JFET Preamp

A Discrete FET Guitar Preamp

By : J. Donald Tillman

I've been performing experiments with guitar preamps and on-board electronics since, oh, the Nixon adminstration or thereabouts. Sometime around 1990 I designed this preamp circuit, and have been using it mostly unchanged ever since. In 1992 I posted a schematic of the preamp to one of the Usenet groups and the circuit became somewhat popular.
The goals of the preamp are:

• Sounds great. Of course.
• Discrete FET (Field Effect Transistor) design. Discrete because I don't like the sound of opamps, and FETs because the devices operate in a manner somewhat analogous to vacuum tubes.
• Runs off a 9v battery. In practice a decaying 9V battery, possibly as low as 8.0 volts.
• Very high (3.0 Mohm) input impedance. 1.0 Mohm is the minimal acceptable input impedance for a guitar device.
• Medium (6.0 Kohm) output impedance. There's no need for an especially low output impedance as we're only using the preamp to counter the effects of cable capactance and loading.
• 3 dB gain. You don't need much gain, and given the guitar signal level and the 9v supply voltage, there isn't room for much gain.
• Low noise.
• Graceful overload. Overload happens; the circuit should clip gracefully and recover gracefully.

Copyright 1992, 2001, J. Donald Tillman. All rights reserved.



Danish : en lille guitar preamp som ikke består af ret mange komponenter .. Virker rigtigt godt  er nem at bygge...Giver et lille boost og hjælper til at dine mange pedaler og lange kabler ikke æder hele signalet ...  
 ( især diskanten )
Husk at vende transistoren rigtigt ( Billede 2 )

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Prototype # 1 - Picture 1.

Og denne her sidder nu i min Jordan Vico Vibe Tremelo

Vico Vibe Tremelo

Prototype # 2 - Picture 2.

Parts List - Komponenter

Q1	J201 N-channel JFET transistor
R1	3.0M ohm 1/4-watt 5% resistor
R2	2.2K ohm 1/4-watt 5% resistor
R3	6.8K ohm 1/4-watt 5% resistor
R4	51K ohm 1/4-watt 5% resistor
C1	4.7 uF electrolytic capacitor
C2	10 uF electrolytic or tantalum cap ( den undlod jeg )

Du kan bygge din egen efter dette billede ( Kobberbanen er brudt mellem Elektrolyt kondensatorens ben )

Den modstand der står op ,Ved transistorens øverste ben , er R3 ( 6K8 Ohm. )

Green Wire = Input

Red Wire = 9 Volt +

Black Wire = Ground -

Blue  Wire = Output

The Transistor Pinout is

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On Prototype # 2 Picture 2.

Datasheet JFET 201 N

Prototype # 2 Ready to rock in the Test Rig

Don Tillmans  JFET Preamp

I Build one of these Preamps ... It sounds very good 
The Enclosure is a Hammond 1591 B


Jeg byggede sådan en fætter her og smed den Lige i en transparent  blå Box i Solskin på Solitudevej...

Handmade in Denmark