Print Page - Any magic in RM Axis bias system?

Title: Any magic in RM Axis bias system?
Post by: brett on April 05, 2004, 11:13:56 PM

To see the schematic (including a few bugs), paste this link in your browser. Sorry, but the direct link doesn't seem to work. http://www.geocities.com/j4_student/axisfuzz.gif
My question is about the 180k/820k dual bias resistors between the supply line and the base of Q1.

At first I thought it might be providing extra AC resistance to ground (ie for the collector of Q2), but wouldn't the AC path to ground be via the battery or power supply?? This arrangement would lower the input impedance very slightly, but that wouldn't be the reason. I think I'm missing something.... :roll:

Can anyone explain (simply) why this system is there instead of a 1M resistor, and the usual cap (eg 22uF) from supply to ground?

thanks

Title: Any magic in RM Axis bias system?
Post by: R.G. on April 05, 2004, 11:37:26 PM

It's to further remove any noise from the bias voltage. The bias resistor is split, then effectively grounded in the middle by that capacitor to ground. Any noise or hum on the bias voltage is NOT conducted into the input of a high gain fuzz stage.

This is (was...) a common practice back in the Golden Age.

Title: Any magic in RM Axis bias system?
Post by: brett on April 05, 2004, 11:46:47 PM

Thanks heaps RG.

Legend!

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DIY Stompboxes => Building your own stompbox => Topic started by: brett on April 05, 2004, 11:13:56 PM