I am loosely familiar with the theoretical concept of "biasing"...but I have some questions about practical application:
1.what effects pedal bias? (type of pickup etc...)
2.I have a pedal with adjustable bias, how should I tweak it? like what should I listen for?

Thanks!   

"Biasing" is when you set a device, like a transistor, to operate partially in the region that it CAN operate in, so that your input signal starts somewhere near the middle of the possible range of the device.  These devices have a curve that they operate over...usually you want to be amplifying on the linear (straight) part of the curve, for less distortion (the kind we don't want). 

If a transistor will amplify anything from say 1 to 8 volts....and your input is .5 volts....you really want to have it amplified to come out something like 3V to 6V.   If you don't, then you might end up with an outgoing signal running 2V to 5V, and 2V to MINUS 1 volt (can't do it, so it clips the signal off).

Does that make sense?    You look at the device's load line (data sheet) and find where a good bias point is considering your input signal and what you want to get out, then adjust your resistors to feed that DC offset to the device.  So it idles (quiescent point) at that point, waiting for your signal to drive it more positive, or more negative. 

External things don't affect bias - this is a DC level applied to the device, and it's kept from your guitar, or other effects, by capacitors on the input and output which, due to their nature, block the passage of DC.

Do a net search on "transistor biasing", and esp. watch some Youtube videos, which will SHOW you how biasing affects your output signal for a given input!  Well worth the time.   

Once you 'get' this, we'll talk about adjustable bias      What is it, a FF?   

Here, dude...this vid gives a description of how biasing affects your signal in a pretty easy to understand way, that you can see:

https://www.youtube.com/watch?v=c6cmkm3UPUI

Quote from: nognow on January 16, 2015, 01:14:34 PM
I am loosely familiar with the theoretical concept of "biasing"...but I have some questions about practical application:
1.what effects pedal bias? (type of pickup etc...)
2.I have a pedal with adjustable bias, how should I tweak it? like what should I listen for?

Thanks!   

Quote from: GibsonGM on January 16, 2015, 03:50:53 PM
"Biasing" is when you set a device, like a transistor, to operate partially in the region that it CAN operate in, so that your input signal starts somewhere near the middle of the possible range of the device.  These devices have a curve that they operate over...usually you want to be amplifying on the linear (straight) part of the curve, for less distortion (the kind we don't want). 

If a transistor will amplify anything from say 1 to 8 volts....and your input is .5 volts....you really want to have it amplified to come out something like 3V to 6V.   If you don't, then you might end up with an outgoing signal running 2V to 5V, and 2V to MINUS 1 volt (can't do it, so it clips the signal off).

Does that make sense?    You look at the device's load line (data sheet) and find where a good bias point is considering your input signal and what you want to get out, then adjust your resistors to feed that DC offset to the device.  So it idles (quiescent point) at that point, waiting for your signal to drive it more positive, or more negative. 

External things don't affect bias - this is a DC level applied to the device, and it's kept from your guitar, or other effects, by capacitors on the input and output which, due to their nature, block the passage of DC.

Do a net search on "transistor biasing", and esp. watch some Youtube videos, which will SHOW you how biasing affects your output signal for a given input!  Well worth the time.   

Once you 'get' this, we'll talk about adjustable bias      What is it, a FF?   

Thanks!

Quote from: GibsonGM on January 16, 2015, 03:50:53 PM
"Biasing" is when you set a device, like a transistor, to operate partially in the region that it CAN operate in, so that your input signal starts somewhere near the middle of the possible range of the device.  These devices have a curve that they operate over...usually you want to be amplifying on the linear (straight) part of the curve, for less distortion (the kind we don't want). 

If a transistor will amplify anything from say 1 to 8 volts....and your input is .5 volts....you really want to have it amplified to come out something like 3V to 6V.   If you don't, then you might end up with an outgoing signal running 2V to 5V, and 2V to MINUS 1 volt (can't do it, so it clips the signal off).

Does that make sense?    You look at the device's load line (data sheet) and find where a good bias point is considering your input signal and what you want to get out, then adjust your resistors to feed that DC offset to the device.  So it idles (quiescent point) at that point, waiting for your signal to drive it more positive, or more negative. 

External things don't affect bias - this is a DC level applied to the device, and it's kept from your guitar, or other effects, by capacitors on the input and output which, due to their nature, block the passage of DC.

