Ampeg B100R crackle

[jeffkaplan]

hi all. my first post. could use some help/advice.

i acquired an Ampeg B100R. It has begun to crackle when certain notes, especially low ones, are played as the note decays. i've searched the web and found others with a similar problem. i've checked the speaker connection, looked for fried components and just generally looked for loose or disconnected/desoldered parts. checked guitar cables, checked my bass through another amp (i only have the one bass) and did the old "bang it hard" test.

it all looks very clean and put together in the chassis so i'm looking for advice short of swapping parts since while i'm handy with a soldering iron, i'm reluctant to get too involved in testing and parts replacement. i do have a volt meter but that is the extent of my equipment other than a soldering gun. i doubt i would take it to a tech pro as the value of the amp is likely not worth the diagnosis/repair costs.

thanks in advance for any help.

jeff

[Enzo]

Isolate the problem. Does it happen in the headphones too? The cutout contact on that jack may be dirty, in which case the phones would work, but the speaker would fail.

Connect the amp to a different speaker, this one may be failing.

J3 is some sort of line out or preamp out or something similar, it has the preamp signal, is that output affected or clean?


When you whacked the amp, did it react in any way?

[jeffkaplan]

hi enzo, thanks for your reply.
i did test headphones and i believe it crackled through headphones as well (it was a couple of weeks ago.)
no reaction with the bang
not sure what J3 is? the sound is clean through the speaker. just the crackling on note decay, when it's played loud or soft.
i'll need to check the cutout on the headphone jack. think i did but i'll need to do it again to be sure.

if it's none of those do you have have other suggestions short of electronically testing components?

[Enzo]

Somewhere on it is a panel jack, and it ought to be called line out or preamp out or something similar. it is called J3 on the schematic. J1, J2 are the input jacks, and J4 is the headphones jack.

It matters a lot if the phones crackle too or not.


You say the sound is clear coming out the speaker, just the crackling on note decay. Well, that crackling is coming out the speaker isn't it? That is why we need to disconnect that speaker and connect the amp to some other speaker. The speaker itself could be causing the crackling on decay. That is a classic symptom of a rubbing voice coil - noises on decay.

[guitardad]

mcm electronics has some pretty generic (cheap) drivers (speakers) that will work with that amp. I have seen a few B100's with bad speakers causing the symptoms you describe.

[jeffkaplan]

thanks all. i'll do a little more "smoke testing" and see if i can isolate it to either the speakers or, um, not the speakers. back in a few days. thanks folks. appreciate the help.