Modifying soft clip distortion module into a distortion for rock, metal

[contrataque7@gmail.com]

I bought this module in ebay thinking it was a full distortion but it turned out to be more of an overdrive. I want to know if it it posible to turn it into a versatile distortion. I would like it to resemble the distortion of a dual rectifier if possible. I made 2 guitar amps a 212 and a head using tda7293 poweramp  and a ne5335 pre amp boards each amp is 200w the only thing left is 1) turning this overdrive into a distortion 2) making the clean and distortion channels change with a footswitch (i got this one figured out im going to use relays) 3) a clear led iluminated faceplate 4) and maybe- haven't decided yet, an effects loop with footswitch control.

[GibsonGM]

Hi Contra, welcome.

If you can change out the 1M pot, VR1, for a 1K, you will get something very close to an MXR Distortion+ in sound, as this already IS a Dist+, basically!.  It is not full metal (check on Youtube) but will hit those diodes on h3ll of a lot harder than what the opamp is doing now.    You don't get hard distortion with the pot way down low in its last little bit?  A 1K lets you adjust inside that range much closer is all.

You might try putting the diodes on a switch to lift them, then you'll get clean (ish), but may have to again adjust feedback resistance to lower the output of the opamp to be closer to unity.    I would probably switch this whole module in/out, and have another for clean and use a relay as you mentioned....

[iainpunk]

Hey

Euhm, if it was up to me, is do several mods:

Replace the R2 (4.7k) with something a lot smaller (i think id go for 100 ohm)this increases the maximum amplification (gain) by 4,7 times.

Id replace one of the diodes with an red LED ( keep track of the polarity) this brings about a more pleasant distortion sound because of the asymmetric clipping (according to some it becomes more tube-like)

Replace C5 with a 102 (10nF) capacitor and replace R4 (10k) with an jumper to take out more bass and increase signal before distortion, since you want an more 'Mesa like' sound.

Before I end this post i want to compliment you on the look of your amp, im jealous. I making an amp my self and have chosen for a tweed-like look with a doom monster inside, but this almost makes me reconsider my decision on the aesthetics!

I wish you the best of luck with building your amp and hope I helped you

Iain

[GibsonGM]

You can play with the 4.7K if you want to, but my suggestion to change the pot to ground to 1K would "over-ride" any benefit that will do.   By the time you get to 4.7K (pot value of zero), you are already tweaking the opamp to hard that it cannot possibly give any more gain.    That's the 'beauty' of the Dist +, it is also causing the opamp to hard clip.

Non-inverting opamp gain is 1+ Rf/R2
Rf = 1Meg feedback resistor
R2 = 4.7k with your pot set to min

Gain = 1+ 1Meg/4.7k = 212.8,  which will clip the opamp; the 741 is being totally beat up at this point.  The 1M resistors also starve the bias. 

It would be very hard to make this into a Mesa-type sounding distortion, IMHO....you would want some real tone shaping.  Mid cut, fatten up the low end...and would thus require a couple more opamp stages, for active filters, to really "do it up".   

It's a Distortion +.     

The LEDs are a good idea, will increase the clipping threshold and sound gritty, which I personally like; I often use 2x in either direction, different colors for assymetry.  But the Ge diodes in there already will clip earlier and thus provide MORE of a 'metal' distortion that the OP asked for. 

Just my 2 cents, messing around with these circuits is always a good thing.  But they do have limits, it's a very simply clipper.   *shrug*

[iainpunk]

Hey,

Tho i appreciate what gibsonGM says about the 10k pot, the only thing thats going to do is decrease the range of available gain, not the maximum amount.

If you really want to go crazy, replace C3 with 150pf, this wil put gain on only the frequency's above 1 kHz (limited to 16x by C9) but this is only if you want it to sound over the top sharp/thin/harsh (just awful)

However, i'd still refer to my earlier post for what i actually recommend.

Iain

[GibsonGM]

Yes, the lower pot value would allow you to better 'dial in' within the range that the opamp is clipping.   With the 1Meg gain pot shown, you can DECREASE the gain more, moving toward more of a clean boost sorta thing.   When you get into clipping, you will have less control over it (with the 1M pot).   The value of the pot isn't that important.     

