It seems to be the concensus that the fet preamp is pretty useless.
Can anyone elaborate? Does anyone use and like it?
Also the schematic shows "adjust to bias the fet" anyone know what criteria? (guess: half supply voltage on the source (~6V)?)
Thanks!
FET preamp ?
Moderators: pompeiisneaks, Colossal
Re: FET preamp ?
Useless in that I think most people prefer the sound of the straight amp. The FET is cool if you need a higher input impedance, or if you want to boost your guitar's signal to overdrive the inout of the amp. However, the FET circuit is pretty noisy as per my (many) experiences with it.nickt wrote:It seems to be the concensus that the fet preamp is pretty useless.
Can anyone elaborate? Does anyone use and like it?
Also the schematic shows "adjust to bias the fet" anyone know what criteria? (guess: half supply voltage on the source (~6V)?)
Thanks!
The adjust to bias is something I have always done by ear... Sometimes, depending upon the voltages involved and the particular JFET you use, it can sound "bad" (like there is a bad connection somewhere) and you can correct that varying the source resistor.
Cheers,
Gil
Re: FET preamp ?
Useless in that I think most people prefer the sound of the straight amp. The FET is cool if you need a higher input impedance, or if you want to boost your guitar's signal to overdrive the inout of the amp. However, the FET circuit is pretty noisy as per my (many) experiences with it.nickt wrote:It seems to be the concensus that the fet preamp is pretty useless.
Can anyone elaborate? Does anyone use and like it?
Also the schematic shows "adjust to bias the fet" anyone know what criteria? (guess: half supply voltage on the source (~6V)?)
Thanks!
The adjust to bias is something I have always done by ear... Sometimes, depending upon the voltages involved and the particular JFET you use, it can sound "bad" (like there is a bad connection somewhere) and you can correct that varying the source resistor.
Cheers,
Gil
Re: FET preamp ?
My only direct experience with a FET in this sort of configuration is with an effects pedal. There, you want to bias the FET to split the supply voltage in half (as you've conjectured) to get maximum signal swing without clipping.
Based on that, I think you'd check the supply voltage above the 10K resistor then vary the 5.1K resistor to get the voltage at the FET drain (probably get the same reading at the source as well) to be half that. I'm not sure which schematic you've looked at, but i have one in front of me that indicates the voltage at the drain should be 10-11V, so i assume if you put your meter above the 10k, you'd see something like 20V.
With any luck, I'll be building this FET preamp myself in a few weeks, so I'll be able to test this out first hand.
Based on that, I think you'd check the supply voltage above the 10K resistor then vary the 5.1K resistor to get the voltage at the FET drain (probably get the same reading at the source as well) to be half that. I'm not sure which schematic you've looked at, but i have one in front of me that indicates the voltage at the drain should be 10-11V, so i assume if you put your meter above the 10k, you'd see something like 20V.
With any luck, I'll be building this FET preamp myself in a few weeks, so I'll be able to test this out first hand.
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html
Black chassis' availble: http://cepedals.com/Dumble-Style-Chassis.html
Re: FET preamp ?
Good luck with your build - I'm still assembling parts - who will win?odourboy wrote:With any luck, I'll be building this FET preamp myself in a few weeks, so I'll be able to test this out first hand.