Question About Gain Mod for Boss SD-1 (& Now Question's About Keeley Mods)

[SECONDandBOWERY]

I'm thinking about trying a mod on my Boss SD-1 and I just had a question before I decide whether its what I'm looking for or not.  The mod is as follows:
R6 4K7 -> 470 Ohm 
C3 47nF -> 470nF   (680nF or 1uF if you need more bass)
You will get 10 times more gain.
Now, the mod says that I will get ten times more gain.  Is the gain the only aspect of the sound that is changed?  For example, if I performed the mod and then turned the drive knob one-tenth of the way up (or around one-tenth since the taper of the pot might not be perfect), would it sound like a stock SD-1?

Thanks in Advance!

Rock'n'Roll,
--Andy

[wampcat1]

No, basically what you are doing is affecting the frequencies in the clipping stage so the tonality is definately different. In fact, with the sd-1 you definately will encounter bypass bleed through (easy fix for that though), and possible oscillation problems. I would try 1k/.22uf first, then if you want more, go to 470 ohm/ .47uf or .33uf if it is getting really muddy sounding.

Hope that helps!

bw

[SECONDandBOWERY]

Hmm... is there any way to increase the gain without changing the tonality?

I really like the way this pedal sounds, I just wish I could eek some more gain out of it.

Rock'n'Roll,
--Andy

[rockgardenlove]

Different diodes?  There are some mods on the stompboxmods.com site, link in sig(the image).
Maybe LED's?

[wampcat1]

Hmm... is there any way to increase the gain without changing the tonality?

I really like the way this pedal sounds, I just wish I could eek some more gain out of it.

Rock'n'Roll,
--Andy

Well, you may like the above changes I mentioned, it shouldn't drastically change the tone or anything. But, if you are looking for an easy way,  run a clean boost before the sd-1 that way more of the signal is clipped.

bw

[SECONDandBOWERY]

Thanks rockgardenlove!  First off, i'd never seen that website, so thanks for making me aware of it.  Secondly, it's not that i doubt you, but i didn't know that the diodes could affect the amout of gain - i thought they only affected how the clipping occured/sounded.  Then again, if changing the stock diodes to LEDs will create the illusion of more gain by producing harsher/more distortion, then i'll have to try it!

Can anyone explain to me the technical side of what will happen if i change to LEDs?  In other words, will i just be creating more distortion, or will there actually be more gain?

Secondly, will the LEDs change the tone more, less, or about the same as the previous mod that i asked about?

wampcat1: You say that the change in tone with the orignal mod is posted is not drastic.  Exactly how minute is the change.  Are we talking about changes that only people with golden ears will be able to pick up on, or will it be noticable enough so that anyone could tell the difference but still minute enough to keep the tone close to the original?  Sorry if that was wordy and hard to follow, i just didn't know how else to word it.

[rockgardenlove]

Oh sorry, I always associate gain with distortion(Fender amps you know.)

You could always try putting resisitors in series with the diodes, that would help too I think.  That would cut down on distortion though, I'm pretty sure.
Sorry, its all my newb mind could come up with


As for that site, its actually one I'm hosting...I just didn't mention that, because I don't like self promoting, but the link needs to be spread a bit you know...its never gonna get anywhere if noone sees it.  We need more mods in the database too.  I just thought I'd post it because its got Brian's(wampcat) SD-1 bypass mod.

[SECONDandBOWERY]

It's ok - i'm a big fan of the blackface twins, deluxes, and supers.

I mean, if LEDs will give me more distortion (which is my final goal) then i'll try it.  I guess i shouldn't have beaten around the bush.  I wanted more gain so that there would be more distortion - it looks like i have the same problem as you!

There are lots of mods for the SD-1 i've seen that you might want to post on your site.  Search this forum for SD-1 Mods and you'll find a whole lot of them!  At one point i compiled them all (including the Keely mods, Fulldrive mods, and everything from every forum i could find) into a word document, but my computer crashed.

Rock'n'Roll,
--Andy

[wampcat1]

It's ok - i'm a big fan of the blackface twins, deluxes, and supers.

I mean, if LEDs will give me more distortion (which is my final goal) then i'll try it.  I guess i shouldn't have beaten around the bush.  I wanted more gain so that there would be more distortion - it looks like i have the same problem as you!

There are lots of mods for the SD-1 i've seen that you might want to post on your site.  Search this forum for SD-1 Mods and you'll find a whole lot of them!  At one point i compiled them all (including the Keely mods, Fulldrive mods, and everything from every forum i could find) into a word document, but my computer crashed.

Rock'n'Roll,
--Andy

LED'S won't give it more gain (meaning drive), but it will give it more volume. The diodes can affect the amount of distortion a bit, though not as much as changing the values that we are talking about (I *think* it's c3 and r6 on the sd-1, IIRC).

As far as how much...it TOTALLY depends on the person and their ears. I think most of us on this board spend so much time listening to the little intricacies of each little change we make that our ears are probably more sensitive to it. Many guitarists may not hear much of a change and think that is sounds 'more distorted'. You could always try it and keep the old parts to see what you think and that'll give you a chance to change it back if you wish.

