4 pt2399's in series / long clean delay..

[deadastronaut]

i moved this project to this thread ...(as it is a more relevant title.)

here's where i am with this project..its all on breadboard/s at the moment,

heres the schematic/s for this beast of a delay....

however i have a little problem which i'm stuck on  , when i bypass (fet switch) .. i get runaway repeats (oscillation)

or get more repeats than when effect is on?...ive tried all sorts but i just can't get it balanced so the repeats are the same when on/bypassed..?

other than that its good to go.. any ideas?..cheers guys.

[Mark Hammer]

That sounds damn fine.

[pinkjimiphoton]

rob, you are a sick young man, one hell of a guitar player, and did i mention sick?
wow... WOW

[GodSaveMetal]

I xtremely LIKE this proyect, I wana do a rack with all the delays PTs based, chorus, flangers, echoes, rebervs and wetheber tried with this CHINESSE CMOS!! Is a budget cost IC in PERÚ, I buy 100´s thanks to post this great man; I stay TUNED!!!!

[pappasmurfsharem]

That is actually very nice sounding.

Any particular filtering changes or just stock PT2399 Datasheet?

Might just be your recording but this seems to sound better then others I've listened to.

*Edit

ahh that bit at the very end was majestic. is that lush kind of sound that modulation I've heard people talk about with pt2399s? Is it possible with one or is it all 4 with light modulation?

[samhay]

^however i have a little problem which i'm stuck on  , when i bypass (fet switch) .. i get runaway repeats (oscillation)

Do you have the repeats feedback loop and bypass FET switch set up the same way as Merlin's Small Time delay?

[deadastronaut]

Hi Sam, i,m not sure, i didn,t look at that section in merlins...ill take a look.

[deadastronaut]

hmmmm i just re-arranged my breadboards and tried the ST on its own out of curiosity...and yes its a good balance of repeats..on/off..

however, when i rig them in series with the ST + the current mirror, i no longer get delays (using the same pt2/3/4 setup, but using pt1 for control of  them all....hmmmmm...

[knutolai]

Nice work! One question: In the LFO schematic it says the output should be connected to "PT1 Pin 1". Are you modulating the actual supply of the chip? And wouldn't this modulate the supply of all of the chips as they are all connected?  
I don't know if its just a typo or something (I'm not that experienced), but if this is the case how it this working compared to modulating the Vref of the chip (as the One Chip Chorus and the Little Angel Chorus does)? Any advantages?

Also I like the 220n value of C5 in the fourth PT. A trick also used by Rring in his PT2399 delay (link to v.1: http://circuitsalad.com/2012/09/04/how-to-significantly-improve-a-simple-pt2399-delay-circuit/). Seems like a really overlooked trick which might  help with taming the noise of the delay repeats. He actually uses a 470n cap.

[deadastronaut]

Nice work! One question: In the LFO schematic it says the output should be connected to "PT1 Pin 1". Are you modulating the actual supply of the chip? And wouldn't this modulate the supply of all of the chips as they are all connected?  
I don't know if its just a typo or something (I'm not that experienced), but if this is the case how it this working compared to modulating the Vref of the chip (as the One Chip Chorus and the Little Angel Chorus does)? Any advantages?

Also I like the 220n value of C5 in the fourth PT. A trick also used by Rring in his PT2399 delay (link to v.1: http://circuitsalad.com/2012/09/04/how-to-significantly-improve-a-simple-pt2399-delay-circuit/). Seems like a really overlooked trick which might  help with taming the noise of the delay repeats. He actually uses a 470n cap.

modulating the vref was unstable..the lfo became very random, thats why i went with modulating the supply..(check out madbeans zero point deluxe) using current mirrors to get the pt's in line/sync

yes the 220n worked great yes, but i found it will thin the sound of repeats over time, and contributed to runaway repeats too somewhat....i put that back to 100n just for now. (may be switchable later on)

to get the repeats bang on with tails..then i will re-think/tinker it.

[deadastronaut]

ok after a lot of swearing...i'm back to the full schemo/s above again..

and back to ''unbalanced'' repeats...

[deadastronaut]

right, well i tried the ST feedback loop again, and altered/removed a few components..(bastardized)

i now have 'sort of' balanced repeats...but i'm being pretty anal about it...fussy bugger that i am. ..but its more acceptable now.

anyway, the problem with the ST is that it will not oscillate (infinite repeats)

which is what i intended for this, so i can play over the long delayed tails.....hmmmmm..

[rousejeremy]

Sounds awesome!

[deadastronaut]

Yeah, getting there....

[bean]

I have not tried using the same value resistors on the emitters of the current mirrors, but slightly different sequential values may prevent any unwanted heterodyning from what I've heard.

Also, consider doing multiple feedback paths between the PT2399s. It's well worth the few extra parts! Looks like a great project you have there!

[deadastronaut]

cheers brian, yeah its pretty cool so far. 

yep i thought about those emitter resistors, and samhay mentioned that too...

though it has been performing fine, no problems with locking up etc...i'll just alter the values a little on each i think..just to be sure though.


multiple feedback paths?..what would be the benefit of that?..excuse my dumbness

[bean]

Multiple feedback paths gives you subdivisions. With four chips, you should be able to rig up eighth note divisions in duple or triple. Just look at the schematic for my Zero Point DD delay to get the idea. It just requires one cap and resistor per feedback path and it sounds great. If you want maximum tweaking, use a variable resistor on each one to tailor the division levels.

[Jdansti]

Nice Rob!

Hey Jimi, you got this one Veroed yet? 

[deadastronaut]

@brian: ahh gotcha, yes i did experiment with that, accidentally though...pretty cool, i'll look into that..

cheers man.


@john:  vero..

[samhay]

^, the problem with the ST is that it will not oscillate (infinite repeats)

If you reduce the value of the 10k resistor from the Repeats pot's wiper, you will get infinite repeats. I think mine is about 7k, and it works nicely.

RE heterodyning of the chips. This will not cause them to lock up, but may cause audible whine. Yours sounds nice and quite, so it seems like you have got away with it.