If a TS and a BMP had a baby...

[earthtonesaudio]

...I think the gain stage would look like this:


The first pot blends from a TS-type, non-inverting clipping stage (complete with buffer) to an op-amp BMP-type, inverting clipping stage.  I really like how simple the control is and how drastically it changes the circuit.  A cool thing about this arrangement is that in between these two settings you get a different sort of distortion that is not quite like the other two.

I really like this idea of a simple control that blends between the two different characteristic circuits, but I'm struggling with the tone stack.  How could you blend between the treble shelving filter of a TS at one end, to the BMP's panning tone control at the other end, with a minimum of parts?

[ayayay!]

Not to peepee on your parade, but haven't we already seen this on this forum?  Anyone? 

Dunno if anyone ever followed through with it.  Or was that you?   

[caspercody]

Could you put the tonestack at the end of the op amp output? Than use a dual op amp IC and use the other stage as a recovery stage for the level loss from the tonestack?

[earthtonesaudio]

Not to peepee on your parade, but haven't we already seen this on this forum?  Anyone? 

Dunno if anyone ever followed through with it.  Or was that you?   

Guilty as charged.  I first posted this here: http://www.diystompboxes.com/smfforum/index.php?topic=78134.0
But I wanted to draw more specific attention to the concept here.  With the "blend" pot fully rotated clockwise, it's a fairly accurate workalike of circuit A.  Fully clockwise makes it a fairly accurate workalike of circuit B.  And in between are many shades of gray, with elements of both A and B.

Could you put the tonestack at the end of the op amp output? Than use a dual op amp IC and use the other stage as a recovery stage for the level loss from the tonestack?

Both the TS and BMP have their tone sections located post-clipping, so that fits with the concept.

But it's the details of this post-clipping filter that are giving me trouble.
The TS tone stack is a cut/boost treble shelving filter that follows a fixed, single pole lowpass.  The BMP tone stack is like a see-saw (with a notch in the middle) which can "tilt" toward one end of the frequency spectrum while tilting away from the other.  So to suit the concept, the new "hybrid" circuit should be able to cop both of these responses and be able to blend between them, with a minimum number of extra controls.

[liquids]

I mean not to insult your intelligence, as I feel like you know all this, and I have no groundbreaking ideas.  But here are the simple hack ideas that came to my mind....

1) Since both original tone stacks are single knobers...you could duplicate both circuits (and any buffering/impedance needs), and use a crude switch to 'send' the output of the circuit to one tone stack circuit or the other, and get away with only two pots.  The IC Big Muff has a tone s tack bypass, right?  Likewise, switching between one tone stack path or the other (or put them in series and be able to choose one, both, or neither!) would probably offer the closest match to the two very different original tone stacks.... and probably some really interesting variants combined with the blend pot!

A baxandall is a passive way you can get some play with both mid boost and cut, and if you tinker with values, you could get some kind of compromise, I'd think.  For active, The LM833 datasheet has the classic active filters, blah blah...you could tweak to get more of the frequency response your looking for from active bass/cut, with some tweaking....though now we're pretty far from the originals...

The simplest, passive tone stack idea: Use the BMP tone stack of you liking.  From there, tinker with the values to get more of the TS vibe option....If you look at the TSC, one way to get rid of the scoop of the BMP stack would be simply switching in/out caps in series/parallel with what the TSC labels C1, or C2, to get a different response.  As C1 approaches C2 (and visa versa) in value, the BMP mid dip goes away, and the control acts more like just treble cut  as you go CCW, bass cut as you go CW without the variable mid dip or shifting, and with an apparent boost on the other side.  I'm not familiar with the TS curves from more than a quick glance at R.G.'s article, but for example, just make C1 and C2 both 22n or both 4.7n for starters, as a simple solution from what the TSC starts with...

Last but not least, you can do a TS-like tone stack, but use a superfuzz-type mid scoop control that can be switched in or out, to cop some BM vibe. Mark Hammer offers a simple way to make such a tone control have a variable level of dip or two:   http://www.diystompboxes.com/smfforum/index.php?topic=75716.0.  Though if you look at it, it's just a crude BMP tone stack without a tone control, or a mid control instead.

Hoping this is not just a rehashing of everything you've already thought of.  

[John Lyons]

Cool ideas going on here.
How close can the single clipping stage get to the
big muff though? Most of the magic is the dual clipped
stages no?

John

[MikeH]

I'm digging this; one of my favorite dist sounds is a TS and BMP in a splitter blend.  Perhaps this will be the same sort of thing in a smaller package...

[earthtonesaudio]

Cool ideas going on here.
How close can the single clipping stage get to the
big muff though? Most of the magic is the dual clipped
stages no?

John

That's a good point, John.  How about adding feedback clipping diodes to the transistor stage?  When in "TS mode" the gain of the transistor would be low enough so the diodes did not conduct, but with the wiper of the blend pot turned toward the emitter, the gain would increase and perhaps get clipping from the transistor.


