Horrible crackling sound from old mixing desk

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WarmJetGuitar

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Hey guys!

We're using two old PA-desks for mixing as they despite their lack of practical options such as mute buttons and effect loops got the sound we're looking for as we're on a budget and can't afford a nice 16/24/32-track desk with external reverb.

However one of our desks, a Yamaha EM-300 desk from the late 70's got this rather bizarre problem:
Sometimes the left hand power amp section is making horrible crackling sounds. It's not there all the time, it goes on and off for appareantly no good reason at all. Sometimes it's just the crackling sounds, sometimes the entire output on L-channel disappears till the unit have been switched off for a little while. Volume seems to have a saying but even at low levels it will occur at some point. It happens on phones out, on line out and on a third output which name I can't recall. It doesn't happen using the monitor out but this workaround don't solve anything as we can't use the main faders on each channel strip or the built in spring reverb.
We had this problem with the unit before, it had it's power amp section replaced but the problem occurs again.

Any ideas for what it could be? Is it something we can easily fix ourselves or is it a job for an experienced techie?
Hope you can help us out here, at least with some hints that could make the job easier for any techines. We're keen on saving this desk as it gives a nice flavour to the sound and is surprisingly clean for a desk that wasn't made for studio use in mind.
 
I used to use an old Yamaha EM series powered desk for many years for PA work, in the seventies. It developed similar symptoms, before dying altogether.

Maybe you can get it repaired, but I didn't. I figured that I would prefer to direct repair money to something more current. Contemporary mixers are cheaper, more versatile and have many more features. Perhaps you are attached to its particular sound. I wasn't, so it was no hardship to let it go.
 
I just can't think of any other affordable way of getting a 70's sound than using these old desks for mixdown. Recording to tape is one thing but the EM-300 adds a flavour I really love. The spring reverb is a main attraction, if we want digital reverb we just connect an Alesis or a guitar pedal.

We're saving up for a pro 70's or early 80's desk but it'll take some time before we get there as there's many requirements to be met if we are to spend serious money on a desk.

I know new desks have more features but I'm used to be creative about strange workarounds.
 
My educated guess is that the power supply is beginning to fail, quite possibly capacitors leaking/drying out. I hope I'm not right because that would be a repair for experts and probably not economic.
 
Recapping the supply shouldn't be too hard. If it were mine, I'd consider doing it on principle. However, the prospect of recapping the entire desk would not make me happy.

And ugh, standalone spring units seem to have become expensive lately.
 
jpmorris said:
Recapping the supply shouldn't be too hard. If it were mine, I'd consider doing it on principle. However, the prospect of recapping the entire desk would not make me happy.

And ugh, standalone spring units seem to have become expensive lately.
Click to expand...

Yeah, spring reverb units is freaking expensive - and so is tape and having the kind of lifestyle providing enough inspiration to make psychedelic rock :D

Thanks JP, good to know it's not beyound saving.
So weird, yesterday I did an overdub session where the thing caused no problems at all. This is really a strange world.
Think I'll ask a good technician to look at my Yamaha, I'm so clumpsy. Hopefully he'll show me how to fix the issue if I pay him a bit more.
 
Is there a direct out (possibly called tape out) to go to the recorder so you can bypass the crackly amp?
 
No, unfortunately no direct outs. A shame as it's preamps sounds pretty good.

For some bizarre reason it have stopped it's crackling. Very good news indeed but also quite weird. How could it be? Can't find any logical answer to it.
 
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