Scott bernardi PT2399 VC delay

[211]

hi all,

I built Scott Bernardi VC echo ( http://home.comcast.net/~sbernardi/elec/og2/og3_echo.html ) , but as I don't got vactrols, I used Ryan Williams NPN current sink technique ( http://sdiy.org/destrukto/vc-echo.html ) to control delay time.

Unfortunately VC delay don't works, I only obtain a loud Buzz instead of a delay (it don't seems to contain input sound on delayed output, but I can hear it on the mix output)... I checked every voltage on IC before powering on..

Buzz frequency vary while turning "Time knob" (or controlling it via CV) so, I don't really know if PT2399 is blown, as it seems react again.. I tried with another chip but I got the same troubles..

Does anyone built this delay, and/or used this NPN current sink ?
Any idea to makes this module work ?

I redrawn the shematics with eagle and made a PCB, I can upload these files if it could help

Thanks for your Help
fred

[211]

bad wiring solved, works great !

[bugbrand]

Cool! I've gotta try this out...

[Scott Stites]

So was it the Bernardi or the Williams circuit you got working?

I've used a FET to control the delay time of the PT2399 - the cool thing about the FET/transistor sink route is that the delay time changes instantanously, which makes S&H modulation out of this world. If the Williams circuit works, I'd use that over a FET, for sure.

Cheers,
Scott

[211]

Hi scott,

I made a pcb with bernardi design, but with williams control.

I had a wrong trace on the pt 2399 feedback circuit, the feedback overdrived 2399 input.. I obtained something like a low tuned VCO.. Hopefully I had no trace to cut, just a wire on the MIX pot to solder on another place ..

I d like to publish the pcb, and some pics on the forum, but I had to draw a wiring diagram, and correct the wrong trace. I really like to discuss with you guys, about this circuit because it's really nice but probably may be optimised.

I notice PT2399 clip when input signal is not attenuated, a bit boring when feeding it with a VCO or VCF.. ( no more place on the panel to add a input level pot )

A resistor on the current sink should be adjusted to find the lowest delay time when the pot is fully turned.

At low setting (>2sec) the delay is a bit noisy, may be others caps values should be used (as in PT-80 DIY pedal on general guitar gadgets ?)

At very low setting weird funny noises are produced, LFO controlled delay is very fun, and Chorus like effect are also easily obtainable.

What a FET change instead transistor in the current sink ?
++

[synth_ollie]

Ive seen at least 3 different pt2399 designs ; bernardis,
rebote 2.5 and the pt-80

Im a little tempted to build a delay with this ic, but wich one... ??

OLLIE

[Wild Zebra]

211, a pcb would be awesome. Generating some discussion on this circuit would be great. It could spark some interesting modifications. I was wanting to build this in the future. So it would be nice to see some opinions on the subject. I have a stock rebote 2.0 and I really like it, but a cv delay, with more adjustable delays (even if it gets lo fi) would be sweet.

[nisios]

I have made a double rebote 2.5 with cv on time and feedback.
I love the rebote but the filter is to agressive. I would love an echo that wouldnt filter so much from repeat to repeat. I have messed with the filtering section wile in bread board and the thing is: if you raise the filter cutoff frequency you start to hear the timing oscillator. Is there any way to implement tthis pt2399 ics with a higher cutoff without noise?

[211]

here is the wiring diagram


(open the pic in a new window for a better resolution)

and the pcb http://sdiy.free.fr/CVdelay/ScottBernardi_VCdelay_PCB.pdf
enjoy !

[vtl5c3]

Ahh. Sweeeeet. Been looking for a good PCB layout for this chip.

Merci mille fois!

[211]

here is the schematics :

http://sdiy.free.fr/CVdelay/ScottBernardi_VCdelay.pdf
++

[waterbuffalo18]

i know i'm a little late but i just found this place.

I'm interested in how well the current sink works for you. I've tested its performance with the pt2399 pretty well, but didn't get a full delay built with it to test how well it works with my synth. How is the CV -> delay time response?

about noise and changing out caps: I think you could change out the .1u integrator caps to optimize it for long delays, but that would probably effect short delay quality also. I've never actually messed with changing those caps because I didn't want to mess with calculating the proper values.

in the pt-80 schematic, he lowers the filter cutoff. That helps the noise a lot but limits the response too much for me. I found that even with lower cutoff on the 2nd order filters, the quality was pretty bad on long delays (due to the sample rate). The only option I like so far is switched cap filters, but that still isn't perfect and is expensive.

interesting side note: In my last experiment (several months ago) i was actually using the pt2399 and my current sink as a wide range VCO to clock a pt2396. the vco clocked pt2396 showed some potential, but i left it alone since I moved and started working.

[211]

Hi Ryan,

I m very happy to share my experience with you
I used the same current sink than you.

I experienced some trouble with the delay pot range. It's really difficult to find the longest delay setting for the Delay pot. Perhaps should I use a trimmer instead of a resistor, and/or a zener diode to set the maximum input voltage, because the delay stop to work when the pot is set after 8/10 (3 o'clock) with no CV

It's more difficult to deal with high amplitude CVs.

[Scott Stites]

Ryan! Nice to see you here!

[synth_ollie]

[211]

no, I finished it, built lts the frontplate and play with it some days.

One day, I powered it to play with a LFO. This echo unit is on a second power supply (my main PSU don't have 5V output.) It's the only module powered by this second supply.

I turned ON the first Main PSU with LFO patched in Delay Input, then the delay's PSU. I don't know what happened, but the delay didn't output anything.

I checked my patch but everything was correct. I put my finger on delay PCB, PT 2399 and CA3080 were hot.. I retried later but same result, but didn't search more..

I don't know what's wrong, I hate when Diy stuff do something like that, especially when the module is finished and fitted in the cabinet

May be a shortcut somewhere, but all is correctly wired, and don't have a flying wire inside the cabinet..

Perhaps the trouble come from the second PSU, Should I turn it ON at the same time than the first ?

Perhaps My LFO sent to high voltage (0-10 V), witch provided to much current to PT2399 and damaged it ? But in this case, why the CA3080 became hot too (sure it control the feedback.. )?

I need builder reports too

[vtl5c3]

Hey, I want to make a copy of your 2399 PCB. Did you ever figure out the heat problem?

Romeo

[shawn]

I know this sounds crazy but have you looked at your solder work with a magnifying glass? There quite possibly be a bridge somewhere that you can't see by just glancing at it. Only reason I am suggesting this is this once happened to me due to a pot making smoke! I checked, double checked but when I finally brought my light/magnifier i saw that there was in fact a bridge on the board, super small bridge.

[Uncle Krunkus]

First, I wouldn't run it off another PSU. Just take a jumper from the +15V line into the unregulated input to the LM7805.

[etaoin]

[211]

Very Cool Etaoin

I didn't had the time since my last post to search the reason of my troubles..

On your audio sample, i can hear the same trouble when CV input range is to High, PT2399 stop to work.

You should use a resistor instead a link on the "Red Free" resistor on the diagram (Top right). Even a diode as Ryan did, could be better idea..

[etaoin]

[Fernando]

hi all,

grateful for 211's pcb
and amazed by Etaoin's sample...!


I'd like to know about the highest limit of this chip (how short a delay can be before loosing the clock pulses)
I'd love to use it in the microsecond range

[bugbrand]

PT2399 datasheet

shortest delay is c.30msec

[Fernando]

thanks bugbrand

I asked assuming someone tried to explore the limits using faster clock rate...