EHX Full Double Tracking

[Alex]

Here are two layouts for a modified EHX Full Double Tracking slap back pedal.
Here is the original thread:
http://freestompboxes.org/viewtopic.php?f=1&t=10741

First layout is the buffered original version.


Second layout is true bypass version with added output boost (SHO)

[heuermh]

Cool, thanks, Alex!

From the FSB thread I started thinking I would want stereo outs.  I already have a buffer and split though, so maybe I could lose the blend and go 100% wet.  Then a feedback pot and momentary 100% feedback stomp switch would be nice to have.

Just thinking out loud ... will let you know how I get on with any mods!

[zombie_rock123]

The true bypass/SHO modded one can be marked as verified for anyone else who wants to build it. As in the link to the discussion, the biasing trim has a tiny window - about 1/3 rotated suited mine but if I was to build again I'd use a multiturn to dial it in a bit more accurately.

Thank you Alex, this shall be boxed very soon

[Alex]

Thanks for verifying it!
I've moved some components around to fit a multiturn trimmer.
How does the pedal sound?
Could only find one video on the internet.

[zombie_rock123]

It sounds really nice to my ears. I've set up a PT2399 on a breadboard with one repeat and it could be my confirmation bias but I do prefer the BBD. I've only tried it after overdrives so far - the longer MS setting sounds better overdriven whereas clean sounds better with the shorter time. I guess thats painfully obvious to most as the gain hides the shorter repeat..

I've been thinking about the switch and how to vary that gradually to give a better impression of double tracking. So far I can only think of taking out the resistors that the switch chooses between - using an LDR and resistor in parallel then using an LED to vary the time. If that goes too fast and the LED with inbuild oscillators can't be slowed then maybe the pseudorandom LFO could be a good candidate for slowly changing the speed of the tracking with a slow rate and the glide option.

Then just need to think about pitch... or maybe just some filtering. Do you think it's best to tap the delay line for filtering/experimenting around the R11 area before the (assumed!) output buffer? Thinking that it might make a nicer effect with some variation (warble?) to the double tracked sound.

[gul]

I posted this in the main section as well...

I built the version with the multi-turn trimmer. I couldn't get the echo to kick in at all with the multi-turn trimmer (I tried 3, just to be sure it wasn't the trimmer itself). I switched it to a regular single-turn trimmer and it worked straight away. Just thought I would add this info here in case someone else builds it and runs into the same snag.