, undetectable to the human ear in "typical" setups? Close. The Hifi People (different subspecies...) approach this.  
 
To avoid hiss - get rid of carbon comp resistors. they have excess thermal noise. Replace every carbon comp with metal film. The plate resistors are particularly important. Resistors hiss in proportion to their materials (metal film and wirewound are best) and in proportion to their temperature and the voltage across them. Plate resistors are particularly important.  
 
Start at the input stages, both guitar jack and reverb, and do them first. You may get enough hiss reduction to not need to go later stages. The hiss in the input stage is then amplified by the following stage, so the noise in the first stage is typically 20-26db louder at the output than that of the second stage. That's a big change.  
 
Select tubes, or buy selected tubes for lowest noise.  
 
Leaky filter and bypass caps effectively have a resistor in parallel, and this can contribute noise.  
 
Bad solder joints can be noisy, but it's usually a crackling, not a hiss.  
 
This applies only to hiss, not hum.  
 
Choke will not help.

 
Replies:
Joel Thanks to everyone for the help. -- 1/30/1998 10:57 PM