crap fi delay turbo: easy pt2399 thing

[allesz]

Hallo, I want to share my last pt2399 project.

It's a really simple thing, and I had to omit a level control: I put it in a 1590LB box, so I had space only for two knobs.
I think it is possible (but I did non try) to substitute the 4,7K buffer's base resistor with a 5K pot (or a 10K one maybe), to control the delay level.

The pedal works good with a band in a live situation (and at home too); before I tried in a lot of ways to avoid using buffers, but I ended always with poor results: mostly unity gain problems when the effect was engaged. In the end I came to the conclusion that I don't like true bypass delays... maybe it's just that I am not good enough.
The buffer is actually a darlington transistor, not a bjt (but an high gain one will probably work).

The delay is quite clean and nice sounding, until the time pot does not pass the mid point; I had only 50K pots btw, but a 25K would have been just perfect (if you, like me, need only short time repeats of course).

The key for getting undistorted repeats was a small (well, smaller than the usual 100nf) cap between pins 9 and 10.

[anotherjim]

That's a neat diagram and an unusual way of mixing the dry and delay (to me anyway).
Why not post links to some audio clips?

[allesz]

Hallo. I don't have audio clips right now. Monday I will rehearse, so I will try to record something.
It's a crude way of mixing, but it works; I had to use very few components due to space problems.
Actually I only wanted to share the pins 9 and 10 cap trik: for me it solved a lot of problems with the quality of repeats, avoiding distortion.

[~arph]

Lowering the 9-10 cap also lowers the output volume, i have messed with it too to keep away from self oscillation

[allesz]

Hallo harp.
You are right of course: lowering that cap lowers the wet volume; but you can get around this problem adjusting the gain of the op amp between pin 16 and 15. That's what I did.
I did not try 33nF, but 47nF still showed some clipping with hard hit notes (or when an overdrive or boost drive slams the input ).

But now I am reading about the Hamlet delay by our fellow Midwayfair (really nice sounding unit, and the player too on the demo) and I noticed the diode trick on pin 7.... wow, I will definitely try this out.
I will soon start again on the breadboard because I have another insane idea: use the free op amp (pins 14 and 13) to make an overdrive. What do you think about it? 

[~arph]

Cool,

You can also use the free opamp as an envelope follower and modulate the delay time.

[allesz]

Brrrr, please not. I hate modulated delay, and chorus btw.
I only love phasers and flangers; but they are difficult to build and I rarely find a way to use them making music (my music, at least).

The only problem I expect is digital noise bleeding in (but it's a dirt box afterall), and copyrights problems when I will steal the "stupid simple overdrive" idea from pinjimiphoton   

[allesz]

Hallo, I finally had a chance to breadboard this circuit again; it fired up only at the second try... and I had to change the values of the delay output path components (47nF cap and 4,7K resistor coming from pin 12): with the value as I draw on the schem the delay is too high and the circuit oscillates, I had to use a 22nF cap and a 100K resistor... maybe it's the breadboard, maybe it's the chip who knows...

After the delay was ok again, I tried to use the op amp between pins 13 and 14 as an overdrive and first results are good: 22nF input cap, then a 22K resistor, 500K gain pot and  a 470pF cap between the pins, 100 nF output cap and anoter 22k resistor before the output; you don't even need diodes to get dirt (I tried the usual 1n4148 ant they were too fizzy, maybe leds would be better?), probably because at 4,5 V it's easier to get the op amp to distort.

[Mac Walker]

I made a negistor LFO for this circuit to modulate the delay time, here is what a came up with:



Strangely enough, I have never had any luck getting a 2n2222 to work in a negistor circuit.  At any rate you could probably play around with this to reduce a few components.  Not sure about latch up in this case, or if that would be a concern at all.

Also you can play around with the 15 uf to change the duty cycle, it does have a discernable effect on the sound...

[blackieNYC]

Your minimum resistance to ground from pin 6 appears to be 4.9k. Isn't this a bit long of a delay time for a chorus? I've seen anti-latch minimums of 1k (that I believe correspond to around 30 ms IIRC,) that being fairly long for chorus but good enough.  Is it working well for you?
To the OP- love it. Minimized and dirty. I myself have long been considering a delay with two switches and no knobs at all - I always end up using
1.a doubling/slap, something like 30-50 ms, and no repeats, and
2. Around 300 ms, no repeats, for guitar hero moments.
A bypass (with only one repeat, little need for "tails") and a long/short switch. I'm a recuperating  knob junkie - trying to cut down.

[Ben Lyman]

...I always end up using
1.a doubling/slap, something like 30-50 ms, and no repeats, and
2. Around 300 ms, no repeats, for guitar hero moments.
A bypass (with only one repeat, little need for "tails") and a long/short switch. I'm a recuperating  knob junkie - trying to cut down.

Me too, I love this idea. Please make it happen and share! 
Here's what I'm thinking: Two footswitches, bypass w/LED and fast/slow w/2 LEDs.
Inside would be trim pots for mix, rate and repeats of each channel.
Does that sound too far fetched?

[~arph]

Your minimum resistance to ground from pin 6 appears to be 4.9k. Isn't this a bit long of a delay time for a chorus?

This is not a chorus 

[allesz]

Thank you Mac Walker, I was really curious about the use of the negistor to modulate delay time.

Btw I made a single knob overdrive with the free opamp of the pt 2399 and, even without diodes, you get a nice dirty mid bump. I think I posted a sort of schem, but not here  .

Next time I will work with the pt I will give it a try.

[Mac Walker]

Sure no problem.  I think you could get a square wave oscillator LFO from the following, with fewer components, using the spare op amp as suggested earlier.............maybe.  Not sure if it would work in a unipolar configuration without modification.  I might have to try that next, also using the emitter follower buffer.

[allesz]

It could be a nice idea, but I admit I am not expert with IC oscillators.
Since you plan to try this with an IC, in order to keep minmum parts count, you could try with a double opamp: so you will be able to use the second half of the IC to make a buffer, avoiding the bjt buffer.

[Plexi]

I made a negistor LFO for this circuit to modulate the delay time, here is what a came up with:



Strangely enough, I have never had any luck getting a 2n2222 to work in a negistor circuit.  At any rate you could probably play around with this to reduce a few components.  Not sure about latch up in this case, or if that would be a concern at all.

Also you can play around with the 15 uf to change the duty cycle, it does have a discernable effect on the sound...

Any update on this?? I'll try this one