SD1 mods (with Fet input buffer)

[nooneknows]

I've never liked so much standard Boss SD-1. It has a good basic sound but the lack of clarity is a big drawback.
I implemented the various SD-1 modifications I read in this forum. After all the mods I ended up in a very very good sounding overdrive, clear, with tight low-end but still not too fat to cause bass troubles to an already pushed Fender amp for example.
I changed the input buffer using a fet (raising a lot the input impedance), changed most of the signal path caps, shifted a bit the rolloff frequency of the HP filter on the dist section feedback, changed the opamp, add some TS9 features.
That's the list of mods I've done, I think you already know them (apart the fet stuff) but it's a nice sum up, I hope they will be useful for someone, first the new value, between brackets the older one:

C1  0.1 uF metal film  (.047 uF)
R2  2.2M (470K)
Q5  2n5457 (2sc2240) - check out the pinout, it's different, you have to 'switch' source with drain to fit the existing holes  
C2  0.1 uF metal film  (.018 uF)
C3  0.1 uF metal film  (.047 uF)
C6  Eliminated (0.01 uF)
C7  1 uF tantalum (1 uF elect.)
C8  0.1 uF metal film  (.047 uF)
C9  0.1 uF metal film  (.047 uF)
R16 100 (1K)
C10  1 uF tantalum (1 uF elect.)
R17 10K (100K)
U1  TL072 (RC4558DD)

add a 47pF ceramic cap accross D4 (I put it copper side)

bye,
Marcello

[Rich G.]

Nice!

I have an SD-1 I'm thinking about modding.  Do you have any before/after sound clips?

[nooneknows]

hi,
unfortunately I don't . I hadn't dopne all the mods in once and in the beginnings I didn't think about recording any sample...
I have to find an original SD1 from some friend of mine... :)

[stm]

Thanks for sharing this info!  

I built an SD-1 a year ago and liked the sound, but wasn't fully satisfied with it and so this pedal is standing somewhere in a closet.  I will try your changes during this weekend to see what comes out. I will try to record samples of the "before" and "after" sounds, if possible.

By the way, did you check sound differences between symmetric and assymmetric clipping (i.e. 2+1 and 1+1 diodes)?  I've read that many people likes better the TS rather than the SD. In fact, perhaps it seems that the "exclusive patented assymmetric overdrive circuit" used on Boss OD's is not necessarily the key for good overdrive sound.

1) I invite other people that have tried the symmetric/assymetric clipping mod to state their opinions. I didn't notice much difference, except for a slight level increase when using one more diode.

2) Also, I tried a Texas Instruments TL072 and a NOS JRC4558D ordered from Small Bear Elec, but didn't notice any change in sound ?! What about you?

Cheers.

[ildar]

I've actually daisy-chained 2 Ge didoes in D6-not sure if this comes out symmetrical or asymmetrical, but the sound is very nice-smooth and tubey. I think the key here may be the combination of Si and Ge diodes. In my Sd1 I have a RC4559P right now, which I like. It seems more responsive than either the TL072 or the JRC4558D, both of which I've tried. However, I just got a TI OPA2134PA that I'm going to try.
Also, instead of the 1uf tantalums, try the equivalent box-type film caps. Much more clarity.
Incidentally, what's the advantage of a FET buffer in this circuit?

[MartyMart]

Nice ideas guys, I've modded a few SD-1's and prefer the mods to TS-9 or 808 specs, the SD-1 is almost an 808 anyway, apart from symetrical / asymetrical clipping.
Here's a couple of nice additions:

Swop D4 and D5 for a single 1N4001 or a pair ( 1N4002 also works )
Change D6 for a 3mm LED or germanium diode, LED has more "Raunch" to it. or leave it out all together!.
R6 change to 2.4k
R30 change to 1k for brighter LED.
100pf silver mica across D4-D5 smooths things out a little.
Thats about it so far,
Enjoy.

[timrand]

Hey

I have been tweaking this pedal for a while lately. The C6 cap removed definately takes the cushion in front of the speaker effect away.

I have found that the assymetrical clipping I like better but I recently added 51pf cap across the diodes and found it smoothed out the sound.

Replaced .027 C5 with .047 metal film

However I am still finding the unit to honky

[ildar]

If C6 is removed, should it be jumpered? Probably a stupid question, but....

[timrand]

just cut it out

[cd]

What schematic are you guys using in reference to the R1, C6, etc?  Or is it on the PCB itself?

[ildar]

Trannies and diodes are labelled on the board.
Schem is here: http://fuzzcentral.tripod.com/sd1/SD1.gif

[nooneknows]

Hi,
I prefer an asymmetrical clipping, It sounds a bit richer to my hear.
I introduced a FET input and a TL072 because I think a higher input impedance permits a better overall clarity and more focused basses.  
I really don't know how much psycoacoustic and self induction can influence me, but I'm quite sure I heard some significant difference in the sound.
However it's just a matter of taste, have a try with these mods and let me know....
bye

[nooneknows]

I added a few things, now I like it even better:

R6  3K3   (original  4k/)
D6 1n34A (1n4148)

D6 is a 'classic' R.Keeley mod , I have to say it sounds good.
R6 shift the rolloff on the bass on about 450 Hz and I think it's a good balance, nice basses and reduced crossover distorsion

bye

[drew foppe]

Okay, here is my question for the SD-1 and TS-9 enthusiasts...

I want to install a switch so I can go back and forth between assymetrical and symmetrical style clipping of the Boss SD-1. So far, I have installed a switch to switch between .1 and .047 capacitors to compensate tele/les paul. It is a very nice and easy mod to do. I installed the switch and ran the wires to C3 on the board. I have also done most of the mods on the Fuzz Central site. It is currently one great sounding pedal.

I REALLY DO want to be able to switch between Boss/Ibanez style clipping in this pedal because I have 3 of the DS-1's on my pedal board. One for mild overdrive, one for gritty gain and the last one to boost the other two.

If anyone can help me with instructions on how to do this I would truly appreciate it!!! Boss and Ibanez in one pedal is my goal...or at least as close as possible...you know, best of both worlds.

And yes, I like to have my cake and eat it too!  :wink:

[cd]

Install a switch to short out one of the clipping diodes on the side that has 2 of them.  That's all.

[drew foppe]

Would I need a DPDT switch for this? Also, on the board D4, D5, and D6 are all together. Can I just short any one of these to create the symmetrical clipping?

[cd]

You can use a SPST toggle.  Don't short D4, only D5 **OR** D6.

[Phorhas]

From my experiance, it's dosen't change the sound noticably. if' you you put a 1n914 (or 1n400x) diode back to bak with an LED - around, big sound.

the MOSFET + Doide should be interesting as well