Simple DIY one Transistor pedal

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GuyBodenGuyBoden Frets: 634
I built a simple one transistor circuit to show how easy these are to build.

Here's the typical circuit:
image

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


"Music makes the rules, music is not made from the rules."
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  • GuyBodenGuyBoden Frets: 634
    It's doing nothing special, just amplifying the signal, a simple one Transistor treble boost, but as with all devices it adds something else to the output signal.

    A smaller input capacitor results in less bass before transistor, a smaller output capacitor results in less bass after the transistor. Using one or both capacitor options results in a Treble boost pedal.


    I'm getting some Jfets tomorrow, so I'll compared this circuit to a Jfet circuit.

    Any advice on the sound, will be very welcome.
    "Music makes the rules, music is not made from the rules."
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  • ICBMICBM Frets: 57390
    Transistors are cool :-). I think they can be more varied and interesting-sounding than valves.

    I can't listen to the clip at the moment but I will later.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • GuyBodenGuyBoden Frets: 634
    edited May 2014
    I've created a schematic, so anyone can build this simple circuit for treble boost. You can add diodes for a bit of distortion.

    image

    Here's the Transistor pins for the C B E locations.
    image
    "Music makes the rules, music is not made from the rules."
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  • Does that mean it's essentially a clean boost?

    Pretty cool though :) I might have a cheeky go and put a couple of sockets on for diodes.
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  • ICBMICBM Frets: 57390
    Any single-transistor circuit with no clipping diodes is essentially a clean boost, up to the point the input signal is so large it causes the output to clip at the supply voltage - which is hugely loud, so unless you're going into a heavily overdriven amp or another distortion pedal it doesn't have much practical use.

    What they do that's interesting is produce harmonic distortion - even then not a lot, but enough to add 'something else' to the signal, as Guy said - or alter the frequency response a bit.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • AlanPAlanP Frets: 53
    edited May 2014
    So a quick analysis for the uninitiated...

    The 500k and the 50k are i) setting the input impedance to about 45k (the resistors appear in parallel for AC purposes -  a bit low really for use direct from a guitar, but fine if after something with a buffer)... and ii) biasing the base of the transistor to about 0.8Volts (potential divider off of the 9V).

    The BE junction of the transistor will drop about 0.7V (looking at the spec sheet for it will get a more accurate value - but that is ok for a quick analysis), so there will be about 0.1V appearing across the 500R resistor, which will set the emitter current & collector current (the same for practical purposes here) at about 0.2mA.

    So with 0.2mA collector current through the 10K, the voltage drop across it will be about 2V, so the no-signal operating voltage at the collector will be 9 - (10000 * .0002) = 7V.

    For the greatest +/- signal swing (lowest distortion), setting that operating voltage at around 4.5V would be the thing to do, but to try different styles/amounts of distortion, you could reduce the 10K to 3k3 or lower, as it will reduce the available amount of +ve swing (due to transistor cut-off), or increase it to up to 33k or so, which will cause clipping of the -ve wave due to saturation.  

    (The latter would also have the undesirable side-effect of increasing the output impedance quite a bit, and an emitter-follower buffer directly after that transistor and  before the output cap would be a useful move... but probably unnecessary for experimental purposes.)

    Hope this was of interest... 
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  • imaloneimalone Frets: 743
    edited May 2014
    Isn't there also emitter load? That 500R draws current, and 1/g of that current comes from the transistor, meaning effectively another 50k or so in parallel drawn from the base, it doesn't affect the analysis of the operating point, but the incoming signal needs to supply it. There's a nice trick if you add a FET as input follower before the BJT amplifier. Since the FET gate doesn't draw current (but does have capacitance) the FET bias can be set with very high input impedance with very little capacitive loss to soak up treble (using the FET as amplifier does have significant frequency-dependent impedance due to gate-emitter capacitance).
    Edit: of course the various effects of having a lower impedance input are part of the whole sound and character of these basic boosters, so a high impedance input buffer isn't always what you want.
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  • GuyBodenGuyBoden Frets: 634
    AlanP said:
    S


    For the greatest +/- signal swing (lowest distortion), setting that operating voltage at around 4.5V would be the thing to do, but to try different styles/amounts of distortion, you could reduce the 10K to 3k3 or lower, as it will reduce the available amount of +ve swing (due to transistor cut-off), or increase it to up to 33k or so, which will cause clipping of the -ve wave due to saturation.
    On a similar circuit, I added a trim pot for the 10K, so I could experiment using different resistor values.

