FET questions

[10thTx]

I have done a search for FET and read some, but still have some questions:

1) FET is some type of a buffer?

2) FET would be used when playing an acoustic thru the amp?

( I noted some players with strats like it, but I am specifically
wondering about an acoustic such as LC would use with his Dumble)

3) Would it be useful to have the 10k trimmer pot external or is that
really going to be somewhat a "set and forget" pot?

4) Could a 12A_7 triode be substituted for the FET using similar component
values otherwise?

5) OR has anyone done a 12A_7 circuit that provides a similar function
as HAD's FET circuit?

With respect, 10thtx

[martin manning]

I have done a search for FET and read some, but still have some questions:

1) FET is some type of a buffer?
2) FET would be used when playing an acoustic thru the amp?
( I noted some players with strats like it, but I am specifically
wondering about an acoustic such as LC would use with his Dumble)
3) Would it be useful to have the 10k trimmer pot external or is that
really going to be somewhat a "set and forget" pot?
4) Could a 12A_7 triode be substituted for the FET using similar component
values otherwise?
5) OR has anyone done a 12A_7 circuit that provides a similar function
as HAD's FET circuit?

1) It's a booster (~16dB) with very high input impedance (3M).
2) As I understand it that was the original intent. The high impedance was needed since acoustic instruments commonly used piezoelectric pickups. That's still true, but many now have on-board preamps. Single coil pickups have lower output, so the high impedance and boost can add some girth, and Steel players (David Lindley, for one) like it too.
3) That has been done. A good plan is to replace the FET jack with a pot that has a pull switch to select either the boost or normal input.
4) and 5) Could be done, but the high input impedance would not be there.

[ToneMerc]

I have done a search for FET and read some, but still have some questions:

1) FET is some type of a buffer?

2) FET would be used when playing an acoustic thru the amp?

( I noted some players with strats like it, but I am specifically
wondering about an acoustic such as LC would use with his Dumble)

3) Would it be useful to have the 10k trimmer pot external or is that
really going to be somewhat a "set and forget" pot?


With respect, 10thtx

1&2) a very high impedance preamp circuit which originated from a 60's Barcus Berry piezo preamp. I've mainly used the 4416 and 4416A FET and I've come to the conclusion that you need to buy 50 so the you can cull 8 with the same gain.

There's a couple of tweaks you can do to make the freq response more conducive to an elevtric guitar pickup. The one in my 183 build is an enigma, it's a perfect transparent clean boost.

3) I have done a couple of amps with the external trimmer, if you need to tweek it, it sure beats going inside.


TM

[10thTx]

Thanks for the responses! That's very helpful and I appreciate it.

Ironically on my D-inspired amps, I use an acoustic/Larrivee with a K&K Western pickup and have to turn the volume knob way down to 2 or 3 instead of the normal 4-6 that I play with an electric. The acoustic sounds beautiful thru those amps though.

With respect, 10thtx

[grtamp]

NTE452 is not more available on mouser!

[Structo]

I found the NTE452 at a local surplus dealer.

But any transistor with the same characteristics will work there.