Question: Keeping STOCK Boss SD-1 sound, but making it a little better?

[dlilly69]

Hi folks,

Bit a of a newbie here. I really like the sound of a STOCK Boss SD-1. I have tried a bunch of the mods on here and elsewhere, and I keep coming back to loving the original stock sound, but I feel it can be shaped just a little bit to make it smoother and more "tubey". I don't want to change caps to add bass, or remove C6 in the tone area as I tried these mods and didn't  like the sound.

My 2 questions:

1. What would be the best and easiest mod to keep the stock sound, but just punch it up a bit (and maybe smooth out the overdrive a bit)? Change the D4,D5,orD6 diodes ? If so what kind of diodes and where? A resistor change?

2. How can I make the tone knob more usable to roll off more high end, or have a wider range of control? a Cap change? Where?

Again, I don't want to change this SD1 circuit drastically. I just want to juice up the stock sound a bit. I want to keep it as simple and stock as possible.

Thanks for yout time and help!

Dan

[Melanhead]

My fav is this:

D4 Germ. And 1n4001 series
D5 1n4001
D6 Germ. And 1n4001 series

This is part of one of Brian's (wampcat1) mods ... I've also done it with a TS pedal and my M.O.S pedal ... love the tone ...

[dlilly69]

Sounds good. Any other suggestions?

Also, any suggestion on how to give the tone knob a wider range?

[Mark Hammer]

The best way to figure out how to mod the tone control is to understand how it works.  You can take a look here for a schematic: http://www.freeinfosociety.com/electronics/schematics/audio/pictures/bosssd1.gif

If you take a look at the tone control, you will see that it essentially provides a path to ground (through a common cap and resistor) for two points in the circuit. 

One of the paths is from the junction of the 10k resistor and input of the op-amp.  If the tone pot is rotated in the direction that makes that resistance smaller, that allows more treble to bleed off to ground via the cap and 470R resistor, dulling the tone.

The other path is from the inverting ('-') input of the op-amp.  Here, as the resistance of the pot between the cap and op-amp input gets smaller/lower some boost is introduced in that stage.  The boost will be modest because the 470R ground resistor and 10k feedback resistor will limit maximum boost to around x22.  How is that "modest"?  Well, the boost at max treble starts around 12.5khz, and is counteracted by the lowpass filtering of the 10k+.01uf feedback network which starts around 1.6khz.

The action of this pot is complementary so that when you introduce the treble boost in one direction, you reduce the treble cut on the other section, and when you introduce more treble cut at the input to the op-amp, you simultaneously reduce that treble boost in the gain-setting network.

So, how would we get more variation out of it?  There are a couple of things to try out.

1) If you would like no change in the muting aspect, but would like a little more bite available, consider this.  Increase that 10k fixed resistor to 12k, and lower the .01uf cap to .0047uf (4700pf).  This will shift the lowpass function of those components from a rolloff starting around 1.6khz to a lowpass starting around 2.8khz.  It will also change the boosting aspect as you turn the tone control in the treble direction.  At maximum treble, the .027uf cap and 470R resistor, in tandem with the new 12k+4n7 network, will introduce a gain of just under x27 at 4.8khz.  Since the gain is now greater, and the counter-filtering action of the feedback components is reduced by the new 2.8khz rolloff, you will get a noticeable increase in bite available.  When the tone control is rotated over to min treble, there will be no change in the treble-cut action at the input to that op-amp.  There may be a *bit* more treble coming through at max bass because of the change in the feedback network (to 12k + 4n7), but with the counter-acting treble cut just ahead of it, not that much.  My one worry here is a bit more hiss leaking out.  I'll let your ears be the judge.

2) More treble cut and a "gronkier" midrange boost.  The treble cut introduced by the tone control occurs at a frequency determined by the .027uf cap and 470R resistor.  If we bump up that cap to .039uf, the treble cut will be a bit more in full bass setting.  If we change nothing else about the stock circuit, when the control is rotated to full treble the boost will now occur starting around 8.6khz.  Bump the cap up to .047 and that now becomes 7.2khz.  That shift in where the midrange hump occurs comes along with what might be a more excessive muting of the treble in the full counterclockwise position.  To soften that somewhat, the simplest thing to do is to insert a small-ish value resistor between that end of the pot and the junction between the pot and + input of the opamp.  Something in the range of maybe 3k9 to 6k8 is probably about right.  This will have no effect on the max treble position.

[dlilly69]

Mark, this is AWESOME! Unfortunately, I can't get the schem link to work. Can I get the schem somewhere else?

I am looking for more treble roll-off on the treble knob.

Do you have any other suggestions to make the stock pedal sound a little better? The post above about diodes is helpful, but I am looking for some otehr suggestions.

Thanks so much for any help and advice!