study of the SSL 9k FET muting system

[Svart]

I noticed that the Jfets used to mute/bypass the filters and EQ on the ssl9k have unity opamps driving their gates through a resistor/capacitor network. Is this to decrease the distortion through the jfet by introducing some of the signal to the gate? That would make it similar to a fet based limiter wouldn't it? with a sidechain driving that fet gate... :green:

 

[JohnRoberts]

[quote author="Svart"]I noticed that the Jfets used to mute/bypass the filters and EQ on the ssl9k have unity opamps driving their gates through a resistor/capacitor network. Is this to decrease the distortion through the jfet by introducing some of the signal to the gate? That would make it similar to a fet based limiter wouldn't it? with a sidechain driving that fet gate... :green:[/quote]

Without seeing the schematic this is a bit of a guess. The technique of adding a fraction of the drain (AC) voltage back into the gate improves linearity while the channel is biased somewhere between highest conduction and pinched off. If the FET is used in a mute/bypass circuit it seems it would be used one way or the other. This treatment might reduce audible distortion while ramping slowly between on and off states. or not...

JR

 

[SSLtech]

Svart,

Where exactly... Gimme an indication of where to look and I'll have a peep.

You got a page number/grid ref, or if you onoly have an excerpt, describe the circuit position and I'll find it.

Keith

 

[Svart]

I have the drawings at home, they are after the EQ sections and the Filter sections, used in the bypassing/muting of the sections. I am sure they are used elsewhere too though.

 

[TomWaterman]

I'm not sure myself but just had a nice trip round the factory and a kind gent there told me that the soft switching on the Duality uses Fets that are driven to reduce the noise floor during the switch transition (improving signal to noise).

They are soooo silient!

-Tom