Ersatz Verben - PT2399 pseudo reverb

culturejam · Post by **culturejam** » 27 Jan 2012, 00:06

Inspired by the Crap-Fi Delay by allesz, I decided to see if a similar simple circuit would work at lower delay times for reverb and slapback. It does.

Once the basic circuit was up and running, earthtones helped me refine it and make it much nicer. He's wicked smaht like that.

Delay time range is about 40ms up to about 140ms. As delay time is increased, more highs are rolled off by C4 (that was ETA's idea). So it's pretty much hiss/noise free no matter the delay time.

I've got a 2-sided layout done and prototypes ordered. But I thought I'd post this in hopes that someone who was interested would work up a vero layout or a one-sided PCB layout. If there is a DIY-friendly layout, I can move this thread into the the "Complete" folder. <now completed>

Here is a demo clip:

: ersatz_v1-4.png (5.93 KiB) Viewed 4695 times

madbean · Post by **madbean** » 27 Jan 2012, 01:34

That is very clever and sounds really good. Nice, nice work, CJ!

Would it be okay if I try the SS layout? Maybe a 1590A?

culturejam · Post by **culturejam** » 27 Jan 2012, 03:47

madbean wrote:Would it be okay if I try the SS layout? Maybe a 1590A?

I would be honored if you would do the layout. And please feel free to post it at your site as well. And shit, I'm sure you'll think of a cool tweak while working up the layout and probably end up with an improved version.

Oh, and I should add the pads J1 and J2 are there in case anyone wants to add some wires and do something funky with that unused low-pass filter/op amp thingie in there. That was earthtone's idea well. He says that if not used, the pads should be jumpered.

Another note while I'm thinking about it: I tried to see if a 10k/12k voltage divider would work in place of the regulator. It does...sort of. The chip gets pretty noisy this way unless there is like 470u or more filtering right near pin 1. And that takes up more space than the regulator and a small cap. And it also doesn't protect the IC if somebody plugs in a 12v supply. I was just trying to see how many rules I could break.

Here's the layout I did. It's 1.55" x 1.25".

: ersatz_v1-4_2S.png (15.52 KiB) Viewed 4681 times

madbean · Post by **madbean** » 27 Jan 2012, 04:04

Cool, I'll take a crack at it. What about a 5.1v zener and then a 10uF tant right next to pin1? You could eliminate the PS filter cap, I think.

culturejam · Post by **culturejam** » 27 Jan 2012, 04:11

madbean wrote:Cool, I'll take a crack at it. What about a 5.1v zener and then a 10uF tant right next to pin1? You could eliminate the PS filter cap, I think.

Yeah, I think that would also work. There's no real need for the main filter cap, I suppose. And C11 can probably go bye-bye. A lot of delay circuits omit that one. I threw it in hoping it would somehow make things quieter.

If I can find a 5.1v zener, I'll give it a try. I still have the circuit on a breadboard. I'll see about dropping C11 as well.

And apparently I left out the polarity diode. Not sure if that even matters in this one.

madbean · Post by **madbean** » 27 Jan 2012, 14:19

Here's my 1590A layout. The borders are 1.4"W x 1.425"H. Obviously unverified ATM. It's meant for 1/8 or 1/4W resistors, multi-layer ceramic or box caps, and tantalum electrolytic. The only liberty I took was in the values of the PS filtering caps.

Probably best to use either 9mm or 12mm Alphas for fitting in the box!

ErsatzVerben.png

ErsatzVerben_PNP.png

ErsatzVerben_Schem.png

madbean · Post by **madbean** » 27 Jan 2012, 14:46

I just thought of a neat mod you could add here. Add a dual op-amp as an envelope filter off the input. Connect that to an LED and attach a photocell to the 1k off pin6 and then a switch to ground. When the switch is engaged, the reverb amount will respond to pick dynamics, so when you play hard, the reverb is short and when you play soft it's long.

culturejam · Post by **culturejam** » 27 Jan 2012, 14:56

See, I knew you'd think of something cool.

