Sonic Distortion SD9 Mods (GGG Version)

[otokomae]

Hi,
   I've just put together the GGG version of the SD9 (finally working after all my postings on this site!), and I was wondering if anyone's played around with it yet, or has any ideas?  
LOOK:  http://www.generalguitargadgets.com/diagrams/sonic_sc.gif

Specifically, I'm looking to increase the Volume of the pedal, but I'm really not sure where to start.  I also have been changing the resistor at R5 in order to get the Distortion to a more tolerable level (currently at 3.3K and sounding much better), but I was wondering if there was any other place in the schematic that I should try to affect the Distortion level.  I'm really trying to increase the volume output a little though, so any help there is truly appreciated.  Thanks!!!

[WGTP]

First think I would try, especially if your wanting less distortion and more volume is replacing the the 2 SI diodes with 4 SI's or with 2 LED's, or try combinations.  The higher the clipping threshold, the higher the output and less distortion.  

Also using a much smaller capacitor for C3, like 1uf or smaller should start rolling off some bass and reducing gain.  Try the diodes first.  Good Luck.  

[otokomae]

Hey, thanks for the excellent advice!!!  I tried a few combinations of different diodes (LEDs, 1n914s in series, 1n4001s in series, a 1n914 and a Germanium Diode in series), and decided that I get the best sound with an LED in the D2 position and the stock 1n914 in the D1.  So, for anyone looking to mod this pedal, I'm so far using the LED w/ the 1n914 in the clipping section, and a 3.3K resistor in the R5 position, and getting a great sound from it with everything else stock!  Thanks!!  Anybody else got any more advice?  Oh, and the volume problem is fixed.

[RDV]

http://www.generalguitargadgets.com/diagrams/rdv_sd9_sc.gif

RDV

[WGTP]

I noticed later that there was an unused op amp left over for a variety of purposes.  Again, you could add a couple of LED's in the loop of the volume recovery stag and change the 22k to 100k.   :twisted:

[RDV]

http://www.generalguitargadgets.com/diagrams/rdv_sd9_sc.gif
The .68uF caps could easily be 1uF or larger.
I've got both sizes for sale for cheap!

[otokomae]

Wow, that lasst one looks really cool, but I think splitting the IC like that is just a little too complicated for me right now.  It's already me taken 2 weeks just to get it working right!!!  Anyway, it does actually work now, and with the LED in the clipping section it sounds a lot better.  I found that when I play it on my regular amp, I don't really have any volume problems, either.  I was just on the little amp at home that I thought I needed more volume.  Thanks a lot everyone!!!

[otokomae]

I do have one more question for all the serious electronics people here.  Can anyone tell me why the Resistor at R5 has such an effect on the Distortion?  I mean, looking at the schematic, I guess that that resistor leaks different amounts of currrent to ground or something, depending on the size of the resisitor, but it was really kind of a guess that that raising that one resistor value would cut a little bit of the gain.  Can anyone give me a little bit of an explaination of how this works and why it effects the distortion signal that way?

Also, what do theVbb and Vcc things on the schematic mean?  What's the difference between Vcc and Vbb?

[WGTP]

It looks like someone knowledgeable isn't going to respond, so I'll take a shot at it.

If you understand that the feedback loop is negative (if your not this far into it yet, find some info about basic op amp operations) to the input, the less negative feedback that gets thru, the more gain there is.  Basically R5 "drains" the negative feedback off increasing the gain.  The lower R5 is, the higher the gain.  I have seen as little as 100 ohm used.  Some distortions use this as there gain control rather than a 100k to 1meg resistor across the feedback loop.  

The lower the resistor, the larger the capacitor following it has to be for the same low freq roll off.  For example:

10K and .1uf = 160hz
1K and 1uf = 160hz
100 and 10uf =160hz
5k and .1uf = 320hz
etc.

I'm not sure about the abbreviations, but basically you should have 9v, 1/2 or 4.5v and ground.  Not very technical, but hell I'm a guitar player.

I'm sure someone will correct me if I'm mistaken.  

[RDV]

IAlso, what do theVbb and Vcc things on the schematic mean?  What's the difference between Vcc and Vbb?

Vcc is the 9volt+ supply, and Vbb is the 4.5volt+ bias supply. WGTP's explanation of the feedback resistor was quite good I think.

RDV

[otokomae]

Ok, I think I'm getting it!!!  Now, I've already raised the Resistor R5 to a 3.3k,so, to control the distortion a little better, I should also raise the Cap c3, is that right?  Would a 47uf Cap do (I think I have an extra one of those)?  I'm really trying to smooth out the distortion here.  

I also read that lowering the 47uf caps would help smooth out the sound on this pedal.  I was thinking about swapping C6 and C3, making C6 a 22uf, and the C3 mentioned above a 47uf.  Can anyone give me an educated guess as to what that might do to the sound?  Thanks!!!

Also, big thanks to everyone who's posted on this thread so far!!!  You've all been a big help!!!

[WGTP]

I'm thinking you need a much smaller cap, like .1uf to .47uf. to roll off some bass and smooth things out.  

[Mark Hammer]

Why on earth are the components after the volume control needed?  Caps upstream do a nice job of removing any stray DC so the 0.1uf cap on the output is superfluous, and the 2M2 to ground is as well if you take the cap out.

My advice is tap your output directly from the wiper of the volume pot.

On the subject of the volume pot, you MIGHT get a little more output with a 100k pot in the stock circuit shown.  Just a guess.

As per usual, a quick read through the articles related to the BMP-style tone control over at AMZ (http://www.muzique.com) will be useful in identifying the optimal component values for your tonal needs.

Ricky Vance's suggested gain recovery stage is always good advice, and since its an easy perfboard build and, since most folks will have dual op-amps rather than singles in their parts bin, wise use of the "leftover" half of the chip.

Note that use of a gain recovery stage buys you a LOT more latitude in choice of clipping diodes.  The tone-control stage eats up signal because it works by selectively leaking signal to ground.  Enough that E-H sticks a recovery stage in after the tone control on a BMP (and so do other companies using similar tone-controls on other designs) to compensate.
If, however, you boost the signal after the tone control, then you can afford to care much less about how much signal level you lose via the diodes.  Where a pair or trio of Ge diodes would result in a discouragingly puny output level with the unmodified GGG circuit, following the tone control stage up by a second gain stage (and there is no reason why you couldn't pump up the gain on the second stage in Ricky Vance's version by changing the 22k resistor in the feedback loop of IC1b to 47k, 68k or even 100k) would bring the pleasing sizzle of Ge diode clipping up to respectable levels.

The other advantage of the recovery stage, as I'm fond of repeating ad nauseum, is that you can tamper with tone shaping.  So, a cap in parallel with the IC1b feedback resistor can tame hiss or even mellow out some of the fizz from over the top clipping.  If you want to go super nuts, stick another pair of clipping diodes (1N914 proibably optimal) in the feedback loop with the resistor and get yourself some swell double-clipping for even more audio stress.

In principle, the SD-9, the Boss DS-1, the DOD YGM308, and the MXR Distortion+ are all siblings from the same family.  The SD-9 and DS-1 have additional discrete gain stages up front, and tone controls after, but that's pretty much all that's different about them in the critical sense.  Feel free to generalize from what anyone has noted about modding any of those four to any of the others.