Chorizo, the Argentine chorus.

[ppaappoo]

Hello after doing the little angel chorus, I thought of making one, also using the PT2399, but with a sinusaidal wave generator on the LFO. The result was this, a warm chorus on a PCB no longer easy to do and with very few components.

NOTES:
* depth control can be 250k or 500k, the higher value, the lower the effect attack.
* R19 is the resistance responsible for controlling the delay time of chorus, you can put a 5k potentiometer in series with R19 to have a time control.
* Speed ​​control depends on C1, C2, C3 and R2. Enlarging the three capacitor or the resistance we can get slower repetitions, achieved in configuration C1 = C2 = C3 = 470nf and R2 = 100k have a balance between fast and low speeds.
* 78L05 voltage regulator is invested in the circuit because it had not as a component in the libraries of the eagle, but is the correct posisicion Layout.






Downloas PCB http://www.mediafire.com/?c3yap3cqj01yp56

[jcgss77]

Nice circuit!  
Can the remaining section of the opamp be used for a small tonestack?

You got some sound clips?

BTW-I love chorizo!

[chi_boy]

So the only major difference is the LFO, right?  It looks like everthing else is the same.

Also, shouldn't that last opamp be stabilized if it isn't used?  Tie 13 to 14 and 12 to ground?

[ppaappoo]

So the only major difference is the LFO, right?  It looks like everthing else is the same.

Also, shouldn't that last opamp be stabilized if it isn't used?  Tie 13 to 14 and 12 to ground?

The PT2399 section is a standard configuration, so the only part to change is the LFO.
Tie 13 to 14 and 12 to ground is easy to do, but leaving them in the air does not cause problems.

[frequencycentral]

Nice upgrade! Would be nice to use the spare opamp as an output buffer. Soundclips?

[merlinb]

Also, shouldn't that last opamp be stabilized if it isn't used?  Tie 13 to 14 and 12 to ground?

Yikes, don't do that or you risk burning the thing out! To properly stabilise an unused opamp you should connect the + input to a suitable reference (e.g. Vbias) and connect the - input to the output (i.e., set up as a voltage follower).

Also, if you arranged the input opamp as a non-inverting gain stage you could get higher input impedance and much less noise 

[StephenGiles]

Very nice - I also like bife chorizo!!!

[chi_boy]

Also, shouldn't that last opamp be stabilized if it isn't used?  Tie 13 to 14 and 12 to ground?

Yikes, don't do that or you risk burning the thing out! To properly stabilise an unused opamp you should connect the + input to a suitable reference (e.g. Vbias) and connect the - input to the output (i.e., set up as a voltage follower).

Also, if you arranged the input opamp as a non-inverting gain stage you could get higher input impedance and much less noise 

Well that stinks.   I researched a while back and concluded that it had to go to ground.   I did a layout based on that information.   I didn't etch the board yet so no real loss, but I think that may really mess up my layout.   

[cpm]

Also, shouldn't that last opamp be stabilized if it isn't used?  Tie 13 to 14 and 12 to ground?

Yikes, don't do that or you risk burning the thing out! To properly stabilise an unused opamp you should connect the + input to a suitable reference (e.g. Vbias) and connect the - input to the output (i.e., set up as a voltage follower).

Also, if you arranged the input opamp as a non-inverting gain stage you could get higher input impedance and much less noise 

Well that stinks.   I researched a while back and concluded that it had to go to ground.   I did a layout based on that information.   I didn't etch the board yet so no real loss, but I think that may really mess up my layout.   

probably you read "ground" right, but it would be ground from dual supply +/-. For a single supply configuration, that actually means a mid voltage. The point is to avoid the output to go to the rails

[ppaappoo]

Interestingly the idea of using the last section of the TL074 as a buffer but I manter the plate as simple and small as possible.

The effect works well, soon I'll upload some sound clips. Will not regret making this chorus

[Govmnt_Lacky]

Looks interesting 

Might I add a few suggestions?:

1) Connect the unused lug of the 250K pot to the wiper. A generally good idea.
2) Add a polarity protection diode somewhere in the circuit.

Might try this out in the future. Gonna wait a bit until this levels out 

[merlinb]

Well that stinks.   I researched a while back and concluded that it had to go to ground.   I did a layout based on that information.   I didn't etch the board yet so no real loss, but I think that may really mess up my layout.   

You can connect the + input to anything as long as it is within the normal limits of the opamp, i.e, between about 2V and 7V. Maybe there's some other PCB track passing by that has some DC bias on it?

[Barcode80]

Interesting circuit! I agree about the output buffer, I'm all about output buffers lately. I'll try to knock up a layout including using the other opamp as an output buffer.

[ppaappoo]

Interesting circuit! I agree about the output buffer, I'm all about output buffers lately. I'll try to knock up a layout including using the other opamp as an output buffer.

Well, could modify the circuit and use that last opamp as buffer.

[ppaappoo]

Interesting circuit! I agree about the output buffer, I'm all about output buffers lately. I'll try to knock up a layout including using the other opamp as an output buffer.

Well, could modify the circuit and use that last opamp as buffer.
and would have to do?

[cpm]

or use the opamp to invert the input, and then mix the delayed signal with either the positive or negative input, for a different flavour

i've done this with a phaser and is quite cool

[StephenGiles]

I couldn't resist this - http://www.youtube.com/watch?v=TFSsJE2UhIU&feature=related

[chi_boy]

Well that stinks.   I researched a while back and concluded that it had to go to ground.   I did a layout based on that information.   I didn't etch the board yet so no real loss, but I think that may really mess up my layout.   

You can connect the + input to anything as long as it is within the normal limits of the opamp, i.e, between about 2V and 7V. Maybe there's some other PCB track passing by that has some DC bias on it?

Turns out there are quite a few "opinions" about how to do this.  After doing some more research, I did find this:

http://pdfserv.maxim-ic.com/en/an/AN1957.pdf

This App Note clearly states that the best way is as you said.


As for my problem, I don't want to hijack.  Wasn't my intent.  I may opt to leave it though, primarily because it is a clone of the Barber Dirty Bomb and that is the way it was traced.


Regarding your suggestion for DC Bias, what would I be looking for?

The schematic in on the "Other" forum if you care to look.  The layout there isn't current though.  I would need to pick something up around IC1A.  Taking anything from C & D totally blows my layout.

http://www.......org/viewtopic.php?f=7&t=5592&hilit=dirty+bomb&start=40#p134709

[merlinb]

Regarding your suggestion for DC Bias, what would I be looking for?

Look for any trace sits between 2V and 7V, i.e., it is biased above ground. For example, you could connect pin 5 to pin 3 in your layout (I mean this one www.....org/download/file.php?id=11665&mode=view ), since that sits at 4.5V. That wouldn't spoil your ground plane under the IC. There is signal on pin 3 of course, but that doesn't matter since it is within the headroom of the opamp (it must be, since U1a has to handle the same signal!) All you're trying to do is turn unused opamps into buffers that don't go anywhere or feed anything.

[ppaappoo]

I think the output impedance is relatively low, less than 10k. If so we would not need to place a buffer.
As polarity protection, I always use in my pedals a 1N4007 diode in series with the positive. I don't like the idea of putting it between the positive and negative.