Circuit idea - Clarifier Distortion

[PBE6]

Hi all,

Just wanted to post an idea for a circuit and see if anyone spots any obvious issues.

The basic idea behind the circuit is to cut some bass from the input signal, apply gain to create distortion and then boost the bass back to original levels. This is nothing new, but in this circuit I tried to make the bass cut and boost as symmetrical as possible by using a dual-ganged pot. I also added a few tweaks to make it more flexible - the distortion mode is selectable between Dist+ and Tubescreamer type methods, and the tone stack is AMZ's Big Muff tone stack with presence control to give you flat or scooped tones.

If the circuit sounds any good in real life, I think the next tweak would be to add SEND and RETURN connections that bypass the gain section so the "clarifying" aspect could be used to adjust the harmonic content of other gain devices like pedals or amps.

If anyone sees any major goofs please let me know!

Thanks.

 

[Kipper4]

you might run into some tone sucking at the last IC.
Maybe make the two x 1k at least 50k's.
Suck it and see.

[ElectricDruid]

My only query would be whether it's really doing *enough*.

The bass is only cut by a 6dB filter, and then that filter is limited to a maximum of a -6dB cut (100K+100K divider is worst case 50% of the the signal, right?). That's not a huge bass cut.

Also it's fixed at a single frequency. That's not a problem if it makes a good sound and you're happy with where you've got the cutoff, but if I wanted to add a knob, I'd want to add a "cutoff frequency" knob.

HTH,
Tom

[amptramp]

Everything here goes through the diode clipper stage and since it is an inverting stage (unlike the Tube Screamer), once the diodes conduct, the waveform flatlines and gets some muddiness.

I would either go with a non-inverting stage, put resistors in series with the diodes to prevent killing the signal or as an alternative, split the signal into bass and mid/treble streams and recombine them after the mid/treble goes through the diode clipper and the bass goes only through an amplifier.  The alternative with the split signal allows separate control of the level of bass and higher signals.  If you split the signal, keep the phase the same or there will be a frequency at which everything is nulled.


The 220 pF feedback in the clipper stage should limit the clipping of the treble, which doesn't need clipping since that only creates harmonics of the treble, which you don't need.

[dschwartz]

You can do it with a single pot..
Try this:
Use a variable bass cut filter (4.7nF/ 100k pot to ground)
Connect the cap to pin 1 of the pot, and the wiper to ground. Add a series resistor so it doesn't shunt to ground (or Vref if you prefer)

At the output..place a 10n and connect to pot pin 3 (also add a series resistor to avoid shunting the signal)

Since the wiper is grounded (or Vref) the pot will act as 2 variable resistors, not connected to each other, and of complementary value (if linear).

As you turn it up, it will cut the bass at the input and add bass to the output and viceversa..find the C and R values that works best...

[samhay]

I would ... put resistors in series with the diodes to prevent killing the signal...

You missed the switched 1k resistor. I might make more use of this and replace the 1k with a 10k pot (as variable resistor) to give more control over the clipping. No need for a switch then.

I also agree with Tom regarding the bass cut control. You could use a 2-pole filter here and vary the corner frequency. Would make a more interesting feature.

Also, not sure you really need 5 op-amps to do all this. Why not ditch the 4th op-amp and then use the last stage to do the variable make-up gain, although I'm  not sure you will need much. Ultimately, the 2-things-with-one-pot idea is great in theory, but not sure it will really be so great in practice.

[PBE6]

Thanks for all the feedback! ...I'll get my coat... ;->

I wanted this effect to be on the subtle side, so I didn't want the bass cut to be too extreme.  I thought a 6dB cut (50% of the original level) would be a good target for "clarifying" the sound without killing the bass-generated harmonics completely, but if it ends up being too subtle I'll probably end up lowering the value of the ground leg resistors.  Using a pot to blend two capacitors is also a great idea!  If I find that the frequency range isn't quite right on mine I will try adding that blend control.  I also have to say I'm blown away by how clever it is to ground the wiper of a single pot to control two different parameters simultaneously in a complementary way - I'm not sure if this is a common trick to avoid the use of dual-ganged pots, but it sure should be! (I happen to have a bunch of 500kA dual-ganged pots lying around just waiting to be linearized and used up, but next time...)

With regard to the clipping stage, I needed something there otherwise there wouldn't be much "clarifying" going on.  I chose the inverting clipper because of some math/thought experiments that show it's more flexible than typically recognized, but I should be a little more careful when I'm describing it.  When the blocking resistor is engaged, and that blocking resistor has the same value as the input resistor, high gain levels make the inverting clipper act like a high gain non-inverting clipper - but admittedly the similarities decrease as the gain levels are brought down.  When the blocking resistor is disengaged, it does a very good impression of a Dist+ at all gain levels.  I thought I'd try it out here, and also add Jack Orman's BMP tone stack because it gives a lot of control with only 1 knob and 1 switch.

I thought I would have a chance to finish this one on the weekend so I would have sound clips, but no such luck.  Hopefully in the next few days!

[dschwartz]

Just as an idea.....
What if instead a bass cut, use a treble/mid boost, and control the tone stack "contour" at the same time?
You could morph from standard vintage distortion to a tight/scooped modern tone with one knob twist