Introducing the "One Chip Chorus"!

[adielricci]

I built Viktor's version and, IMHO, the chorus sounds way better

Define better?

I'm assuming you mean that the chorus is a bit brighter than the first version...

Sorry, my bad.  By "IMHO" I supposed everybody would understand that it was a subjective point of view, I beg your forgiveness for being so careless.

I meant it lacked brightness and the modified sound was somewhat below the level of the bypassed signal.  Was the oscilation part clear to you, Ark Angel HFB, or do I have to be more specific?

[mistahead]

Stating it was in your opinion doesn't really attach any adjectives to what you observed...

Thanks for clearing that up - your perception is in line with a lot of the folks here, that said the slightly murky/less than unity sound can be exploited with a few tricks... should you want that sort of outcome (which most don't seem to).

[adielricci]

Stating it was in your opinion doesn't really attach any adjectives to what you observed...

You're right.  I will be more careful in the future.

[Ark Angel HFB]

Sorry, my bad.  By "IMHO" I supposed everybody would understand that it was a subjective point of view, I beg your forgiveness for being so careless.

I meant it lacked brightness and the modified sound was somewhat below the level of the bypassed signal.  Was the oscilation part clear to you, Ark Angel HFB, or do I have to be more specific?

woo woo take a breath buddy. My comment on defining "Better" was asking you to explaining what result you got. "Better" IS really subjective and could mean anything since no one on here knows you. For example maybe you play jazz and like darker tones with really muted highs... your "Better" might mean a sound with less highs in the signal because you like that.

It is like me telling you that I recently changed the tires on my car and now it is "better". Do I mean the new tires are more slick because I like to drift corners, or do they have more grip and a built in fast air release for off road'in? You have no clue because you don't know what my "Better" is... so "Better" doesn't tell you a damn thing.

The oscillation part was clear... because you actually stated the result.

I hope the above "Better" explained why I asked you what you meant.

[adielricci]

Perfectly, Ark Angel HFB.  Points taken.  

Interestingly, the popping was also reduced (but still there) after those modifications.

[psychedelicfish]

Here's my version of the One Chip Chorus:

It's pretty similar the stock OCC, but I've made a few changes based on my readings here (an excellent article, anyone experimenting with these chips should read it) and my breadboard experiments. The one problem I have with the stock OCC is that the high frequency response is, quite frankly, terrible. Improving this was one of my goals, and was achieved by putting the 47pF capacitor across the 470k resistor at the input, and removing the 100nF capacitor from the delay output to vr (neither of these changes seemed to affect noise levels, which was nice).

My other major goal was fixing the lockup (I ocassionally had chips lock up on me with the stock circuit, even when I had pins 3 & 4 connected). I tried the lockup fix from the article mentioned above using a BC337 transistor. The delay time was noticeably shorter (shorter than with pin 5 grounded ), so I measured the resistance from pin 5 to ground, and with my multimeter probes around one way, I got open circuit, and when I reversed them, I measured around -3k!!! I'd heard about some transistors that do this, and had always wanted to try it out in a PT2399 circuit to see if it was possible to get a short enough delay for flanging.

This circuit does have a hint of flanging in there, but it's not strong enough to call it a flanger yet... I'll leave that to someone else. I had read however, that there is more feedback in flangers than choruses, so I tried adding some. It didn't make it sound any more like a flanger, but it did seem the whole thing sound a lot more natural, so I left it in. I also changed a few of the 10uF capacitors to smaller ones to reduce the physical size.
In short, this is a brighter chorus with shorter delay times, giving a slight flanger sound as well as ordinary chorus.
Enjoy,
Edward

[ANDYEFFECT]

Hey all, before I forget... the micro-sized layout I promised several pages ago, lol. 1.2" x 1.5", scaled for 300 DPI Print. You'll need to mirror the image for toner transfer etching, I have it set up for silk screen transparencies.

I have the ground plane extending under the chip in an effort to isolate the power side from the signal side (at least I think that's what my idea was). Also note either resistors OR trimpot for the output. Lush control is set up as a trimpot in case you want to make a "No-Knob OC Chorus" NoKnOCChor? 

Anyhoo...

this layout tested this? some modification?

[Perrow]

The 78L05 needs to have its middle leg grounded, so I'd say it's probably not been verified.