Liquids, you've hit on an important distinction between the TS and BMP tone sections.  The BMP is essentially a passive control with a make-up gain stage, while the TS is an active boost/cut.  I like the idea of that scoop-shift control, where you basically get two different tone control "characters" to play with... There are just so many ways it could be done that it's hard to pick one.

[John Lyons]

With the wiper at/towards the emitter the gain is lowest as that is the buffer/emitter follower.
In the big muff the first transistor is a boost amplifier somewhat like the EH LPB. That stage
drives the fist clipping stage and then through another identical clipping stage to give us the
big muff sound. Without the second clipping stage the BM is pretty limp. By clipping the first
transistor may get towards the BMP sound but I think the first transistor has a lot to do with
driving that first clipping stage a good bit.
Either way, it seems like something fun to play with. Just a matter of some crafty signal routing
and maybe a dual pot here or there...

John

[Ben N]

What is the value of your "Nature" control (to borrow a label)? Perhaps you could dual-gang it with an AMZ "Body" control so that as you turn toward the Muff side, you reduce the mids, other way increase them, using the basic BMP stack topology.

BTW, have you breadboarded this thing? Did the transistor phase splitter eliminate the signal drop in the middle of the pot travel that you had originally? Wait, that was actually in another, even earlier thread, right?

[Ben N]

With the wiper at/towards the emitter the gain is lowest as that is the buffer/emitter follower.
In the big muff the first transistor is a boost amplifier somewhat like the EH LPB. That stage
drives the fist clipping stage and then through another identical clipping stage to give us the
big muff sound. Without the second clipping stage the BM is pretty limp. By clipping the first
transistor may get towards the BMP sound but I think the first transistor has a lot to do with
driving that first clipping stage a good bit.
Either way, it seems like something fun to play with. Just a matter of some crafty signal routing
and maybe a dual pot here or there...

John

John, take a look at a schem for an opamp BMP--there are additional gain stages, but the (diode) clipping is all bunched up in one. Presumably there is opamp clipping going on ahead of that. In any event, it is pretty different from the classic transistor BMP topology you are referring to. Perhaps the way to get anything like that kind of gain in the picture here is to add some gain (in the sense of boost, not distortion) ahead of the phase splitter, although that would probably affect the TS side of the rotation, too.

[John Lyons]

That's true, I'll look at the Op amp BM...

[earthtonesaudio]

With the wiper at/towards the emitter the gain is lowest as that is the buffer/emitter follower.
In the big muff the first transistor is a boost amplifier somewhat like the EH LPB. That stage
drives the fist clipping stage and then through another identical clipping stage to give us the
big muff sound. Without the second clipping stage the BM is pretty limp. By clipping the first
transistor may get towards the BMP sound but I think the first transistor has a lot to do with
driving that first clipping stage a good bit.
Either way, it seems like something fun to play with. Just a matter of some crafty signal routing
and maybe a dual pot here or there...

John

Ah, sorry if I was unclear.  I meant to put some diodes from transistor collector to base (essentially turn it into a clipping stage from a transistor BMP).  And when the wiper of the "nature" pot (which is tied to a virtual ground reference) is more toward the emitter, the gain of the transistor (not the op-amp stage) increases, since the coupling cap off the emitter basically becomes an emitter bypass cap for AC signals.  That would then cause the signal at the collector to be larger, allowing clipping to occur if there were diodes placed between collector and base.  Not quite the same as driving the transistor with a larger signal, but closer to the dual clipping topology.

What is the value of your "Nature" control (to borrow a label)? Perhaps you could dual-gang it with an AMZ "Body" control so that as you turn toward the Muff side, you reduce the mids, other way increase them, using the basic BMP stack topology.

BTW, have you breadboarded this thing? Did the transistor phase splitter eliminate the signal drop in the middle of the pot travel that you had originally? Wait, that was actually in another, even earlier thread, right?

I used a 10k and later a 100k.  I don't recall the value making a huge difference, but then the collector and emitter resistor values were also rather low.  I don't recall there being any signal drop at the midpoint of this control.  The op-amp is getting full differential gain at that point, so I would somewhat expect an overall volume boost if the transistor was not loaded down too much.

I like the idea of using a dual pot to change the nature of gain and tone stages simultaneously.  I'll have to go buy a dual pot to try it out...

[Ben N]

collector to be larger, allowing clipping to occur if there were diodes placed between collector and base.  Not quite the same as driving the transistor with a larger signal, but closer to the dual clipping topology.

That's a pretty cool twist, thanks for pointing it out.

[soggybag]

This looks very interesting. But I'm lost as to how it works. I can see the TS clipping section. I can't see how this would act as a BM?

[aziltz]

kudos for coming up with something this cool!

[Ben N]

This looks very interesting. But I'm lost as to how it works. I can see the TS clipping section. I can't see how this would act as a BM?

Lookee here. Note how the 741 is configured as an inverting opamp, with the non-inverting input grounded, diodes in the FB loop? Now, look at what happens when you turn Alex's pot toward the emitter of the phase splitter tranny--the non-inverting input of the opamp is grounded, the signal is fed into the inverting input, and the whole stage starts to look a lot like the 741 stage of the BMP. There ya go.