I think modulated reverb would be a nice next step.

briggs · Post by **briggs** » 27 Jan 2012, 14:59

This looks and sounds very nice! The mod Madbean suggesting will probably work quite well too, you'll get some strange minor pitch bends too as it speeds up/slows down.

EDIT - that combined time/treble roll off control is a really good idea!

[EDIT 2 - Madbean suggested the mod - personal note; read the thread briggs....]

culturejam · Post by **culturejam** » 27 Jan 2012, 15:01

briggs wrote:EDIT - that combined time/treble roll off control is a really good idea!

I know! I wish I could take credit for it, but that's all earthtonesaudio. I was going to have a switch to crank up the low-pass for longer delay times, but he just said, "Why not tie into the delay pot to make it progressive?"

briggs · Post by **briggs** » 27 Jan 2012, 15:09

culturejam wrote:
briggs wrote:EDIT - that combined time/treble roll off control is a really good idea!
I know! I wish I could take credit for it, but that's all earthtonesaudio. I was going to have a switch to crank up the low-pass for longer delay times, but he just said, "Why not tie into the delay pot to make it progressive?"

So simple, I can't believe someone hasn't noticed this one before! Well in Earth...

madbean · Post by **madbean** » 27 Jan 2012, 15:32

I didn't think about the pitch bend---that could sound awesome or be a deal breaker.

Here's a quick draft of what I had in mind.

briggs · Post by **briggs** » 27 Jan 2012, 15:43

I did an experiment years ago with an envelope follower, sequencer and LFO with the PT2399, they all sound good and create some weird pitch bending sounds... The sequencer was truly insane but very fun!

culturejam · Post by **culturejam** » 27 Jan 2012, 15:47

Yes, I like that. I like it a lot. I suppose as long as you can turn off the envelope, the pitch bending is a great feature.

And while we're at it, the output could probably use a buffer to keep things at unity. The version I posted is at unity, but it can sometimes sound quieter with the mix set at certain spots.

Next draft, you might as well put everbody's names on there: allesz, earthtones, me, and you. And probably Briggs too.

briggs · Post by **briggs** » 27 Jan 2012, 16:02

It could probably make a really nice sounding bare bones chorus/flanger too if you used the LFO from Tim Escobedo's Wobbletron/Bigfoot FX Magnavibe (I've been using that recently

) to modulate the delay time....

culturejam · Post by **culturejam** » 27 Jan 2012, 16:26

briggs wrote:It could probably make a really nice sounding bare bones chorus/flanger too if you used the LFO from Tim Escobedo's Wobbletron/Bigfoot FX Magnavibe (I've been using that recently ) to modulate the delay time....

The minimum delay time is a bit too long to make a good chorus or flanger. See frequencycentral's "Little Angel Chorus" for a neat trick to make a 2399 do the chorus thing.

But hell, I'm all up for trying it another way.

madbean · Post by **madbean** » 27 Jan 2012, 16:32

Yeah, you could just attach an LFO, or maybe this envelope idea to pin2 instead. I haven't really played with that, though.

earthtonesaudio · Post by **earthtonesaudio** » 27 Jan 2012, 16:51

madbean wrote:I didn't think about the pitch bend---that could sound awesome or be a deal breaker.

Here's a quick draft of what I had in mind.

The inverting input is a virtual ground, which will mute the signal if connected directly. Also the input is at GND dc bias, so AC couple to the envelope detector or there will be scratchies.

culturejam wrote:See, I knew you'd think of something cool.

I think modulated reverb would be a nice next step.

LPF2 could be used as either a LFO or an envelope detector... maybe both.

culturejam · Post by **culturejam** » 27 Jan 2012, 17:25

earthtonesaudio wrote:LPF2 could be used as either a LFO or an envelope detector... maybe both.

That's what I was hoping.

madbean · Post by **madbean** » 27 Jan 2012, 17:40

earthtonesaudio wrote:
madbean wrote:I didn't think about the pitch bend---that could sound awesome or be a deal breaker.

Here's a quick draft of what I had in mind.
The inverting input is a virtual ground, which will mute the signal if connected directly. Also the input is at GND dc bias, so AC couple to the envelope detector or there will be scratchies.

D'oh, good catch! Thanks.