Dual PT2399 delay design: block diagram inside

[Morocotopo]

Hi people! I´m in the design stages of a new box, and I wanted to run it by you to see what are your opinions on it.

It´s a PT2399 delay (yup, another one...). I made the Rebote, the Ping Pong, the Echo Base. All good designs, but I wanted my own take on this, so out goes the paper and pen. My objectives are:

-Dual delay chips, series or parallel connection switch, but not like the Ping Pong, where the feedback and level are global. Each chip will have it´s own controls to get more variety of sounds.
- Cross feedback between chip 2 to 1. This to get even more posssibilities of sound
- LFO Modulation
- Wet only option. Dry only output (for connecting to two amps, one dry, one FX)
- Tails switch (or maybe always in tail mode. Don´t know yet.)
- No true bypass option. FET switching.

Well, that´s about it. Here´s the modular diagram:



This kind of FX can easily grow more knobs and switches than a Minimoog, so I tried to keep the controls count to a reasonable number. For example, I thought briefly about using a third delay chip, but the level of complexity scared me away, or having an LFO for the second chip...

Well that´s it. What do you think??? What would you add/remove? I´m already making the actual schem.

Thanks for reading.

EDIT: I wanted to have a level control for each delay that goes from no delay to ONLY delay to be able to eliminate the wet only switch, not a control that, at full, gives a 50/50 mix. That could be done by replacing the mixing resistors with a pot. Great, but I have to mix THREE signals, so that´s not possible. Or is it?

[midwayfair]

that's a lot of controls even for a "simplified" version.

First, I don't think you need two mix controls. Hardwire one of the mixes to be at or just below unity, but make it so that you can set the time to the absolute minimum and feedback to 0 repeats (though I'm not sure that's possible in a PT2399. Similarly, do you need a separate feedback for the second delay if you also have cross feedback? That seems redundant.

You can get "wet only" via the mix knob. I don't think you need a switch for it.

The series/parallel switch is interesting, but in practice, how useful will it be? If someone wants parallel, they might as well have two delay boxes. And when they're in series, you'll still get the dual echo effect.

It might be possible to reduce the LFO to one knob like on the memory man.

[slacker]

Looks cool to me.
You could have 100% wet to 100% dry mixer pots for each delay, I can draw something up if you like. I experimented with this on the Echo Base, it makes having tails a lot harder though because you have to be able to go from whatever setting you have on the mix pot to a 50/50 mix with the bypass switch. This would be even trickier with two mix controls. Level controls are easier to do tails with because the dry signal is always present and doesn't need switching.
Instead of a separate feedback and cross-feedback controls on delay 2 you could have one control and switch it between the two functions. Depends if having both at once is interesting I guess.

[Morocotopo]

that's a lot of controls even for a "simplified" version.

Yep. Imagine how many knobs the full featured one would have! I want the minimum number of controls, but retain the flexibility.

First, I don't think you need two mix controls. Hardwire one of the mixes to be at or just below unity, but make it so that you can set the time to the absolute minimum and feedback to 0 repeats (though I'm not sure that's possible in a PT2399. Similarly, do you need a separate feedback for the second delay if you also have cross feedback? That seems redundant.

I don´t quite undertand this...

You can get "wet only" via the mix knob. I don't think you need a switch for it.

Not if it´s a 50/50 mix one.

The series/parallel switch is interesting, but in practice, how useful will it be? If someone wants parallel, they might as well have two delay boxes. And when they're in series, you'll still get the dual echo effect.
It might be possible to reduce the LFO to one knob like on the memory man.

Two delay boxes would require a splitter, a mixer... and in series you wouldn´t have the crossfeedback that I propose. The LFO could have a fixed depth or speed, but I want the versatility.

Looks cool to me.
You could have 100% wet to 100% dry mixer pots for each delay, I can draw something up if you like. I experimented with this on the Echo Base, it makes having tails a lot harder though because you have to be able to go from whatever setting you have on the mix pot to a 50/50 mix with the bypass switch. This would be even trickier with two mix controls. Level controls are easier to do tails with because the dry signal is always present and doesn't need switching.
Instead of a separate feedback and cross-feedback controls on delay 2 you could have one control and switch it between the two functions. Depends if having both at once is interesting I guess.

About the controls on delay 2, I think the separate feedback controls will give me more possibilities. We´ll see. Thanks for the offer, if I get stuck I´ll give you a shout to help me!

Thanks guys.

[Morocotopo]

Sorry Slacker, I just noticed I didn´t respond to the first part of your reply. I think I have a way to implement the wet only switch and have direct signal in bypass. I´ll post my draft schem soon, still working out some things.

[Nasse]

Tone control at the echo feedback would be nice, like roland echo, i use it all the time

[Morocotopo]

Nasse, yup. This will have a fixed rolloff, not a variable one, can´t have more knobs!

Well, here´s the first tentative schem:



I have implemented a way to have a wet only switch and the direct signal at the out when in bypass, with FET switching. Also FET´s for all switching needs. Mostly this is a patchwork of pieces from all over: LFO from the Boss CE2, delay lines and buffers from the rebote with some mods, FET control from Merlin´s Smalltime, and so on. When in doubt, steal from others!

I have doubts about some of the FET´s bias. We´ll see how that works. Absolutely, positively not tested (except the basic delay lines)!
Out comes the breadboard.

[Morocotopo]

OK, breadboarding the thing. Already had to make some mods, so disregard the previous schem, but it´s basically working, still have to try some things.

By the way, two ideas that came to me while working:

- Since the fidelity of the signal deteriorates with longer delay times, all the schems I have seen have lowpass filters that are calculated to sound good in the worst possible case, meaning the longest delay times, or at least achieve a good compromise between losing too much trebele and not sounding awful. But at shorter delay times we could have less agressive filters, right? So, wouldn´t it be possible to use a dual pot for the delay time, and use the second "section" of that to control the filter(s) cutoff frequency?

- How about using another delay chip to delay, not the audio, but the LFO signal? Maybe we could get different LFO shapes... wild modulation!!

[GodSaveMetal]

OK, breadboarding the thing. Already had to make some mods, so disregard the previous schem, but it´s basically working, still have to try some things.

By the way, two ideas that came to me while working:

- Since the fidelity of the signal deteriorates with longer delay times, all the schems I have seen have lowpass filters that are calculated to sound good in the worst possible case, meaning the longest delay times, or at least achieve a good compromise between losing too much trebele and not sounding awful. But at shorter delay times we could have less agressive filters, right? So, wouldn´t it be possible to use a dual pot for the delay time, and use the second "section" of that to control the filter(s) cutoff frequency?

- How about using another delay chip to delay, not the audio, but the LFO signal? Maybe we could get different LFO shapes... wild modulation!!

Stay tuned for these man!!!!
DALE ARIEL tú puedes!!!

SALUTIS desde PERÚ!!!!!