What is it good for, what changes in sound doest it have?
thanks
Andrew
What is it good for, what changes in sound doest it have?
thanks
Andrew
Dont Matter if you feel alone, your fender is always there for you...
application?
do I look like I know what I'm doing?
In an amplifier, it sets the running condition of your power tubes. If you set it wrong, it can either sound kind of crappy, or the amp can self-destruct.
Kind of like setting the idle on the carb of a gas engine. Your power tubes are set to their optimum range by dialing it in with your bias pot.
The way I understand it, bias pots (usually trimpots) control the level of -VDC on the power tube grid in a fixed bias circuit. The -VDC value is what keeps the tubes in check; that's what 'sets the idle' so to speak (as trvorus and Markl8 said). In a fixed bias circuit, there may be a resistor in place to set that -VDC voltage. It's what makes the tubes sound/run hotter.
No bias = power tube meltdown. Kind of like control rods in a nuclear reactor; remove the control rods, the nuclear reaction goes out of control and you get a Chernobyl.
Fixed bias circuits sound tighter, and cathode resitor biasing is more dirty (in a desirable tweed sort of way). For example, the Fender Tweed Pro has two popular incarnations; the 5E5 is cathode biased while the 5E5A is fixed bias. There are other features that changed between the two also, but the bias type is what a lot of folks use to decide between the two.
Right, Fezz?
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
(sorry...double post)
Bottom line - Don't go twisting the bias pot unless you know what you're doing. Going too far in one direction could make your amp sound thin and crappy and going too far in the other direction could blow up your power tubes and maybe take out some other components (like your output transformer) as well.
Here are some technical links where you can read up on some of this stuff. I use the Hoffman and House of Jim links all the time:
http://www.hoffmanamps.com/charts/Biascircuits.htm
http://members.shaw.ca/house-of-jim/...as_tables.html
http://www.aikenamps.com/TI_Aiken_Q&A.html
http://www.aikenamps.com/Biasing.html
Last edited by PhatTele; 02-23-2007 at 10:50 AM.
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