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FF: More Treble Wanted!

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8/22/1999 5:46 AM

FF: More Treble Wanted!

Hello!

I just finished building my Fuzz Face clone and i am extremely happy with the results. (i followed R.G.'s advice and with a set of AC 128's i was on my way) My only gripe is that the unit does not seem to be as tonally balanced as it should. I would like for the unit to accent the higher notes as well as it does the lower ones. The treble end seems to get lost when chords are struck.

Suggestions??

Should i lower the bass response of the unit, or could i up the higher frequency response?

Thanks in advance!!!!

Rob W. ;-)

;-)

8/22/1999 11:54 AM
AMZ	You can lower the value of the input capacitor from 2.2uF to 0.05uF or even 0.01uF. Try it and see if the freq. response is more to your liking. regards, Jack

8/22/1999 1:33 PM

Losing treble when you put chords into a distortion device is one of the classic problems with distortion devices. What is happening is that the lower frequency notes pull the signal into clipping one way or the other and the treble notes may not be big enough to pull the signal back into a more linear area, so the higher (and usually smaller) notes get washed out. One way of dealing with this is to not play chords, or to only play simple two note intervals.

The other is the way Jack alludes to, the way that is discussed in some depth in "The Technology of the Tube Screamer" at GEO. The tube screamers use a small input cap and other bandwidth limiting to cause a single-time-constant bass cut. This pre-emphasizes the treble into the distortion and gives the usually smaller high notes a chance to be clipped. You can adjust the degree of bass cut by messing with the input cap.

The input impedance into a FF is just the junction resistance of the first transistor's base-emitter times its Hfe, which is usually fairly small, Hfe*(25mv/Ie). In the case of the FF where Ie is maybe 1ma, the resistance is probably centered on 1000 to 3000 ohms. With a 2uF input cap, the bass rolloff starts at about 39 Hz, depending on the device. 0.2uF would move it up to about 390Hz +/-, and 0.1uF would put it at 780Hz, about where the Tube Screamers have their input bass breakpoint.

There is actually a third way to ensure the treble doesn't get lost. John Greene's post about using MOSFET devices as clipping diodes gives a way to preserve some of the treble content even with large clipping. It's unfortunately not adaptable to the FF, though.

8/22/1999 2:14 PM
AMZ	>>a third way to ensure the treble doesn't get lost. John Greene's post about using MOSFET devices Although I saw the original posts about this, and have used many different clipping diodes in tests, I don't recall the proposed theory that treble content is preserved. Can you refresh my failing memory? regards, Jack

8/22/1999 9:59 PM

The clipping is so soft that the tops of the waveform never quite squash out to flat. If you have a mixed bass and treble signal, you can still see treble wiggles on the tops of limited bass swings.

The original article on using a diode connected MOSFET in EDN had scope traces that showed exactly that.

Note that the content is reduced, but not lost - in fact that was one point mentioned in the article. The higher frequency information was not lost, but remained in the waveform until it was massively overdriven. "Preserved" is probably not the right word - "not lost" is, I think.

8/23/1999 4:08 AM
Rob W.	Thanks very much for the input!!! This is my first foray into the Fuzz world. Before this pedal I was strictly a tube screamer guy. (This explains my tonal tastes) I will give that cap change a try. Now just to locate that damn Mouser catalog. Cheers! Rob W.

8/23/1999 2:03 PM

R.G. the input Z is even lower I think. The feedback resistor lowers the input z due to negative feedback and if I understand the circuit the z of the pickup goes up with freg causing the gain of the circuit to reduce. I think the gain of the circuit is the output section gain X the input section (feedback r /pickup z). This is a current to voltage amp I think. That is why there is a buffer in the 3tran fuzz. Please correct me if my thinking is wrong.

Gus

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