Another SD-1 Question

Okay,

So what will it take to smooth out the 'sizzly' treble frequencies
and\or make the tone control more effective?

I've tried replacing all clipping diodes with 1N400x (helps quite a bit, but not enough)

I've also replaced C6 with a lower value cap (.0047) as opposed to eliminating that part altogether.

And I've toyed around with C5, to no worthy effect.

Any ideas?

Thanks!

IMO, C2 (.018uF) should be bumped up, because it's really pinching the eq spectrum after the input buffer tranny. Don't be afraid to "go big" - TS type pedals are typically 1uF in this slot.

C8 (.047) also pinches just a tad on the back end. Standard size here is .1uF in other pedals.

It really helps to bypass (i.e. piggyback) D4 with a small cap - usually 100pF to 150pF. This should really smooth things out.

To kill some more top end at the tone control, you have a few options. Probably the easiest would be to slightly increase R7 (10K). And just as easy would be to bump up C4 (.018uF) or C5 (.027uF), but don't increase both at the same time. C4 is fixed, C5 is variable.

I always yank C6, and only put something in it's place if I'm doing some intensive mods, like bumping R9 up to 22K or higher.

And obviously changing the HP filter frequency at R6/C3 will help as well - if you shift it down slightly, you won't lose all of the mid hump, and some of the emphasis will be taken away from the higher frequencies. Just bump up C3 slightly to keep the gain the same - .056uF is not too bad. Or increase R6 slightly - you'll lose just a touch of gain, but shift the HP filter down a bit. 5.1K to 5.6K seem to work pretty well.

11G,

You never disappoint. I've asked that question elsewhere, and to some pretty knowledgable folks, and I've never received such a clear, direct and specific answer before.

At last! Info I can use

Thank you very much!

As soon as I get moved and unpacked I have three SD-1's that are going "under the knife"

IMO, C2 (.018uF) should be bumped up, because it's really pinching the eq spectrum after the input buffer tranny. Don't be afraid to "go big" - TS type pedals are typically 1uF in this slot.

Okay, so I'm finally getting around to all your suggestions in this post.

I've tried several of these. But my question about C2 is this - Will increasing C2 increase the amount of pre-clipping bass frequencies?

Thanks.

Okay, so I'm finally getting around to all your suggestions in this post.

I've tried several of these. But my question about C2 is this - Will increasing C2 increase the amount of pre-clipping bass frequencies?

Thanks.

It just basically bandpasses the full spectrum after the input buffer. Since that buffer is running at unity gain, it isn't really boosting anything. You could actually make it bigger than 1uF, but it has a negligible effect at sizes beyond that.

The high pass filter is the combination of R6 and C6. Increasing either one will lessen the amount of bass that is cut. But of course increasing R6 will also decrease the available amount of gain.

Thanks for the info 11G.

The thinking behind the question was really "How do I avoid increasing pre-clipping bass frequencies?" I thought it was increasing C2 or C3 that did this. I wanted to avoid this.

But since you mentioned it - Does C6 affect the bass frequencies post-clipping?

It just basically bandpasses the full spectrum after the input buffer. Since that buffer is running at unity gain, it isn't really boosting anything. You could actually make it bigger than 1uF, but it has a negligible effect at sizes beyond that.

The high pass filter is the combination of R6 and C6. Increasing either one will lessen the amount of bass that is cut. But of course increasing R6 will also decrease the available amount of gain.

I'm not following you...
Do you mean c6 and r9?
http://www.indyguitarist.com/schematics/boss/SD1PG2.JPG

If so, that isn't a high pass filter - it's a low pass shelf - it's cutting highs. That's why removing (or making smaller) c6 works to provide clarity and a different tone control spectrum.

C2 will just allow full frequencies to get boosted and clipped if it is made larger - however, the real change is r6 and c3. Stock, is is boosting and clipping right around 723hz or so. Change either r6 and/or c3 for different frequencies (http://www.indyguitarist.com/filter.htm for an easy calculator).

In other words, if you want more bottom end, make c3 larger (r6 the same) for a bit more bass PRE-clipping... however, if you want it AFTER clipping there isn't anything that's going to give you a ton of bass without adding circuitry. Change c8 (raise value) if you want more bottom end post clipping, but the change is going to be very subtle.

Brian

Mr. Wampler,

Thank you for the reply. Actually NO, I'm not wanting to boost the bass. I'm wanting to AVOID doing so. And consequently, I'm leery of increasing C2 because too much bass pre-clipping makes for a fuzzy sound with TS type circuits. Going back to the original point of this thread, WHAT I'M TRYING TO ACCOMPLISH IS TO GET A VERY SMOOTH OVERDRIVE FROM THE SD-1.

I'm not following you...
Do you mean c6 and r9?

No - I meant R6/C3 as the HP filter, shelving it at ~740 Hz, a la TS, et al...

I tend to reply to these things when I'm a bit sleep deprived (which is just about always, these days):wink:.

I personally like to shift the HP filtering down to around 450-500 Hz, and don't like to add any add'l gain. So I'll typically go with .068uF for C3, but I could see how many folks would probably be content with something more subtle, like .056uF.

I already touched on R6/C3 here, with a bit more lucidity:

And obviously changing the HP filter frequency at R6/C3 will help as well - if you shift it down slightly, you won't lose all of the mid hump, and some of the emphasis will be taken away from the higher frequencies. Just bump up C3 slightly to keep the gain the same - .056uF is not too bad. Or increase R6 slightly - you'll lose just a touch of gain, but shift the HP filter down a bit. 5.1K to 5.6K seem to work pretty well.

No - I meant R6/C3 as the HP filter, shelving it at ~740 Hz, a la TS, et al...

I tend to reply to these things when I'm a bit sleep deprived (which is just about always, these days):wink:.

I personally like to shift the HP filtering down to around 450-500 Hz, and don't like to add any add'l gain. So I'll typically go with .068uF for C3, but I could see how many folks would probably be content with something more subtle, like .056uF.

Gotcha ;)
I personally like about 400hz or so as well personally.
For extra fun, stick in a jfet gain stage on the end of the overdrive circuit and it adds quite a bit to the tone - more thickness yet a bit smoother. Of course it'll be quite a bit louder too. :mrgreen:

bw