MXR Dist + with tone stack

[jtkiv]

my 1st project is electrically finished (now just working on the enclosure), so i decided to choose the next victim.

I plan on making the "MXR Distortion +" pedal, but would like to add a 3-band EQ to it, 1. so i can use it, 2. to make the project more challenging (therby learning more).

I made this up using gEDA Schematic Editor (awesome program for the linux guys)



sorry its kinda big...

either way, does this look like a decent/profitable addition to the MXR?  the arrow near the mid-right-top marks the end of the Dist +circuit (before it hits the DPDT switch)

pdf http://cid-74ef76ee56094dfe.office.live.com/self.aspx/Public/mxrdist-3eq.pdf
png http://cid-74ef76ee56094dfe.office.live.com/self.aspx/Public/mxrdist-3eq.png
sch http://cid-74ef76ee56094dfe.office.live.com/self.aspx/Public/mxrdist-3eq.sch

.pdf is really small (3kB bigger than the .png  ) - .sch is for gEDA

[igerup]

Interesting. Very interesting.

[earthtonesaudio]

Just a suggestion:

An 8-pin DIP single op-amp takes up the same space as an 8-pin DIP dual op-amp.  You could add a unity gain buffer at the output for better output impedance and only have to change the layout slightly.

[MmmPedals]

Your not gonna have very much output after the tonestack. You should add a recovery stage.

[petemoore]

  Dist+ +Treble Rolloff.
  100k gain knob [the lions share of 500k is 'wasted'...or not, 100k covers the gain control quite sufficiently unless the not so lusterey cleans need to be available.
  Between these two simple controls, enough output and Dist+ ish tone abound.
  For the circuit you've proposed, check the 741 output impedance there, and the TS passive losses, some kind of a buffer at the output, probably gain recovery after the TS. Duncans TSC of course lets you know before hand what can be expected as frequency/gain lost from the tonestack with all the various TS settings/output use the sliders and watch the frequency output curve shapes change...very very cool and empowering, note that when the line is toward the bottom, losses are greater than if near the top of the graph.

[Mark Hammer]

Once you start adding 3-band EQ and a gain recovery stage, you've stepped outside the perimeter of a Distortion+ and walked into this: http://www.tonepad.com/project.asp?id=20  Build it instead.  You'll be happy, and glad someone else made the layout for you.  Promise.

[jtkiv]

petemoore:

clean tones aren't needed, so i can swap out the 500k for a 100k.

got Duncan's TSC going under WINE - here's the "sweep" and then all at 50%



is that good?  line seems to be fairly close to the top, so that means less lost?

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Mark Hammer:

thanks for the alternate project, but i wanted this project to involve a little more experimenting so i hopefully learn more through trial and error, etc. 

and i planned on another switch to bypass the EQ so i can play through a standard Distortion +.  Still, that pedal sounds pretty good in some of those soundclips!

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MmmPedals:

is a recovery stage more or less a boost?  i could do that.

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earthtonesaudio:

(i might have no clue what im saying) - a dual op-amp would have 2 inputs, 2 outputs?  but if the buffer is after the output, what difference will the two inputs and outputs make?  or does the buffer go between the second input and output.  sorry, i have done much research on op-amps.  as you can probably tell.

[slacker]

(i might have no clue what im saying) - a dual op-amp would have 2 inputs, 2 outputs?  but if the buffer is after the output, what difference will the two inputs and outputs make?  or does the buffer go between the second input and output.  sorry, i have done much research on op-amps.  as you can probably tell.

A dual op is just 2 completely separate opamps in one 8 pin chip so it would be the same as using two LM741s, except you only need one chip not 2. What earthtonesaudio meant was that you could use one of the opamps instead of the LM741 and use the other as a buffer after the tonestack.
Like MmmPedals said though you will find that the tonestack reduces the volume a lot so you could use the second opamp as a boost after the tonestack.

[petemoore]

  The Db losses are indexed along the left hand side, 'taller' is 'louder', actually 'greater potential' at output, less loss = up higher on the graph.
  Recovery is really another way of saying 'gain stage'.
  Tonestacks remove content, @ certain frequencies [dialing the knobs changes this so it's hard to say whats removed] bass treble, whatever...the lines show which frequencies are attenuated, and by how much.
  The words 'bass boost' and treble boost are veils, behind the scenes, there is passive attenuation to make 'a' frequency controlled signal [by taking something out], and a gain stage boosts what is left...if the treble is removed, and the knob that adjusts the volume has only bass in it's signal, it sounds like [and is often labeled as]  'bass boost'.

[jtkiv]

found a amp schematic in an old electronics book... good addition? 

and can someone explain to me why the battery doesn't just drain through the 10uf capacitor?

[petemoore]

  The 10uf is a small power supply filter capacitor, [more uf is ok too] connected across the supply rails to de-ripple the DC by storing 9v there, helps  when power supply is used.
  No need for it with battery.

[Mark Hammer]

You realize that you are maybe a half dozen components away from the Orman schematic I posted?  I mean, I salute your diligence, but you've essentially re-invented something that already exists.

Areas for "experimentation"?  Sure.  One you've already addressed, and that's the bypass cap on the volume pot.  But there are also cap values for the tone stack, messing with the ground leg of the opamp, Rat-style, and so on.

[petemoore]

  Does everything?
  Does a certain thing?
  Does some of everything and almost that' certain thing..?
  These are some of the possibilites.
  What is it that'd make it better ? [greater or fewer components?
  The Dist+ has some places where components make a difference, diodes, and changing the threshold instantly changes volume output.
  Carefully chosen staging caps [for bass rolloff, cap-value-switch at input] and a Treble Control [stupidly wonderful tone control is what I will try next though] might be 'enough'.
  Full flexibility of diode arrangements, preboost, Distortion 'engine', buffer, T/C, postboost and input basscut might do 'it'.
  I just like to hit the button once, but 3 treble re-adjustments to compensate for when volume changes isn't too bad, the bass-lift switch...I know which way I want that usually. A Dist+ with a couple extra +'s...
  Adding actives to the circuit pretty much puts in a category of 'has a Dist+ in it' realm, had the Dist+ sound zone, does good, but altered +tones.
  Getting it set up to where I was satisfied with 'just the bypass switch' went through the above stages [AMZ OD PRO, various other variations and encarnations].