freestompboxes.org

Got one of these in for repairs. To begin with, original pots were fastened with hot glue, stomp switch had turned into momentary, DC jack was shattered and the battery snap was dead. Swapped the broken parts and tested it. Sounded really nice. I figured that there has to be a schematic available on the web as it quite old and very nice sounding OD/Dist. So i packed it up with a ton of packaking tape, ready to be sent back to the owner.

In the evening i started to watch some Voyager episodes on the couch, armed with a mug of cola and a laptop. Started looking for a Mysto-Dysto schematic as i figured i might want to clone one for myself at some point. Damn. No schematic anywhere. Only some random mentions about the circuit being OD250/Dist+ with BMP-style tone control. Just a few hours back i had the unit wide open on my desk and a camera about one meter away from it. Didn't occur to snap some photos at the time. Asked around for the schem, and no-one had a copy. Or even seen one.

The next day i opened the parcel i had taped shut last night and opened the Mysto-Dysto up again. Snapped couple of photos and wrote the component values down.
Haven't have time to trace it to a schematic yet (nor will have in the next week or so). But i thought i'd share the values and photos anyway.

Opamp is 6552, there are two 2SK30As and four 2SC1815 transistors in there. All three diodes seem to be Si signal diodes. Should be pretty close to modern 1N4148s.
Pots are: Distortion C500K, Tone A100K, Volume A100K (I'd suggest trying linear for tone and volume...)
"Bypass" switch is latching SPST. LED-, SW2, Dist lug 3 and DC jack tip connect to ground with in/out jack sleeves I have no idea what colour the original LED was. Swapped the hot glue blob for a 5mm diffused red. Works fine...

Give me a few days/some hours of undisturbed time and this should be enough to make a full circuit diagram.

Cool!

Would love to see your schematic of this Dirk!

I recently traced the Panther Distortion, it gots the same PCB.
The schematic is very much alike but still different in some componets.

[quote="Manfred"]I recently traced the Panther Distortion, it gots the same PCB.
The schematic is very much alike but still different in some componets.

I don't mention it, the schematic shows the Locobox distrotion, with the proper values form the Locobox PCB shots.

The Schematic was faulty, the IC pin lables were wrong and the capacitor to the level pot is 47nF not 47uf.
Here the corrected schematic.

Schematic is still wrong. there is no cap in parallel to the diodes, this cap is after the 27k-resistor near the tone-pot

tube-exorcist wrote:Schematic is still wrong. there is no cap in parallel to the diodes, this cap is after the 27k-resistor near the tone-pot

Thanks for the hint, you are right.

In accordance with the Panther Distrotion corrections,
here the corrected schematic.

Missed 1N914 reverse polarity protection diode added.

1981:

Drawing error in the switching control part fixed.

I got one for dirt cheap (10€) but it sucks big time...tone is useless, so the gain, and the feeling you get is that you have a blanket on your (possibly true bypass) distortion pedal...not an heavy overdrive, not a good distortion, not a good pedal at all...think I'm gonna rip it up on the fly and have something better to fill the box!!!

Could there be something wrong with yours? After all, it is a 250/Dist+ with BMP tone control. Upping the cap at gain control would be a nice mod to get slightly better balance and possibly even tweak the tone stack more usability. For me this circuit isn't bad sounding thing at all.
+m

It seems to be in good working order, it's just a not so good sounding pedal IMO. Gonna try to skip the switching part and make it TB, Else I could try to skip the tone part too, and have a regular 250 alike...

Right, just desoldered the output wire (it's purple if anyone cares) and soldered to the output diodes, so now it's a 250 with input buffer. now it's more usable IMO, yeah you haven't got tone but that BM tone was cutting too much and it was usable only at its middle point...otherwise it was too shrill or too muffled...now you can get 80s riffs and sound good, not bad...gonna try to use the other IC side and get a more usable tone, else I'll leave it this way.

...or take the second part of the OCD schematic, so invert the pins at the op amp making it non inverting and have the tone control at the end.
damn, I wish this forum had the EDIT button!!!