Shorter delay times for PT2399 Delay

[rock soderstrom]

I am still working on my tube PT2399 delay which should be optimized to generate shorter delays. The delay should complement a tube spring reverb and should generate early reflections and short slap back echoes.

As you know, the delay time of the PT2399 is set on pin 6. The current flow is the variable to be changed, pin 6 sits constantly at half operating voltage, i.e. 2.5V.

As far as I know, a current of 2.5mA must not be exceeded, which corresponds to a minimum resistance of R=2.5V/0.0025A=1K, which corresponds to a minimum delay time of approx. 35mS. However, this varies from chip to chip, my available chips are above 40mS.

Other sources say that you should not go below 2k, because otherwise the "PT2399 will latch-up during the power-on sequence and the internal oscillator won't start."

My chips are fine with 1k, but I want even less. This analysis shows some possibilities to realize shorter times without "latch-up" , would my variant work?
What minimum delay time can I expect?

 

[L´Andratté]

Merlin Blencowe/Valvewizard´s Jenny Greenteeth chorus has an anti-latch-up circuit which works very well:
link to schematic
I just am afraid much shorter delay times won´t be possible even with more current out of that pin- that was my experience at least!

EDIT: just now looked at your circuit and it´s the same

 

[rock soderstrom]

Merlin Blencowe/Valvewizard´s Jenny Greenteeth chorus has an anti-latch-up circuit which works very well:
link to schematic

Thanks!

I just am afraid much shorter delay times won´t be possible even with more current out of that pin- that was my experience at least!

@merlin could apparently reach 25ms, that might be enough...

EDIT: just now looked at your circuit and it´s the same

Similiar, but his version is more refined. The parallel resistor determines the maximum delay time (of its chorus). What advantages the second transistor has over the potentiometer is not quite clear to me yet...

 

[L´Andratté]

25ms/40 Hz - too long/low for karlus strong, that would have been interesting to me...
Have you seen this? (it says 30ms)
2399 analysis

 

[L´Andratté]

If you are not focused on the idiosyncratics of the 2399 (which are real), THIS delay chip works from a couple of ms to 4 sec. with only very little more complexity (at least for line level with good sound and not too much noise).
Maybe you already know all that (;.

 

[rock soderstrom]

25ms/40 Hz - too long/low for karlus strong, that would have been interesting to me...
Have you seen this? (it says 30ms)
2399 analysis

Yes, I know the analysis, good information, but the web is somewhat contradictory on this point, maybe the min. delay time also varies slightly with the chips/manufacturers?

 

[rock soderstrom]

If you are not focused on the idiosyncratics of the 2399 (which are real), THIS delay chip works from a couple of ms to 4 sec. with only very little more complexity (at least for line level with good sound and not too much noise).
Maybe you already know all that (;.

Thank you very much, no, I really didn't know the chip yet! Very interesting.

It's true that the PT2399 has certain limitations, but on the other hand it's very musical, I can't say otherwise. In my current application in the aux path of my Mackie 802 workshop mixer, the thing is really fun, I jam with it very often.

 

[L´Andratté]

Yes, I meant "idiosyncrasies" in a good way
It´s good-sounding in a lo-fi way, like the old Casio Sk1 sampler...
With heavy lowpass filtering it becomes BBDy and with very long delay times it gets nonlinear enough as to get into audio synthesis (I love that about Rob Hordijk´s Zeitgeist circuit, which sometimes even sounds not unlike "physical modelling" of a bookshelf breaking down or something).

 

[rock soderstrom]

With heavy lowpass filtering it becomes BBDy

That's what I'm doing right now. I'm trying to realize the sound of old tape echoes, it's working well so far.

Thanks for the project tips, I also like the more freaky implementations of the PT2399 chip, but that's not my actual goal ATM.

A really crazy PT2399 noise box would also be a nice new project!