[knutolai]

My other major goal was fixing the lockup (I ocassionally had chips lock up on me with the stock circuit, even when I had pins 3 & 4 connected). I tried the lockup fix from the article mentioned above using a BC337 transistor. The delay time was noticeably shorter (shorter than with pin 5 grounded Shocked), so I measured the resistance from pin 5 to ground, and with my multimeter probes around one way, I got open circuit, and when I reversed them, I measured around -3k!!! I'd heard about some transistors that do this, and had always wanted to try it out in a PT2399 circuit to see if it was possible to get a short enough delay for flanging.

Thats is interesting! Have you been able somehow calculate the delay time? I could see this be interesting for some applications

[psychedelicfish]

My other major goal was fixing the lockup (I ocassionally had chips lock up on me with the stock circuit, even when I had pins 3 & 4 connected). I tried the lockup fix from the article mentioned above using a BC337 transistor. The delay time was noticeably shorter (shorter than with pin 5 grounded Shocked), so I measured the resistance from pin 5 to ground, and with my multimeter probes around one way, I got open circuit, and when I reversed them, I measured around -3k!!! I'd heard about some transistors that do this, and had always wanted to try it out in a PT2399 circuit to see if it was possible to get a short enough delay for flanging.

Thats is interesting! Have you been able somehow calculate the delay time? I could see this be interesting for some applications

Never mind about that, it was almost definitely the voltage from the chip stuffing up the resistance measurement

[knutolai]

Would it be possible to control the mod-depth by adding a voltage divider (pot) between the "MOD" label and pin 2 of the chip?
Whats the advantage of modulating pin 2 opposed to pin 4 (as on the echo base delay)?

EDIT: Never mind, looking at the Little Angel Chorus pretty much answered the question

[pinkjimiphoton]

fwiw, i got this in the mail the other day as a possible "fix" for the lockup issue...

Subject: Re:_Jimi_Pocius_Dot_Com

Hey Pinkster,

We were doing some searching for the PT2399 latch-up issues and found your problems on the tagboardeffects website  and we had the same problem as you with the latching up everytime we powered it on and only after unplugging and waiting to plug it back in did it start working again.... We may have found a fix which is a 0.01uF capacitor across pins 2 and 3 of the PT2399. Worked for us anyways.

Let me know if this fixes your problem!!

Craighton Hale

Keeley Electronics, Inc.
www.robertkeeley.com
1733 S. Fretz Ave. Suite C
Edmond, Oklahoma 73013
405-341-2025

[Canucker]

Fun project! I always love it when I have all the parts on hand before I even see a project.  

[anchovie]

Nice to see this still gets a look-in once in a while! 

The main aim I had with this was a proof-of-concept that you could get a LFO running in the PT2399 without any extra ICs. By all means tweak the filters to taste - the only judge of right and wrong is your ears! For me personally the frequency response of the original was fine, but that's probably because I tune down to C and play distinctly un-jangly riffs. 

[Canucker]

whatever it was set to as a result of not the cleanest solder job when I first put it together would have been nobodys taste but mine! Tons of noise followed by what you might call a faint delay after about two seconds....it basically sounded like something breaking but not nearly as loud as my clean signal....it was violent but I liked it lol

[Magnus]

Hello,
I am working on my layout based on the schematic from the first page
but with the "ground-fix" and "mix-pot-mod" from Vikt0r and I have two questions:

What value does the mix-pot have (10k lin?) and what does it actually do?

My layout is almost finished, its as small as possible and I think it went really well


Greetings
Magnus

[davidmauroweb]

Hello, this is my first action in this forum. I build the version 1590a of page 2, when I turn it on there is no chorus, only after making a bridge between pins 5 and 6, releasing it, appears working correctly.
Apparently starts blocked and then the bridge works properly.
Thank you

[bluebunny]

Welcome David.  Shorting to pin 5 is a bit of a red herring.  Sounds like the resistance at pin 6 may be too low.  You might want to try two things.  Try instead shorting pins 3 and 4 (thereby grounding the end of the 1K resistor); they are supposed to be connected internally by a low resistance, but some people like to short them explicitly (they are both flavours of "GND" connections).  And/or check that the 1K resistor is indeed 1K and isn't itself shorted.

[Ksander]

Does anyone still have Anchovy's initial design as a schematic? Anchovy has not been online since 2020, so I guess asking him won't help. I'd like to try it, and tracing the schematic  from the PCB's is confusing me!

is it essentially using the 'free' op amp as a phase-shift oscillator and using passive mixing of the output at pin 12 with the signal?

[duck_arse]

here's something from searching. is it this?