Skreddy Echo clone?

[vizcities]

Has anyone ever reverse engineered the Skreddy Echo? My guitarist has one and it's by far the best sounding PT2399 delay I've heard - it beats my Multiplex Jr. and virtually any YouTube demo I've come across, both in terms of tone and softly noisy repeat oscillations. I've recently realized that, thanks to the fact that I'm nearly 3 years deep into this hobby, most of my Base Pedals - OD, distortion, phase, chorus, boosts, buffers, fuzz, trem - are covered several times over*, and I foresee an Aquaboy DM-2 build on the horizon. But I'm still lacking a tape-ish delay I can believe in. Any thoughts?

(*Not that this matters - I still have like 10 pedals on deck, about 3/5 of which are ODs/fuzzes/distortions.)

[madbean]

AFAIK it was never completely traced. Maybe 75% of the way. Couple unusual things about it: it uses two 2n7000 diodes for soft clipping in the second inverted op-amp of the PT2399 and it used inductors for two different LP filters at the PT2399 output. For the modulation, it uses an EA trem style LFO. From what I gathered, the LFO uses optical to modulate an LDR in parallel with a depth pot which is in series with the delay pot...but I'm not positive that's correct.

[somnif]

Man it would be a lot easier to find info on this if Photobucket hadn't gone stupid....

[Boba7]

I'd love to know more about it too. A shame the pics are all unavailable now...
Maybe I should try the 2x2n7000 in a Multiplex build. Thanks for the tip!

[madbean]

Yeah, I saved all that stuff.

http://www.madbeanpedals.com/misc/SKECO.zip

[Boba7]

Smart! Thanks for the link!! So he uses 120nf instead of 100nf between pin9 and 10 and pin 11-12. Good to know.

[vizcities]

Great stuff! I'll pore over the info in the .zip and see if my guitarist would be willing to let me open his up and poke around. More soon(ish)...

[Boba7]

I wonder what difference it makes to increase the value of the caps at pin 7 and 8 (usually 100nf, in the Skreddy echo 220nf). Anyone has any idea?

[culturejam]

I wonder what difference it makes to increase the value of the caps at pin 7 and 8 (usually 100nf, in the Skreddy echo 220nf). Anyone has any idea?

The internal schematic has never been fully published by Princeton, but pins 7 and 8 are connected to the Modulator and Demodulator sub-circuits in the PT2399. It seems like the caps that connect to them set frequency gain in whatever is going on in that part of the chip. If you got with bigger values, the bass frequencies *seem* to have a lot more gain. On a typical (Rebote-ish) delay setup, going higher than 100n usually makes bad sounds. But I suspect the Skrecho does a lot of high-pass filtering before the PT2399, and so it adds back some low end with those higher cap values on pins 7/8.

[Boba7]

Very interesting, I had never heard/read that. I usually go with a slightly higher value for the 9-10 cap, I may tinker with 11-12 too (using Skreddy values) and try different caps on pin7 and 8 just to hear the difference.
Thanks a lot!!

[culturejam]

Very interesting, I had never heard/read that. I usually go with a slightly higher value for the 9-10 cap, I may tinker with 11-12 too (using Skreddy values) and try different caps on pin7 and 8 just to hear the difference.
Thanks a lot!!

When I last experimented with this, it was a few years ago. It's possible I am mistaken. So keep that in mind!