Is it ok to replace the VGS multiplier circuit with a resistor for biasing a p-p mosfet amp? This is for a balanced amp with matched output mosfets, so a little offset voltage wouldn't show up at the speaker terminals. The stage in question is folded cascode with a constant current source.
nobody special said:Is it ok to replace the VGS multiplier circuit with a resistor for biasing a p-p mosfet amp?
Hi Steve
Yes it is ok....but only if you are using lateral mosfets (like the Hitachis 2SK135/SJ50) or equivalents.
Regards
nobody special said:Why not with the other mosfets?
Because the vertical Mosfets have a positive temperature coefficient ,in the "normal" (100...200mA) bias current of power amps.
And ,they only have negatif temperature coefficient ,with much higher currents, in the case of a IRF 530 above 12 Amps of bias current...
nobody special said:1 more question:...Do I need some resistance to ground on the output mosfet's gates? If so, what value is typical?
If the output mosfets are used in the usual source follower
configuration...you don't need any resistor to ground.
Only a series resistor connected directly to the gate pin.
This resistor is for parasitic oscillation protection and the value depends of the input capacity capacity of the mosfets.
Typical values for lateral Hitachi mosfets 220 Ohms...and for vertical IRF mosfets 47-100 Ohms.
nobody special said:By the way, what kind of motorcycle is that in your avatar? Looks like a Honda or Yamaha?
No...is my new "baby" a Suzuki GSX 1400...
See it at ...and click in the photos to enlarge
http://www.lerepairedesmotards.com/actu/2001/actu_010520roadstergsx1400.htm
I ride a Honda ST-1100.
Good bike
Before the Suzuki I have a Yamaha GTS 1000....good technology but too heavy...
I wonder how many other DIY audio guys ride.
I think that people that ride a motorcycle and the people that like DIY audio have something in common....they like "strong emotions"...
Cheers...
PS: Take care in the road...
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