This is just an MXR Distortion +.   A gain stage with clipping diodes.  It's not rocket science, and it's really not a very versatile circuit.  1 trick pony....clipping stage, and set up in such a rough way the opamp also clips.    If you want REAL bass boost/mid scoop, one or more stages are going to need to be added to this. 

Yes, contra's got a very nice looking build, and with a bit more work he can get a big-ass, nasty, distortion for it.  Since he considers the Dist+ to be "just an overdrive", just seems like some more is going to be needed for him to be happy; like a BSIAB II or something.    Happy building. 

[duck_arse]

Hey
.....

Replace C5 with a 102 (10nF) capacitor and ,,,,, consider my decision on the aesthetics!

can't be both - pick one. 102 = 1,000pF = 1nF.
103 = 10,000pF = 10nF.

[iainpunk]

Hey
.....

Replace C5 with a 102 (10nF) capacitor and ,,,,, consider my decision on the aesthetics!

can't be both - pick one. 102 = 1,000pF = 1nF.
103 = 10,000pF = 10nF.

Indeed, i meant 1nF, not 10, im sorry

[contrataque7@gmail.com]

Ok lets forget about the mesa boogie/ bass mid scoop.
How can we just add more distortion so we can play metal or rock out of this module? I play metal and rock mostly but I like my distortions of the normal type I really dont like those type of mosquito attack, broken speaker, razor blade metal type distortions. I would like it to have a lots of distortion so i can play metal but not harsh sounding.

I made 2 channels each one with its own independent eq, one for the clean and one for distortion so I dont have to worry about the bass/ mid scoop. So what I need is lots of normal type distortion so I can play metal.

The module sounds like a soft distortion or overdrive, metal riffs can't be played with this, it is imposible even with the knob all the way up. I use this type of overdrive/ soft distortion for solos and effects as it makes them creamy and scream but i use a fx pedal for when I need this.

So the objective here is make it produce more distortion. How do we do this?

This is not important but the preamp is ne5532 not 5335 as I wrote earlier.

Thanks to GibsonGM and iainpunk for the fast response.

[ashcat_lt]

Gain = 1+ 1Meg/4.7k = 212.8...

That's not all that much really.  A Rat has 100K max in the feedback loop , and two legs on its "to ground" section.  One of those is 560, which is the same ratio as 5.6K in this circuit.  The other, though is 47.  Theoretically that's 10 times what this thing does.  Now you're talking distortion! 

[GibsonGM]

Gain = 1+ 1Meg/4.7k = 212.8...

That's not all that much really.  A Rat has 100K max in the feedback loop , and two legs on its "to ground" section.  One of those is 560, which is the same ratio as 5.6K in this circuit.  The other, though is 47.  Theoretically that's 10 times what this thing does.  Now you're talking distortion! 

Mmmm, yes! LOL.    But - if you were to squeeze much more out of a 741...won't you just get a fizzy farty crappy sounding POS instead of actual "Distortion"?    There is only so hard you can clip an opamp, AND hit those diodes, before you lose any touch sensitivity or dynamics...just thinking, maybe there IS more room to play there, but I don't see it!    You are amplifying your input signal 212 times!!  Good God, man!   LOL 

I wonder if something is wrong with the build. Every Dist + I've ever built offered up a lot more like "Godzilla" by BOC or some GnR tones, not "overdrive"...dude says "can't play rock", I am thinking this is NOT sounding right.     Esp with Ge diodes!   Should be hard enough as-is to get some rockin' done, if not shredding...

For future reference, if you want HARD with real TONE, one of the FET-based PREAMPS with tone shaping done in between gain stages might be exactly what you're looking for...just another opinion....doing your clipping in stages and playing with EQ between them tends to sound a lot better than trying to squeeze it out of one stage like this does.  I love the Dist +, for ROCK, but not 'textured' tones...

[thermionix]

D+ needs a cranked tube amp after it, no?

[GibsonGM]

Hard to say...yes, I use a tube amp, but even on very low vol. it was still pretty high-gain distortion due to the clipping diodes, and thus was not pushing the preamp tubes or anything...are you thinking Tube Screamer?  To me a TS doesn't do jack unless driving a tube amp.   

For the record, Gibson etc use the same sort of diode clipper in their SS amps to create their distortion...

