Small Time: PT2399 Delay with tails

merlinb · Post by **merlinb** » 19 Jan 2012, 09:40

After designing the Equinox I decided I ought to build a simple PT2399 delay, much like the Rebote or DBD. A lot of people complain about the lack of tails with those two projects, so I added that too. Includes my usual full buffering, electronic switching, and 3dB quasi companding. Heavy filtering allows for useful delay times and the usual analog-ish sound, although above about 300ms you start to hear the digital hiss. You can hear it at the end of the sound clip, when all controls are turned to maximum:
Clip: https://dl.dropbox.com/u/57831278/SmallTime.mp3

PCB layout (fits in a 1590b if you shave a millimetre off the sides) and all files can be found here.
https://s81.photobucket.com/albums/j207 ... e%20Delay/

rocklander · Post by **rocklander** » 19 Jan 2012, 11:27

sounds really nice too... thanks very much!

juanro · Post by **juanro** » 19 Jan 2012, 13:56

merlinb wrote:and 3dB quasi companding

Hi Merlin, by "quasi companding" are you refering to the preemphasis / deemphasis in the input and output buffer? Or there is another function of the circuit I'm missing? Great minimalist use of the PT2399, btw

Regards,
Juanro

dlab · Post by **dlab** » 19 Jan 2012, 16:41

That's a seriously sweet etch job.

Only thing is, I can't find the flux capacitor in your schematic

Hides-His-Eyes · Post by **Hides-His-Eyes** » 19 Jan 2012, 16:56

Is there a noise cost to that switching arrangement (PT2399 output always in the chain)?

HEAD · Post by **HEAD** » 19 Jan 2012, 17:18

Hides-His-Eyes wrote:Is there a noise cost to that switching arrangement (PT2399 output always in the chain)?

Edit: should have read more carefully. sorry.

merlinb · Post by **merlinb** » 19 Jan 2012, 17:26

juanro wrote:
merlinb wrote:and 3dB quasi companding
Hi Merlin, by "quasi companding" are you refering to the preemphasis / deemphasis in the input and output buffer?

Yep! Sounds more clever than it is

pedalgrinder · Post by **pedalgrinder** » 20 Jan 2012, 00:42

I built myself the Echo Base using the PT2399 it's great for a guitar as my mate proved when he tried it. But on a bass the unit stinks. Won't repeat the low notes very well bottom E and A just sounds shit the D and G strings it starts to respond. Iam not sure if i can mod the unit i have or it's just the pt2399 doesn't like low frequency's out iam of my league to know what iam talking about here so i thought i would bring it up. I'd like to build even the equinox but i have been unsure wheather to as if it will not respond on a bass for bass frequency there is no point. Can anyone here enlighten some thoughts on this.

merlinb · Post by **merlinb** » 03 May 2012, 14:34

Just made a vero layout for this project:

geiristudio · Post by **geiristudio** » 17 Jun 2012, 13:20

Merlinb, is it verified? I'm desperate for a delay circuit that works. I've gone through a few rebotes that never work (only 1 out of 4-5).

What's that footswitch for?

merlinb · Post by **merlinb** » 17 Jun 2012, 21:30

geiristudio wrote:Merlinb, is it verified? I'm desperate for a delay circuit that works. I've gone through a few rebotes that never work (only 1 out of 4-5).

The vero layout is unverified, but thoroughly checked. These delay circuits are very simple- if you've had problems it may be that you're making a systematic error?

What's that footswitch for?

Um...that's the footswitch. You know, the thing you stomp on to switch between clean and FX? It's not true bypass if that's what you mean- it has tails.

mictester · Post by **mictester** » 19 Jun 2012, 00:07

merlinb wrote:After designing the Equinox I decided I ought to build a simple PT2399 delay, much like the Rebote or DBD.

