Volume rising and falling and a strange throat-clearing sound

viz

Help! Carvin Legacy 1 head. On the 50W and the 100W settings, the volume is sometimes ok, sometimes it drops to half or even less. The transition takes about 0.5 seconds to complete. The tone itself sounds just about Ok - a little more trebley but passable - even when the volume drops. It only seems to happen when the pre-amp is being employed - haven't noticed it when going straight from my vox modeller into the return socket. And when I switch standby on after playing there's a throat-clearing sound. What's the problem? @icbm, @ecc83, @jfpamps and other gurus?

ESchap

 

 viz said:

And when I switch standby on after playing there's a throat-clearing sound. What's the problem?

If it starts saying "one, two ... one, two" then it clearly has aspirations to be a PA amp.  >:D<

viz

Lol thanks very helpful! It also started making the sound of a teaspoon hitting a dessert wine glass.

ESchap

It'll be calling bingo numbers next ....  :-S

Seriously, it could be so many things wrong with it.  I'd try swapping pre-amp valves first then if that doesn't find the problem, see if any of the the control pots have any part to play.  After that I'd be calling for the gurus on here, or more likely taking it to ICBM to look it over.

ecc83

A rather faded schematic shows a lot of ICs in the signal path and no input protection diodes.

Could be the old TL07XX latchup problem? 

Transient noises on switching power or S/B on or off are not unusual.

Dave.

viz

Ok thanks - this noise has coincided with the volume problem so I feel they're related

ICBM

Try swapping each preamp valve in turn with a known good one first. If that doesn't fix it, it's probably not something you can do yourself.

Probably 90% it will be that, though.

viz

Will try it. Trouble is, all my spare 12ax7s are known unknown ones of dubious quality and reliability having beem swapped in and out of things over the years. But my reverb is working I think so will use that.

ICBM

viz said:

Will try it. Trouble is, all my spare 12ax7s are known unknown ones of dubious quality and reliability having beem swapped in and out of things over the years.

Yes, but since it's unlikely that they'll have exactly the same fault, if you swap in one of them and the original fault goes away - even if a new one arrives - then at least you'll know which valve you need to replace .

octatonic

Amp cancer.

viz

Wisdom icbm lol octa.

Wazmeister

Try Tesco cold 'n flu.... Never fails for me...

viz

It was dirty send and return jack sockets I think. Problem gone away now anyway.

Fortheloveofguitar

viz;212547" said:

It was dirty send and return jack sockets I think. Problem gone away now anyway.

Used to happen on my cornford mk50 a lot. Always kept switch contact cleaner on the shelf.

viz

Yep I squirted wd40 up there and rammed a jack plug in and out a few times.

impmann

WD40?  

Never use WD40 on amps, it breaks stuff...

viz

Oh really? Thanks, good to know.

ICBM

No it doesn't. I use WD40 for cleaning and lubricating pots and jacks in cases where contact cleaner either leaves the pot too 'dry' or the problem comes back. It works very well and doesn't cause any harm.

You wouldn't want to spray it on parts of the circuitry that carry high voltages because it's probably electrically conductive, but pots and jacks don't.

viz

Indeed contact cleaner is conductive too, no?

impmann

Sorry ICBM, I know you and I clash on some things, but seriously in the repair shop that I manage we have at least one unit a month where someone has destroyed the track on a pot by using WD40. Its is a water displacer, (hence the WD) but it also contains other compounds that attract dust, grit and grime and that is then ground into the tracks of the pots. It is not recommended (even by the company themselves) for use on delicate electronic parts.

viz

Is it ok on jack sockets or have i ruined my amps?