Coupling cap?

[cellardweller]

What are symptoms of a "coupling cap" going out on an amp?

I've read that some of the wierdness I associated with the usage of my DD20 in the effects loop of my Solo50 might actually be caused by this "motorboating" which is indicative of a coupling cap going out.

:?:

 

[Micah]

My guess would be that if you hear the sound of metal bumping together like a 2 capacitors humping inside of the case its a good sign of "cap-coupling". Initially you wont have any tonal effects while your playing, but long term effects could include an overpopulation of capacitors within the case and possibly some over-load on the circuit board--this could be kind of messy for the person having to clean it up.. :lol:

 

[Monsta-Tone]

That's some funny stuff.


Motorboating, premature Preamp tube failure, loss of sound, drastic change in tone (still there after a tube swap).

I haven't seen many go bad, but I had a Dual Rectifier that had a bad cap in the Loop circuit. It sounded like a blown speaker when I used the Loop.

 

[ytse_jam]

aren't coupling caps those which are used to separate different circuitry stages? a coupling cap failure could cause problems like oscillation, since for example different bias voltages would be matched together...
not sure 'bout this!!!!

 

[Monsta-Tone]

Yeah, the coupling caps block the DC voltage from the next tube's input stage.

Basically, most output stages are on the same pin as the DC voltage in.



You might want to just stop playing and get it to the tech quickly. There might be a potential for injury.

It might be nothing, it might be a Cathode Capacitor, which basically sets up the initial gain and tone for each gain stage. If it ends up being a Cathode Cap, you won't get hurt, but you might not want to take a chance.


It could also be a few other things, I would just get it fixed.

 

[cellardweller]

This oscillation only occurs when turning the feedback rate up above 12' o'clock on the dd20, which is why initially I assumed there was a problem with the dd20.

There has never been a problem EXCEPT when using the dd20 in the effects loop with the feedback rate above 12 o'clock.

Could this just be a limitation of the parallel effects loop, or does this sound like something more serious?

I'm reluctant to take it in, because there is no one I trust in the area.
Read~have had bad experience with local "techs".

 

[cellardweller]

bump

 

[Monsta-Tone]

Are you sure it's the amp? It could be that the pedal and the amp just don't get along.

I would try some other delay pedals in your loop.

You could also try the DD in another amp's loop.

Basically, if it only does it with the one pedal, I would think that the pedal just doesn't like the amp.



You could also try another Preamp Tube in the Loop position. I'm not sure which one it is, you would have to look at the manual.