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If I have time, I'll try to take some pics of building a prototype circuit using these simple electrical connectors.
A diode and capacitor is going to ground from the source 'S' on the jfet gives some slight distortion and more output. The diodes on the output also give very slight distortion.
Latest clip sounds good, too.
That circuit in fact has a gain of approximately Rbase over Z in. The latter being of course the impedance of the guitar and the coupling cap. It is a shunt feedback circuit and the guitar is "seeing" a virtual earth or short circuit!
There are some design rules of thumb.
Chose Ic. 1mA is reasonable and with a 10V supply we would like Vc to be 5V, Rc is therefore 5k or 5k1 or 4k7 whichever is handy.
Rb is about hfe times Rc and for most small signal, low noise audio transistors this will likely be 200 or more. That gives Rb as around 1meg and if that gives a Vc within a volt or so of 5 yer cooking. If Vc is way out I leave you with the exercise of working out the solution.
Those that want to dabble would do well to buy a solderless "breadboard" I resisted for many years but eventually succumbed and bought the "K&H Model AD-12 from Maplin and very useful it has proved to be.
Couple of tips. Make up an input and output jack for rapid patching. CAT5 solid pair is JUST the right size as plug in jumper wire.
Dave.
10mA might be preferable for a 2N5550, but means more input current draw at base and therefore lower input impedance, 1mA is fine, and easier to control with just passive components.
I'd like to have a go at building this, but I'm a beginner - built a pedal, can solder OK etc. But I don't know how to fully read the diag - what do the blue and red waves mean, and what are the horizontal lines at top and bottom? I don't know how to visualise it as an onboard thing.
What sort of value caps and resistors could I start with?
I have a guitar in build and thought about adding an onboard preamp or something, just for learning a bit and what have you.
Cheers.
I see, thanks for that
The red and blue waves are just illustrative, input and (amplified) output signal.
See ecc83's post for suggested values for this one:
Chose Ic. 1mA is reasonable and with a 10V supply we would like Vc to be 5V, Rc is therefore 5k or 5k1 or 4k7 whichever is handy.
Rb is about hfe times Rc and for most small signal, low noise audio transistors this will likely be 200 or more. That gives Rb as around 1meg and if that gives a Vc within a volt or so of 5 yer cooking. If Vc is way out I leave you with the exercise of working out the solution.
Rc is the resistor on the transistor collector ("load" in the diagram), Rb is the resistor to base. Not sure how robust this is to variations in the transistor gain, but think it should get to the right ballpark. (most 2N5551 I've measured have been around 130, though the max is 250, BC547s come in different grades, B and C are supposed to be above 200).This is the FET + BJT one, probably a cleaner amplifier than single device ones (and less interesting as an effect). Getting them biased is tricky, but adding in an Rbase (1Meg or so) makes it a bit less sensitive. Manufacturers have occasionally made combined devices to do this job (though it's not very common).
If I might drone on a bit more?!
The above circuit is a true "diode clipper" . Two words often misused about the other distortion device, the feedback diode amplifier where the diode (usually two) are connected from output back to input, sometimes with a series pot to adjust effect.
I think it is very important in a thread dealing with ACTUAL circuitry that we use the correct terms and try to avoid confusing wordage. Not so important in the rough and tumble of amp and sound description since that is a purely subjective matter.
This accuracy is also important for the new comer to electronics. It is hard enough to learn without being sidetracked by sloppy nomenclature.
Back to the circuit. I would say the 680R in the emitter circuit is redundant but it might have an effect on the sound. In any case it might be interesting to shunt it with a cap'? Start at 1mfd and see the effect. Should get a treble boost but since decoupling the resistor will also lower the input impedance,who knows!
If anyone has a question they think SO daft they dare not speak? PM me.
Dave.
This link has some great beginners projects, the step by step info is very clearly done:
http://tonefiend.com/tonefiend-diy-club-projects-resources/
This link shows how to build a simple jfet boost circuit, and how to bias a jfet.
http://www.tonefiend.com//wp-content/uploads/DIY%20Club%20Project%203%20v02.pdf
As a total beginner I don't mind admitting that, or asking super-noob questions I have just built a Tillman preamp, but added a trimpot for biasing, and a switch which adds a bypass cap over one resistor. Seems to me the pot's worth having permanently because it suits different guitars (pups) differently. Using Mk1 Human Ears instead of the suggested bias voltage, which people seem to differ on anyways.
And the bypass cap was interesting, different boost & treble boost depending on values. So I'm going to throw it into a pedal form with a rotary with different caps on, to play with. So it can be a no-gain buffer, booster, or treble booster etc.
Still can't entirely follow a schem and am right at the bottom of the hill of learning, but enjoying it. Links and posts here (thanks all for these) are great. My 14 yr old has started building the one-transistor circuit too