What is causing this horrible clipping sound?

[Yata]

Hey, I'm wondering if anyone can help me shine some light on a problem I have. I have an ibanez valbee practise amp and it makes this horrible farting clipping noise every time the signal hits a certain level. I assumed at first that I somehow ripped or damaged the speaker and replaced it with a jensen Ch6. After turning it back on and getting sound unfortunately I still have this weird farting/clipping sound. The noise originally happned a few months ago after turning it on and playing, but before that I had been using a makeshift audio probe to try and diagnose problems in a pedal I was building, I assumed the damage has something to do with this as the probe was making large clips and pops ect. as I went along my circuit trying to find the problem. Does anyone have the slightest idea what sort of component would cause this? It would be nice to be able to rescue this amp as it is my main practise amp and sounds pretty nice for it's size.
I've attached an audio clip so you can hear it yourself
https://clyp.it/wmlec1ns

[tonyharker]

Have you checked for DC on the speaker?

[wavley]

http://www.diystompboxes.com/smfforum/index.php?topic=99272.0

Probably a bad solder, but check the other things in the thread I linked to.

I don't think that's the sound of blocking distortion

[Yata]

Have you checked for DC on the speaker?

DC?

[wavley]

This is a tube output right?  There's an output transformer so there can't be DC on the output, this is a good place to look when the amp is solid state.

[Yata]

Little update, I tried plugging straight into the effect return and the sound seems fine. I can only surmise that it must be some sort of component on the pre-amp. Can anyone think of anything common on a pre-amp circuit that could be damaged in some way by the input (from when I had an audio probe plugged into the amp to fault find a pedal)

[anotherjim]

Sometimes amp problems are vibration related, which is when strong playing can cause nasty bursts of horrible noise. The FX send-return jacks have contacts that get dirty and can interrupt normal signal flow. Using the jacks can self clean the contacts, so is the normal input still causing issues?

I would check around the amp while gently tapping things with the back of a pencil. Don't tap the tubes too hard!

If there are panel control pots, switches and jacks mounted on PCB, check the soldered side for broken solder or cracked copper tracks. Sadly, that can often mean undoing a lot of fixings to achieve.

This image is supposed to represent a Valbee, I don't know if yours is the same - with that distortion circuit in the pre-amp.

[GibsonGM]

I had an experience that sounded a lot like that with a small practice amp...turned out to be a bad solder joint on a jack (think the input jack) that would kind of oscillate as the amp vibrated, making intermittent contact and noises like that.  I imagine any number of components could do the same thing if they had a bad joint.

Pencil chopstick test, yup...

[DIY Bass]

I once had overload cause problems in a bass amp.  My symptoms were a bit more severe - no signal at all.  My problem was in a graphic EQ board that comes after the preamp - so after all the gain stages for maximum signal boost.  The zener diodes that provided regulation of the power to the board were gone, and every op amp on the board was fried.  No other problems.  Given that, I would wonder if one of the op amps towards the end of the preamp section might be felling a little sick.

[GGBB]

A combination of two things already mentioned: vibration and bad solder joints. One of my tube amps was making a similar but worse noise at loud volumes - reflowing all the tube socket solder joints fixed it.

[Yata]

If it was the solder connecting the tubes then surely the sound would still be present when I plugged into the effects return? The pre-amp stage is almost all solid state, am I right in thinking the solder problem is somewhere possibly between the input jacks and the op-amp/diodes, I also don't want to mess around too much with anything in the power amp stage for obvious reasons

[GibsonGM]

Like I said above, my similar problem was with the input jack.  Never would have guess that sort of sound could come from a vibration affecting a bad solder joint.   

From your reporting, it sounds like it's before the effects send, yes.

[GGBB]

If it was the solder connecting the tubes then surely the sound would still be present when I plugged into the effects return?

My point was to reinforce what others have stated - that it sounds like bad solder joints affected by loudness related vibration (as it was in my case and Mike's) - not that it's your tube socket joints specifically. Clearly your test shows that the problem is pre-send, assuming you still had enough volume/vibration with the pre-amp bypassed.

You say that the pre-amp is almost all solid state, which I take to mean it has at least one tube so its not purely solid state (the block diagram that was posted confirms this). Tube socket joints are often the most stressed joints because of their proximity to the heat of the tube and because of the fact that we remove/replace the tube from time to time (at least once when manufactured and for some people many times due to experimentation). So they are a great place to start looking when you suspect solder joint problems. Jacks and pots - especially PCB mounted ones - are another high stress area for obvious reasons.

[wavley]

If it was the solder connecting the tubes then surely the sound would still be present when I plugged into the effects return? The pre-amp stage is almost all solid state, am I right in thinking the solder problem is somewhere possibly between the input jacks and the op-amp/diodes, I also don't want to mess around too much with anything in the power amp stage for obvious reasons

Did you try connecting the send and return of the effects loop like in this thread?

http://www.diystompboxes.com/smfforum/index.php?topic=99272.0

Probably a bad solder, but check the other things in the thread I linked to.

I don't think that's the sound of blocking distortion

That wasn't the solution for his amp, but I own a repair shop and that was the problem in two amps I fixed last week.  If you don't use the effects loop the jacks can get dirty and mess up the signal, which would be fixed by plugging into just the return.  Jumping the send to the return with a patch cable will tell you if this is the problem.  It's also really likely that it's a bad solder in the preamp, usually on a tube or the input jack.  Wiggle any ribbon connectors that might be in the amp.