Contra:  do you get a sound anything like the sounds this guy is getting?  https://www.youtube.com/watch?v=K7dMfGmoNCE

[amptramp]

Germanium diodes have a relatively soft clipping function.  You would need more gain for silicon, which would give harder clipping and even more than that for LED clipping.  To go with silicon, reduce R2 and increase C3 by the same ratio (a factor of 2 or slightly more would work nicely).  This would increase the gain so that you can clip at silicon voltages.

Having the same clipping diodes for positive and negative voltage means you have largely odd-order harmonic distortion.  Unequal diode materials will lead to more even order distortion which is usually considered to be better sound.

[contrataque7@gmail.com]

Contra:  do you get a sound anything like the sounds this guy is getting?  https://www.youtube.com/watch?v=K7dMfGmoNCE
[/quote]

They are the same, maybe the mrx dist + has a little bit more distortion than the module but they are almost the same. It is a mild distortion it works for rock but is not enough for metal /palm mute.

[ashcat_lt]

But - if you were to squeeze much more out of a 741...won't you just get a fizzy farty crappy sounding POS instead of actual "Distortion"?

I don't know anything about that particular opamp.  It might be one that latches up or inverts if asked to go too far past its limits.  ()

I know a Rat sounds like distortion to me.  I don't think it ever really gets up to 2000 times gain at any given frequency.  Like a TS, when the gain pot is cranked, most of the gain is in the upper mids, with progressive less both toward the top and toward the bottom.  That IS the difference between fuzz and distortion.  But the max gain on the curve is still significantly more than a Dist+.  Somewhere in the high 900s IIRC.

I know I've used something similar to the Rat circuit with a number of different opamps - TL080, 07x, LM324, and it's worked really well from crunch all the way up to metal and through stoner/doom depending on the tone shaping in and around it.

I also know that LEDS means you need even more gain to get the same amount of distortion, so that's kind of going the wrong way assuming that actual output level is not a factor.  If you want to push the amp harder, switch to LEDS, but if you want more distortion out of this thing itself, leave them as they are or swap them for something smaller like a Shottkey or germ. 

The OP wants more distortion, so they need more gain.  We can worry about the tone shaping part (which is really more important than anything else in the way it ends up sounding) once we get that far.  So, let's make that 4.7K resistor a lot smaller and see what happens. 

[thermionix]

are you thinking Tube Screamer?

Always, but the D+ likes it too.  Maybe with the dist knob down some.  Rat can be a mildly dirty "OD" as well.

[stonerbox]

They are the same, maybe the mrx dist + has a little bit more distortion than the module but they are almost the same. It is a mild distortion it works for rock but is not enough for metal /palm mute.

That MXR sound terrible... In order to get what you are after (palmchugging, more distortion and not too harsh) you need to do quite a bit of work with this thing. It needs pre and post filtering of highs and lows, it needs more stages that can crunch the signal. You also probably would want an EQ somewhere in there.

I am sorry, but I believe you would have more luck just building something from scratch instead of modding that one. Check out some of the very heavy and smooth sounding amp clones around here that uses FETs for tubes. I designed one not so long ago (Green Mujina) and it does the palm mutes and smooth but over the top distortion very nice. Maybe that particular project is a little too big so I suggest you check out the Orange amp FET-clones too. Good luck!

[GibsonGM]

Contra:  do you get a sound anything like the sounds this guy is getting?  https://www.youtube.com/watch?v=K7dMfGmoNCE

They are the same, maybe the mrx dist + has a little bit more distortion than the module but they are almost the same. It is a mild distortion it works for rock but is not enough for metal /palm mute.
[/quote]

Yeah, I also think you should find another distortion for the music that you want to use this for!   The distortion is doing what it's supposed to as-is.  You probably would use your time better to build a multi-stage 'thing' with the mid scoop and things you want!   Stoner already said it...FET-based sound really good.      It's very hard to get a good distortion from ONE gain stage...

Thermionix - sure, anything that boosts is good for a tube amp!

[Ice-9]

You should double check the schematics posted to the actual module, while it may be very similar to the D+ there is one very obvious thing that stick out in the module picture that says it differs. A DUAL GANG POT, which way is that wired up ?