Another multi PT2399 project, ideas? help?

[iefes]

Hey there!

Inspired by all the great PT2399 layouts out there, I started working on my own circuit, including different ideas I liked the most.
I decided to use three PT2399s.

My goals with this project are:
- Three independant delays which can be combined (parallel and serial operation), inspired by the Red Witch Titan
- long delay times due to three Chips in series, inspired by the Sagan, Abductor, Zero Point SDX etc.
- seperate Time, Feedback and Volume Controls for each delay
- Switchable feedback-paths (seperate for each delay or one for all the three)
- reproduction of the rythmic patterns provided by the "Multiplex"
- Preamp section of Jons "Hamlet" (18V)
- Filtering section of Jons "Hamlet" which may give the opportunity to tune each delay a little different if desired

Below you can see the circuit I came up with so far. I got most of the values from the Hamlet but I also learned a lot, looking at the Multiplex, Saban, Abductor 2, Zero Point SDX, Dirtbaby, EchoBlue etc. (Thanks to all those guys!) I included Jons idea of putting a LED between pin 7 and GND. I also included the "Dirt"-control on one of the Delays for some nice rythmic noise. I think the rest of the circuit is pretty self-explanatory but feel free to ask :-)

I would like to ask you experienced people here to have a look at the circuit and tell me if you see any things that seem not to make sense or if any other ideas pop into your mind. I included pads for modulation, in case I want to use external modulation on it. I also included one pad for +18V to power one external effect by this charge pump.

I also have a few questions I would like to point out here:
- Why has every chip a 100n cap from pin 1 to GND in most circuits? Couldn't you just put one of them from +5V to GND to get the same filtering? Or do you need a higher capacity with each chip (because the Cs are all in parallel)?
- How could I include a simple (low parts) clipping circuit in the long feedback path so that the repeats get saturated more and more with every repeat? Like in the Zero Point SDX but without adding a complete active filtering-stage? Thought about one transistor-stage with diode-clipping but would appreciate other ideas.
- Is a capacitor from the feedback path to ground necessary (C39,38,53)? I saw this in some layouts but not in all.

I am going to socket a lot of parts, to find what suits me best. In all the different layouts I used to come up with this, values vary a lot. I am looking for a more tape-like feeling of the delay rather than analog.

Thanks a lot in advance!

I am going to let you know if I come up with any new questions or something :-)

cheers, iefes

[solderfumes]

Re: 100n cap from pin 1 to ground, I think it's probably to provide extra filtering right next to each chip to keep that digital noise from getting to other parts of the circuit.

[iefes]

Thank you, so I should try to locate each cap as close to pin 1 as possible? Seems to make sense.

[diablochris6]

It looks pretty interesting. One of the modes has all the delay chips in parallel, but each chip gets feedback from just the third delay. I'm wondering how that would sound.

I do wonder if having three delays in parallel will sound too busy. I built a pedal that had two delays in parallel, and it could get quite claustrophobic. When I prototyped the Sagan Delay, I created some modular boards that only had a PT2399 and the associated passive components. That way, I could use my breadboard for the tone-shaping and signal routing circuitry and patch in the delay circuits with banana clips. It looked like a mess, but it was easier than trying to fit everything into one tiny breadboard. I can share those files with you, if you want, so you can test and tweak with a modular approach.

As far as the saturation goes, I guess you could add those hard clipping diodes to ground after the feedback pot, much like the ZPSDX and other delays, but you would have to do that to all three feedback pots. Looking at the ZPSDX build doc, there is an option for a simple low pass filter for a decent tape sound. It's late, and I am sleepy, so I can't think of how to incorporate one saturation/filter circuit into the pathway so that the sound increasingly distorts with the way you have your feedback loop set up. It will probably be easier to have your saturation/filter right before the mix pot so it clips the whole sound once.

Coincidentally, I was planning on making a series/parallel delay circuit for a custom-build for my friend. My thought on how to accomplish this is different than the way you are going about it, but we have different goals in mind. Good luck!

