Wednesday, 15 February 2012

Boss SD1 without output buffer

With switch to change between symmetrical and asymmetrical clipping.

17 comments:

  1. Thanks for sharing all these awesome layouts! These effects have enriched my guitar tone tremendously, and I'm sure they have for many others - much appreciated!

    I just have a few beginner questions here, having just picked up the whole electronics thing:

    1. Which resistor(s) are responsible for biasing the NPN silicon transistor here? I'm currently getting quite a bit of dirt even when the drive knob is brought to zero. I'm using BC109 for Q1 and 1N4148s for the diodes.

    2. I'm experiencing a volume drop when I toggle to the symmetrical clipping side. What's the purpose of having both D1 and D2 for symmetrical clipping? Does it change the amount of clipping on one side of the waveform?

    Thanks in advance for your patience.

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    Replies
    1. Hi Darren

      The 510K resistor to the 4.5V rail biases the stage, but this transistor is just a buffer and so adds no gain to the circuit. The gain of the circuit is the Drive pot value added to the Drive 1 resistor value, divided by the 4K7 also attached the the IC pin 2. And so the gain range from minimum to maximum Drive pot rotation will be approximately 7 to 220 (17 to 47dB). So to decrease the minimum gain, reduce the 33K resistor (10K will give you a gain or 2 for instance), to decrease the maximum gain reduce the Drive pot value.

      You will get a volume drop when you switch more diodes in. D1 to D3 clip the signal asymmetrically, 2 in one direction, one in the other which just means there is more clipping on one half of the waveform. I've just noticed though that I've shown that switch incorrectly, D1 and D2 should be in series with each other, not parallel, to mimic the SD1 clipping, so you may want to make that change. The other side of the switch is just a single diode and so only clips one half of the waveform. I just included this as another option though, and you could include any secondary clipping option here such as two diodes (one in each direction) to give you symmetrical clipping. Or maybe a couple of red LEDs etc etc.

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  2. Thanks! That helped. After putting D1 and D2 in series, there is a noticeable change and it sounds more like the SD-1 indeed.

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  3. Do you know the orientation of the 1uf mate (mine are radials)

    cheers.

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    Replies
    1. Negative at the top mate

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    2. Cheers mate, Do you think 20 or even 22nf's would detract much from the sound of the 18nf's?

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    3. I wouldn't expect so, maybe a little darker but not too much difference.

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    4. Ok cheers, Well you may have indirectly just invented a 'dark' switch ;o)

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  4. Just wired this one up, I absolutely love it. I installed a "fat switch" (DPDT switch in the feedback loop selects between stock 47n or 100n), and used a 3 position DPDT for the clipping (3 1N914, none, or red+yellow LED). My least favorite mode is definitely the stock, and my favorite is the LED clipping. In the LED mode with the 100n cap activated, it's actually really nice on bass! Overall, this is an awesome TS alternative.

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  5. Any opinions on how to give this pedal a bit of a bass boost?

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    Replies
    1. Would using a larger Tone pot do the trick? I'd just like to get a bit more tone control out of this pedal. It seems too bright.

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  6. I build this yesterday and it didn't work, when I turn it on the sound is like a fuzz oscillation, there is no gain at all, can you help me? I'm using 2N5088 for Q1 and 1N914 for diodes.

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    Replies
    1. Turn the transistor 180 degrees

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    2. thanks for the reply mark, but still not working :(

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  7. HI Dudes & Dudettes. Just trying to figure out which one of these I should build. Buffer or no buffer? Besides the diode clipping switch added to this layout, would buffered version mean I could use A DPDT foot switch and not wire it for true bypass (like how it is shown in the offboard wiring section), and does the no buffer version mean I can wire it for true bypass with a 3pdt footswitch? Or am I completely off?

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  8. Hi !
    First, thanks for this schematic !
    I'm a beginner in electronic, and do you know if I could replace the IC by a NE5532 ? I don't want exactly the sound of the original pedal, I just want a good overdrive...
    And what's exactly the difference between with/without buffer ?

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  9. Hello guys,

    Just finish this one and I think I was too confident... I don't even have "unity" gain. :(
    I double checked the components positioning, reflowed the solder, passed the exacto knife between the strips and still, I don't have volume neither gain.
    Here the voltages from the IC:
    1- 5,75V
    2- 5,14V
    3- 5,04V
    4- 0V
    5- 5,44V
    6- 5,45V
    7- 5,44V
    8- 9,25V

    As for the transistor (2N5088):
    C- 9,25V
    B- 4,52V
    E- 4,13V

    Do you see anything weird ?

    Thank you!

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