how many different passive fx are there

[sbgodofmetal]

so i recently read johnh's thread on passive O.D. using schottky diodes and a tone pot. but how many other fx can be done passively like this one??? and will it fit onboard in a guitar or will a pedal box be needed???

[newey]

OK, so now you've touched the "third rail" of G-Nutz- The question of "passive fx".

In my earlier days on the board, I posed the same question, although I was really thinking along the lines of electro-mechanical things; one idea was that, instead of a whammy (vibrato, erroneously called a "tremolo" by Leo), that an actual trem effect could be achieved by having the whammy bar operate a vol pot down in the cavity, with a rack and pinion set-up just like a wah pedal- pushing/pulling the lever would rotate the pot for volume swells.

That lead to a more general discussion of "passive fx", which included JohnH's Shottky diode experiments.

I call it the "third rail" because the late ChrisK broadly hinted, both on the board and in PMs to me on the subject, that much more was possible along those lines, but that he wouldn't publicly disclose all he knew. He felt that there might be a commercial application in the future- and if he didn't exploit the commercial application but someone else did, he had a ready-made patent lawsuit, since he had, as he put it, "substantial prior art" in the field ("prior art" is a specific legal concept in patent law).

Although he never told me his thinking, he did encourage me to continue to think, and perhaps experiment, along the lines of "passive fx". Unfortunately, time constraints intruded, and I haven't followed up on any of it.

As those who knew Chris will verify, he was often cryptic in his answers, in order to try to get people to think for themselves. Nowhere was this more true than on this subject.

One thing that he may have been referencing was his prior work on "Pickup Coil Response Tuning". Unfortunately, his diagrams in that post have now disappeared into the ether. The general idea was that the classic parallel interaction between 2 coils could be "tuned" with the use of one or more caps of the correct value, such that certain parts of the frequency curve would be enhanced relative to other parts, thus making for a sort of "passive boost"- there would be a subtle "spike" at certain frequencies.

This effect was roundly debated at the time. If it does exist, it is very subtle at best- nothing that is going to make you toss out your tubescreamer.

Chris also hinted that more was possible, but (being dense) I couldn't pick up in most of his cryptic comments.

I'll repost the guts of this stuff when I can find it. No firm conclusions as yet on anything, but maybe some food for thought.

[newey]

Also, in his Shottky post, JohnH linked to this manufacturer from Downunder who makes purely passive stompboxes. John's link thereto was broken, here's the new one:

Cave Passive Pedals

[sbgodofmetal]

those are nice but i would really like a passive chorus, a compression, and an octive booster, if diagrams can be found my roommate is being a real pain about me being online so i may be silent for awhile but if anyone can get me diagrams to these passive fx w/parts list i'd greatly appretiate it thanks

[JohnH]

Here’s a site that claims to produce more passive effects than you might think are likely, and charges quite a lot for them to. It is interesting to speculate on what they do:

www.cavepassivepedals.com.au/

Ultimately however, they are limited by having a lack of electricity available. Since 1887, when dry cell batteries were first invented, mainly practical devices have benefitted from these useful items, including guitar effects!

[newey]

Here's a demo of Cave's "Bass grunt" pedal. As you can hear, the effect is quite subtle.



The only diagram any of us has is JohnH's diode-clipping thing. Whatever Cave Effects is doing, they're unlikely to share their schematics.

Essentially, as JohnH noted in his thread, they are doing some variations on diode clipping. The "boost" may be more of an EQ illusion- some frequencies are relatively louder than others, tricking the ear into thinking the overall level is up.

The phase, trem and other effects seem to use an opto-resistor controlled with one's foot, and only work in a well-lit room.

Apart from the boost effects, the basic problem with these things (as noted) is the volume loss. A guitar pickup only produces fractions of a watt, and you don't get something for nothing, at least not in those jurisdictions that have adopted the Law of the Conservation of Mass/Energy.

EDIT:JohnH must have missed my post, and I was composing again as he posted his.