[iefes]

Thanks Chris!
The mode you mentioned is just a consequence of the other modes I wanted to realize. I don't know if it will be useful, but I am keen to try it.
You are probably right about the "busyness" of three parallel delays. You will have to be very precise when dialing in each delay-time to get a proper rythmic pattern. When it gets too noisy, you can just turn down the volume of one or two of the delays. This Volume-knob on each delay really gives a lot of opportunities.

I also thought about voltage-mirroring the delay-pots like you did in the Sagan but as I also wanted independent delays, it would have been to complicated with switching.

I think I won't bother too much about the saturation, maybe just try to incorporate something like the low pass filter of the ZPSDX. In your build doc you mentioned that the two hard-clipping diodes in the feedback-path won't make a difference in sound, so I was wondering if it is worth it to incorporate them...?

I'd be happy to have a look on your files if it was okay for you. And I'd also be interested in your approach for the custom-build for your friend, if you wouldn't mind sharing your ideas.

Thanks!

[JC103]

I'd recommend including an fx loop to process the wet signal. If you have a Darkside build, try that out in the loop for tape saturation. Also IMHO don't overdue the tape like filtering or the delay will wind up too dark. Have fun.

[iefes]

I'd recommend including an fx loop to process the wet signal. If you have a Darkside build, try that out in the loop for tape saturation. Also IMHO don't overdue the tape like filtering or the delay will wind up too dark. Have fun.

Thanks JC103! I thought about including an fx loop but I know me and I know that I don't like bothering with external effects too much. I have included the LP-filter which is in the Multiplex and in the ZPSDX and will give this a go.
I did a quick research on the darkside. it looks interesting , but a bit too much for this purpose. If I decide to put in an FX-Loop I will try my Germanium-COT50 in it, this could give some sweet saturation. I will let you know :-)

[diablochris6]

I think I won't bother too much about the saturation, maybe just try to incorporate something like the low pass filter of the ZPSDX. In your build doc you mentioned that the two hard-clipping diodes in the feedback-path won't make a difference in sound, so I was wondering if it is worth it to incorporate them...?

I'd be happy to have a look on your files if it was okay for you. And I'd also be interested in your approach for the custom-build for your friend, if you wouldn't mind sharing your ideas.

I think the reason that the hard-clipping diodes in the feedback loop didn't have much of an effect is because I already some clipping diodes incorporated into the active filtering section of my circuit. It was overkill. It might be worth breadboarding in your case though.

As far as plans for the custom build delay, I just have them rattling in my head right now. Two PT2399-based delays, each with their own time, feedback, and mix controls, some sort of switching to place them in series or parallel, switching to move the output of the feedback loop between the two delays, and send/return buffers on each delay's wet signal. My friend likes doing wild stuff with effect patching, so I think he will appreciate the extra jacks. I am thinking about tweaking some cap values on the PT2399 so that one delay line is more tape-like, and the other has more of an analog voicing. I need to finish up another project so I can clear out my breaboard and start planning!

[iefes]

I think the reason that the hard-clipping diodes in the feedback loop didn't have much of an effect is because I already some clipping diodes incorporated into the active filtering section of my circuit. It was overkill. It might be worth breadboarding in your case though.

As far as plans for the custom build delay, I just have them rattling in my head right now. Two PT2399-based delays, each with their own time, feedback, and mix controls, some sort of switching to place them in series or parallel, switching to move the output of the feedback loop between the two delays, and send/return buffers on each delay's wet signal. My friend likes doing wild stuff with effect patching, so I think he will appreciate the extra jacks. I am thinking about tweaking some cap values on the PT2399 so that one delay line is more tape-like, and the other has more of an analog voicing. I need to finish up another project so I can clear out my breaboard and start planning!

Ah, yes this makes sense. So I will try it. I ordered some PCBs and will start with populating just the first Delay unit and socket all the values which might be worth playing around with. When I decided which values sound the best to me I can finish populating the whole thing.

Your ideas sound quite interesting as well! I also thought about voicing some of the delays differently, so I will see what I can achieve with Jons tone control. For the effects-loop you will include an actual buffer for each Delay? Is this necessary?

[diablochris6]

For the effects-loop you will include an actual buffer for each Delay? Is this necessary?

After researching a few different pedals with an FX loop, I noticed that the better designs had buffers before the send jack to handle any impedance discrepancies between the delay signal and what ever pedal is in the loop.