Squealing Deluxe Memory Man, anyone?

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goose42
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Squealing Deluxe Memory Man, anyone?

Post by goose42 » Wed Jul 20, 2011 9:16 am

My friend/sometime client has a Deluxe Memory Man (think it's early 90s) that has seen some hard times on the road. The input jack and Chorus/Vibrato switch were both hanging inside the case, so I offered to take a look at it. Immediately on opening, the ground wire snapped and the hanging input jack fell out like a Crackerjack prize. A couple of hours with my rudimentary soldering skills later, and the jack, switch, and ground wire are back in place and functional.

Now, the unit squeals like an AM radio, a kind of ring-modulator sound. I don't know if this problem was there before, or if I inadvertently caused it (it only got used live, and under VERY VERY LOUD conditions). I'm glad that we agreed up front there was no guarantee that I could fix it! Has anyone had/been able to fix this problem before?

Here's what I know:
1. The contacts on the three-pole switch to switch from Chorus to Vibrato only reach two poles at a time, so I don't think I f'd that up.

2. Though the input jack was broken clean off, I could tell that something was soldered to both the tip and sleeve leads. There's a bare wire that runs to the other two sleeve leads (Direct Out and Echo Out), so I soldered that to the new Input sleeve lead, too.

3. An insulated wire was already soldered to the tip lead on the Direct Output, so I soldered that to the new Input tip lead.

4. I've read that this kind of squeal usually means the clocking signal is leaking into the audio. Makes sense, because it changes pitch when I change any control that doesn't have to do with levels... however, turning the delay time way down doesn't kill the noise. I also made sure no wires were running across the back of the board that weren't there already.

5. What does kill the noise: turning Blend control all the way to full dry signal. Also, it seems to peter out when I stop playing for a while, so I'm guessing there's a gate keyed to the input that closes. Signs point to the problem being somewhere in the delay circuit.

If anyone's got a minute to check it out, I made a Reaper project with some audio recorded through the instrument input on my Focusrite Saffire, which I chose to eliminate the amp. I dropped markers where I changed controls, so you can hear how the noise varies with the changes.

Thanks for taking a look!
Cheers,
Stephen "Goose" Trageser
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honkyjonk
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Post by honkyjonk » Wed Jul 20, 2011 9:35 am

This is just an aside, as I don't know what the squeeling is from, but incase you had a TLO72 opamp around, it sounds pretty nice to replace U1, the input opamp with a TLO72. Seems to make it a bit more round, full, and more headroom.

I did this with mine and liked the difference a lot. Maybe not worth it though if the opamps aren't socketed. I think the MM has both socketed and un socketed versions.

Anyway, good luck. Just thought I'd mention this.
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goose42
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Post by goose42 » Thu Jul 21, 2011 5:35 am

Hey, honkyjonk, thanks for the tip! U1 is currently a socketed MC4558CN. If possible, I'll try that upgrade, quick search shows I can probably get them for a dollar each. Looks like there are five of these guys on the board. Worth replacing any of the others?

It bugged me, however, that the PCB sits off-center and at an angle in the box. I pulled the caps off the pots so i could remove it... looks like at one time the footswitch got rammed into the board when its nut came off. There are several components laying over or whose legs are bent, including all the pots. This thing may be beyond my capability to repair properly. :(
Cheers,
Stephen "Goose" Trageser
bucketcitymobilesound.squarespace.com

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Scodiddly
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Post by Scodiddly » Thu Jul 21, 2011 10:49 am

Probably worth your trouble to go through and check or refresh all the solder joints, tug on each component to make sure it's still fully connected, etc.

I don't think I have the service info, but I believe that there are some trimpots in there for things like tweaking the clock and filtering and such. There's a bit of a calibration routine, setting the correct clock speed and then setting a filter to keep the clock noise out of the audio path. I worked on one years ago, so that's what I'm remembering.

goose42
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Post by goose42 » Fri Jul 22, 2011 6:40 pm

I will go over the board again as soon as I get a chance. Nothing LOOKED loose or cracked from the bottom. I tugged on everything that looked impacted by the footswitch on top, but I didn't look at anything else.

If anyone's ever curious about the guts, or trying to repair one, here's a lengthy forum post, including a reproduction of the schematics, lots of pictures of the circuit board, and an email from Howard Davis, the guy who designed the Memory Man, about how to modify/repair Memory Men (Mans?).

For the clock issue, search the post for the words "BBD balance." It's a five-step process, requiring a scope and an oscillator. I don't have either, but I bet I can find someone who does.

Of course, since this pedal has had so much abuse, it may still be beyond repair. Will let you know how it goes.
Cheers,
Stephen "Goose" Trageser
bucketcitymobilesound.squarespace.com

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Post by Nathangrn » Sat Jul 23, 2011 8:52 am

I would definitely check the other solder joints out. I have a Russian Big Muff that had 3 or 4 that weren't even soldered.
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