Introducing the "One Chip Chorus"!

[Govmnt_Lacky]

Has anyone built it on to a pcb yet?

Waiting on this as well. This whole project looks very promising 

[askwho69]

do we need some mix on this? for more versatility?

[anchovie]

Replacing the two 10K mixer resistors with a pot was mentioned earlier in the thread.

[Kearns892]

R13 on the vero is listed as 10K while on the schematic it looks like it is 100K. What is the intended value?

[anchovie]

Well spotted! Should be 100K as per the schematic.

[Govmnt_Lacky]

Has anyone verified Scruffie's or Kearns' PCB layouts on Page 2?

[anchovie]

Has anyone else got this working on a breadboard, even? 

[merlinb]

Here's another take on the one chip chorus. This one has deeper modulation, so it generates a very thick warble, more like the deep settings on a LA. It also has an improved latch-up fix that may be useful for other projects.

[Scruffie]

Has anyone verified Scruffie's or Kearns' PCB layouts on Page 2?

Don't think so, atleast no one's mentioned it to me.

I'll verify it if you wanna etch me one 

Here's another take on the one chip chorus. This one has deeper modulation, so it generates a very thick warble, more like the deep settings on a LA. It also has an improved latch-up fix that may be useful for other projects.

Damn that looks nice... looks like i'll be making another PCB layout this evening... and using the breadboard if I can clear some space.

Has anyone else got this working on a breadboard, even? 

Same as above, if I can get some space on the breadboard i'll try tonight... it's kindaaa full at the moment.

[Slade]

Just saw this thread...
I'm amazed... Congrats on this new design!

[Thomeeque]

Is this drawing correct? I'm trying to figure out how the LFO works here and I don't see it.. LTSpice neither.. Thanks, T.

[Govmnt_Lacky]

I wondered if it would be possible to make a chorus effect using a PT2399 and no external op-amps and the answer is yes! Instead of using the internal amplifier intended for the output mixer, I've given it a new role in a phase shift oscillator. I originally intended to use the LFO output to modulate delay time, but the nice surprise was that there was no need - the oscillator uses the chip's Vref pin (famously exploited by frequencycentral in the Little Angel as a place to inject modulation) as its ground point and, just by being there, it makes the PT2399 wobble.

This is how he did it Thom 

[Kearns892]

I was going to try and etch my board today, but I am not sure I have enough PTs to complete this and the other PT based projects I'm rushing to finish.

[Thomeeque]

I wondered if it would be possible to make a chorus effect using a PT2399 and no external op-amps and the answer is yes! Instead of using the internal amplifier intended for the output mixer, I've given it a new role in a phase shift oscillator. I originally intended to use the LFO output to modulate delay time, but the nice surprise was that there was no need - the oscillator uses the chip's Vref pin (famously exploited by frequencycentral in the Little Angel as a place to inject modulation) as its ground point and, just by being there, it makes the PT2399 wobble.

This is how he did it Thom  

Well, that's how anchovie did it, but I'm asking about Merlin's magic, that's completely different circuit T.

[Govmnt_Lacky]

Well, that's how anchovie did it, but I'm asking about Merlin's magic, that's completely different circuit T.

SLAPS FOREHEAD PROFUSELY!!!!!!   

[merlinb]

Is this drawing correct? I'm trying to figure out how the LFO works here and I don't see it.. LTSpice neither.. Thanks, T.

Pah, there's always something! Resistor in the wrong place- drawing has been corrected. (If it still looks the same try going directly to http://i81.photobucket.com/albums/j207/merlinblencowe/OneChipChorus.jpg)
It's a relaxation oscillator, just like in most modulation effects, e.g. Phase 90.

[Govmnt_Lacky]

What resistor was moved and where? I do not see a change even after clearing history 

[Thomeeque]

Is this drawing correct? I'm trying to figure out how the LFO works here and I don't see it.. LTSpice neither.. Thanks, T.

Pah, there's always something! Resistor in the wrong place- drawing has been corrected. (Clear your browsing history if it still looks the same)
It's a relaxation oscillator, just like in most modulation effects, e.g. Phase 90.

Actually, integrator capacitor 4u7 is in wrong place, it should lead to pin 13 not 14 of PT2399 (I see only thumbnail in your gallery corrected, full picture is still the old one - some photobucket issue I guess).

Funny, this LFO works only thanks to weak internal reference voltage divider If it was harder, it would not tick (voltage at positive input of LFO op-amp must be alternated for this type of oscillator).

Problem is, that you don't get triangles on the reference voltage this way (triangles are only at the integrator capacitor) - what you get there are rounded squares*..



That's why it sounds as you describe it (it generates a very thick warble) probably..

T.

* Edit: But now I see that it can be rounded almost to sinusoidal wave (when increasing C1 and C3).. and of course I don't know how exactly internal reference voltage source looks..

[frequencycentral]

Here's another take on the one chip chorus. This one has deeper modulation, so it generates a very thick warble, more like the deep settings on a LA. It also has an improved latch-up fix that may be useful for other projects.

I *think* this is based on the updated version. Please check before attempting - it's late - I'm tired.

[David]

How crucial is it to use a BC337?  Would substitution with a 2N series transistor be possible?