Bride of Zen - mosfet gate capacitance

[Bigun]

Do you know a simple way to reduce the gain of the preamp?

Attenuate.

Or change to different parts with lower transconductance (see post 32)

 

[Zen Mod]

damn

increase source resistor , rebias for same Iq

 

[killmister]

Can I reduce the drain resistor and refer to the source resistor?
ex:1000 ohms drain / 100 ohms source -> 500 ohms drain / 600 ohms source ?

 

[mjf]

some years ago i used in my BoZ a 180 ohm source res and a 820 ohm drain res to lower the gain, iirc..............

 

[Zen Mod]

gain is roughly (Rd // Rpot)/ Rs

do not alter first part too much

 

[killmister]

rd = 1000 rpot=100000 rs=100
(1000/100000) /100 = 0.0001
I don't understand. thank you to explain to me the formula

 

[Zen Mod]

Rd 1K
Rpot 5K
Rs 100

A= (Rd // Rpot) / Rs = (1K // 5K)/ 100 = 833/100 = 8.33 x

log(8.33) x 20 =18.4db

Papa sez 15db , and difference is due to , as I already wrote , rough calculus (say that I'm lazy to stare at IRF610 graph and data, to present all details) ; however - what's important is that you gain idea what's in game

do not alter Rd , if you don't know what's happening with load-line ; fiddle with Rs , to increase local degeneration , and decrease stage gain

 

[killmister]

Thank you Zen Mod .
Sorry but I do not understand the math: (1K // 5K) = 833 .
What does the operator // ?
Rpot is the input potentiometer ? If this is the case 5k appears to me very low.
I read somewhere that the gain is approximately Rd/Rs.

 

[Zen Mod]

// means parallel

for AC analysis , Rd and volume pot (at output) and following stage (power amp input impedance) are paralleled

everything according to schm from Papa's article/manual

attached

 

[killmister]

Hello.
Thank you for everything!
I noticed a significant decrease in gain with IRF510 without modifications. It is therefore the transconductance that is different if I understand. The preamp suits me better now but I find it lacks dynamics and brilliance in the treble.