bias vs. tone

[gutsofgold]

I've never used a fuzz with a dedicated control for the bias voltage, but I had a general concern about it.

Does too much voltage give you a thin, fizzy sound while too little voltage makes it muddy, too thick?? Or is it the other way around??

[JimRayden]

Neither, and both. Usually it's the extremes of bias control that make a pedal 'misbehave'.

---------
Jimbo

[Gus]

The best answer is to build stuff and test. 
http://www.diystompboxes.com/pedals/gusFuzzFace.gif
the bias control is an external pot to adjust for different sounds.  You can use different Si transistors

Don't confuse thin with bias.  Thin can often be cap value at the input or other parts of the circuit.

[gutsofgold]

Well I guess I should rephrase my questions...

In general what should a higher bias voltage do to the tone?
In general what should a lower bias voltage do to the tone?

[JimRayden]

Both depend largely on the pedal design. Really, to get your questions answered, invest into a breadboard and just try out.

In nearly all cases of misbiasing, there is a fair amount of gating effect and asymmetrical distortion.

---------
Jimbo

[Solidhex]

There is a certain point bias-wise with the fuzzface circuit where you get the perfect balance of output and dynamics. Too much voltage will give you lots of output but a farty, overcompressed sound. Too little voltage will get you too low an output and a sort of weak fuzz sound. If you roll off your guitar volume a bit and adjust the bias you should find a noticeable "zone" where the two come together. The 4.5v zone is recommended for a good reason.
  I think just about all the different voltages have their uses. Fat single note riffs are great with an overbiased fuzz, under makes some cool buzzy dying battery tones.

--Brad

[frankclarke]

Theory:
http://www.electronics-tutorials.ws/amplifier/amp_4.html

[petemoore]

In general what should a higher bias voltage do to the tone?
  Have the tendency to make one side of the waveform signal swing approach first, notice, then slam into a power rail, causing clipping/attenuation/... of that side, and the other side will have increased voltage difference between the bias point and it's power rail, producing smaller or no clipping to that side of the waveform.
In general what should a lower bias voltage do to the tone?
  Generally the same as above, but in reverse.
  I assume we're talking about a FF, but any gain stage, when bias shifts closer to one rail, the signal swing [on one side from bias point] has less room/distance before it hits that rail.
  Moving the bias point and gain settings on FF around...why not...no self respecting FF afficianado hasn't messed with the bias a lot.
  Stick an 8 pin IC socket or two in a 2'' x 2'' copperclad perfboard, make copy of ROG's perfboard template, draw in the circuit...use the sockets for transistors, caps...maybe even the 100k ? third socket and bigger board to accomodate the 1k in socket...a 20k pot as Q2 collector resistor, or see emitter bias options.
  Leave some resistor lead lengths above board for EZ Bias and 'tack on a mod' [tack on mod works great with largest percieved value of resistor desired as failsafe,  clip a pot on and find a chosen value, then tack that value the pot found as permanenty fixed resistor {..lol..that can be removed].
  Consider anything else...
  Build it...
  Now you have a FF board to put next to your FF board.
  And it will tell you in ways much better than inadequate descriptive terminology can, what's up with the tone when the bias is towards + or -.
  I found the FF to sound best somewhere near 'center strong', maybe a touch on the high side [toward top rail]...and with bias knob sounds very cool having off-bias being 'pushed' by a booster or.

[Dragonfly]

There is a certain point bias-wise with the fuzzface circuit where you get the perfect balance of output and dynamics. Too much voltage will give you lots of output but a farty, overcompressed sound. Too little voltage will get you too low an output and a sort of weak fuzz sound. If you roll off your guitar volume a bit and adjust the bias you should find a noticeable "zone" where the two come together. The 4.5v zone is recommended for a good reason.
  I think just about all the different voltages have their uses. Fat single note riffs are great with an overbiased fuzz, under makes some cool buzzy dying battery tones.

--Brad

all good points...

I might add that the 4.5v recommendation is merely a "simplified" way of saying "1/2 the supply voltage". For instance, if you're supply voltage reads 9.6 volts, then setting the bias at 4.5V wont sound as good (well...depending on what you're looking for) as setting it at 4.8V. I know seems like I'm "splitting hairs", but in some circuits it makes a tremendous difference in the sound.