[JFrankParnell]

those pedals sound pretty dang cool. I'm almost as amazed as i was when dad and i put together that crystal radio

[sbgodofmetal]

so no dice for the most part... we all need to pool some $$$/£££ (or what ever your currency may be) together to buy one of each of these passive fx pedal's and you,johnh, & ashcatit get together and disect each one and making schems of them for posting and theres nothing that company can do about it... do to u.s. & international copyright laws a person or persons may distribute copyrighted materials without permission of its owners or monitary benefit for eduational, news, parody, and information purposes

[ashcatlt]

Ring Modulation can be created passively, though I think it's difficult to do at passive guitar levels. Kind of the same problem as with the clippers: the signal needs to overcome the diode drop for it to work.

[sbgodofmetal]

this is stated in section 107 of the u.s. copyright laws as a ''fair use'' clause which is in legal accordance with title 17 u.s.c. section 107 the material may be distributed without profit (assumed monitarily$$$)for educational and informational purposes only...[SOURCE INFO: www.law.cornell.edu/uscode/17/107.shtml ]

[sbgodofmetal]

BUT.... for those of us who read, saves to hard drive and prints those schems in triplicate if we do build one or all of them theres still absolutely nothing the law can do to you unless you attempt to sell it claiming its your design but i'd like to hope no'one here's that stupid

[sbgodofmetal]

your sounding greek to me, ash. ring modulation would be what exactly??? i'm still learning the terminology here, remember i'm still a beginner at guitar electronics

[newey]

Ring Modulation (w/ audio examples)

I'm no copyright lawyer, but I doubt the fair use doctrine would apply here. There also may be patent issues in addition to copyright issues.

But this is all irrelevant anyway, since we don't have a copy of their diagrams.

Buying one of their pedals and making one's own drawing from it is not an issue of copyright, but potentially could be a patent infringement, if they had a patent- which I doubt, there's nothing new here.

IOW, SBG of M- one can search the US code at the Cornell U. website, or one can ask a real lawyer . . .

[sbgodofmetal]

this infernal mobile contraption wouldn't let me open the audio links but going by what was written it sounds as though ring modulation is a form of a simple phase shifter. and yeah i'd consult an actual lawyer before hand the cornel thing was sent to me for some other topic that i'll not go into, and a convieniant legal source at the 'wee' hours of the morn.

[ashcatlt]

Nope. Not really anything like a phase shifter. It sort of turns one audio signal up or down based on the instantaneous voltage of another audio signal. What you get out depends on the complexity of the input signals as well as their harmonic relationship. I used it on my voice for a song with the "carrier" signal a low frequency sine wave and it came out sounding a lot like I was singing through a fan. Other applications will have radically different effects. It's typically described as creating a "bell-like" or "metallic" tone, but that really only happens in certain circumstances.

[sbgodofmetal]

so the one you used that made it sound like you was singing through a fan..... Got a diagram? ;D and it was in a pedal form right?

[ashcatlt]

Nah, it was the Ring Mod patch in my Alesis Quadraverb. It has a built in oscillator for the carrier signal and I set that somewhere around 50Hz, but probably in tune with one of the notes.

[JohnH]

One interesting thing on the cave site is the use of optical sensors to control tone. Maybe this could be applied in an effective way in a guitar. Suppose an out of phase combo is set, with twin volume controls so that a null point can be set that maximises the cancelling of bass from the pickups. A very small change from such a position makes a large change of tone. So if a light dependent resistor (LDR) was built into one leg of one of the volume controls, changes of light intensity might change the tone significantly. Place the LDR under the strings, at a place where strumming near the neck will put it in shadow, but moving your hand back to the bridge lets more light reach it. Maybe a sort of wah effect might occur?

John

[sbgodofmetal]

That sounds very interesting! now i'm wondering??? If one were to make a sort of a wah pedal, w/ a mirror under the foot board (but in a 'safe' hard to break it manner) and those light sensative thingies, if it would work like a wah?, like you were saying about it being onboard guitar, johnh do you think theres application for such a wah?, and could it be done effectively?

