Introducing the "One Chip Chorus"!

[deadastronaut]

@james, love it, nice n clean chorus.....brilliant.

[anchovie]

Congrats James to this design, brilliant idea and it sounds really sweat!

Would you mind to make short sample with heavy distorted guitar, please?

Btw. thanks to additional 4k7 (output LPF) on the wet path and R11=R12=10k you don't get exact 1:1 dry/wet mix (wet is cca 3.3dB weaker), is it on purpose?

Cheers, T.

Thanks!

I did settle on the 4.7K after trying various resistor/cap pairs to get the same cutoff frequency - that dry/wet mix is my personal preference with the pitch movement of the wet signal being just short of really obvious. As has been mentioned, you could always replace the two 10K mixer resistors with a pot to vary the balance.

I'll get a high-gain sound sample done this evening if my wife has stuff she needs to do on her own, otherwise I'll take a break from being antisocial in the garage and wait until the weekend! 

[Thomeeque]

I did settle on the 4.7K after trying various resistor/cap pairs to get the same cutoff frequency - that dry/wet mix is my personal preference with the pitch movement of the wet signal being just short of really obvious. As has been mentioned, you could always replace the two 10K mixer resistors with a pot to vary the balance.

Sure sure, I just wanted to know where this comes from (as "normal" default chorus ration is 1:1), thanks! Looking forward for the samples, good luck, T.

[robmdall]

And the build list gets longer...

Great design James!!!

[DougH]

That sounds very good! 

[Earthscum]

22k+(33k and 100k)=24k

You have just forgot to add those 22k here, it should be 46k (just for the record, it's obviously "typo").. T.

Doh! Yep. Last thought before I went to bed last night, surprised I got it that complete, lol.

So, 1 pot can replace 2 10k resistors, and we can take another resistor away from the PSO. Without simplifying the PSO, I think that is about it for shaving parts. Too cool!

BTW, my thoughts on the PSO... You're using the internal voltage reference, thus you are modulating it with out of phase signals, which we typically only use one of for the output. This, I think, accounts for the unique sweep. You have current from the rejected highs of the wet signal, and the bottom of the resistors that are injecting 2 shifted out of phase LF signals. The highs from the wet signal may be contributing a significant amount to the PSO signal, helping to create the "warble". Either way, it's very sweet sounding, indeed!

I gotta say... Sorry, Zombie Chorus... I think I found my build. I'll use the PLL for something else, lol.

[Brymus]

I breadboarded this.
The chorus works,but its covered with noise.
A static,mixed with distortion that pulses in and out ,but it doesnt sound in sync with the chorus.
The static pulses about 1 time per 1.5 secs roughly.
Double checked everything,more power filtering seemed to help a little.
But still really bad.
Any ideas ?

[anchovie]

The noise I found when I was tweaking on the breadboard was related to the LFO, which is where the 22K resistor to limit the Lushness control came from. I take it you're getting noise no matter where the control is set?

[Pigyboy]

Has anyone built it on to a pcb yet?

[Earthscum]

Sounds like the LFO is dragging the bias too close to the rails at some point.

I have a super compact PCB (1.25"x1.5") to finish on Monday, and I'll try it out. I can't decide if I wanna do my PCB AND the others, or just do my layout... I dig the 1590A layout... looks like it may fit for a mod to a DOD pedal I'm doing. My layout is set up for a add-on to a friend's pedal, which may be getting the same treatment.

[askwho69]

mmhhh now there's little angel and a tini winny angle hear! love the sound man thank you so much! Congratss too

[Brymus]

The noise I found when I was tweaking on the breadboard was related to the LFO, which is where the 22K resistor to limit the Lushness control came from. I take it you're getting noise no matter where the control is set?

Yes,noise no matter where its set.
The lush control does work.But doesnt change the noise.
I thought it was the LFO noise becuase of the cycle.
But instead of a thump or tick ,its static and distortion that cycles over and over.
I connected pin 4 to pin 3 and that helped alot but it also reduced the chorus effect.

[anchovie]

Hmm, I did wonder what the risk of using the chip for something it wasn't designed to do would be, in terms of production variations. These are complete guesses: what happens if you increase the cap value from pin 2 to ground, and what happens if you swap the pin 7 & 8 caps for the recommended 100n?

[merlinb]

You could add a 4.7nF cap from the output to ground, which would at least give you *some* low-pass filtering to reduce PT noise.

[Earthscum]

@Bryan - is it in phase with the LFO? Basically, does it cycle within some kind of consistency with the LFO? It sounds like it cycles slower than your LFO.

I'm thinking along the same lines as James.  Maybe drop down to 1uF's on the mod/demod pins? 100u on the Vr pin (2). The 100u may help keep the LFO from dragging the VR so close to the rails, if that's the issue.

Last time I had a PT do something like that,it was powering up and down. I figured out I had some stuff backwards , lol. I cannot believe the amount of abuse I have put my original chip through. The newer ones don't like being molested like that. Wish we could get our hands on a group buy of old stock from Princeton.

[tubelectron]

Congratulations ! A very nice sounding chorus - worth to make a try, indeed...

[anchovie]

The newer ones don't like being molested like that. Wish we could get our hands on a group buy of old stock from Princeton.

I bought a couple of tubes of them about 3 years ago and I'm still getting through them, I'll have to get some new ones to see how they compare (I noticed in the Little Angel thread about the delay resistor spec now being 1K minimum despite the delay time table still having an entry for 0.5R!).

Who'd have thought we might end up with legendary "mojo" karaoke echo chips? 

[~arph]

The new ones have weak pins too  not too breadboard friendly

[newfish]

The newer ones don't like being molested like that. Wish we could get our hands on a group buy of old stock from Princeton.

I bought a couple of tubes of them about 3 years ago and I'm still getting through them, I'll have to get some new ones to see how they compare (I noticed in the Little Angel thread about the delay resistor spec now being 1K minimum despite the delay time table still having an entry for 0.5R!).

Who'd have thought we might end up with legendary "mojo" karaoke echo chips? 

Yeah, the first chip I bought was really warm and lush.  It gave an almost 'tape-like' sound, sort of mid-90s U2 sort of sound.
I bought a chip last week and it sounds like Jive Bunny.  I mean, there *must* be some Mojo in there, right?

[Yazoo]

I really like the sound of this. I was going over the Scruffie pcb before I etch it. Could you check the pad for the minus side of the 100uf capacitor going from pin 1. It's sitting between pin 2 and pin 3 at the moment and looks like it is connected to both. Should it be moved down a bit so that it is just connected to pin 3?