That's a nice build, and it sounds pretty good from your clip. I tried something similar, but found that the 2399 was too noisy for comfort, even if I used pre- and de-emphasis. My current version has an NE571 giving 2:1 compression on the way in, and 2:1 expansion on the way out. I used an NE5532 instead of the internal op-amps in the 571 and used a second 5532 for the input buffer and the output mixer. I did the bypass switching with a 4066, and had "tails on, tails off" footswitches to give two quite different effects. I also found it necessary to limit the maximum delay, because beyond 250 ms, things got nasty! I'm trying out a dual 2399 for longer delay (with the option of tapping the delay line) and might try a triple if the results are encouraging.

I really don't want to give up on the 2399 for stage effects (it's nowhere near good enough for the studio) as it's a really good, cheap solution.

Yonatan · Post by **Yonatan** » 07 Aug 2012, 09:01

Quck question: If I wanted to adopt this tails feature to add it to any other delay, what is consider the "in" and "out" points of the effect i.e. where does the actual delay circuit start/end?

Where does "input" to the delay circuit start?
- At the J112 source?
- Just after the 100n (after the J112 source)?
- After the 10k resistor?

And where is the "output" to the delay circuit?
- After the "mix" pot? (before the 10k resistor that connect to the mixing opamp)

Then, I could keep the tails/bypass feature from this circuit, except for the actual delay part, and replace it with a delay circuit that I already have.

merlinb · Post by **merlinb** » 07 Aug 2012, 14:52

Yonatan wrote: Where does "input" to the delay circuit start?

The delay line starts just after the 100n (after the J112 source). This capacitor is just a coupling capacitor to block DC, so you might need it, you might not, depends if your substitute circuit has one already. The JFET acts like a switch, allowing audio to pass, or not.

And where is the "output" to the delay circuit?

After the "mix" pot (before the 10k resistor that connect to the mixing opamp). The mix pot simply adjusts the total output volume from the delay line, which is then mixed with the dry signal.

Yonatan · Post by **Yonatan** » 07 Aug 2012, 17:36

Thanks! I didn't mean any disrespect to your delay circuit

, I was just wondering how to adapt to add tails to any delay.

Pruttelherrie · Post by **Pruttelherrie** » 07 Aug 2012, 19:25

Check here for another take on a (switchable) tailsloop: http://www.aronnelson.com/gallery/main. ... 1.jpg.html
or this one, simpler, no feedback, not switchable: http://www.aronnelson.com/gallery/main. ... p.jpg.html

(not my schematics, just passing along)

samhay · Post by **samhay** » 11 Sep 2012, 11:48

Sorry to reserect an old thread, but this seems to be the most recent discussion of the Small Time. I built this recently using Harald Sabro's (sabrotone) vero layout. Its a nice effect and works like a charm - nice job Merlin. I assume like other PT2399 dealys it can be tweaked to give (near) infinite repeats, but after I blundered around for a while, I couldn't get it to do so - has anybody tried/got any advice?

Dirk_Hendrik · Post by **Dirk_Hendrik** » 11 Sep 2012, 16:43

Late to the party too.
I'd like to ask for a a pullup resistor to 4.5 volts at the PT2399 side of the J112. In the current case it's unclear if the FET will fully close.

merlinb · Post by **merlinb** » 11 Sep 2012, 21:30

samhay wrote: I assume like other PT2399 dealys it can be tweaked to give (near) infinite repeats, but after I blundered around for a while, I couldn't get it to do so - has anybody tried/got any advice?

See the 10k resistor in series with the wiper of the Repeats pot? Reduce that resistor to 8.2k or maybe 6.8k and it should infinite repeat.

Dirk_Hendrik wrote:Late to the party too.
I'd like to ask for a a pullup resistor to 4.5 volts at the PT2399 side of the J112. In the current case it's unclear if the FET will fully close.

The other side of the FET is pulled up by the FET's own resistance. Good enough for government work anyway.

samhay · Post by **samhay** » 12 Sep 2012, 11:21

See the 10k resistor in series with the wiper of the Repeats pot? Reduce that resistor to 8.2k or maybe 6.8k and it should infinite repeat.

In retrospect, that makes sense. Thanks merlinb, again, much appreciated.

Small Time: PT2399 Delay with tails [documentation]