Budda Superdrive 18 series II - volume drop after warmup

[akadave]

Hello all! New to the forum with a sick amp.

I have a Budda SuperDrive 18 that sounds great for about 20 minutes then the volume starts to fluctuate then finally loses all bass and mids and most of the volume. I have tried new output and rectifier tubes and have been able to reproduce the problem reliably. I took it to a so-called amp repair person in in Anchorage AK (we have basically nobody with amp repair skills here that I know of) and he was unable to reproduce the problem. My guess is he was too lazy to leave it on long enough to actually reproduce it.

I will likely have to ship it to a repair person or back to Budda, (emailed Budda, no response) but if its something I can possible repair myself I am willing to try as shipping heavy items from AK is very spendy. I have done a couple of minor repairs on some of my amps but I am by no means a tube amp tech. Any Ideas what this issue could be? I hear cold solder joints as the most plausible talking to friends. Also I would like to find a Schematic for my amp. A lot I know.

Thanks

Dave

[Jazz P Bass]

Two things that you could try.

First, run a cord from the FX Send to the FX Return jacks.
If the Return jack is dirty it will tend to drop the signal going from the preamp to the power amp.

Second, do you have another speaker to try?

[Enzo]

Budda is a division of Peavey, try contacting customer service at Peavey.

I agree with Jazz, THE most common problems with amps losing signal levels and tone is faulty or dirty FX loop jacks.

[akadave]

So it could be the speaker? I usually don’t use the effects loop. I will test it though

[g1]

The fault we are thinking of is more common when the FX loop doesn't get used.
There are switches in the jacks that route the signal through when the loop is unused. The switches oxidize and cause dropouts. Putting a patch cord between send and return bypasses the switches in the jacks.

And yes, it could be the speaker, speaker cable, or any other cable in use.

[Jazz P Bass]

I usually don’t use the effects loop.

Bingo.

Exactly why I suggested jumpering it.

Not using the jack does not mean that it cannot get dirty.
Probably the opposite.

[akadave]

I will give it a try in the morning when I get it back together. Its kind of an odd duck in my amp collection, everything else is 16 ohm and this little guy only does 4 or 8 ohm so a speaker test may be an issue. Odd that the effects loop would take warmup before having issues.

Thanks for all the suggestions I will let eveyone know the results. God I hope its that simple!

The fault we are thinking of is more common when the FX loop doesn't get used.
There are switches in the jacks that route the signal through when the loop is unused. The switches oxidize and cause dropouts. Putting a patch cord between send and return bypasses the switches in the jacks.

And yes, it could be the speaker, speaker cable, or any other cable in use.

[SoulFetish]

I will give it a try in the morning when I get it back together. Its kind of an odd duck in my amp collection, everything else is 16 ohm and this little guy only does 4 or 8 ohm so a speaker test may be an issue. Odd that the effects loop would take warmup before having issues.

Thanks for all the suggestions I will let eveyone know the results. God I hope its that simple!

I wouldn’t worry about an 8/16 ohm speaker impedance mismatch if your trying a quick audio test of cables or connections. Unless it goes open, your hardly to do any damage to the amp that way. The rated impedance is a nominal impedance at a given frequency anyway.
But, as long as you have more than one 16ohm speaker handy,just hook two up in parallel to give you an 8ohm load.

[akadave]

Well, I didnt have a lot of time to test last night. I did get the chassis back into the cabinet and then jumpered the effects loop. I played for about a half an hour total and couldnt reproduce the issue. I will clean the jacks tonight and test again. Hopefully this wasnt a fluke and I possibly jostled a cold solder joint in chassis for a temporary fix. We shall see tonight I hope.

Thanks for all the suggestions guys!

I wouldn’t worry about an 8/16 ohm speaker impedance mismatch if your trying a quick audio test of cables or connections. Unless it goes open, your hardly to do any damage to the amp that way. The rated impedance is a nominal impedance at a given frequency anyway.
But, as long as you have more than one 16ohm speaker handy,just hook two up in parallel to give you an 8ohm load.

[g1]

If you go to the 'maintenance & troubleshooting' sub-section of the forum, there is a sticky post about "the dreaded switching jack problem" which gives a better explanation of these types of jacks and the related fault.

[Enzo]

The way to do the test is use the amp as before, and THEN when the problem starts plug the spare cord into the FX loop. If that makes the problem go away, you are there. The key is waiting for the symptom to see if we can cure it.

[akadave]

I will give it a try tonight. I would have never thought that this was a pervasive problem with tube amps. Some of my amps I do use the loop a lot so, I suppose it makes sense with this one.

The way to do the test is use the amp as before, and THEN when the problem starts plug the spare cord into the FX loop. If that makes the problem go away, you are there. The key is waiting for the symptom to see if we can cure it.

[Enzo]

"Tube amp" has nothing to do with it. ANY sort of amp can have a jack problem. it is one of THE most common problems in audio. Tube or solid state, any can have dirty jack contacts.

Using FX loops usually keeps them clean. It is the return jacks that are never used that accumulate electrical dirt, and thus can interrupt the signal path.

[akadave]

Sorry I made the distinction. Guitar amp should imply tube or valve otherwise its not much of a guitar amp

In any event I cleaned the jacks and couldnt reproduce the issue. Im going to tentatively call this fixed...need more time on the amp to be sure.

"Tube amp" has nothing to do with it. ANY sort of amp can have a jack problem. it is one of THE most common problems in audio. Tube or solid state, any can have dirty jack contacts.

Using FX loops usually keeps them clean. It is the return jacks that are never used that accumulate electrical dirt, and thus can interrupt the signal path.

[Enzo]

I wasn't really editorializing. MY intent is to point out to people that troubleshooting is not dependent upon the technology. Many times someone writes in claiming they know how to work on tube amps but can't work on solid state. I feel obligated that the troubleshooting is the same, only the details are different.