Generic NPN Booster Project, Tips.

[chromesphere]

5mv seems pretty low.  PRR suggested something closer to 400mv RMS..?  My squarewave was set to 200mvpp.  If you guys want to see any oscilloscope screenshots let me know.  Its a new toy, so please say yes
Paul

[Thecomedian]

Sure. I just find myself getting better Sine wave out values while using 5mv in simulations so I figured that's what's most common, otherwise fuzz faces would never sound good. It also corresponds to the type of statements about the fuzz face itself that smallbearelec describes where the fuzz only starts sounding at the last 10%. With a 1V input, full on distortion is square waved into the electronica music range, and it's still heavily square waved with the fuzz pot turned down halfway. This behavior does not correlate to the observed behavior smallbear and typical third person reviews of fuzz pots claim (need 90%+ for the fuzz). Even at only 25%, 1v is heavily squared.

The same holds true for 500mv signal in.

in LTspice, the wave drives into and out of hard clipped distortion by changing the fuzz control potentiometer (simulated via voltage divider with Polcap wired between the pair) smoothly and evenly at 5mv input as a sine wave.

None of these values are RMS, they are strict peak-to-peak..

[chromesphere]

im sure the spread from one pick up to the next is very different, i havent measured these before tbh, but it's obviously going to be difficult to cater for every pick up ever made...i think i would perfer though (personally) to use the upper limit, because clipping (in a booster) annoys the hell out of me... (like the lpb1!!  )
Paul

[Thecomedian]

5mv base input, 1K fuzz pot turned all the way down (so full resistance of pot between feedback capacitor and transistor, as if they are in series)



same input, fuzz pot turned all the way up (so no resistance between feedback cap and transistor, as if cap is in parallel to pot to ground)



500mv input, fuzz pot turned all the way down.



500mv input, fuzz pot turned all the way on.



I'm sure there's probably also impedance changes that allow a stronger output voltage signal to work, I'm just saying that straight into a fuzz face (and other builds) input of equivalent 5mv peak to peak seems to behave like the ideal source.


The op's circuit does work with a 1v in. It doesn't work at all with lower voltages.

[duck_arse]

chromesphere, you could put a low-pass RC filter between yr sq wave and yr booster input. look on the scope, see the resulting different waveform.

[PRR]

> using 5mv in simulations ..... With a 1V input

Guitar is *percussive*. Strong attack and long decay.

The fuzz sound-quality changes with signal level.

So you really need to try various levels.

Also: the caps charge-up, but not as fast as that first pluck, then decay.

(Some sims support a damped sine wave which decays.)

The simpler fuzzes are very critical about source impedance. Try 50K in series with your source. Better, 10H inductor plus 5K. (Gus has posted even better pickup sims.)

[Thecomedian]

I thought the Voltage / Time with the time part of the graph would deal with the cap charging. I'll try those source impedances. Im using 5mv sim because I get 5mv input on attack with my instrument, and 5-4-2.5mv on decay, and I measured the volts for hardest single string, hardest all strings, normal all strings, and normal single string, to establish the ranges of mv output, and 5mv was the max, so that's what I used when constructing the circuit. OP used 1v input and that works for ops circuit, but it doesn't work on the original fuzz face schematic at all while a 5mv does. Im thinking that 5mv with low impedance might be similar in interplay of a stompbox circuit to 1v with high impedance, or is it reverse?

[Hallmar]

I'm confused, am i supposed to use 500mv or 5mv or are guitar pickups so versatile when it comes to the output voltage that i should pick something between 5mv and 500mv?

[PRR]

> Im thinking that 5mv with low impedance

Are you using a guitar that can plug into a standard guitar stage-amplifier? Or some low-impedance job like Les Paul's Recording Guitar? (Or a Direct Box, which amounts to the same thing?)

Most traditional guitar amps need 20mV to overload at "10", can take 200mV clean at lower volume settings. So a report of 5mV seems unusual.

[Thecomedian]

> Im thinking that 5mv with low impedance

Are you using a guitar that can plug into a standard guitar stage-amplifier? Or some low-impedance job like Les Paul's Recording Guitar? (Or a Direct Box, which amounts to the same thing?)

Most traditional guitar amps need 20mV to overload at "10", can take 200mV clean at lower volume settings. So a report of 5mV seems unusual.

Yep. I bought a cheapie 15w peavey to play on until I get cash for something decent. It measures 5mv out at the tip/shaft of a connected audio cable with a DMM, while strumming the strings. It's a 9v battery powered active eq 2 passive humbucker setup. It plays pretty well.