PT2399 Literature.

[illuminatiNPS]

Hey guys,

  Ive been kicking around the idea of doing a chrous/flange type pedal using the pt2399. I cant seem to find solid literature other than the datasheet on this chip. Ive looked a couple of schematics and compared them to delays to see the difference, but I don't want to copy and paste other peoples schematics. I want it to be original. The right side of the pinout is what confuses me, the LPF pins and how the caps effect them. I figured go with the PT2399 becuase sourcing multiple bucket brigads seem like a pain in the ass.

[ElectricDruid]

This is one of the best pages on the chip:

http://sound.whsites.net/project26a.htm

There's also some design equations for the PT2399 over on my site:

https://electricdruid.net/useful-design-equations-for-the-pt2399/

Finally, the filters that you usually see built around the internal op-amps are Multiple Feedback  (MFB) filters. This is a handy tool to design them:

http://sim.okawa-denshi.jp/en/OPtazyuLowkeisan.htm (2 pole)
http://sim.okawa-denshi.jp/en/MultipleFB3Lowkeisan.htm (3 pole)

HTH,
Tom

[illuminatiNPS]

Thanks so much. Wanna design a chorus that operates off of two paralell LFOs  (all Ibanez Bi-mode Chorus). But at the flip of a switch, a 2nd chorus unit is joined in series and they are both synced to one LFO (kinda like the super phasing config in a Mutron biphase). Options for square and sine would be cool too.

[idy]

Note that it has been said the PT2399 can't do flange, you can't get the delay short enough. Chorus you can.

[ElectricDruid]

Modulation of the PT2399 delay is also an "interesting" area. There are various techniques that replace the effect of a resistor on Pin 6. I've    seen JFETs, vactrols, digipots and current sinks. The other possibility was discovered by our very own Frequency Central, as applied in his Little Angel Chorus. This uses modulation of the Ref voltage on Pin 2 instead, which apparently works, although without knowing what's going on inside the chip, I never understood exactly why.

Tom

[mth5044]

This is one of the best pages on the chip:

http://sound.whsites.net/project26a.htm

There's also some design equations for the PT2399 over on my site:

https://electricdruid.net/useful-design-equations-for-the-pt2399/

Finally, the filters that you usually see built around the internal op-amps are Multiple Feedback  (MFB) filters. This is a handy tool to design them:

http://sim.okawa-denshi.jp/en/OPtazyuLowkeisan.htm (2 pole)
http://sim.okawa-denshi.jp/en/MultipleFB3Lowkeisan.htm (3 pole)

HTH,
Tom

Merlin's got a nice couple o' pages as well:

http://www.valvewizard.co.uk/PT2399_Data_Notes.pdf

[illuminatiNPS]

Bummer that it can't do flange. I did watch a video on Youtube of a pt2399 "flange" pedal, but it seemed like the "swoosh" just wasn't there. Would have been cool to build a PT2399 based flanger like the old Mutron flanger, foot pedal and all. Anyways, Im gonna start breadboarding this idea dragging and dropping schematic portions. Electric Druid, I may run some prelim schematics by you.

[Kipper4]

Search for valve wizard flanger.
You might get some inspiration there.
I'm gonna look into the idea if a pt2399 flanger too. Good luck
Rich

[ElectricDruid]

I see! It's a two-delaylines PT2399 flanger, like the through-zero designs, but with PT2399s?

After all, it's the *relative* delay of the two signals at the mixer that makes the swoosh. Use one PT to delay the"dry" path by a fixed amount (35msecs or so) and then modulate the other around 35msecs to get a very short delay between the two channels.

[merlinb]

I couldn't find my own records of this circuit -I had to dig it up from a Russian website! 

[anotherjim]

Dual delay flanger ought to be pretty good - so long as you don't need to filter out the highs to get decent sound quality. One of the pitfalls of BBD flangers is, the designer makes the clean signal really clean, but over-does the lowpass filtering for the delay path. Flanging is most effective when both wet and dry have the same sonic content, so the varying add/subtract of different frequencies (particularly the subtract part) can be heard as obviously as possible.