Demedash t120 mods

ZorakIsStained

New member
Looking at the gutshot from another similar pedal not made by Demedash, it looks like one way to change the repeat tone is to replace R26 with a pot. I played around with the low-pass filter section using LTspice and I think a 50k pot would produce the biggest tone range. The only other obvious change they had made was to increase C17 from 330n to 470n. I think I'm going to get a Magnetron PCB and breadboard this out, though I won't have a T120 for comparison.
 

seiche

New member
replace R26 with a pot.

This is what I did, albeit with a 25kB pot in line with the 10k (to get the regular tone on 0). The change is subtle. I'll try a 50k and report back.

I also used a 470nF.

Which "other similar pedal not made by Demedash" are you talking about?
 

ZorakIsStained

New member
Well, regardless of all of that, Demedash is probably doing a little more than just adding a pot somewhere. There are a bunch of gutshots of normal T120s, 3 ICs are clearly visible; in one pic it's the PT2399, a LM358P, and LM324N. there's also a transistor-looking device that's probably the 5V regulator. The last two ICs are double and quad opamp parts, so Demedash has 2 more opamps in his design than in the Magnetron. Chances are those are used for some sort of active filter, maybe a multiple feedback filter like this: https://www.diystompboxes.com/smfforum/index.php?topic=76222.0
Something like that would loan itself pretty well to a daughterboard. I'm not sure where to insert it in the circuit, maybe before the last RC filter in the feedback path. Or maybe in place of that filter.
 

Boba7

Active member
This is what I did, albeit with a 25kB pot in line with the 10k (to get the regular tone on 0). The change is subtle. I'll try a 50k and report back.

I also used a 470nF.

Which "other similar pedal not made by Demedash" are you talking about?

Hey

Yes, I think a 50k pot would work better than 25k. I'm not sure that's how Demedash implemented it though, it seems to be cutting lows, not cutting highs, on some demos I've seen.
Also the other ICs are probably for switching, not audio.

His pedal has evolved a lot, but to my ears it stills sounds pretty much like the Magnetic Echo from Keeley, just with a lot of extra features, which is quite cool I must say! But the base sound is definitely the Keeley circuit.
 
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