ROSS distortion->SD9

[aron]

The SD9 is basically an op amp driving diodes like an MXR dist+. However it does have a tone control after the clipping.

http://www.muzique.com/schem/sonic.gif

The ROSS distortion is similar:

http://www.home-wrecker.com/ross_distortion_black.png

So I'm thinking that I might graft on the SD9 tone onto my ROSS distortion.

http://diystompboxes.com/pedals/photos/SD9tone.jpg

I think it might work.

[Ed G.]

I used to have an SD9 years ago, a real nice sounding unit from what I remember.
The tone control looks like a BMP tone stack with different values.

[aron]

I built the SD9 before but I don't know where the board is. I never use my Ross Distortion so I figure I might as well tack on the tone control.

[Mark Hammer]

The asymmetrical diode arrangement of the Ross will be helpful in compensating for the passive bleed through the tone circuit.

[aron]

Well it took me this long to do this simple project. I test it today.

[Mark Hammer]

here's a wacky idea that occurred to me.  Imagine you had a pot wired up such that the diodes went to the pot wiper.  One outside pot lug goes to ground, and the other goes to the junction of C5/RV2.  A medium-value fixed resistor (let's say 10k-22k) is placed in series between R5 and the C5/RV2 junction.  The value of C5 might need to be changed since the lowpass corner frequency is now set by C5 and R5 plus the added resistor.

Rotate the pot in one direction and the diodes are tied to ground (or almost ground), with a large resistance to ground in parallel.  Rotate the pot in the other direction, though, and now the resistance between the diodes and ground gets big while the resistance between the diodes and the output level pot gets small enough that the diodes present a more efficient path for the signal to pass.  Voila, a single pot that sweeps from amplitude clipping to crossover distortion and clipping of the side of the wave.

Whattya think?

[slacker]

Whattya think?

I like it.

[Mark Hammer]

Well, my wife is off for a week tomorrow morning, so I think this bachelor is going to try it out and see.

I suspect that pot tapering (via parallel resistors) will make a huge difference in whether such a control provides added value beyond the two extreme rotation points.  I suppose the alternative is to ignore use of a pot and simply use a toggle to flip the ground side of the diodes to the output pot.

I modded a Gretsch Controfuzz clone to combine diode clipping and crossover distortion, and I have to say I like what x-over distortion adds.  Sounds great on bridge humbucker pickups.  And because series diodes do not remove anything from the signal amplitude, the cool thing is that a person could use the 2+1 diode complement to ground and a pair of series diodes, if they felt like it.

[aron]

Sounds like a cool idea. What does crossover distortion sound like with 2 diodes? Is it musically interesting?
BTW: the SD9 tone mod sounds GREAT!!!!!!!! I'm putting this distortion on my smaller board.

[Mark Hammer]

What does crossover distortion sound like with 2 diodes? Is it musically interesting?

Not sure what you mean.  Do you mean a 2+2 combo in series?

[aron]

I posted after you posted. I guess you like the sound of diode crossover distortion.

[Mark Hammer]

It's not "better" than the traditional, but it is musically useful, as you term it, and can produce a nice change of pace/character without being outlandishly or jarringly different.  Note that combinations of crossover distortion and clipping are used in the Boss HM-2 pedal.  That's not to give x-over distortion some sort of annointment or blessing, but given how much Boss aims for the happy medium, you can assume that it won't be "out there".

[Tonemonger]

I thought that the Ross cct looked familiar and it IS exactly the 1st half of the Ibanez overdrive II that appeared here recently.

[aron]

I'm not sure I like asymmetrical distortion. I have experimented with it and I like a _little_ but not too much. I don't like the intermodulation that it gives.

[Electron Tornado]

I just tested a circuit similar to the SD9, but I used a 741 (so no input buffer), a modified BMP tone control, and a single transistor amp stage at the end. I thought it sounded a bit flat and lacked sustain, so I'm going to use a 4558 and try something in between the SD9 and a tube screamer.

Mark, the crossover distortion idea sounds interesting, so I'll have to try that. Did you use 1N34 diodes or did you try others?

Aron, when you added the SD9 tone control to the Ross, did you add an amplifier stage after it?

[Mark Hammer]

Mark, the crossover distortion idea sounds interesting, so I'll have to try that. Did you use 1N34 diodes or did you try others?

I believe I used a pair of 1N34 diodes.  It wasn't out of any affinity for their "sound", but rather because I needed a lower forward voltage.  Looking at the Controfuzz schematic here - http://www.beavisaudio.com/bboard/projects/bbp_Gretsch_Controfuzz_Rev1_1.pdf - you can see a 220k resistor in series with the distortion amount pot.  I dropped that 220k to a smaller value (I forget what value, but smaller), and stuck in a back-to-back pair of 1N34s in series with a 500k pot.  I placed that in parallel with the reduced R6.  With the 500k pot maxed, the signal goes through R6, and will be limited in amplitude by D1/D2.  Lowering the value of the pot in series with the  Ge diodes provides an alternate path for the signal, provided the forward voltage of the diodes is not too great, and the series resistance is not too high.  This lets me adjust the value of R3 (10k) to drop the gain and minimize clipping by D1/D2, but still get crossover distortion via the added GE diodes...if I want.

The unit provides an interesting array of sounds using 4 knobs: Drive (variable R3 - try 50k in series with 2k2), x-over amount (as described) overall distortion amount/blend, and output level.    You can do the original Controfuzz sounds with it, plus it functions as an ersatz Sparkle Drive, by being able to blend clean with lighter distortion.

Sorry to hijack, Aron.   However, there are many different instances where one can insert a x-over distortion option.  This is one of them, and so is the SD9, the MXR dist+, DOD250, etc, etc.

For asymmetrical distortion, I would recommend something like a 1+1 pair and a variable resistance in series with 1 of the diodes, as opposed to a simple 2+1 diode complement.  Variable "warp" (TM JackOrman  ) can be very useful.

[aron]

>Aron, when you added the SD9 tone control to the Ross, did you add an amplifier stage after it?

No, it didn't need it. It sounds good but I find the Ross distortion rough sounding overall, but in this case, I might just leave it. I have enough smooth sounding pedals and it's nice to have one that's somewhat ragged.

I have a cheap Arion Tubulator that I might mod. It's a tube screamer and it exhibits all the traits of tube screamers that I don't like. Lack of bass, lack of highs.  I may give it a little more bass and maybe lift the .22 going to ground after first op amp stage.

[aron]

Just a follow up, I am really liking this pedal (Ross->SD9 tone). I have it in my "small" pedalboard and it gets a cool rock vibe along with my Dynacomp at the front. It really fattens up the guitar and gives it a new kind of vibe.

[tehfunk]

Just a follow up, I am really liking this pedal (Ross->SD9 tone). I have it in my "small" pedalboard and it gets a cool rock vibe along with my Dynacomp at the front. It really fattens up the guitar and gives it a new kind of vibe.

Thanks for the input; i'll have to try it. I was about to build a ross distortion, as i had the board made already, and this should make it more fun.

[aron]

Just an update on this pedal, man I really like it as I play it more and more. The beauty of this pedal is that it's the first one that I can really make my amp a lot brighter for a brighter strat sound and then kick this pedal in for kind of a grinding sound (with volume turned down) to full on sustained leads. My friend thought it sounded like Eric Johnson's smooth lead sound when I turn my guitar full on.

I have an MXR Dyna Comp in front with the compression down, but the level up - like Steve Kahn did in the 70s.

Just really fun to play!