Simple DIY one Transistor pedal

GuyBoden

Dave_Mc said:

Touché )

I might give that a try actually.

What do you do, just screw them into that? (as you can tell I'm not exactly an electronics guru ) )

If I have time, I'll try to take some pics of building a prototype circuit using these simple electrical connectors.

LastMantra

GuyBoden said:

I prototype the circuits, I just use standard electrical connectors and screw each component together as per schematic on a board. Then you can play around substituting various component values and listen to the result. Nothing special is needed for prototypes.

These connectors are £2 from Screwfix:
http://www.screwfix.com/p/terminal-strips-6a-pack-of-15/37144
 

That's quite a good idea. You can get a little bread board for a couple of £'s too though.

GuyBoden

LastMantra said:

GuyBoden said:

I prototype the circuits, I just use standard electrical connectors and screw each component together as per schematic on a board. Then you can play around substituting various component values and listen to the result. Nothing special is needed for prototypes.

These connectors are £2 from Screwfix:
http://www.screwfix.com/p/terminal-strips-6a-pack-of-15/37144
 

That's quite a good idea. You can get a little bread board for a couple of £'s too though.

Yes, Ive got a bread board, I thought that they were more expensive than "a couple of £'s".

LastMantra

GuyBoden said:

LastMantra said:

GuyBoden said:

I prototype the circuits, I just use standard electrical connectors and screw each component together as per schematic on a board. Then you can play around substituting various component values and listen to the result. Nothing special is needed for prototypes.

These connectors are £2 from Screwfix:
http://www.screwfix.com/p/terminal-strips-6a-pack-of-15/37144
 

That's quite a good idea. You can get a little bread board for a couple of £'s too though.

Yes, Ive got a bread board, I thought that they were more expensive than "a couple of £'s".

You can get cheap mini boards on e-bay for a couple or less. Don't know what they are like though. 

Those connectors could be useful for actually building simple pedals rather than using a board. Solderless. 

GuyBoden

Here's an interesting slight variation on the jfet circuit and a 50sec sound cloud clip.

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.

Dave_Mc

GuyBoden said:

Dave_Mc said:

Touché )

I might give that a try actually.

What do you do, just screw them into that? (as you can tell I'm not exactly an electronics guru ) )

If I have time, I'll try to take some pics of building a prototype circuit using these simple electrical connectors.

That'd be awesome.

Latest clip sounds good, too.

Corvus

Thanks for all this Guy, good stuff. I've built one pedal but things like this are more instructive I think...

ecc83

GuyBoden said:

I built a simple one transistor circuit to show how easy these are to build.

Here's the typical circuit:


Here's my sound clip of the circuit in action:

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.

imalone

ecc83 said:

GuyBoden said:

I built a simple one transistor circuit to show how easy these are to build.

Here's the typical circuit:

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!

Also this circuit is different from the later ones because of Rbase, the later ones Guy posted don't use the same virtual earth arrangement and instead rely on Remitter for feedback, which means they have higher input impedance. Must remember to post that FET + BJT circuit, > 1 Meg input impedance is easily attainable.
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.

thermionic

There's a lot of stuff about these one transistor circuits on the 'net. All these boutique "clean boosts" (Alembic Stratoblaster, Super Hard On, LPB-1, all those 60s treble boosters) seem to be based on this idea.

Corvus

GuyBoden said:

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.

thermionic

Horizontal lines are power rails, top at 9V and the bottom at 0V (ground) presumably. The coloured waves are just a representation of the signal - there's gain so the output has a larger amplitude, but there's also a phase change (peak becomes a trough and vice versa).

Poodle's pedalparts have a variety of these one-transistor amplifiers as kits, including an Alembic Stratoblaster clone which was originally intended to be fitted on-board a guitar rather than in a pedal.

Corvus

I see, thanks for that

imalone

Top and bottom are usually positive supply (here + on your 9v battery) and ground. Though it's naughty not to have written that on...
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).

Corvus

Thank you for that : )  I tried to read the other posts but it was totally over my head... I shall have a go at building.

imalone

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).

GuyBoden

IMHO, a good, easy to build distortion circuit is the Electra Distortion:

 

ecc83

GuyBoden said:

IMHO, a good, easy to build distortion circuit is the Electra Distortion:

 

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.

GuyBoden

imalone said:

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).

Great input, many thanks, yes biasing jfets is not a good place to start if you're a beginner, transistor circuits with diode clipping like the "Electra Distortion" I posted are much easier to build, but jfets sound good, especially in multiple stages.

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

Corvus

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