I have a new bass guitar amp with a mild amount of buzz, not overly loud or objectionable but audible and I would like to reduce it if possible. For reasons I don't need to get into here, I don't want to modify the circuit. My question is if there is anything I can do externally. I'm pretty sure the buzz is coming from AC on the heaters because in Standby there is no buzz; power on and the buzz appears.
2 x TAD 6L6GC-STR
2 x JJ 6SL7
1 x JJ GZ34
(all new)
2 x TAD 6L6GC-STR
2 x JJ 6SL7
1 x JJ GZ34
(all new)
In standby the HT is off so there is no amplification.When it is on, the buzz could be from the heaters, or the HT or external. It would be a good idea to do a couple of extra tests. First it helps to determine if the buzz is at mains frequency or or twice that frequency. If it is at mains frequency then it could be heaters or external. If it is twice mains frequency it is likely from the HT circuit. The second test is to short the input and see if that changes the hum level. If it changes it a lot the interference is mainly external.
Cheers
ian
Cheers
ian
Thanks. I'll mess around and investigate some more as you have suggested. I'm not sure how I can go about determining if the buzz frequency is at 60Hz or 120Hz but maybe the local tube repair tech can help me out.
You basically need to look at the output with an oscilloscope. Your local tube repair tech should have one.
Cheers
Ian
Cheers
Ian
Get a spectrum analyzer program for your phone or computer. That will tell you in seconds what the frequency is.
I found a 60 Hz/120Hz comparison online and I'm almost positive mine is 60Hz (mains in N. America). It's unaffected by the volume pot.
That said, I'm probably going to have to take it into a tech to track down the cause and a potential solution.
The amp has a switch to change between fixed and cathode bias; there doesn't seem to be any difference in the frequency or volume of the buzz in either position.
That said, I'm probably going to have to take it into a tech to track down the cause and a potential solution.
The amp has a switch to change between fixed and cathode bias; there doesn't seem to be any difference in the frequency or volume of the buzz in either position.
If it is 60Hz then the possibilities are poor heating wiring, induction from the mains transformer to the output transformer or poor heater cathode leakage in a tube. As the volume control does not make a difference then that implies the source is not the front end. The easiest test you can do now is to try new output tubes and or phase/splitter tubes. This should show up whether it is a tube leakage problem.
Cheers
Ian
Cheers
Ian
Most common problem which causes hum: failed filter caps.
Dont re-orient your transformer or even replace a single tube until you have new hv electrolytic caps.
Dont re-orient your transformer or even replace a single tube until you have new hv electrolytic caps.