[sbgodofmetal]

Now back to ring modulation. Could such an effect be effectively coupled with the passive diode clipping overdrive? Or would it negatively affect the tone? Or could you add a volume & tone pot to either of them (If not both of them)to compensate for any possible & probable drop in tone

[sbgodofmetal]

check out roadtonevers thread on passive EQ, & go to page 3 i think and chech out my design for a passive EQ plus passive O.D. ;D

[JFrankParnell]

[JohnH]

Mar 30, 2011 7:43:30 GMT -5 sbgodofmetal said:

That sounds very interesting! now i'm wondering??? If one were to make a sort of a wah pedal, w/ a mirror under the foot board (but in a 'safe' hard to break it manner) and those light sensative thingies, if it would work like a wah?, like you were saying about it being onboard guitar, johnh do you think theres application for such a wah?, and could it be done effectively?

I don't know if this will work, but, from the theory as I see it, i think it might work. This is the sort of device:

www.jaycar.com.au/productView.asp?ID=RD3485&keywords=light+dependent+resistor&form=KEYWORD

It has a resistance that varies from a few k, up to 500k, depending on light. The actual variation that you can get in practical changes of lighting remains to be seen, but this range could be right in the money zone for getting involved in guitar volume control circuits and affecting response, say in the range 50k to 200k, combined with 500k pots.

This thought depends on having two pickups out of phase, and the device must only be affecting one, so that the balance between the two pups changes. So if it was on a pedal, it would need its own cable back up to the guitar. But I could really picture it working under the strings - being very interactive with how you strum.

Testing this in concept can be done on any guitar with a 'Jimmy Page' style of wiring - just by clipping the LDR across two lugs on one of the volume controls, in a series out of phase setting.

So I might get one and try it.

John

[ashcatlt]

It will, of course, also be dependent on the lighting wherever you happen to be playing.  Imagine playing in front of a strobe light or one of those fancy programmer DJ light racks!

I honestly don't think the ring mod thing would be very useful with a passive guitar.  First it needs two audio inputs.  I think you could run one guitar into both inputs, or maybe even use two pickups on the same guitar and get a sort of nasty octave up type thing.  But you've still got the problem of the diode drop ("turn on" voltage).  Hot Humbuckers have a tough time getting through even the low drop in a Shotky.  You'll end up with pretty severe crossover distortion which will tend to act like a noise gate - killing most of your sustain.  If you was to then tack Shotky clipping diodes after, you'd be clipping off the little bit that does come through and get (I think?) something very close to silence.

[sbgodofmetal]

(diode clipping+ring modulation) Oh well it was just a thought.... But what if it were active would you get the same effect or would it be totally different (LDR Wah pedal) i had invisioned it as a daylight outdoor stage fx pedal. espescially during summer months i've heard horror stories about fx pedals overheating and causing permanent damage, but i'd think one could be done with an LED on a potentiometer rigged as a dimmer switch, but that would be pushing against the passive part which is what i want

[ashcatlt]

Yeah, active is different. Did you read the recent thread where I describe my recent application of Ring Modulation?

Your thing with the LED/LDR wah has been done. There are some on the market where the pedal opens a "window" between the LED and LDR, varying the amount of light that gets through to get the effect. There's also a fairly common mod known as Craig Anderton's Scratchless Pot mod, which isolates the pot in a Vox/Crybaby style wah from the audio circuit. The pot itself varies the light from an LED, which varies the resistance of the LDR.

[sbgodofmetal]

On the ring modulator what parts will i need to build one (both actively and passively) and can you provide diagrams???

[ashcatlt]

newey's link above shows the basics. I've never built one, but Google is your friend!

[newey]

Again, I don't know from passive circuits for this sort of thing.

As far as active circuits, probably the most well-known Ring Modulator is the Dan Armstrong Green Ringer:



The schematic is courtesy of montager.com


Mind you, I've never seen one much less played through one, so you're on your own as far as ascertaining what you want.

If you've never built anything similar before, a kit might be the best way to get everything you need and a design you know will work properly if assembled properly.

General Guitar Gadgets has a Green Ringer clone kit for $45. They also have online instructions and a bill of materials available which I am not allowed to repost here per their copyright notice (so, go look yourself!)
www.generalguitargadgets.com/component/virtuemart/?page=shop.product_details&flypage=flypage-ask.tpl&product_id=26&category_id=7

[sbgodofmetal]

Thanks ash, and newey. i'll go take a look at that, but like i stared in another thread i'm limited to cash in hand for a few weeks. So i'll either wait and save, or try to locate the parts locally. but still keep the thread going, i enjoy learning about these fx