Do a net search on "transistor biasing", and esp. watch some Youtube videos, which will SHOW you how biasing affects your output signal for a given input!  Well worth the time.   

Once you 'get' this, we'll talk about adjustable bias      What is it, a FF?   

forgot to ask: what tools do I need to set bias? can I do it by ear?

Why do you need to 'set bias'?  It's done at 'design time', usually. Now, of course there are some designs that YOU set, when you build. Notably, some FET circuits.  They typically have a trimmer at the drain, and yes - you set the voltage to about 1/2 supply (generally 4.5V or so for our 9V stuff).   Or, by ear.   If you look at this artice from ROG, it kind of shows you what I mean:  http://www.runoffgroove.com/oldfetzer.html

If you have a fuzz face w/external pot for this, yes you can monkey with it to suit your ear, as it was designed for that.

If you want to just build a transistor booster or something, YOU can decide where to bias it!  Better read up on using load lines, and make sure you know Ohm's Law in out and upside down for that.   It is actually fun, and not too hard to learn once you get over the hump.   In that case, no - you really don't do it by ear too much until you understand what's happening 

I learned the most about biasing (building gain stages, really) from starting with tubes. The principles are the same for transistors, and even opamps, but MerlinB (who is on here, too!) wrote his book in a way that made sense/made this easier to understand than a paper from some university!  If you start reading at page 4, here, you'll get the rundown on what I was talking about...check out the static anode graph - that is ALL about biasing.  Then, go to Youtube and watch some vids of people making an NPN gain stage, and so on.   You'll want to grab a common transistor like 2N5088, and its data sheet so you can see its OWN characteristics....
.
Check out Merlin's take on biasing a gain stage - VERY important stuff!   http://www.valvewizard.co.uk/Common_Gain_Stage.pdf

Glad to see you interested in the 'ins and outs'.  Stick with this and in a few months you'll KNOW why those resistors are on the transistor base, what they do, and why....just remember - all that's happening here is that the device you're using is having a DC offset voltage applied to its input, which STAYS with the device due to the in/out caps.  The DC raises the input signal to a level you've determined will give optimum performance - it puts it within the device's RANGE of ability to operate on without cutting it off (unless that's what you want).

Quote from: GibsonGM on January 17, 2015, 04:12:08 PM
Why do you need to 'set bias'?  It's done at 'design time', usually. Now, of course there are some designs that YOU set, when you build. Notably, some FET circuits.  They typically have a trimmer at the drain, and yes - you set the voltage to about 1/2 supply (generally 4.5V or so for our 9V stuff).   Or, by ear.   If you look at this artice from ROG, it kind of shows you what I mean:  http://www.runoffgroove.com/oldfetzer.html

If you have a fuzz face w/external pot for this, yes you can monkey with it to suit your ear, as it was designed for that.

If you want to just build a transistor booster or something, YOU can decide where to bias it!  Better read up on using load lines, and make sure you know Ohm's Law in out and upside down for that.   It is actually fun, and not too hard to learn once you get over the hump.   In that case, no - you really don't do it by ear too much until you understand what's happening 

I learned the most about biasing (building gain stages, really) from starting with tubes. The principles are the same for transistors, and even opamps, but MerlinB (who is on here, too!) wrote his book in a way that made sense/made this easier to understand than a paper from some university!  If you start reading at page 4, here, you'll get the rundown on what I was talking about...check out the static anode graph - that is ALL about biasing.  Then, go to Youtube and watch some vids of people making an NPN gain stage, and so on.   You'll want to grab a common transistor like 2N5088, and its data sheet so you can see its OWN characteristics....
.
Check out Merlin's take on biasing a gain stage - VERY important stuff!   http://www.valvewizard.co.uk/Common_Gain_Stage.pdf

Glad to see you interested in the 'ins and outs'.  Stick with this and in a few months you'll KNOW why those resistors are on the transistor base, what they do, and why....just remember - all that's happening here is that the device you're using is having a DC offset voltage applied to its input, which STAYS with the device due to the in/out caps.  The DC raises the input signal to a level you've determined will give optimum performance - it puts it within the device's RANGE of ability to operate on without cutting it off (unless that's what you want).

Thanks!

Sure!  Keep at it - the more you read, the easier it becomes...and "DO", too, on breadboard.  Don't let sites with 1,000 awful-looking equations get you spooked, this can be learned without too much head-pain...