variable bias versus fixed bias guitar amp

A pot doesn't work here because the power requirement is high and needs a power resistor, like a multi-watt cement type. Cathode bias is usually adjusted by swapping out the cathode resistor. Some amps have a pot that allows the bias voltage from the transformer to be varied. There are a few other ways, like using a zener diode (which is not too common), and mixtures of the two methods like Fender did, which is not well appreciated, so the subpages below stick with fixed and cathode bias. This offset is called the bias voltage.īias voltage can be applied from a voltage source (fixed bias), usually in the power transformer, or developed by the cathode of the tube (cathode bias). Even better, it gives you the power to create an entirely new amp that is unique to you and the way. Since the input audio signal is AC, and has both a positive and negative portion in relation to ground, a DC voltage offset is used so the AC waveform can 'fit' inside the tube's positive operating range. If you want to dive headlong into the world of amp customization, BIAS Head comes with our amazing BIAS AMP software suite (199 value), which allows you to recreate the sound and feel of nearly any existing guitar amplifier. The amplitude of the output signal will fall somewhere between ground and the B+ voltage. No part of this book may be reproduced without explicit permission of the author.Tubes can only increase the input signal in a positive direction in relation to ground. 6.6 Design of the fixed grid bias power supplyĪll material on this book (pictures and text etc.) is covered by Copyright and all rights are reserved.6.5 Design of the vacuum tube filament power supply.6.4 Design of the amplifier power supply unit for the amplifier stages.6.2 Design of the input and phase splitter stage.Chapter 6: Step by step design of a push-pull tube amplifier.5.3 Power supply for the fixed grid bias.5.2 Power supply for the vacuum tube filaments.5.1 Power supply for the amplifier stages.4.1.3 Reactive load and loadline computation.The resistor on the back of the pot is now soldered to the upper right tab of the bias pot. The wire that leaves the bias board, now goes to the lower right tab on the bias pot. Here is the AA1069 bias system after the conversion. 4.1.2 Impedance of an output transformer The bias pot has two wires that leave the pot from the two outside legs of the pot.Chapter 4: Integrated push-pull vacuum tube amplifier.3.6.3 Gain of the voltage amplifier with self-bias.1.1 What is in this book and what is not.

Variable bias versus fixed bias guitar amp