Interesting pedal - Yamaha DM-100

[Mark Hammer]

I had a significant birthday the other day, so a longtime friend generously gifted me with a box full of pedals he had picked up over the years a various yard sales, thrift shops, etc.  Virtually a complete pedalboard.  I'm a lucky guy to have friends like that.

One of the pedals was a Yamaha DM-100, that I gather was their attempt to mimic the Boss MZ-2 Digital Metallizer.  Or maybe the MZ-2 came after.  I don't know. It's a distortion pedal, with several modulation presets - short delay, chorus, flanger - that can be used with the distortion or on their own.

Naturally, I had to take it apart and see what was in there.  Unlike the Boss unit, that generates the modulation digitally, this one is all analog, for better or for worse.  Much to my surprise, it houses an MN3007 and MN3101 as its modulation source.  The chorus and flange sounds aren't too bad at all.  The "doubling" sound is basically the longest short delay they can squeeze out of the BBD, which is nothing special.

The board is pretty tightly packed, but it would be interesting to see if I can spot the components for the modulation sub-circuit, and maybe insert  a mini-toggle or two to coax more out of it.  Yet another post-retirement project. 

[loscha]

Hi Mark,

I have the service manual for the DM-100.
Copy date on the manual is January 1989.
Boss MZ2 service manual is dated January 1988.

[Mark Hammer]

Well thanks so much for that!  Deeply appreciated.
Clearly much to tinker with in there. in the way of trimmers.

[ElectricDruid]

Do let us know what you discover, Mark. I don't think I'd want to clone it exactly, but it might be one to be inspired by. I like the idea of a pedal that doubles up a distortion sound for extra thickness, but it needs to do something more than you'd get by just running your dirt pedal into a chorus.

T.

[Mark Hammer]

I played with the trimmers a bit.

T2 sets the feedback amount for the flanger mode.  As per the BF-2, full feedback is annoyingly metallic and boxey.  I may drop the value of C41 to shave off some bass from the feedback.
T3 and T4 dicker with the clock time, although I can't seem to get different delay ranges for chorus and flanger, which I thought would have been the case.  Perhaps there is some magic combination of trimmer settings that does so.
The doubling is useless, though perhaps I can render it useful with some mods.
What would be nice is variable sweep rate for the modulation.  I had popped a hole in the side, by the Volume pot.  Initially, it was to install a mini-jack for remote switching, but I may use it for a pot to make the sweep rate variable.  I assume that would involve some substitution for R76/77/78.

[Ran]

I also played with the trimmers. Dialed back T2 and got a much more usable flanger. However, I got overly curious and started messing with the other ones, and testing connections on the back ala circuit bending. I found a really good sounding pitch bend point, but then I got a few sparks...

Nothing looks out of the ordinary and everything works just fine. Except the chorus and flanger are incredibly subtle now (chorus is almost nonexisitent, and flanger is just a light metallic overtone). I can't seem to get the trim pots set to make them as deep as before.

T1 ranges from no effected signal on both sides with a ramp in modulation turned counterclockwise before inverting and dropping out. T3 fades out any signs of modularion fully counterclockwise, and brings more modulation in as turned clockwise. I can't tell what T4 is doing.

Any suggestions? I have a multimeter, but I would like to avoid investing in an oscilloscope just yet if possible.