Grind Customs FX DeProundis Delay : tone problem

[eve-the-frog]

Hi,
I've built the GrindCustom DeProfundis delay and everything seems to work fine...



But the tone of the delayed sound (not the first sound, but the following delayed ones) is too dull for me even with tone pot maxed.

I thought I could lower some caps (or resistors ?), maybe the 100n between "tone 1 & 2" and "FB1" next to 22k and 1K resistor ? But I tried to replace it with a 47n cap and it mades no differences to my ears.

What do you think ?
Any suggestions or ideas are welcome.

Thanks

[Addy Bart]

Pretty sure that the tone pot works like so: the more clockwise you turn it, the more filtered the delay signal becomes. Have you tried with the pot fully CCW?

You could lower the cap values across pins 13 and 14 (and maybe also 15 and 16) to make it brighter. It does get more noisy though. I've used 1n5 caps in those positions and that's worked fine. Also, the 10n cap below IC2 filters the sound, so you could try a lower value there. Personally I think the De Profundis sounds great with the caps in the layout but there's no harm in trying out some different values. Put some sockets in if you can, it makes life a lot easier when testing things out.

One thing I've done to my build is remove the 500pf cap to the left of IC2. I found it dulled my clean signal. I put a 5pf cap in there instead. Seems to be working ok... no radio stations coming through the amp etc.

[eve-the-frog]

I read something about pins 15 and 16 cap in another thread...
I'll try all of this this evening (Europe time) and tell you what happens.

By the way : I want to use this pedal with both guitar and bass. I don't know if it makes a difference to which frequencies I want to filter...?

A big thank for your help !

[Addy Bart]

I use mine with synths, and so I put in 330n where the 100n cap (the one near pin 9 of IC1) goes. The higher the cap value, the darker the filter can go. Again, I would socket there and try out different values. Good luck!

[eve-the-frog]

Tests done !

I've socketed all the caps mentioned above and tried a bunch of values.

I have to say that the better tone to my ears is without any of the four caps, but the sound become pretty crappy. Too much, I admit.
I found a good sound with 680pf between 13-14 and 15-16 legs, but I have self oscillating sound if feedback is turned above 12 O'clock.

The middle solution is 1n5 instead of 2n2 (13-14 and 15-16), 4n7 instead of 10n between ICs and 10pf instead of 100pf at the right of IC2.

But what I want is a clear sound, as clear as original, in the repeated ones. And it is not.

Maybe this pedal is not for me.

I'll try Madbean Cave Dweller 2015 to see if I can get something better to my ears.

And you're right : dull sound is achieved with tone pot maxed and clear sound with CCW.

Anyway, many thanks for the tips and advices !!

[induction]

This is normal for the PT2399. It works by converting the analog signal to digital, then converting the digital signal back to analog and sending it to the output. For multiple delays, some of the delayed output is sent back to the chip input to go through the whole process again.

The analog/digital conversion introduces all kinds of nasty noise, mostly in the high-frequency range. So we aggressively filter high frequencies out of the repeats, which reduces the noise and makes the repeats darker. True analog delays are also fairly dark and low-resolution as well, so the PT2399 is considered analog-esque. (See? It's not a bug, it's a feature.) In fact some commercial pedals with 'Analog' in the name actually use the PT2399. Nearly all DIY delays use the PT2399, including the Cave Dweller, which also has a reputation for dark repeats.

Ray Ring from circuitsalad.com has designed a PT2399 circuit that does the filtering with a special (i.e. expensive and hard-to-find) 8-pole switch cap filter chip (MAX7401). He claims it gets much better performance, noise-wise. I haven't tried it, so I have no opinion about whether that's true, but you might give it a try.

He has another version that uses a rail-to-rail op-amp instead of the MAX7401. Again, I haven't tried it, but it might be worth a shot.

Beyond that, though, if you want "a clear sound, as clear as original, in the repeated ones", you'll probably need DSP, which is not super DIY-friendly. Maybe the Spin FV-1 chip will get you there. I have no direct experience with that device either, but I know that some DIY designs are available. Try google, FSB, and DIYSB to start.

[Addy Bart]

Thanks very much for the info! This is interesting stuff and definitely worth trying.

[eve-the-frog]

A ton of interesting informations !
Seems that I don't have to try Cave Dweller 2015...

Many thanks !