wnorcott
Tele-Holic
I have built Don Tillman's superb and easy to build FET guitar preamp. I would like to share a PCB design and layout I created for it.
Don Tillman's FET preamp is designed to always be in the signal path, and not a "sound effect" pedal per se. It is a beautiful sounding preamp one of the best I have heard. The only thing that makes it stomp box like is that it is portable: you plug your guitar into it first, and then into a regular guitar amp.
The Tillman FET preamp uses a single J201 field effect transistor. The J201 JFET is a common part that should be familiar to many of you. What is different here is Tillman is not trying to drive it to saturation, he is keeping it clean and linear. The circuit has a very high input impedance of 3 Megohm which means it does not suck the tone out of your guitar and in that respect it also acts as a buffer. The tone quality reminds me of the very best of high end tube amplifiers, flat response and no noticeable tone coloration but still has that je ne sais quois that we know it when we hear it. It is just amazing that such a simple, spare design sounds so good. It only has seven parts and one of them is optional.
First the schematic this is from Don's site.
These can be built real small but my days of building a ship in a bottle are over so I scaled it so it is easy to build not clumsy. It will fit in the smallest project box that can hold 2 guitar jacks and a 9V battery.
Here is my parts layout design for it. As seen from the component side.
image removed
Here is my PCB mask to etch your own printed circuit boards, the image may display different sizes in your browser. When you print the finished size should be about 1.2" tall and 1.5" wide. The easiest way to print might be open the image in Paint and print on plain paper first, scaling it until the scale is correct. The size of the PCB is not so critical.
image removed
The preamp is intended to be always in line and always on. There are no controls it is a fixed 3dB gain amp, and operates on a single 9 volt battery. I wired mine with a simple SPST toggle switch to power it on. IF you forget to turn it off I would not sweat it: A 9V battery will last about 300 hours.
I built it with 1% tolerance metal film resistors. There are very few components in this build so use good quality. There is only 1 capacitor in the signal path, C1 is a DC blocking capacitor on the output. So it is not cricitcal, but I used good quality electrolytic. Use shielded cable on the input.
No project page would be complete without a demo so here it is. I have a YouTube demo of it very clean guitar sound:
Stereo link for the above since it is a guitar duet one in left speaker the other in the right:
http://www.youtube.com/watch?v=RDeJXaxguqU&fmt=18
It would be interesting to use the Tillman preamp as building block for a DIY amplifier head, I would say right after the input jacks and before the tone controls. You would probably need and additional clean gain stage to drive a power amp since the Tillman is fixed 3dB gain. Just a thought.
And last but not least, here is the link to the original project page by the master himself, Don Tillman:
http://www.till.com/articles/GuitarPreamp/index.html
I HOPE YOU LIKE IT!
Bill
Don Tillman's FET preamp is designed to always be in the signal path, and not a "sound effect" pedal per se. It is a beautiful sounding preamp one of the best I have heard. The only thing that makes it stomp box like is that it is portable: you plug your guitar into it first, and then into a regular guitar amp.
The Tillman FET preamp uses a single J201 field effect transistor. The J201 JFET is a common part that should be familiar to many of you. What is different here is Tillman is not trying to drive it to saturation, he is keeping it clean and linear. The circuit has a very high input impedance of 3 Megohm which means it does not suck the tone out of your guitar and in that respect it also acts as a buffer. The tone quality reminds me of the very best of high end tube amplifiers, flat response and no noticeable tone coloration but still has that je ne sais quois that we know it when we hear it. It is just amazing that such a simple, spare design sounds so good. It only has seven parts and one of them is optional.
First the schematic this is from Don's site.
These can be built real small but my days of building a ship in a bottle are over so I scaled it so it is easy to build not clumsy. It will fit in the smallest project box that can hold 2 guitar jacks and a 9V battery.
Here is my parts layout design for it. As seen from the component side.
image removed
Here is my PCB mask to etch your own printed circuit boards, the image may display different sizes in your browser. When you print the finished size should be about 1.2" tall and 1.5" wide. The easiest way to print might be open the image in Paint and print on plain paper first, scaling it until the scale is correct. The size of the PCB is not so critical.
image removed
The preamp is intended to be always in line and always on. There are no controls it is a fixed 3dB gain amp, and operates on a single 9 volt battery. I wired mine with a simple SPST toggle switch to power it on. IF you forget to turn it off I would not sweat it: A 9V battery will last about 300 hours.
I built it with 1% tolerance metal film resistors. There are very few components in this build so use good quality. There is only 1 capacitor in the signal path, C1 is a DC blocking capacitor on the output. So it is not cricitcal, but I used good quality electrolytic. Use shielded cable on the input.
No project page would be complete without a demo so here it is. I have a YouTube demo of it very clean guitar sound:
Stereo link for the above since it is a guitar duet one in left speaker the other in the right:
http://www.youtube.com/watch?v=RDeJXaxguqU&fmt=18
It would be interesting to use the Tillman preamp as building block for a DIY amplifier head, I would say right after the input jacks and before the tone controls. You would probably need and additional clean gain stage to drive a power amp since the Tillman is fixed 3dB gain. Just a thought.
And last but not least, here is the link to the original project page by the master himself, Don Tillman:
http://www.till.com/articles/GuitarPreamp/index.html
I HOPE YOU LIKE IT!
Bill
