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Sporadic volume loss

M

Mola Ram

Jan 18, 2010
260
3
Chicago
#1
I'm not sure if this should even go here since I'm not sure the issue is with the amp itself but here goes.

Ok, here's the situation. At band practice I will experience a sporadic loss of volume out of no where. And I'm not just gone in the mix because I'm standing next to the amp and I can actually feel the difference in what the amp is pushing. I'll stop playing for a bit, go back to playing, and the volume is fine. Sometimes its out for longer periods of time.

This has happened with two different basses (one a passive and one with active preamp) so I don't believe it has anything to do with the instrument.

The other issue is that its not my amp. It's my guitarist's STV-4Pro who uses it for recording. And he apparently doesn't have any issues with it.

Is it possible to have this kind of issue with a faulty cable? It is really the only thing I can think of thats a variable.

Any assistance would be greatly appreciated.
 
#2
If I had to take a guess, I'd probably look at the tubes first, starting with the power section. There's a 12 ax7 and a 12 au7 there and my guess would be the au7. If the amp is used for recording from the direct out, it's possible that the problem would never surface as those tubes come after the direct out.
 
#5
Mola Ram said:
Is there any way to truly test if it's the tubes?
Click to expand...

Only way would be to swap in a new tube. Pretty inexpensive, though since both tubes should cost around $20.

I can tell you that I had some trouble with the 12ax7 in the power section where it was pretty consistently low power and occasionally it would get louder. Sort of the opposite of what you've got.

If it isn't solved by swapping the tubes, I'd get it to a tech as nothing else is going to be easy to check.
 
#6
Thanks again. And jsut to be clear, you definitely think this is an issue with the amp itself? You can't think of anything with a passive bass or an instrument cable that would cause this?

I'm just trying to get all my ducks in a row for when my guitarist goes "Dude, its gotta be your gear that's causing the issue".
 
#7
Yes, it could just be a cable. Start with the simple/cheap stuff first and do process of elimination one piece at a time. Battery in active bass and/or pedals. All cables one at a time, including speaker cables and patch cords. Play that amp with a different speaker and that speaker with a different amp.

If you narrow it down to the speaker, look for loose wiring inside and "battery test" it....search that here.

If you narrow it down to the amp, try running a patch cord from the effects send to return and cleaning those jacks. Try swapping pre tubes one at a time with one known to be good. They're cheap, bit you could borrow one from the guitar amp for testing purposes. You'd have to take the top cover off the amp to get at them but they are simple unplug old one, plug in new one.
 
#13
Does the amp have an effects loop? Try plugging a guitar cord from the send to the receive jack to see if corrosion on the jack contacts is an issue. I had a GK 400RB once that would intermittently fade out and crackle, then jump back up. Cleaning the contacts fixed it.
 
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#14
Any way to measure the voltage of the socket you're plugged into? A voltage drop can give you that kind of problem.

Some amps have ribbon cables that feed the FX loop, and if one of those is faulty, it can produce unexplained volume drops.
 
#16
froghat said:
Does the amp have an effects loop? Try plugging a guitar cord from the send to the receive jack to see if corrosion on the jack contacts is an issue. I had a GK 400RB once that would intermittently fade out and crackle, then jump back up. Cleaning the contacts fixed it.
Click to expand...
Your post from years ago helped me hugely this weekend. I was having what appeared to be an amp head failure, the day before my first gig since the pandemic closed everything down a year ago. Plugged a patch cable between the Send and Receive, and everything was fine. So thank you!

Now that the gig is over, I would like to address the problem. How does one go about cleaning the input jack contacts?
 
#17
bassdood said:
Now that the gig is over, I would like to address the problem. How does one go about cleaning the input jack contacts?
Click to expand...

The easy way is to spray some contact cleaner (CRC electrical contact spray or similar at the hardware store, used to be called tuner spray) into the jacks, then insert and remove the patch cord several times. If you can open the amp and get to the contacts, clean them with a pencil eraser or scrape them with a blade. Especially the normally-closed connection which bypasses the effects loop when nothing is plugged in. Then hit them with contact cleaner. Take care, they say the spray can damage some plastics, although I've never had a problem with it.
 
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#18
Never scrap connector contacts, that will ruin the plating on the metal. Also, only the tiniest amount of spray, many "contact cleaners" and "tuner cleaners" contain substances that can migrate to PCBs and other components and create additional problems.

Also, never use "contact" cleaner on pots, the solvents can wash lubricants to places that can cause additional damage, and some solvents are incompatible with the resistive elements and their staked terminations. There may be some others, but Caig DeOxit D5 is the only material that I have tested and found to be a safe solution (used in TINY quantities).
 
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#19
agedhorse said:
...

Also, never use "contact" cleaner on pots, the solvents can wash lubricants to places that can cause additional damage, and some solvents are incompatible with the resistive elements and their staked terminations. There may be some others, but Caig DeOxit D5 is the only material that I have tested and found to be a safe solution (used in TINY quantities).
Click to expand...
Thanks!
Just to clarify, are you recommending the Caig DeOxit D5 for the input jack, or for pots?
 
#20
froghat said:
The easy way is to spray some contact cleaner (CRC electrical contact spray or similar at the hardware store, used to be called tuner spray) into the jacks, then insert and remove the patch cord several times. If you can open the amp and get to the contacts, clean them with a pencil eraser or scrape them with a blade. Especially the normally-closed connection which bypasses the effects loop when nothing is plugged in. Then hit them with contact cleaner. Take care, they say the spray can damage some plastics, although I've never had a problem with it.
Click to expand...
Thank you! I will try it.
 

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