Clipper circuit idea to share

[Transmogrifox]

I have been developing this concept in simulation.  It's roughly based on the Marshall Bluesbreaker voicing but also borrows ideas from Joe Davisson's diode compression discrete op amp.  I haven't breadboarded this yet to see how it sounds but I thought I would share it because it looks like a promising topology for being able to control symmetry and whether it gets soft or hard clipping.




Here is the LTSpice file for anybody who would like to fool around with the simulation:
http://cackleberrypines.net/transmogrifox/Misc/Distortion_Experiment/DiscreteBluesBreaker2.asc

[Kipper4]

Are you gonna breadboard it and give us a sample demo please Ryan?

[Transmogrifox]

Yes, but might take a few days to get time to put it on BB.  Standby...

[Transmogrifox]

Alright, set with some modifications and demos from the breadboard.  More notes on the schematic to hint about what I was thinking.  First revision with current limiting in the PNP produced too hard of clipping and had some of the "splat" that the LM386 distortions have.

By putting the current limit into the form of a constant current source then it is the JFET characteristic that you hear when it limits.

As mentioned previously the voicing is based upon the Marshall BluesBreaker stompbox as cloned at GGG.

I think it comes out sounding pretty amp-like on its own.  I'm pleased with the sound direct into PC with no processing, but it really really sounds sweet in a real amp.  It's a great booster for pushing my drive channel, and it sounds great on its own in my clean channel.  Adds a lot of versatility.

Demos recorded direct into PC sound card, no processing no additional EQ.  Just normalized the tracks.
Guitar: Epi Les Paul
Neck PU: Lynch Screamin Demon
Bridge: DiMarzio Air Norton

Here's the circuit used for recording demos.  Tone control was hard-wired at about 25%:


And here are the demos:
http://www.cackleberrypines.net/transmogrifox/Misc/Distortion_Experiment/mp3/
Most focus on hard rock or some blues noodling sounds.  This clip has an attempt at Collective Soul December varying pick attack just so you can hear the "edge of breaking up" responsiveness:
http://www.cackleberrypines.net/transmogrifox/Misc/Distortion_Experiment/mp3/December_and_some_noodling.mp3
This track is just short & sweet:
http://www.cackleberrypines.net/transmogrifox/Misc/Distortion_Experiment/mp3/OverdrivenChords.mp3
And this is kinda like the rock song finale sound:
http://www.cackleberrypines.net/transmogrifox/Misc/Distortion_Experiment/mp3/Finale.mp3

[Kipper4]

That sounds great mate. You've sure got some chops you animal.
I guess the tone control is c10 r23 r28 ?
Thanks for that.
Is it mostly pedal and not amp?
Sweet

[Transmogrifox]

Tone control is R31, R33, C11, R32, R12.

See this to compare the general outline of the circuit:
http://www.generalguitargadgets.com/pdf/ggg_mbb_sc1.pdf

You will see that R31, R33 compose the terminals of the 25k tone pot (except in my circuit they sum to 20k).  I had originally put a 10k at R31, but it was too dark so I replaced it with a 5k1 just as a "quick n dirty" tone adjustment.

Is it mostly pedal and not amp?
Sweet

It's all pedal.  I went direct to line in on my PC for recording.  The amp was not involved in the recording:
Guitar -> breadboard -> buffer -> PC line-in -> Audacity -> Select All -> Normalize -> Export

As I mentioned in my post it sounds even more sweet when coupled with an amp, but I wanted to keep the demos as uncolored as possible.

[Kipper4]

It has a real amp feel.
Thanks

[Transmogrifox]

Next thing is to mess around with tone stacks. 

Anybody have ideas?  Ideally it would be a 1-knob tone control but maybe the 2-knob abbreviated Fender style ok (like the hot box).  I'm aiming for a small-ish space so I want to keep knob count down.

Maybe the tubscreamer style tone control is all I need.

[midwayfair]

Next thing is to mess around with tone stacks. 

Anybody have ideas?  Ideally it would be a 1-knob tone control but maybe the 2-knob abbreviated Fender style ok (like the hot box).  I'm aiming for a small-ish space so I want to keep knob count down.

Maybe the tubscreamer style tone control is all I need.

This one's a knob and a switch, but it's extremely versatile for a passive EQ:
http://diy.thcustom.com/shop/jon-pattons-cruz-driver-l-pcb/

Hearing the clips, I think a shelf high boost would be very useful, something ranging from ~150Hz on the low end up to 1KHz on the upper end, preferably more than 6dB if you can manage it, but that might just be the lack of upper mids from not having a guitar speaker involved.

[Transmogrifox]

Thanks.  That does look like a very versatile tone stack. 

It definitely needs some help in the upper mids.  My 3-knob tone stack on my amp can't touch it where it really needs some correction.  The treble knob brings in too much of the "ice-pick" sound and the mid knob brings in enough of the lows to make it muddy. 

I think you are correct a high shelf would be useful.  If the high shelf brought in too much "ice-pick" sound I can tune that away somewhere else in the circuit.  I already improved it somewhat by adding a cap across R13 gain pot.

Maybe I should just run it through a 7-band EQ and see what the contour looks like when I have it sounding the way I like it.  It might be all I need is a RAT style tone control once I strip off the hard-wired tone stuff from the BluesBreaker.

[Transmogrifox]

Here's what I came up with for a first try.

1)  De-emphasis filter to somewhat flatten the clean response leaving a bit of treble boost.
2)  Implement high-shelving filter according to Jon's suggestion.

Simulating with a wav file it sounds much better but I still need to breadboard the new tonestack and gain recovery to see where it ended up.

I may try Jon's suggested tonestack if I need the flexibility, but probably the least complicated frequency contour is the place to start.

Tone stack is an abbreviated form of something like this:

http://sound.westhost.com/articles/eq.htm#s8
I removed the bass control and replaced with fixed resistors, then converted the lower leg into a volume pot, restricted range to +/- 6 dB.

Here's the working schematic for now:


This has morphed from a basic clipper circuit building block in a "typical application" circuit into an overdrive pedal based upon the concept. 

Any more ideas/suggestions?  If this de-emphasis filter and tone stack sound as good on the BB as they do in simulation I'll be ready to box this thing up and sell my VOX V810.  I am preferring the Bluesbreaker pre-emphasis voicing.  It make for a little bit brighter booster.

EDIT:  Breadboarded it up last night.  Sounds much nicer with the de-emphasis filter and tone stack.  Opens the sound up a lot. Next experiment will be a typical BMP style tonestack with an intentional mid scoop to see whether I prefer the mid hump or if I want a little scoop.

Jon thanks for the suggestion about 1 kHz shelving filter.  This tonestack boosts and cuts around the 1 kHz range and this sounds like it is happening right where it's needed. You have some well-calibrated ears