Author Topic: PT2399 as a chorus - Dimension P based - delay before the effect comes in  (Read 3642 times)

BluffChill

Hello,
I'm building a Dimension P chorus. I breadboarded a really nice version, then tried to build it on perfboard and something is up with it. So I've started from scratch with a few ideas. This is going to be a voltage controlled chorus, using an LFO (using my MS20 synth's LFO currently) to control the speed of the chorus.

On this new version, I have just breadboarded it and it works as expected, except for one thing. There is a short delay before the chorus voice comes in, like a delay on a very short slapback setting. The voice IS modulating as expected, and for long notes you can barely notice, but when I breadboarded it before, this didn't happen, the voice would come in at the right time. What could I have missed?

I'm following this schematic but have so far only constructed Voice 1 (and I'm not building the LFO part of the circuit)

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anotherjim

Probably because the PT2399 has too much delay in the first place. There is no way to reliably push its sampling rate fast enough to get down to the true chorus range around 20mS without over stressing the device. Even the trick of a reduced timing resistor after power on, though it does makes it faster, doesn't reduce delay enough.

If only, instead of the clock out pin, it had a select for a smaller memory size, then it could have done chorus, maybe even flanging, and this world would be a totally different place.

Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.

BluffChill

The thing is, the first version I breadboarded didn't have this problem!
Kits & Pedals! EctoVerb - HyperLight - Shagpile - http://bluffchilldevices.bigcartel.com/

slacker

Could be something wrong with the anti lockup bit of the circuit, if Q1 wasn't fully turning on that would increase the delay time. Try grounding point "AL" and see if that shortens the delay time, if it does that points to something wrong round Q1.

BluffChill

Grounding AL resistor instead of using the anti lockup makes it whistle very loudly like it's repeating at a really fast rate. Any ideas?
Kits & Pedals! EctoVerb - HyperLight - Shagpile - http://bluffchilldevices.bigcartel.com/

bluebunny

Is R23 present and correct?  Without it, there's no dry, so you'd definitely (probably?) hear a slapback of sorts.

BTW, don't ground "AL" until it's powered up.  Otherwise you might brick your PT.
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anotherjim

Now that you say it Marc, that is very likely.
Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.

duck_arse

you really should ground your pin 4's.
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bluebunny

Good advice duck, but advice that I've ignored (or neglected) on the two occasions I've built this.  Both behaved beautifully (and looked gorgeous, natch).  Lucky bunny, I guess.  :)
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Ohm's Law - much like Coles Law, but with less cabbage...

duck_arse

if you was a superstitious type, having four rabbits foots wouldn't hurt.
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pinkjimiphoton

2399s suck. such a pain in the ass. they sound great when they work. which seems to be infrequently!!

check for a bad cap. leaky caps will take a split second to charge up and discharge sometimes and do exactly that.. its like the pedal needs to wait for the cap to charge to a sufficient level for the circuit to operate. i find this sometimes on stuff peeps mod where they bridge caps too, but this obviously isn't the case.

also check your resistors. i am finding more and more shite resistors all the time. i routinely chuck everything on a meter now before i solder it in, i've found a lot of parts that are crap brand new the last few years, and its easier than trying to debug later only to find a dang resistor has gone open or was open.

i have only gotten 2 2399 based choruses to work ever. one was anchovie's original one, but that latched up at some point and died, and a later tricked out variant i built off a tagboardeffects layout which sounded devastating until it too died.
replacing the chips didn't help in either. i kinda thru 'em in the pile of "get to someday " crap ;)

they also get weird if your power supply sags. at a certain point, 2399's become like little flangers on pure peyote juice and make all kindsa ghostly wheezes and noises and trailing crap that may bend up or down depending on the starving chip's whim.

if its on the breadboard, try wiggling connections too, breadboards can be a pain sometimes... things like to not connect, or wriggle free enough where they only seem to be pushed in ;)

good luck man!
"maybe you should stay with yo mama....."

what the @#$% do you mean, it doesn't sound distorted enough, are you high???????????????????

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chemosis

Re: PT2399 as a chorus - Dimension P based - delay before the effect comes in
« Reply #11 on: February 27, 2020, 09:12:46 PM »
2 spdt switches but only 4 wires?? I don't get this. if they were spst then id understand