Touch responsive circuits...

[Mark Hammer]

One useful, though not always universally appreciated, approach to producing touch responsive clipping circuits is that adopted by the EHX Graphic Fuzz.  Here the heard dynamics of the output are essentially the dynamics of the input.  An envelope follower tracks the input signal before it gets clipped and then applies that envelope to a VCA/OTA after the clipping has occurred.  So, while picking harder may not get you any more volume coming out of the clipping stage, it will get you more volume from the VCA.

I should emphasize that this is only one aspect of "touch sensitivity".  There is the potential for amplitude variation and the potential for timbral/tonal variation.  The ideal touch sensitivity would be the case where as you pick harder you get changes in tone and volume.  The EHX circuit uses standard diode-pair clipping, and appears to adopt the philosophy of "Okay, so you may be somewhat limited in how much change in tone you can produce via your picking, but that doesn't mean you have to be simultaneously limited in volume changes".

"Sag", of course, is the kind of inverse of what many people think of when they think touch sensitivity.  There, the signal and system responds the same way children do when you try to get their winter clothes on: the harder you try the more difficult its going to get and the more noncooperation you'll face.  So, picking harder or pushing the circuit harder results in it being less capable of respondin to the dynamics of the input signal.  This needs to be distinguished from an absolute maximim beyond which dynamics can not be increased.  When there is sag in a circuit, delivering a signal with more and more dynamic range (generally the result of higher and higher peaks) results in less and less dynamic range on the output.

[WGTP]

Since there are multiple stages in the whole process, especially if listening to recorded music, at which point(s) in the process the various clipping and compressing and expanding, etc. occur probably has an influence.

People talk about a pickup with an Alnico II magnet sounding more compressed.  The speakers used may not handle the full dynamic range of the amp.  Your home speakers may compress when driven hard, etc.  Heavy Les Pauls have a different response than Dan Electros.   

[DDD]

The "touch-sensitivity" is an entacoustic sensation for sure. What about me, the hi-gain (and loud) stompbox with unnoticeable noise produces the impression of very touch-sensitive gadget.
Of course, it's not a full description of the "touch-sensitivity", but it's surely the important part of the subject.

[PaulC]

One useful, though not always universally appreciated, approach to producing touch responsive clipping circuits is that adopted by the EHX Graphic Fuzz.  Here the heard dynamics of the output are essentially the dynamics of the input.  An envelope follower tracks the input signal before it gets clipped and then applies that envelope to a VCA/OTA after the clipping has occurred.  So, while picking harder may not get you any more volume coming out of the clipping stage, it will get you more volume from the VCA.

There you go...  You think you're working on something a little different only to find it's been done before.  I've not seen a schematic for that (can't find one - know a place??), and I didn't know they were doing that.  I've been playing around with that type of thing for a couple of years.  Thought I was on to something - bummer.


there is another way to do something like it.  This one came from messing around with pwr tube grid clamping and bias shifts.  You can have diodes to ground, but set up with a variable compliance circuit.  You can dynamically change the thresholds by having a control voltage dynamically change a bias voltage (need +&- for the two diodes).  This could give you hi threshold to let the attack come out, and then have the threshold drop to clamp it down.  Later, PaulC
Heritage amps/Tim & timmy pedals

[Mark Hammer]

It,s on the 1981 E-H pricelist I have posted on my site (hammer.ampage.org),

[PaulC]

Is there a schematic around? I can't find one.   I'd like to see if it's being done the same way I was messing with (talked about doing this type of thing in another thread about sag stuff a few weeks ago).  If so I'll find another way of doing it.

Later, PaulC
Heritage amps/Tim & timmy pedals

[Mark Hammer]

Yeah.  I have two schems.  One from Jack Orman from a half dozen years ago or more, and there was another more neat one that popped up a little more recently.  The circuits are a little different from each other, but then that's E-H's style isn't it?

Forgot to add that I don't have them on me here at work.

[Processaurus]

My favorite distortions are ones that have a constant, compressed output, but change a characteristic (like asymmetry of the clipping) depending how loud you play, so you still feel connected to the sounds you're making, but have supa sustain.

The great cheddar fuzz does this to a degree (though I wish I knew how to make it more exagerated) and its a fun one.

Heres an unusual wavefolding touch responsive distortion, it folds up your waveform more and more the harder you play.  Note it needs a big boost (~100x) before it shows its weird beauty with guitar.

http://home.debitel.net/user/jhaible/jh_wavefolder.html

[Steben]

"Sag", of course, is the kind of inverse of what many people think of when they think touch sensitivity.  There, the signal and system responds the same way children do when you try to get their winter clothes on: the harder you try the more difficult its going to get and the more noncooperation you'll face.  So, picking harder or pushing the circuit harder results in it being less capable of respondin to the dynamics of the input signal.  This needs to be distinguished from an absolute maximim beyond which dynamics can not be increased.  When there is sag in a circuit, delivering a signal with more and more dynamic range (generally the result of higher and higher peaks) results in less and less dynamic range on the output.

Yeah, ok, but that's the subjective part: "dynamic" in amplitude: I think an accoustic guitar will get you the most
Less dynamic in amplitude, power sag is touch sensitive when speaking of controlled timbre change

My favorite distortions are ones that have a constant, compressed output, but change a characteristic (like asymmetry of the clipping) depending how loud you play, so you still feel connected to the sounds you're making, but have supa sustain.
http://home.debitel.net/user/jhaible/jh_wavefolder.html

That's power sag to me.

Examples of real sag with dynamic timbre: the mid part of LED ZEP's "lemon song" and the interlude of "heartbreaker"; Hard clipping to almost no distortion. Dynamic in a subjective way. Jimmy Page into crancked supro amps.

[WGTP]

I read that Jimmy liked to set his amps so that he could do that.  Not too much distortion, so that it will clean up with picking technique.  The concept of "sweet spot" comes to mind in terms of the setting of the drive/gain/distortion, etc. on the pedal to maximize the distortion vs. compression ratio that you want.  I do agree that multiple stages help.  The Vulcan's are really cool like that.   

[newbie builder]

Mark Hammer thank you VERY much for those descriptions you offered- I'm not particularly advanced at all this stuff yet that made perfect sense and gave me some great ideas!