Thanks,
Brian

[tubewhimper]

You can change the stock resistor at R9 (in the feedback loop of the tone-recovery stage) from the stock value of 10K to 100K.  I usually change this value to 47K to 150K to generate more gain without affecting the distortion character.  Be aware that depending on which chip you may be using... you might 'enhance' the noise level as well.  I just put a 47K into the R9 position for a pedal that my brother is using and it did not increase the noise at all from what I could tell.

[Gus]

Why do you want to mod this effect?

I am being serious.  This boss effect seems to be at it best at stage volume.

Bedroom practice volume maybe does not sound that great
but the stock parts with the stock gain setup and at stage volume it can sound good.

[Mark Hammer]

Some people like the way a unit like that pushes their amp, but they may need it to push their particular amp a little harder.  The 3-diode arrangement in the SD-1 results in a little more dynamics being preserved in the signal.  In many respects, if that is the sound you like, then nothing should be tampered with in the gain structure prior to the tone control.  Any changes or additions to the circuit ought to be done on the output of the pedal such that gain is applied to a tone already established.  If you look at the schematic ( http://www.freeinfosociety.com/electronics/schemview.php?id=169 ), the easiest place to apply "clean gain" would be on the transistor output stage (the 2SC732 on the bottom right).  The problem with this, however, is that it applies gain to both the effect AND the bypass signal, which may not be what you want.

S, perhaps another better place might be to increase the feedback resistor in the tone control stage.  It is currently 10k, so try 22k with a .0047uf cap instead of the .01 cap that's there.

[Gus]

I should be clearer

I was wondering if people acually use the effect at a stage volume before doing a mod to it.

The stock SD -1 seems to be setup well for stage volume stock IMO.

[vanhansen]

I took mine and did several mods to it, including changing the opamp, but the latest change I did was to the clipping diodes.  All three were changed to 1N4001's.  It still has that great SD-1 overdrive, just warmer.

[SECONDandBOWERY]

Gus:  I want to mod it because even though I love the way it sounds and feels, I want it to be able to distort a little more and maybe even push my amp a little harder.

Mark Hammer:  I'm looking for more 'dirty gain' than 'cean gain'.

Thanks for your suggestions, everyone!  But now I'm starting to think that I might just do the Keeley mods for the SD-1.  What's the general consensus on the Keeley mods?  Does anyone have any sound clips of a Keeley modded SD-1, or even a sound clip of the modded SD-1 being compared to a stock SD-1?

Thanks!

Rock'n'Roll,
--Andy

[wampcat1]

Gus:  I want to mod it because even though I love the way it sounds and feels, I want it to be able to distort a little more and maybe even push my amp a little harder.

Mark Hammer:  I'm looking for more 'dirty gain' than 'cean gain'.

Thanks for your suggestions, everyone!  But now I'm starting to think that I might just do the Keeley mods for the SD-1.  What's the general consensus on the Keeley mods?  Does anyone have any sound clips of a Keeley modded SD-1, or even a sound clip of the modded SD-1 being compared to a stock SD-1?

Thanks!

Rock'n'Roll,
--Andy

The keeley mods change the tonality quite a bit. You may/may not like them, only one way to find out.

[hairyandy]

Gus,

I have a newish, used SD-1 that I just bought two weeks ago at my local Music-Go-Round for about $35.  I remember back in high-school (mid-to-late-80's for me) when Boss came out with the "Turbo Overdrive" and I thought it was the best thing since sliced bread.  It was great through both my Marshall JMP 50-watt and through my Roland JC-120 at the time.  I wish I still had it!  This newish SD-1 though is really different.  Regardless of my playing volume, I get the sense that some of the clean signal is being let through with the overdriven signal and it's driving me nuts.  Actually it sounds pretty horrible to me, nowhere near as good an overdrive as my Fulldrive2, self-modded TS-9 or my stock, original issue Rat.  I bought this thing with the intention of modding it, but also knowing that every other Boss pedal I've ever owned has been more or less "usable" in it's stock state.  This SD-1 is the first Boss pedal that I've ever owned that I can honestly say sucks stock!  I was surprised, shocked and disappointed, but now I'm gonna mod the hell out of it and hope that it will sound better.  If not, back on the Music-Go-Round it goes...

My $.02,

[MartyMart]

Remove D6 and replace one other with a single 1N4001
That sounds "the biz" to me.
I didn't really like any other "gain/tonal" changes so thats all back to "stock"
Takes 5 mins .....

2C's

MM.

[Gus]

Andy

  Interesting post.  It sounds like you used one.  If the new one sound different the first place I would check are the power supply elctros then NP electros and the output electro.

  This bleed issue sounds like the fets being at the edge of working correctly in the switching circuit(as others have posted),  I tried to read all the bleed posts I could find here.  Fets can be a pain to work with because unlike BJTs it is harder to design around the variations in specs.

The mute is a bandaid IMO

Has anyone tried a realy good power supply decoupling cap and voltage spiltter decoupling cap?

  I have not seen this in the posts.

  Use a good brand LOW ESR ones

The signal goes thru the power supply the power supply is a part of the circuit.  At high enought gain you might hear bleed.

If any of you work in the repair world you might have seen the bad chemistry elecros that got/get used in building PC motherboards.