Ibanez Sonic Distortion..mods and thoughts?

[jnee8871]

I just got the board off of G.G.G. I was thinking of trying a few things but I was hoping some of you have been there, done that.

I'd like to place a saturation control between the diodes and ground.

I'd like to use the idea of the AMZ presence control to get more midrange control. Since the tone control seems to be in the BMP family.

Anyone have any idea what the 22k resistor on the tonestack is doing?

Also one last not on General Guitar Gadgets there is a schematic of using the free half of the 4558 as a recovery stage. Has anyone tried this here and heard the tone....better ?

Thanks in advance for your input.

Jeff

[Mark Hammer]

1) It's 2k2 not 22k. If you have used 22k, no wonder you detect a distinct lack of midrange and bite!

2) The BMP-style tonestack (oddly named since it was around long before the BMP, but I guess more BMPs have been sold than other units using the same tonestack, so......) is essentially a parallel highpass and lowpass filter, with a panpot to blend between the outputs of the two filters. Typically, the filter corner frequencies are a little staggered so as to produce a slight dip or scoop in the midrange when the tone pot is set to midway. Ideally, at that midpoint, the outputs of the two filters are balanced, volume-wise. The 2k2 series resistor is part of what helps to set the relative-level balance.

By my calculations, C9/R12 gives a highpass rolloff starting around 867hz, and R8 gives a lowpass rolloff starting around 234hz. The various BMP schematics from different issues tend to have the scoop situated in different places, but also tend in some cases to have less of a pronounced midscoop than the SD-9 appears to have. For instance, the "Triangle" BMP has its lowpass and highpass rolloffs set at around 408hz and 1020hz. That's a just under 2-octave difference vs a just-over 1.25-octave difference. The BMP also positions the scoop zone higher. Clearly the SD-9 is setup for more of a "metal" sound with bass and upper treble made to sound bigger than the rest of the signal. If you want more midrange, I'd suggest changing C9 to .0033uf and making R11 a 10k linear pot used as a variable resistor. That will shift the rolloff of the highpass section down a bit to score more mids and let you adjust how hot the mids are. Alternatively, just swap out R11.

The saturation control is of dubious value in this application. the purpose of the design, after all, is to get LOTS of clipping (max gain = x603) and getting less just seems to be against its nature. On the other hand, if you want to be able to get a big push to the amp with less than max distortion, then I think your idea of using the spare op-amp for a gain recovery circuit is appropriate. The passive tonestack does eat up signal, which is why the BMP has a gain recovery stage after it. Turning down the gain to get less distortion will get you less output, obviously, so a gain recovery stage will let you take that subtlety and push the amp hard with it. The other advantage to be gained is that you can make the gain of the recovery stage variable and switchable, something we are seeing more and more of in commercial pedals these days. So, you could set the pedal itself for a default recovery gain of x3, have a preset boost to x6, set the drive for medium distortion and use a second stompswitch to go back and forth between steady and solo volume (recovery stage) settings.

[jnee8871]

Thank you

Thanks Mark

Actually I didn't use the 22k that was a typo in my note.

I guess I was really impressed with the saturation control on the Fulltone Distortion Pro. Then I saw the article on AMZ. However, i don't want to ever kill the distortion.

I have actually been playing with the tone stack calculator to get the midrange hump . I also was planning on messing witht the AMZ presence control to see if it was something i wanted or to find a different fix value I like.


Thanks for the feedback

[Mark Hammer]

The presence control may well be something you DO like. Just remember that where it adds can be just as important as its ability to vary the EQ curve. As noted, the BMP and SD-9 scoops are in different locations.

[jnee8871]

SD up and running

Hello

I got my SD up and running yesterday. I built it pretty much stock with a few minor tweeks.. I subbed a 2n2222a for the 2n3094. I had to adjust the bias etc. Mod wise I made two. I need to thank Jack O. for both. I used the warp control that allows you to pan between two different diode types. I used 914's and LED's. It works great! The other was I adjusted the tone control circuit and added a presence control. I didn't realize it a the time but I ended up using a very similar set of values to the Mid boost version on Jack's site, I was working with the TS calculator and sort of like how those values looked lol. I ended up pretty close to that but not exactly. Actually I intended to us a 50k for the presence but i got sort shipped and had to improvise with something I had until, I hope, the pot arrives.

Thanks Mark and thanks Jack. All the things I like about the Distortion Pro are in this thing....except I like it more.

[RDV]

Also one last not on General Guitar Gadgets there is a schematic of using the free half of the 4558 as a recovery stage. Has anyone tried this here and heard the tone....better ?

Thanks in advance for your input.

Jeff

Much louder. Helps hit the amp harder. I drew that myself but I could never get that pedal to sound the way I wanted it to.

RDV

[darthpoodle]

I know this is an old thread but I too have built the GGG version of this pedal. Mine is way too bass heavy and muddy/tubby. anyone have any ideas on how to tame the bass a little.

[Mark Hammer]

Using the GGG diagram as a reference, try swapping out C3 - presently shown as 22uf - for a much smaller value, like 2u2 or even 1u. C3 sets the low end rolloff in the gain stage, and presently applies the same gain above 15hz. By reducing the value of that cap, you will move the rolloff upwards such that less gain will be applied to content below the frequency you have selected. With 2u2, the gain rolloff starts around 154hz, and with C3=1u, the gain rolloff begins around 338hz.

Keep in mind that this is a rolloff, and NOT a "brick wall", so you will still have plenty of bass, just not as much of the lower bass. This has no impact on gain for higher frequency content, except that it become easier for mids and highs to clip when they are riding on a large amplitude low-frequency wave. If you fid that you simply don't get enough intensity out of the unit, you can try replacing the 250k gain/drive control with a 500k unit that has a 1M parallel resistor across it (making it a 333k pot).