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noisy vol. pots


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5/25/2000 7:23 PM
steve
noisy vol. pots
i was wondering what would cause hiss when i turn the volume up. this occurs even when there is nothing plugged into the input jack. i have recently  
done a total recap and i was hoping the amp would  
be quieter. seems like the vibrato channel is noisier than the normal channel. hiss increases as vol. increases.  
steve
 
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5/25/2000 8:26 PM
Gil Ayan

quote:
"i was wondering what would cause hiss when i turn the volume up. this occurs even when there is nothing plugged into the input jack. i have recently  
done a total recap and i was hoping the amp would  
be quieter. seems like the vibrato channel is noisier than the normal channel. hiss increases as vol. increases.  
steve"
 
 
The hiss you hear is electronic noise (thermal mostly, plus shot, etc.). In a non Master Volume amp, everything is "on 10" at the power section, so whatever noise buildup you have, starting with the very first component, will compound. It is normal for the Vibrato/Reverb channel to be noisier since it has additional components and stages in it, all of which will up the noise floor.  
 
If your input jack's switch is faulty, there is a chance the amp may not have a grounded input when nothing's plugged into it. That would,of course, make things much noisier but you'd get more than hiss that way. Check that just to be sure though.  
 
If you want to quiet your amp, you might want to consider replacing the plate load resistors with metal film types (the quietest) and the long audip wire runs with good shielded cable.  
 
Gil
 
5/26/2000 10:55 AM
steve

will the metal film resistors make the amp sound any  
different? i have found that any type of modification that i do to my pro-reverb results in  
alot of additional noise. after re-capping the whole  
thing and replacing tube sockets and leads, i think  
the amp sounds alot better. unfortunately i use this amp alot when home practicing at a low vol. and  
the hiss makes the modifications not worthwhile. think i should just leave it be.  
thanks, steve
 
5/26/2000 3:39 PM
Gil Ayan

quote:
"will the metal film resistors make the amp sound any  
different? "
 
 
Sure, quieter. :)  
 
Gil
 
6/1/2000 5:52 AM
Steve Ahola

Gil:  
 
If your input jack's switch is faulty...  
 
    The dead giveaway on that one is if the amp is quiet with a guitar plugged in and its volume set to "0", but noisier if nothing is plugged into the input jack. (Of course you know that, Gil, but I just wanted to mention it for the benefit of someone reading this thread.)  
 
    Overheating the jacks when replacing resistors, etc., seems to cause the metal to lose its "temper" so it is a good idea to just replace a faulty jack rather than just try to bend the contact back into place. (I'm talking about the open frame jacks, not the enclosed ones.) However, if the contacts are just dirty you could try using a contact burnishing tool to clean it up (it is a very fine and flexible fileó GC makes them in two different sizes).  
 
--Thanks!  
 
Steve Ahola
 
5/26/2000 11:12 AM
Graywater

Steve, a little disconnect between your post and the heading - are the pots themselves noisy - that is, do they make a scratchy sound when you turn them? If so this is usually caused by DC voltage across the pot - easily determind with a multimeter set for DC voltage. This symptom is usually caused by a leaky DC blocking cap somewhere (yeah, Iknow that you just did a cap job but new parts are sometimes defective).  
 
Anyhoo, if you problem is the constant hiss, I see that Gil has you covered.  
 
GW
 
6/1/2000 12:47 AM
JC
Re: a bit off topic; help again, please
Is there any url that would explain me with pictures or text the diferences between resistor types?  
 
I know it may sound silly, but sometimes you use terms I don't understand.  
 
I've heard about carbon comp, metal film, ceramics, wirewound... And except the obvious ones where the name explains it all -like wire wound ones...-, the others I can't recognize visually at the shops' trays.  
 
Sorry, I finaly had to ask.  
 
JC
 

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