Author Topic: fetzer or till preamp with 2n5458?  (Read 3049 times)

jogina111

fetzer or till preamp with 2n5458?
« on: October 04, 2012, 11:38:13 AM »
I got a 2n5458 FET from an old box and I've decided to use it for a preamp.. My questions: 1. what would be a better preamp to build?don tillman's discrete preamp or the fetzer valve?
2. What tweaks should I make on either circuits should I do to make them compatible for a 2n5458?
3. I cant find a 100k trimpot for the fetzer(Im gathering materials for both circuits) and 50k is the highest I found. Maybe a fixed value resistor? But what value?

 Please help me.

Davelectro

Re: fetzer or till preamp with 2n5458?
« Reply #1 on: October 04, 2012, 01:11:30 PM »
I wouldn't use a trimpot -it's better to actually measure the fet- but 50K it's ok for a 2n5458. At least in a fetzer valve.


Earthscum

Re: fetzer or till preamp with 2n5458?
« Reply #2 on: October 04, 2012, 11:38:19 PM »
http://www.hawestv.com/amp_projects/fet_preamp/fetpreamp1.htm

read through that concerning Tillman amps using a different fet. The process he uses can be applied to any fet. I much prefer the sound of MPF102's and 2N545(x) to J201's in either Tillman or Fetzer.
Give a man Fuzz, and he'll jam for a day... teach a man how to make a Fuzz and he'll never jam again!

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jogina111

Re: fetzer or till preamp with 2n5458?
« Reply #3 on: October 05, 2012, 08:11:03 AM »
how do I know if the trimpot is in the correct setting? Should it sound clean or overdriven?

Jdansti

Re: fetzer or till preamp with 2n5458?
« Reply #4 on: October 09, 2012, 09:56:56 AM »
The Tillman preamp bias voltage at the drain should be about 6V and it should sound clean unless you're hitting it with some really hot humbuckers. Tillman used a J201 and 2N5457.  His drain resistor is 6.8k.  I'm not sure how the 2N5458 would react, but if it were me and that's all I had, I'd start off around 6V at the drain and tweak it until I got a nice clean boost.

Here's Don Tillman's explanation of his preamp:
http://www.till.com/articles/GuitarPreamp/


Copyright 1992, 2001, J. Donald Tillman. 
All rights reserved.  email: don@till.com
web page:  http://www.till.com


BTW- I put some J201s in the shipment I'm sending you.
R.G. Keene: EXPECT there to be errors, and defeat them...