Octave Up Fuzz Experiment

[mac]

This a simple octave up fuzz I have on the breadboard right now.
Two 741. The first stage is a standard diode clipping fuzz. The second chip does the variable ringing.
It needs biasing. I set the Ring pot to max, and adjusted the 1M trimmer until I got a strong octave up. When the Ring pot is lowered so is the octave up effect.
Since both stages are variable, many different tones in between. I'll be posting a sound clip soon.
Instead of using a transistor's emiter and collector to split the signal like in the Green Ringer, I used the inputs of an opamp.
ref: tech of phasers at geo.



Right now I'm thinking of reducing the 100k in the first 741 feedback loop to 10k. Also the 1M trim could be improved.

mac

[Mark Hammer]

Would there be any utility to replacing R8/R9 with 33k fixed resistors and running a 25k trimpot between them, with the wiper connected to R7, just for balancing?

[mac]

I'll try it. Maybe this can replace the 1M bias trim

BTW, diodes d5 & d6 are not matched.

About R7, R8 and R9. If you look at the GR there are a pair of 22k's and two 68k's. I guess they turn the diodes on a little.
I choose the 50k pot and the 1k after trial and error.

mac

[Mark Hammer]

I'll try it. Maybe this can replace the 1M bias trim

BTW, diodes d5 & d6 are not matched.

Do you mean you didn't match them, or they don't have to be matched?  The addition I was suggesting was intended to compensate for mismatching.  If matching is not essential or helpful, then please feel free to ignore what I suggested.  I'm just avoiding my real work...

[mac]

Do you mean you didn't match them, or they don't have to be matched?

I put them without measuring as they are from the same batch.
This diodes differ by 1.8%, 655 and 643mV.
Anyway I'll replace one with a another kind of diode like a 1n400x and see what happens with a difference of +10%.

mac

[mac]

Sound clip:
copy the link to a new browser window
or go to http://guitarfxs.tripod.com/

Guitar to breadboard to Laney LC30 to crappy borrowed mic (where the h*** is mine???) to ancient mac.
Clean chn
1,2: min drive, med and max ring
3,4: med drive, med and max ring
5: med drive, high ring
6: max drive, med ring, guitar volume at 7 then at 10.
7: max drive and ring
Drive chn
8: a little drive, almost max ring; amp reverb at 4, drive at 7, master at 2 (neighbors, have I got neighbors? ringing my doorbells, all day and all night)

mac

[tcobretti]

That is pretty nice.  Kind of a Octave Overdrive.

[John Lyons]

Those are some nice sounds Mac!
It's nice that you can vary the octave.

Were all the clips done with the bridge PU with the gtr tone control full up?

John

[frank]

Oh, that was your your secret project Mac!  Nice soud and lick.
BRAVO!

[mac]

Glad to hear you like it. Thanks.
This is still an idea, if you have suggestions let me know.

Frank, this project was born last weekend when I was tweaking the Green Ringer. I'm working on a phaser now. But Ibiza is still my main project

John, yes, bridge PU and guitar volume at max, except last take with neck PU. Amp almost flat, B6, M4, T6 (0 to 10), both clean and drive chn. The mic and the sound card sucked a lot of tone.

mac

[John Lyons]

Oh, ok. Thanks.
The reason I ask is because generally the octave sounds best i(n most octave boxes) with the neck PU and the guitar's tone knob turned down and especially with playing above the 12th fret...
If you are getting these sounds with mainly the bridge PU and tone on then the octave should be great with the neck and tone down!!

john

[mac]

John,
I meant tone at max in all takes.
Even though the neck PU sounds better (no exception to the rule) because of the bad mic & pc sound card tone sucking, I decided to use the bridge PU SC-ish to give more emphasis to the octave up by adding treble. You may notice this in take 7.
I say SC-ish because my guitar mixes the bridge/neck HB's with the center SC.
I forgot to mention I use 0.09 strings.

I'll tweak the input/output cap. Also try Ge as octave/clipping diodes.

mac

[pravudh]

nice sound

[mac]

I changed a couple of things.
I replace the octave diode with Ge 1N60. A little more warmer tone. Oh, I forgot to check what happens with the bias point when temprature varies.
I also changed the 1M bias point with a better arrangement, a noisless bias like in the Dist+, but using a 100k trimmer, a 4.7uf cap to gnd, and a 470k from the trim to (+) input.
Oops, I did not check the bias point vs. Vcc. A changing bias point would be a big problem for batts.

mac

[mac]

As expected Ge diodes make the bias point change a little with temperature.
I had to tweak bias a bit when I changed Vcc from 9v to 15v, so a batt at 8v should not be a big problem.
To overcome this two issues I modded a couple of things, following Mark suggestion.
Also used a better Vref for IC2.



There are more tonal possibilities with the new Blend pot, and the bias point is now near the center position.
Diodes d7 and d8 add a little "quack" when gain is at min and blend at one extreme.
At the other side of the blend pot, as the octave up effect is almost gone, volume jump is high.

mac

[John Lyons]

Looking good, If you have some time I'd like to hear a sound clip.
Maybe a dual pot for the blend would work with the second pot controlling some of the volume jump when the pot is set away from the octave?

[mac]

I updated v2 a little so the comments in the above post refers to another schematic, but things are very similar.
Also the sound clip is valid.



As you can see I moved the gain control outside the feedback loop because I noticed that this way IC1 output voltage is constant, and sounds better when reducing gain, more trebly.
I simplified IC2 Vref since biasing involves reducing background noise. A noiseless biasing adds almost nothing.
As Mark suggested I added the balance trim. If set at the middle, max octave up occurs at around 33k in my demo, not when ring pot is at max. Move balance trim to one side to have max octave up when ring pot is fully CW.

This is what I'm going to build, no more tweaks. Sorry for the late response but I broke my wrist recently.