Is r9 really necessary?


2002-02-18 7:53 pm
While looking at the ALEPH power amp schematics, I believe that a have found a way to take another resistor out of the signal-path. A 221ohm resistor is put on the gate of every mosfet to stop it from going into oscillation. However, by moving the zener diodes that protect the q3 to the other side of r2, r9 is no longer needed. Q3 is still safe from shock. There is an illustration to try to explain what I am talking about. If someone knows of any reason why this would not work please let me know.


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Zener location

There is nothing to limit the current through the zener, which could burn it out more easily during certain fault conditions. It also adds little more capacitance for the preamp to drive causes worse RF termination for the preamp cable interface. Gate damping resistors are not as "in the signal path" one might imagine, since they have little very little voltage drop across them at audio frequencies and help damp RF resonances from gate capacitance and PCB trace or wiring inductance. I place them as close to the gate pin as possible and would never use fets without gate resistors. Most of my experience points to a sonic improvement with thier inclusion.


Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
I'm not too worried about protecting the Zeners, just
like I don't worry about protecting fuses :)

However, I have seen source circuits such as preamps
and such which oscillate when they see zeners at the
end of a cable, and that is why they are on the other
side of the resistor.