ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

 
Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

What to do about my humming amp?


 
5/30/2000 12:35 AM
Rob P
email
What to do about my humming amp?
Hi all,  
 
I own a peavey TKO115 bass amp (sorry, i'm building a tube replacement at the moment) actually i don't mind it, seems to sound pretty good to me.  
 
anyway, the problem I have is that it hums. i've tried quite a lot, and i have found that the hum is in the preamp. (when i plugged a jack into the power amp input, all went dead quiet)  
 
i've tried replacing each opamp, with no change in hum. does anyone have any other suggestions, should i maybe start replacing caps? (don't know why that'd create/remove hum)  
 
anyway, i've run out of ideas, so any input is much appreciated.  
 
thanks,  
Rob
 
5/30/2000 11:57 AM
Bob Isaacson
email

Rob  
Does the hum also disapear when you plug your guitar into the preamp input jack? If so, then the jack contact on tip side may not be shorting to ground when the plug is removed,thus causing hum. Cleaning or replacing the jack would solve the problem.  
Another cause, as you mentioned could be a bad or loose filter cap in the preamp power supply. Also look for any loose ground connections.  
 
Good luck,  
Bob
 
 
  Friday
Book Of The Day The Ultimate Tone, Volume III by Kevin O'Connor
Have you ever wondered if there is a better way to build a Bassman, Champ, Plexi, an 800, AC-30, Bulldog or Portaflex? Or you wanted to build an SVT with off-the-shelf parts? How about a master-volume amp that doesn’t change tone with the master setting? Everything you need to know is right here, including: proper grounding techniques, wiring methods, and mechanical considerations. Eighteen chapters cover the “iconic” amps everyone knows and loves, with schematics and layouts for each, along with the technical history of the product. Eyelet-board and chassis-mounted tube socket construction is used throughout, for easy servicing and modding. TUT3 is very accessible even if you cannot fully read a schematic and is a "must have" if you are going to build an amp for your self.

Note: The Ampage Archive is an Amazon Associate site. A small commission is paid to the site owner on any qualified purchase made after clicking an associate link such as the one above.
 
5/30/2000 10:34 PM
Rob P
email

Thanks Bob,  
 
I might give those a try. The amp hums when I'm plugged into the normal preamp input, but not when i plug into the power amp input.(doesn't matter if anything's attached to the other end of the lead).  
 
maybe i should just resolder the preamp connections (sounds like a bit of a bother though)  
 
how do you tell if a filter cap is good or bad?  
 
thanks,  
Rob
 
5/31/2000 6:10 AM
Chris Taylor
email

Since you are plugging into the power amp in, I think you are cutting off the preamp, thusly this means your prblem might lie in your preamp. Just a thought
 
5/31/2000 7:03 AM
Rob P
email

Chris,  
 
thats what i thought, but i'm not sure what to look at within the preamp.  
 
Rob
 
5/31/2000 11:59 AM
Ray Ivers
email

Rob,  
 
I'm not sure what op-amps are in use, but you might try checking from pins 4 and 8 to ground, if they are 8-pin DIP op-amps. Use the DC and AC settings of your meter, and see what comes up - you would want to see + and - 12 to 16 volts at these pins, along with an extremely low AC reading. At least you can eliminate the op-amp power supply as a problem this way.  
 
Ray Ivers  
R.A.G.E. Electronics
 
6/1/2000 1:10 AM
Rob P
email

Ray,  
 
the opamps are 4558 types. i did actually check all the voltages at these, and they all checked out ok- i think they were +/-15V, i didn't check the ac, though.  
 
thanks for your input. i have to wait till the weekend to try out these suggestions, so forgive me if i haven't got anything new to say right now.  
 
Rob
 
   Page 1 of 1