Building Polychorus around PT2399?

[mth5044]

Or any other PT23xx IC? I was looking in the piles of the forum today and saw there was a very small spark of interest in making the polychorus as it was with BBD, but has anyone tried to make it using cheaper, probably less complicated digital delay chips? I understand there was some tinkering with a PT based flanger, but that seemed to die too.

[~arph]

The problem is that the shortest delay time in the PT2399 just is not short enough so the delay will be audible. Perhaps there are some ic's in the PT23xx family with shorter delay options.

[Seljer]

I added modulation to the delay time on my rebote delay, it sounds pretty chorusey when you have it set to the shortest delay time: http://www.aronnelson.com/gallery/main.php/v/seljer/album113/rebotechorus.mp3.html , you'd need something faster for more versatility as far as chorus sounds go or to get into flanger territory

[~arph]

Yes it's just a limiting factor in your chorus options. I does work though. You can hear the modulation at the end of my binson recreation video too.. also done with pt2399's

http://www.youtube.com/watch?v=26lLAmFi5t0

(OP: You have already seen that video  )

[Thomeeque]

Or any other PT23xx IC? I was looking in the piles of the forum today and saw there was a very small spark of interest in making the polychorus as it was with BBD, but has anyone tried to make it using cheaper, probably less complicated digital delay chips? I understand there was some tinkering with a PT based flanger, but that seemed to die too.

You can get flanger effect even when using longer delay chip, trick is to delay even the dry path, see PT2399 FLANGER / FLANGING DEMYSTIFIED.

Pros:

- TZF for free

Cons:

- two delay chips (kills "cheaper, probably less complicated" advantage partially)
- no way for standard FEEDBACK (COLOR) pot (trick does not work here)
- latency (even dry signal is delayed)
- different clock frequency control - you would have hard times to achieve same sweep characteristics (which may be the most important characteristics for flanger effect!) as original POLYCHORUS has

If you could get PT2398 you could get much shorter delay times then with PT2399 (down to 2.4ms), so latency may not be the issue, but rest remains..

My advice: if you want to clone POLYCHORUS (or other rare BBD chip based flanger fx) forget PT family, just adopt it for MN3x07 (see ADA/EM retrofits threads, it's not so complicated after all)

Good luck, T.

[mth5044]

I added modulation to the delay time on my rebote delay, it sounds pretty chorusey when you have it set to the shortest delay time: http://www.aronnelson.com/gallery/main.php/v/seljer/album113/rebotechorus.mp3.html , you'd need something faster for more versatility as far as chorus sounds go or to get into flanger territory

I have built the echobase and another modulated PT2399 circuit, and I've played around with the shortest delay time, but it isn't really what the polychorus sounds like. Definitely a great sound though.

Or any other PT23xx IC? I was looking in the piles of the forum today and saw there was a very small spark of interest in making the polychorus as it was with BBD, but has anyone tried to make it using cheaper, probably less complicated digital delay chips? I understand there was some tinkering with a PT based flanger, but that seemed to die too.

You can get flanger effect even when using longer delay chip, trick is to delay even the dry path, see PT2399 FLANGER / FLANGING DEMYSTIFIED.

Pros:

- TZF for free

Cons:

- two delay chips (kills "cheaper, probably less complicated" advantage partially)
- no way for standard FEEDBACK (COLOR) pot (trick does not work here)
- latency (even dry signal is delayed)
- different clock frequency control - you would have hard times to achieve same sweep characteristics (which may be the most important characteristics for flanger effect!) as original POLYCHORUS has

If you could get PT2398 you could get much shorter delay times then with PT2399 (down to 2.4ms), so latency may not be the issue, but rest remains..

My advice: if you want to clone POLYCHORUS (or other rare BBD chip based flanger fx) forget PT family, just adopt it for MN3x07 (see ADA/EM retrofits threads, it's not so complicated after all)

Good luck, T.

Hmm sounds like a pretty big problem  However, the polychorus itself, even with replacing the outdated BBD with newer ones, is a really big circuit. I was thinking that since the PT series seems to have 'dumbed down' an 'analog' delay circuit, they might be applied to this kind of thing too. I hear the problems though 

Yes it's just a limiting factor in your chorus options. I does work though. You can hear the modulation at the end of my binson recreation video too.. also done with pt2399's

http://www.youtube.com/watch?v=26lLAmFi5t0

(OP: You have already seen that video  )

But I watched it again because I love it so much 

[~arph]

I was thinking that since the PT series seems to have 'dumbed down' an 'analog' delay circuit, they might be applied to this kind of thing too. I hear the problems though 

If you check this months FX-X contest you will see that there is a 15 parts BBd delay in there.. I think bare bone PT2399 will result is something similar in parts count.

But I watched it again because I love it so much 

Haha thanks, so did I.. I like to listen to it from time to time, just for the sound. Not for the playing, because that is just plain noodling...

[Thomeeque]

If you check this months FX-X contest you will see that there is a 15 parts BBd delay in there.. I think bare bone PT2399 will result is something similar in parts count.

Please, could you post link to this project, I did not succeed to find it - I'm not very familiar with the FX-X contest, so I'm probably looking at wrong places.. Thanks, T.

[~arph]

sure..

http://www.diystompboxes.com/smfforum/index.php?topic=84323.0

It's a post near the bottom by maarten.

This is the direct link to the schematic:

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/ADT+schem.gif.html?g2_imageViewsIndex=1

And here is his soundclip:

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/ADT+47K.wmv.html

[Mark Hammer]

My old blue rackmount MXR Digital Delay can impose modulation on any delay range.  So, one can do flanging (sort of; the sweep ratio isn't really wide enough to do it right), chorus, as well as those ultra-thick Pat Metheny-like chorus sounds and doubling, and if you feel like having the wet sound modulate between 40 and 45msec delay, or 125 and 135msec, you can do it (and at modulation speeds up to 1000hz, if you want).

So, it is certainly possible to modulate ANY delay.  The larger question is whether the lmitations of simple-solution chips like the PT2399 permit one to achieve the delay-time modulation within the range that nails you the sound you're aiming for.  I can vouch that modulating between 20 and 25msec can provide a pleasing chorus or doubling sound, and modulating up around the 30-40msec range is also interesting, but for many people, the "classic" chorus sound really demands delay times in the range of 5-15msec.

The bottom line is that one is certainly encouraged to explore modulating a PT2399, but one should be willing to accept the sorts of outcomes it can provide, instead of driving yourself crazy over trying to make it do something it can't.  Remember, there is a reason why folks are still making 1024-stage BBDs.

[mth5044]

That little ADT circuit looks like fun.. hmm..

However, I have been looking around for information about replacing the SAD1024 with MN3207 and I see I'm in for a lot more than I though  Also looking at the polychorus schematic is a whole other beast in itself. I see the delay part and the compander, but that is all I have desiphered so far. I fear this is a bit more than I can chew. I was really looking forward to making a layout too