Now, with Easy to Find Parts! Some time ago, J. Donald Tillman designed an elegant
JFET guitar preamplifier.
He posted the circuit on the Web. Overnight, this circuit became very popular. And it's still a winner today.
The reasons why are easy to see. This amp is easy to build.
The circuit works like a champ. And the JFET's tube-like warmth sounds great. Plus, the
high-impedance input won't load your guitar. At the other end, the medium output impedance combats high-frequency losses due to
loading and long cables. And by the way, this FET preamp is great for microphones, too!
Bad News...and Good. Unfortunately, Tillman's amplifier requires a J201 FET. The J201 is a very special device and an
excellent choice. Yet it's uncommon to hobbyists. But my site solves the mystery. I've designed a similar preamplifier with an
everyday Radio Shack JFET.
Buy It Today. Use It Tonight. I've read the forums.
Hobbyists want to buy now and play tonight. They stop at Radio Shack. But Radio Shack only sells one FET: The famous
MPF102. Hobbyists try to use an MPF102 in
Tillman's original design. Yet Tillman optimized his design for the J201. The specs for an MPF102 are very different. Ignore these differences, and your amplifier might not work.
The J201 requires only 0.2mA to 1 mA of drain current.
The MPF102 operates on 2 to 20 mA. Run it on less, and you may get an attenuator instead of an amplifier! I can
prove that statement. See... Proof
Summary of the Differences
On the table, notice that the MPF102 requires more current than does the J201.
The current requirement is a major reason why you can't just plug an MPF102 into
Tillman's circuit. This is a very poor substitution. It will disappoint you.
(You might as well strum piccolo music on a bass guitar. You'll have more luck.)
IDSS (Drain current, mA)
0.2 - 1
2 - 20
2 - 6.5mS
Achieve results that you can be proud of! When you build a circuit,
you go to a lot of work. Make the effort pay off! My page offers a
new preamp design, starting with the MPF102's specs. Now you have
the right design for an MPF102 JFET
preamplifier. Build carefully. You'll wind up with a satisfying project that you'll appreciate for years.
Oncoming Scarcity of MPF102 & J201
♦ CAUTION. Major manufacturers are exiting the JFET market. Others are
ceasing production of leaded JFETs or MOSFETs. For instance, Siliconix has already left
the JFET market.
In 2011, Fairchild obsoleted the MPF102 and J201. Other JFETs that are
compatible with the MPF102 (2N3819, 2N5458, etc.) are also obsolete! When current stocks
run out, Fairchild will not provide more. For the time being, you can still buy these
devices from vendors or factory representatives (see below.)
In February 2013, Radio Shack discontinued the MPF102 (part 276-2062). Soon thereafter,
stores ran out their stocks forever. Other vendors sell various substitutes, many by NTE.
You'll have to order online. Radio Shack's Web site no longer ships replacement JFETs
to your local store for free. I recommend the NTE457. For more suggestions, click
Substitute parts. Fairchild continues to manufacture the J113, a possible substitute for
the MPF102. Vendors such as Mouser and Digi-Key sell the J113.
Other sources continue to make the MPF102 and J201...
InterFET, the former producer of the Siliconix JFET
line, continues to manufacture the J201. InterFET also provides devices that seem compatible
with the MPF102: Use the Interfet 2N3822 or J113. Note that device pinouts might not
match the MPF102 pinout. For an InterFET sales representative in your area, contact
Central Semiconductor continues to
manufacture the 2N3819. The 2N3819 is a reliable substitute for the MPF102. (The pinout
differs.) Central also offers the J201, which you'll need for the Tillman circuit. Prices for
these “end-of-life” devices tend to be high.
Electronics Parts can find you deals on JFETs from China. Some of these
deals are impressive. If you can arrange for air shipment, your order can arrive
in a few days or weeks. I don't know if the parts come from Chinese foundries or elsewhere.
Chinese MPF102s plug right into my circuit. I've bought 2N5457, J113, and 2SK370 JFETs
from China. So far, the I've received excellent parts.
♦ WARNING. This is your project. Your achievement is entirely yours.
I assume no responsibility for your success in using methods on these pages. If you
fail, the same is true. I neither make nor imply any warranty. I don't guarantee
the accuracy or effectiveness of these methods. Parts, skill and assembly methods
vary. So will your results. Proceed at your own risk.
♦ WARNING. Electronic projects can pose hazards. Soldering irons
can burn you. Chassis paint and solder are poisons. Even with battery projects,
wiring mistakes can start fires. If the schematic and description on this page
baffle you, this project is too advanced. Try something else. Again, damages,
injuries and errors are your responsibility. — The Webmaster