PT2399 Decay Time

[Haynesarama]

Hi People.

I'm currently working on a delay using two PT2399's (Yes I have a reliable source
I hope that somebody could advise me on how to adjust the decay time of the repeats?
If you look at say The Tonepad Rebote 2.5 or Generalguitargadgets PT-80 schematic which components
should I be looking at Adjusting?

Thanks
Michael

[CynicalMan]

You mean the feedback knobs? Both the PT-80 and the Rebote have feedback knobs called "Repeats" which control the decay of the repeats.

[Haynesarama]

Hi There

Thanks for your reply.
The feedback knob controls the amount of repeats, I'm wanting to control the decay time of the repeats
So the length of each repeat if possible. I'm sure there will be a way

Any ideas?  Thanks again people
Michael

[deadastronaut]

if you go for longer delays......they will get very dirty.....

change the 50k pot to a 100k...but it will get nasty...

[Haynesarama]

Thanks for all your help

I think I may be asking the wrong question 
Take for example the Rebote 2.5  It has 3 controls, Delay, Level and Repeats.
I know that repeat control adds more/less repeats. Level controls the amount of wet signal heard in the output. Delay control changes the distance between repeats, The delay time.

What I'm wanting to control is the length of each individual repeat not any of the above.
So the  Lent of time that you hear a repeat before it decays
Does this make sense?

Thanks again.
Michael

[CynicalMan]

Sorry, but not really.

The repeats don't normally decay at all. They're just quieter delayed versions of the input signal. So the repeats are always on, their volumes never change. It would be very tricky to get a decay. You'd need a envelope generator triggered by the input signal before the delay line. It probably wouldn't sound any good, and I don't think that's really what you want.

[Gaetano Capuano]

Your have got it confused with reverb I think.......... 

[PRR]

> the length of each repeat

Resistor on pin 6 sets oscillator frequency and thus delay time.

See chart in data-sheet:   http://www.futurlec.com/Others/PT2399.shtml

The reduction in level of each repeat is set by the "Repeats" pot. Zero, repeat is zero %. 50%, each repeat is half-level. 100%, each repeat is full level (sound never stops, but hiss/distortion accumulates, and 100.1% will feed-back build-up howl.)

[Mark Hammer]

Your have got it confused with reverb I think.......... 

He's correct.  There is no simple way to do what it is you want to do.  The overall decay time of the repeats is obviously controllable, but not the behaviour of any given repeat.

That being said,you can introduce some degree of control over the quality of the repeats such that they can seem to die out faster. 

There is a 15k resistor and .1uf cap providing a feedback loop.  The Tonepad documentation suggests a 10k resistor if one wants "infinte repeat".  That resistance can be used to shape the tone of repeats so that they seem to fade more into the background.

I recently completed a Rebote 2.5 and used a pair of 5k6 resistors in series to replace the stock 15k.  I then ran a 22nf cap from their junction to ground to provide a shallow single-pole lowpass filter around 1.3khz.  That trims some treble off the first repeat but still leaves some treble to trim off even more on subsequent repeats.  The sound achieved is a lot more natural sounding, and allows you to set the Repeat control for max without having the resulting sound get too cluttered.

If you don't like it, or want the stock sound, you can simply defeat the cap to gorund with a toggle.

[sundgist]

I say "1,2,3,4,5" and the dry path says "1,2,3,4,5" but the delayed path says "1,2,3", "1,2,3", "1,2,3" or "1,2", "1,2", "1,2" dependant on the decay pot position?

Might be an interesting addition that I've never seen on any delay.

Theoretically, some sort of gate at the delay input path triggered by input / momentary switch / divided down pt2399 clock output, whose open time could be adjusted by a pot. How possible this is and by what method is beyond me, I'm kind of thinking aloud.

[mth5044]

Mark, would you say your mod makes it sound more tape delay or more analog delay? Tape delay as in the repeats last longer without floating into the ether, or the analog where you get the giant mash up sound?

[Gaetano Capuano]

I say "1,2,3,4,5" and the dry path says "1,2,3,4,5" but the delayed path says "1,2,3", "1,2,3", "1,2,3" or "1,2", "1,2", "1,2" dependant on the decay pot position?

