Dean Markley DMC-80 - A Right Kerfuffle

[TermiteSpeaker]

Let me begin by saying that this is my first post. Hi!

I bought a Dean Markley DMC-80 100w 2x10 combo quite a while ago, and I get the feeling that the previous owner passed it on to me with some knowledge about a few problems that I did not witness when I went to test it out. I searched the model on these forums and have not found any threads, so I hope you don't mind if I just unload all of my problems here.

I don't really know where to begin with this one. There is always some hiss going on, even with everything at zero. The chorus effect, when activated, creates another distinct hiss (so I get some sort of hiss chord going on  ), and when I turn up the speed pot on the chorus effect, I get feedback that presents itself in the form of little blips. These become increasingly faster as I increase the speed of the amp chorus. The pots are all old and need replacement, but I doubt that this is the cause of these problems.

The next set of problems have to deal with things that are a bit more noticeable. Firstly, the drive channel comes on and off intermittently. Not so much a problem anymore, but it still happens on occasion. Secondly, that chorus unit made some pretty wild noises when I checked it tonight. I had never heard anything quite like it before, and I don't know how I would describe it. Maybe like the reverb tank was feeding back into the chorus, which, in turn, was feeding back into itself, while the drive channel was active.  I wish I had recorded it, though, I kind of liked it. Just not on my guitar amp.

The most annoying thing, however, is the tendency for the level to drop off and come back up as it pleases. It's usually pretty quiet, and I tweak around with it, then it gets to the volume it's supposed to be at very suddenly. Then, I'll be playing, and it will fade down gradually. Not cool. The volume problems on this amp seem to be becoming  more and more frequent, which worries me.

I've opened this thing up a few times, and replaced the reverb tank. I didn't see anything too bad going on, except for a broken lead on a resistor on the power amp, which I have soldered back into place. I don't know if that fixed anything. I'll open it up tomorrow to have a look at it, maybe take some pictures for reference. I have a schematic and user's manual from Dean Markley's website, too, if it would help to post that.

This is a really badass amp, I'd hate to scrap it. It's louder on 3 than I've heard a lot of combos on 7, and the tone is to die for. I'm guessing that all of the aforementioned problems can be traced back to the previous owner banging the top of the cabinet to show his thug friends the spring reverb, as he did when I went to buy the thing. There's paint and stickers from crappy punk bands stuck to the tolex; it reminds me of a shelter animal that looks like hell and has a limp leg - I would never mistreat an amp like that - NEVER! If any of you can help me diagnose or fix these problems, I would be very grateful, and there may be a kiss in it for you. Cheers!

[J M Fahey]

Hi Thermite.
Luckily, most of your problem usually are "mechanical", not electronic.
Start by cleaning all your pots and squirting some WD40 into every jack and switch.
Work every switch back and forth many times, and plug/unplug repeatedly into every jack, to clean the rust, grudge and slime you most certainly have there.
¿The hiss? ... It's a fact of life, you'll have to stand it, anyway at jam or show levels it dissapears.
Juan Manuel Fahey.

[TermiteSpeaker]

But with all the levels at zero? I don't know, I guess I've just never noticed any hiss on any other amp when I had everything completely off because I wasn't worried about what it might be.

I've gone over all of the pots with contact cleaner, but I think it might just be time to switch them out; a couple of the knobs are scratchy, and though cleaning and thorough exercise has helped, they're still not 100%.

Thanks, J M!

[J M Fahey]

There *is* what some would call a mistake there, that increases hiss even with both volumes on 0, although it reacts to tone controls,  but let's start with the worst (pots and switches) and later we'll fine tune the amp.
Good luck.
Juan Manuel Fahey.

[TermiteSpeaker]

Thank you, once again, for helping me out here. I'm going to give this thing a thorough cleaning and inspection, and when all of the contact cleaner has evaporated, I'll put an update up.

[TermiteSpeaker]

An update: I have been spraying the insides of the pots with some contact cleaner (M.G. Chemicals brand Electrosolve). I haven't had a whole lot of time to play, but my issues seem to have diminished significantly. I did have a problem getting a proper amount of volume when I turned the amp on tonight, but that's not unusual; I tweak the volume pot, and after a loud and unpleasant pop, the level shoots right up. I have noticed that if I play before I fix my volume problem, it sounds like the speakers are perforated. This surely can't be the case, though, as after I fix the volume, it sounds perfectly fine.