#Easiest way to bias guitar amp manuals
#Easiest way to bias guitar amp driver

In most cases, the true relevance of the bias point only shows up when you analyze the whole amp's distortion characteristic.Ĥ. Anything higher than the bog-standard 1M input impedance should consider it, but nobody uses higher impedances so no one mentions it.ģ.

The 12AX7 develops a fair amount of self-bias, which may or may not show up in normal use. The 12AX7 likes at least 100v on its plate, but isn't too picky about either this or it's nominal maximum of 330v, or much of anything else, for that matter.Ģ.

#Easiest way to bias guitar amp manuals

The tube manuals suggest a variety of plate resistors, as a way of getting the desired amount of gain per stage with differing plate supply voltages, or for other design criteria. Nearly everyone in the world uses 100k plate resistors (except for Ampeg and a few Gibsons, which use 470k), pretty much regardless of plate voltage, bias point, or tube function.

#Easiest way to bias guitar amp driver

Does either of these have any bearing on preamp distortion? Why choose a 150v or 350v preamp supply, as long as the driver can drive the power amp? Does it matter? But preamp tube high-voltage operation is recommended for better linearity, not more distortion. Power tubes supposedly only sound good when overstressed.

Or is it just a 'you'll get away with it if you don't abuse anything else at the same time' situation, like power tube voltage, current, and power ratings seem to be? I suppose if you drop it all across the plate resistor and control the input, and/or operating point, so that the tube never cuts off, you could, I think, get away with it. Does the 1M affect the bias actually seen by the tube, or is it still too small to matter? This also implies that a 10M input impedance for a piezo would have to be biased differently, no?Ī couple of other designs run the tube from a 485vDC supply. Where is THIS bias coming from, and does anyone talk about it in relation to guitar circuits? The same chart recommends a 100k grid resistor rather than the guitar-amp standard 1M. This isn't supposed to work.Įxcept it is - according to the design chart in the 12AX7 datasheet, with a 10M grid resistor, you use no cathode resistor, with a 240k (220k) or 510k (470k) plate resistor, and DC supplies from 90v to 300v.

As far as that goes, a coupe circuits run a 12AX7 with no grid bias at all. Some of them run the tube on 130VDC, with a plate voltage of around 80v. What I get from my reading, including this DIYaudio thread are a few confusing points, as follows.Īt first glance, it appears that lots of little amps run grid current in their preamp tubes (based on the Fender, Ampeg, Magnatone/Estey, and Gibson schematics in my Jack Darr guitar amp book), but they don't, actually, or they'd sound hideous. Anyone for class C?, otherwise known as fuzztone? Or you may require the absolute maximum p-p signal swing before clipping.