Might be an interesting addition that I've never seen on any delay.

Theoretically, some sort of gate at the delay input path triggered by input / momentary switch / divided down pt2399 clock output, whose open time could be adjusted by a pot. How possible this is and by what method is beyond me, I'm kind of thinking aloud.

Very cool thoughts!   maybe  tonegod can whip that up!!!!!

[Haynesarama]

Thanks everyone for your words of wisdom

Mark. I'll try your suggestions with the feedback loop and subbing the 15k resistors and cap.
I'm also adding an eq control to the regen path to alter the eq of the repeats
With an additional control to control how much of the eq signal gets added to the repeats.

Now to just figure out how to affect the decay of the repeats. I'm not sure if I'm phrasing that right so apologies if not.
Sundigist your correct. That's how I want to affect the repeats but how?

The controls I'm adding are on a delay vst I use and wanted similar controls on a stompbox design.
There's also going to be an LFO to modulate the signal in an attempt to get some tape wobble.

I've got the circuit laid out on the breadboard and I'm surprised at how it's sounding with two PT2399's in series.
There's the usual buffered input being fed into half of an NE570, then the delays (both switchable) being fed into the second half of
The NE570 to the output stage.
I've swapped the delay pot for 100k as that's all I have available at present. I thought the repeats would sound dirtier than they are

I'll happily post the layout and schematic one it's complete. Just figure out these extra controls first

Thanks again for all your help people
Cheers
Michael

[CynicalMan]

Which vst is that?

[Mark Hammer]

Mark, would you say your mod makes it sound more tape delay or more analog delay?

Neither.  I'd say it makes it sound a little more like the real world, where the spectral content of reflected sound changes over time.

Mark. I'll try your suggestions with the feedback loop and subbing the 15k resistors and cap.
I'm also adding an eq control to the regen path to alter the eq of the repeats
With an additional control to control how much of the eq signal gets added to the repeats.

Well, what I suggested IS an "eq", it's just fixed rather than variable.  If you want variable, then perhaps consider running a 25k pot from the junction of the two 5k6 resistors to a .047uf cap to ground, so you can tailor the high-cut.

[Gaetano Capuano]

I think the 2 PT's could be adding to the clean tone, I have built a delay with one PT and it was very easy to tweak to get a good tape type tone off it. Also I used a dirtier IC TL082 for just a touch more grit.

[Haynesarama]

It's an ableton delay called Ping Pong.
It has similar features to what is described above.

Thanks
Michael

[Haynesarama]

Thanks for your advice mark.
I'll use your suggestions for the variable eq.
I presume adding some kind of blend control in the regen path to
The EQ would serve to adjust how much of the eq signal gets added to the repeats?

Do people think I need to be looking at an envelope circuit to control
The decay of the repeats then?
If so where's a good starting point?

Thanks
Michael

[Gaetano Capuano]

Live has the sickest parameters, I specifically love the reverb parms, 60 second decays anyone 

[Mark Hammer]

Do people think I need to be looking at an envelope circuit to control
The decay of the repeats then?
If so where's a good starting point?

Cast your mind back, and try to recall the impact Phil Collins had on the way in which gated delay was used on drums.  A similar sort of thing might be used to do what you want, by applying an external gate to delay repeats, but there are a number of accompanying caveats:
1) to process the repeats specifically, you would need to have an insert loop with appropriate buffering, level control, etc.
2) the gate used would need to have superfast gate-on (rise) time, and variable decay time, along with a threshold control suitable to the level of the repeats.
3) gates presume a fixed signal threshold level, whereas any delay set for something other than infinite delay will have progressively lower amplitude, meaning that the gate threshold would also have to steadily lower in order to have any impact on the decay.

In general, the circuitry needed to accomplish this one sound in the analog/hybrid domain in real time, is cumbersome and complicated, to say the least.  Whether, after all that trouble and expense, it would even sound as you imagine in your head is a whole other thing.  If you want some sort of sharply gated thing, though, probably the simplest method would be to stick a back-to-back pair of diodes in the feedback path so that if the signal falls below their forward voltage, you get no feedback at all.  You'd need to pick your diode type carefully, though.