JFET Preamp Pages
- Introduction
- Schematic & Parts
- How It Works
- Spec Spread
- Improve Performance
- MPF102 in Tillman Circuit
- Troubleshooting
- FAQ
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Frequently Asked Questions
Don Tillman brought up several excellent questions about the JFET amplifier. I have a little different take on these questions. For you half-dozen supporters of www.hawestv.com, here are my five cents. I've also added one or two questions of my own. To read my answer, click a question below.
PREAMP BASICS
- What type of battery should I use with the preamp?
- Can I buy a preamp from you? Will you build me one?
- I don't know electronics. Can I build your preamp?
- Where can I buy the MPF102 FET?
- What are some advantages of working with FETs?
- Will the JFET preamplifier work with a piezo pickup or a piezo element?
ABOUT RESISTORS
- I can't find the right values of metal film resistors at Radio Shack. Can I use carbon film or carbon composition resistors?
- Can I substitute for some resistor values that I can't find?
- I can't find a 3.3M resistor at Radio Shack. What should I do?
- Why do some players prefer carbon resistors to metal film resistors? Aren't carbon resistors noisier than metal film resistors?
MODIFYING & TROUBLESHOOTING
- Can I use a different FET?
- What's your technique for FET substitution?
- Can you get me a schematic for a different preamp?
- Can I run the preamp off some other voltage?
- The preamp doesn't work. Can you help me to debug it?
- I reversed the drain and source leads. Will this reversal cause a problem?
- How can I greatly increase the output swing from your preamp?
- What's the easiest way to design my own preamplifier? A trimpot in the drain circuit?
- Would a variable capacitor across the source resistor allow me to change the gain?
- You mentioned that I could boost the bass. How?
POWER AMPLIFIERS
- I'm building an amplified cigar-box guitar. The JFET preamp is a great start. But how can I boost the output enough to drive a speaker?
- I bought amplified speakers, but they didn't come with a power supply. How do I find the right power supply?
- Could I replace the preamplifier stages of my tube guitar amplifier with circuits like your JFET preamp?
- Could I use another MPF102 stage as the power amp?
- How do I get more power out of the amplifier?
- Tubes and FETs are not interchangeable.
ARDUINO MICROCONTROLLER INTERFACES
- I need to connect your preamp to an Arduino microcontroller. How would I do this?
- Please provide me with a circuit for a five-volt buffer.
- Do you have an opto circuit to isolate an ULN2004 stepper drive chip from the Arduino?
OTHER PREAMPLIFIERS
- JFETs are too fragile and fussy for me. Do you have a more durable circuit that will do the same thing?
- The Darlington output is very weak. Did I wire something wrong?
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▲ 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 |
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Copyright © 2007 by James T. Hawes. All rights reserved.
•URL: http://www.hawestv.com/mtv_FAQ/FAQ_fetpreamp1.htm
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