    Many thanks for the good analysis, these circuits are very easy and safe 9volt builds for DIY'ers.
    "Music makes the rules, music is not made from the rules."
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  • imaloneimalone Frets: 743
    The gain is roughly the collector resistor divided by the emitter resistor (there's an effective intrinsic emitter resistance which limits it, about 25R in a 2N5551), though it gets complicated because increasing the collector one starts to drop the current going through the transistor, these things are always a balancing act. Like AlanP says, it's operating quite close to the positive rail. One way to address that is to bring the bias voltage up a bit and get more current through the transistor, that causes the collector resistor to drop more voltage. Bringing it up to 0.4mA would get you a 4V drop, a trim pot could be used to adjust the bias.


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  • GuyBodenGuyBoden Frets: 634
    edited May 2014
    Here's a simple jfet treble boost circuit with clipping. I used parallel Mosfets for very soft clipping. It's an easy circuit that anyone could build.


    I liked this circuit, so here's a quick 50sec recording on sound cloud.
    image
    Here's the pin out for the jfet 2N5457.
    image


    "Music makes the rules, music is not made from the rules."
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  • ICBMICBM Frets: 57390
    GuyBoden said:
    these circuits are very easy and cheap builds for some boutique pedal makers, usually sold with marketing guff that proclaims them as being like specific amps they bear no relation to.
    Edited for accuracy ;).

    Basically it's the Electra Distortion circuit…

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • GuyBodenGuyBoden Frets: 634
    ICBM said:
    GuyBoden said:
    these circuits are very easy and cheap builds for some boutique pedal makers, usually sold with marketing guff that proclaims them as being like specific amps they bear no relation to.
    Edited for accuracy ;).

    Basically it's the Electra Distortion circuit…

    :)
    "Music makes the rules, music is not made from the rules."
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  • imaloneimalone Frets: 743
    GuyBoden said:
    H

    I liked this circuit, so here's a quick 50sec recording on sound cloud.



    Nice.
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  • Dave_McDave_Mc Frets: 1128
    GuyBoden said:
    Here's a simple jfet treble boost circuit with clipping. I used parallel Mosfets for very soft clipping. It's an easy circuit that anyone could build.


    I liked this circuit, so here's a quick 50sec recording on sound cloud.
    image


    Holy crap with that elevator music clip there I reckon you could sell that for $250 on TGP.

















    (Just kidding I liked the playing and clip. I actually like jazz/blues, but it's a pretty easy target for TGP-lulz.)
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  • GuyBodenGuyBoden Frets: 634
    edited May 2014
    Dave_Mc said:
    GuyBoden said:
    Here's a simple jfet treble boost circuit with clipping. I used parallel Mosfets for very soft clipping. It's an easy circuit that anyone could build.


    I liked this circuit, so here's a quick 50sec recording on sound cloud.
    image


    Holy crap with that elevator music clip there I reckon you could sell that for $250 on TGP.

















    (Just kidding I liked the playing and clip. I actually like jazz/blues, but it's a pretty easy target for TGP-lulz.)
    I'm just trying to encourage players to have a go and build these simple DIY circuits, the parts cost about a £3.

    Thanks for taking an interest, you could easily build one to suit your style.
    :)>-
    "Music makes the rules, music is not made from the rules."
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  • That sounds great! You can *just* hear the notes breaking up slightly.  

    Definitely interested in having a go, thread bookmarked.
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  • GuyBodenGuyBoden Frets: 634
    That sounds great! You can *just* hear the notes breaking up slightly.  

    Definitely interested in having a go, thread bookmarked.
    Yes, the jfets circuits sound good. The 2N5457 jfet costs about 80p.

    Have fun
    Guy
    :)
    "Music makes the rules, music is not made from the rules."
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  • Dave_McDave_Mc Frets: 1128
    GuyBoden said:
    Dave_Mc said:
    GuyBoden said:
    Here's a simple jfet treble boost circuit with clipping. I used parallel Mosfets for very soft clipping. It's an easy circuit that anyone could build.


    I liked this circuit, so here's a quick 50sec recording on sound cloud.
    image


    Holy crap with that elevator music clip there I reckon you could sell that for $250 on TGP.

















    (Just kidding I liked the playing and clip. I actually like jazz/blues, but it's a pretty easy target for TGP-lulz.)
    I'm just trying to encourage players to have a go and build these simple DIY circuits, the parts cost about a £3.

    Thanks for taking an interest, you could easily build one to suit your style.
    :)>-
    Yeah I'd kind of have to practise a bit of soldering first :)) But yeah theoretically I'm interested in pedal circuits and the like. I know most boosters are pretty simple, and even a lot of fuzzes.
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  • GuyBodenGuyBoden Frets: 634
    edited May 2014
    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
    image 
    "Music makes the rules, music is not made from the rules."
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  • Dave_McDave_Mc Frets: 1128
    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 :)) )
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