I want to use guitar with HiFi headphone amps and I need to make hi impedance input circuit. I already made it with a single JFET transistor and it works perfect, but I want another version with a bit more available gain, right about two stages, that seems like optimal gain reserve.
I already built it some time ago, with this circuit I found on Google images and I remember I had a lot of trouble getting it to work and to find optimal bias points and at the end I couldnt make it, I ended up with circuit that has less gain than single transistor version. So I would like to do it better this time, mandatory JFET at first stage and another JFET or BJT for second stage.
https://www.next.gr/uploads/8/JFETBJTBUFFERSCH.png
https://apocalypseaudio.blogspot.com/2010_05_01_archive.html
For available JFETs I have BF245C and 2N3820, and for BJTs 2N3904 and 2N3906. What circuits do you suggest, I appreciate schematics and links to articles. Working voltage 5-9V single rail.
I already built it some time ago, with this circuit I found on Google images and I remember I had a lot of trouble getting it to work and to find optimal bias points and at the end I couldnt make it, I ended up with circuit that has less gain than single transistor version. So I would like to do it better this time, mandatory JFET at first stage and another JFET or BJT for second stage.
https://www.next.gr/uploads/8/JFETBJTBUFFERSCH.png
https://apocalypseaudio.blogspot.com/2010_05_01_archive.html
For available JFETs I have BF245C and 2N3820, and for BJTs 2N3904 and 2N3906. What circuits do you suggest, I appreciate schematics and links to articles. Working voltage 5-9V single rail.
Relocated to instrument and amps forum as the people who know how to make a good DI box will be found here. Welcome to the forum. 😀
Adding a couple resistors to the Apocalypse circuit will give you the gain you want but there is a fundamental problem with pedals etc that run on a 9V battery, and that is that guitar signals can be a couple volts strong so if you amplify them, you need high voltage power for the pre-amp (etc). I suggest you download LTC spice and ~test circuits in simulation. The problem with JFETs is that their characteristics are unpredictable and a circuit that works with a wide range of Idss parts are tricky. A DIYer will have to tweak the resistors in his circuit for whatever parts he actually gets. JFET op-amps are more predictable, but you may not like the sound as much as a simple discrete circuit.
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Do you have some example for HI-Z input with TL072 with adjustable gain 1-5 times on 9V?
I will use 9V battery for trade of, I will use this to practice with headphone HiFi amp, not for recording so top notch sound quality is not huge priority.
The pot is intended for gain control, but bass response is also affected (reduced) at high gain setting. Maybe C2 should be a higher value, just try.
The output cap is a bit arbitrary, small value=more bass cut. Here also just try what sounds good.
The output cap is a bit arbitrary, small value=more bass cut. Here also just try what sounds good.
Bass cut at high gain is probably what you want anyway. The only question is how much. With circuits like this you can fool around with it and not worry about frying anything. Once you use an op amp, you need to start being careful with it. I’d stay with the two transistors.
Depends on the opamp and pickup output.
single supply 9 volts pretty normal for guitar pedals.
Usally wont get much more than a gain of 3 to 5 before clipping.
So preset gain of 3 probably good enough with volume knob after.
Depends you might get enough boast from normal guitar pedal distortion pedal.
Already has the right input impedance.
For clean tones and buffer. Using opamp be good idea than
simple transistor circuits.
Far as low noise and power supply rejection with wall adaptors.
Pedal power adaptors are definitely cleaner now though.
too late nowfor me bedtime where im at, but could draw up a simple opamp buffer with gain.
Not much more than a textbook single supply non inverting stage with gain.
And then use typical 1 meg on input.
Would use something compensated cant beat TLO71/72.
toss a 10 or 50k volume knob on output.
Little buffers are fun to make of course, also easy to just buy small
amp in a box headphone practice amp
after case, pots, board etc etc about same cost
single supply 9 volts pretty normal for guitar pedals.
Usally wont get much more than a gain of 3 to 5 before clipping.
So preset gain of 3 probably good enough with volume knob after.
Depends you might get enough boast from normal guitar pedal distortion pedal.
Already has the right input impedance.
For clean tones and buffer. Using opamp be good idea than
simple transistor circuits.
Far as low noise and power supply rejection with wall adaptors.
Pedal power adaptors are definitely cleaner now though.
too late nowfor me bedtime where im at, but could draw up a simple opamp buffer with gain.
Not much more than a textbook single supply non inverting stage with gain.
And then use typical 1 meg on input.
Would use something compensated cant beat TLO71/72.
toss a 10 or 50k volume knob on output.
Little buffers are fun to make of course, also easy to just buy small
amp in a box headphone practice amp
after case, pots, board etc etc about same cost
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