"Little Angel" - Super Simple PT2399 Mini Chorus

[markeebee]

I love you, Rick. I just do.

[~arph]

And now you've all tried that..

try this:  remove the 1n cas between 13-14 and 15-16: no audible difference -> saves two components

Make the two caps between 9-10 and 11-12 -> 220nF
Make the two caps to ground from 7 and 8 small.. say 10 - 22 nF

sounded a bit better to my ears.
Still I think it's not really chorusy sounding, more vibey...

[slacker]

Little mod for anyone who's interested try changing the resistor connected to pin 15 to 22k, that makes the wet side a bit louder and sounds more chorusy to me. It might mess with to overall level though.

[earthtonesaudio]

I would caution that it might be harmful to the chip to exceed Vcc at any pin, including pin 2.  It might be worthwhile to add a clamping zener from pin 2 to ground, or else limit the LFO output in some other way.

[frequencycentral]

Super kudos to Rick.  

And super kudos back at culturejam for etching, drilling, populating and testing the PCB layout all in one day!

[dmc777]

Sounds great! Anyone know how to go about adding a level or blend control into this? 

[culturejam]

Something I just noticed is that the Depth control also has an affect on tone. As Depth is turned down, mids are accentuated, and I think maybe highs are attenuated just a hair. With Depth more than about half-way, tone does not seem to be affected (ie - it sounds like the bypassed tone, just modulated).

There are some really cool sounds in this thing, although I probably wouldn't classify it as true chorus. It's got chorus settings, and it's got vibe settings. And it also does some other stuff.

With both Depth and Speed at minimum, it just makes the guitar sound a little bigger and fuller.

[culturejam]

I had a partially gutted enclosure already painted and it had two knob holes drilled....

All I had to do was solder a few wire, slap on some stamp artwork, and take photos. 

[Slade]

Cheers! That was fast!

[soggybag]

The length of the delay can describe the difference between phase shift to chorus to flange then on to real delay. I wonder if increasing the resistance on pin 6 a little might move the whole thing into flange territory?

[frequencycentral]

Very inspiring, great work. I love this chip. Pin 2 is still sort of a mystery to me. What exactly does this do?

According to the datasheet pin 2 is the vref for the internal opamps.

Sounds great! Anyone know how to go about adding a level or blend control into this?  

You could add blend control by cutting the traces to the left of C12 and C15. Take a suitable pot (10k or 22k maybe?), connect C12 to lug 1, C15 to lug 3, connect lug 2 to ground via a 100k resistor. Take you output from lug 2.

The length of the delay can describe the difference between phase shift to chorus to flange then on to real delay. I wonder if increasing the resistance on pin 6 a little might move the whole thing into flange territory?

Increasing the resistance on pin 6 will take it further away from chorus into short delays. The PT2399 really has too high a minimum delay time to do flanging, as flanging requires shorter delays than chorus. Maybe something interesting to try would be to feed the dry signal through a second PT2399 set to a very short fixed delay, that way the modulated delay would wobble either side of the fixed delay. Perhaps it would sound like flanging, but with ~30ms latency.

[soggybag]

What's happening here when you're modulating the VRef on pin 2? Seems like this shouldn't change the delay time. Is it effecting the signal passing through the two internal op-amps, creating a sort of phase shift on these?

[frequencycentral]

What's happening here when you're modulating the VRef on pin 2? Seems like this shouldn't change the delay time. Is it effecting the signal passing through the two internal op-amps, creating a sort of phase shift on these?

Search me! I was hoping some clever guy would come tell us. My instinct tells me that the internal VCO must also be referencing the vref. The datasheet should be called '101 things you'll never know about the PT2399 and other mysteries'.

[Earthscum]

looks to me like you are wobbling the Vref only on the filters. Since they are all inverting, they all wobble the signal back and forth, so you are getting a phasing of the filters moving away and towards each other...

I don't know. Makes sense to me... like wwobbling an all pass filter.

EDIT: BTW, awesome idea! I've been looking for something kewl like this... I've been trying to figure out something awesome to make for my bass with the delay. This overqualifies, IMHO. Most delays cater to guitar, and well... bass acts a bit differently   

[frequencycentral]

looks to me like you are wobbling the Vref only on the filters. Since they are all inverting, they all wobble the signal back and forth, so you are getting a phasing of the filters moving away and towards each other...

I don't know. Makes sense to me... like wwobbling an all pass filter.

There is way way way more wobble available than a few dozen all pass filters could muster. This is not phasing. I have a 14 stage phaser on my other breadboard that can't do these tricks.

[soggybag]

Search me! I was hoping some clever guy would come tell us. My instinct tells me that the internal VCO must also be referencing the vref. The datasheet should be called '101 things you'll never know about the PT2399 and other mysteries'.

Thanks for the reply, as long as we're all in the dark I'm OK. The use of pin is still a total mystery.

[Earthscum]

There is way way way more wobble available than a few dozen all pass filters could muster. This is not phasing. I have a 14 stage phaser on my other breadboard that can't do these tricks.

Nice... did I miss sound clips somewhere in the thread, or do you have any? I'm really curious now. I'd go breadboard it, but my roomie camped the TV as soon as he got off work like a baby. That's where all my stuff is at, and don't wanna bug him.

[Mugshot]

funny, i breadboarded this last night (it's morning here), and thought the 500K depth pot wasnt really useful so changed it to 250K, but thought the minimum depth was still lacking prominence of the chorused signal, so i thought maybe trimming the 100K minimum depth resistor to 47K would give me a more prominent chorus. and then here im reading it was already changed to 33K!  

i also tried bridging pins 16 and 14 of the PT chip with a 47K resistor for feedback, but wasnt convinced. will try insteda the 33K minimum depth mod later tonight. nice one Rick!

[culturejam]

Clip!

http://www.archive.org/details/LittleAngel-Pt2399-basedChorus

Here's what's up:

Same basic progression each time.

First clean >
Speed 12:00 / Depth 2:00 >
Speed 12:00 / Depth MAX >
Speed turned from min to much higher / Depth MAX >

And then I just move around and try to show the main types of tones you can get. I think I did a total of maybe 8 settings or so.

And then clean again.

Straight into Garage Band through a UX1 with a hint of (software) reverb.

[12Bass]

From that sound of the most recent sample, given how it is phasing the midrange, I'd guess that the delay is under 20 ms.