Ciss Input C - 271pF
Coss Output C - VDS = 100 V, f = 1 MHz, VGS = 0 - 15.7pF
Crss Reverse transfer C - 0.68pF
That's impressive!
Many usefull MOSFETS listed above for Source Follower use.
The "trick" is to choose Vd sensibly such that at max positive signal swing at the source you still have +20V or so across the Drain to Source. That will minimise Crss AND minimise changes in Crss with signal. It is this last (changes of Crss with signal) which can give less pleasant audible results.
You don't want Vd too high, else you are just wasting power in the MOSFET but allow at least that 20V (higher for some of the devices listed). Check the Crss vs Vds chart in the datasheets.
I use the ones Ely recommended as his goto devices. I can also confirm that taking "proper" control of the output tube grid by direct coupling it to a source follower (just the grid stop in between) really does give sonic benefits.
Sonic benefits include lower noise as the output tube grid current noise has less of an impedance to develop a noise voltage across.
I can also confirm that loading the source follower with a current source (simple ring of two transistor CCS is fine) gives additional sonic benefits.
See schematic at post 604 for an example:
http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-61.html
Cheers,
Ian
The "trick" is to choose Vd sensibly such that at max positive signal swing at the source you still have +20V or so across the Drain to Source. That will minimise Crss AND minimise changes in Crss with signal. It is this last (changes of Crss with signal) which can give less pleasant audible results.
You don't want Vd too high, else you are just wasting power in the MOSFET but allow at least that 20V (higher for some of the devices listed). Check the Crss vs Vds chart in the datasheets.
I use the ones Ely recommended as his goto devices. I can also confirm that taking "proper" control of the output tube grid by direct coupling it to a source follower (just the grid stop in between) really does give sonic benefits.
Sonic benefits include lower noise as the output tube grid current noise has less of an impedance to develop a noise voltage across.
I can also confirm that loading the source follower with a current source (simple ring of two transistor CCS is fine) gives additional sonic benefits.
See schematic at post 604 for an example:
http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey-61.html
Cheers,
Ian
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measured about 99x gain(ecc803 85), with unbypassed cath.resistor.. try that with anode resistors
(12ax7wb bypassed gives 113x)
sounds nice.
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