Octave Fuzz blend issues???

[david1991ross]

I'm designing an octave fuzz with a blend control but I'm having issues while breadboarding it. The blend pot works but I'm getting a bit of residual octave fuzz when it should be completely clean. I can't explain this. Also, when I remove the jack from the guitar I get a high pitch squealing noise that I can't explain either. I feel like that's an issue with the design of the circuit. Can anyone clarify why I'm having these issues? Particularly with the blend pot not completely filtering out the octave fuzz?

[11-90-an]

When doing something like this, the pot basically acts as a blender, so no matter what you put, no matter how small, it's still there... 

A better way of wiring your pot would be like this:



Basically, when the pot is turned to one extreme, that side is directly connected to ground, and cancels the signal.

[david1991ross]

I appreciate the response. I've seen similar blenders which use op amps and fairly large capacitors. Is there a benefit to these designs over yours? I'd prefer not to use more op amps, I already have a lot and I'm planning on adding more.

[11-90-an]

I appreciate the response. I've seen similar blenders which use op amps and fairly large capacitors. Is there a benefit to these designs over yours? I'd prefer not to use more op amps, I already have a lot and I'm planning on adding more.

Mine only contains resistors...

This type of blender is based on the blend in the Theremin Fuzz by Parasit Studio: https://www.parasitstudio.se/uploads/2/4/4/9/2449159/theremin_fuzz_doc.pdf
(Scroll down for schematic...)

IMO, it's all up to you, so breadboard all possible combinations and find out! 

[david1991ross]

I'll definitely give it a shot. Is this what I would be looking to try and do?

[11-90-an]

yep, that should do fine...

I also think you should add 100n caps before R31 and R30... to prevent dc from reaching the next pedal.....

[antonis]

Without DC blocking caps, Blend pot will crackle..

P.S.
Can't get the values of R15, R16 & R17 for differential U2.1 configuration..
It calls for 262*V2 - 2.2*V1, where V2 is clean signal & V1 is octave modulated one..

[david1991ross]

Can't get the values of R15, R16 & R17 for differential U2.1 configuration..
It calls for 262*V2 - 2.2*V1, where V2 is clean signal & V1 is octave modulated one..

Can you elaborate on this? I don't understand.

Also, I breadboarded with the second lug of the pot going to ground and the resistors going to lug one and three and I'm still getting the same problem. I can hear an audible amount of the octave fuzz in the mix even with the blend pot all the way on the clean sound. There's also a noticeable drop in overall volume with is consistant with my LTSpice simulations.

[11-90-an]

since it's on breadboard... can you try plugging the output wire straight up the "clean"? (disconnect the octaved signal...)
there might be a chance of your "clean" signal to actually be the one with a hint of octave...

yes, there would be a volume drop.

[david1991ross]

since it's on breadboard... can you try plugging the output wire straight up the "clean"? (disconnect the octaved signal...)
there might be a chance of your "clean" signal to actually be the one with a hint of octave...

yes, there would be a volume drop.

That was a good call, I am getting some octave signal in my clean signal when I plug the output of the breadboard directly into pin 7 of the opamp, also the beginning of what should be my clean signal. Is there a way to get rid of this? Would a buffer between the clean signal and octave fuzz help? Or is there a simpler way?

[antonis]

Can't get the values of R15, R16 & R17 for differential U2.1 configuration..
It calls for 262*V2 - 2.2*V1, where V2 is clean signal & V1 is octave modulated one..

Can you elaborate on this? I don't understand.

[Mark Hammer]

Question: Is the goal to have the option of ONLY clean or ONLY octave, or is the objective to be able to blend in varying amounts of octave-up with an always-on clean signal?  The two require slightly different sorts of solutions.

Take a look at the Craig Anderton Octave-doubling fuzz for an idea.

[david1991ross]

Question: Is the goal to have the option of ONLY clean or ONLY octave, or is the objective to be able to blend in varying amounts of octave-up with an always-on clean signal?  The two require slightly different sorts of solutions.

Take a look at the Craig Anderton Octave-doubling fuzz for an idea.

The goal is to be able to blend in varying amounts of octave-up with an always-on clean signal.

[david1991ross]

Can't get the values of R15, R16 & R17 for differential U2.1 configuration..
It calls for 262*V2 - 2.2*V1, where V2 is clean signal & V1 is octave modulated one..

I'm intrigued by your post but I have a couple of questions.

What do you mean by "Can't get the values of R15, R16 & R17 for differential U2.1 configuration" ? Should I not use these values?

Also, when I did the math in Excel from the drawing you provided I got very different numbers than you did. Where are you getting 262 and 2.2 from and why is it relevant?

[Ben N]

Your octave section is the same as Tim Escobedo's Octup Blender. Any reason why you didn't choose to also mix it the same way?

[antonis]

Where are you getting 262 and 2.2 from and why is it relevant?

If you notice the 500k pot in Octup Blender posted by Ben, and place an arbitrary value instead of 0 right after R16 on the denominator of first fraction, you might get what I'm saying..

(just compare the two schematics..)

[david1991ross]

Where are you getting 262 and 2.2 from and why is it relevant?

If you notice the 500k pot in Octup Blender posted by Ben, and place an arbitrary value instead of 0 right after R16 on the denominator of first fraction, you might get what I'm saying..

(just compare the two schematics..)

When I use the 500k pot as the clean blend in the Escobedo schematic, there doesn't seem to be any variation in the sweep of the pot. Does this mean that the amount of voltage from the clean signal is being dwarfed by the voltage of the octave signal? After playing around with the math I think I see where you got your numbers from basically. What values are you using for VClean and Voctave? Are they a fixed value?

[david1991ross]

Your octave section is the same as Tim Escobedo's Octup Blender. Any reason why you didn't choose to also mix it the same way?

I've been modifying this schematic for awhile now and felt like I had success with not using the clean blend in the initial layout. I didn't want to have two pots and thought that I could just bypass the 500k pot in the schematic with a separate clean blend pot. Also I tried breadboarding it just now and got strange results. My LTSpice simulation confirmed my results.

[11-90-an]

try inserting my ckt after C8 and C9... that *should* work...

[david1991ross]

try inserting my ckt after C8 and C9... that *should* work...

What do you mean by ckt? The resistor blend configuration?