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Cmos Inverter As An Onboard Guitar Amplifier


grtvrm
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Did you ever see or hear implemented CMOS inverter as an onboard guitar amplifier. One chip has 6 inverters and each one takes 2 resistors to become an amp. Sounds good especially for hexaphonic amp. Voltage may be down to 3 volts, high impedance, linear gain does not matter but sustain should be extremely long, Most important you may play sustained chords unlike the normal 1 channel distortion!, the rest will do a multi effect pedal that is cheap, like Zoom G1

See that link on CMOS

http://www.fairchildsemi.com/an/AN/AN-88.pdf

Next idea – piezo 6 channel pickup DIY from piezo cigarette lighter, saves you some 150$. I dismantled a lighter it has tiny cylinder inside – should be piezo element

Sounds stupid but all you need – fit these bustards under the string or bridge saddle and solder 1X6 wires right to the CMOS invertors, then you need 1 resistor only for each channel. If it makes a spark, can it drive a high impedance amp? :D

2AAA bats + 1 CMOS chip + 6X3.3M resistors + 6 lighters = almost moog guitar

Edited by grtvrm
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Interesting idea...those inverters are pretty low fi and designed for digital signal work...no analogue audio and I am not too sure about the piezo idea...but do some tests and see what you come up with. There have been some lo-fi uses of hex inverters and other devices for badly tracking analogue snthy type guitar effects and stuff as I recall.

Welcome to PG...pete

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Craig Anderton built a distortion around a similar chip. Sounded pretty good, but I wouldn't try getting a decent clean tone from one. As pete said, they're not particularly hi-fi, and there's no good way to set the gain.

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Craig Anderton built a distortion around a similar chip. Sounded pretty good, but I wouldn't try getting a decent clean tone from one. As pete said, they're not particularly hi-fi, and there's no good way to set the gain.

Thanks for info, Do you have a link for this?

I was really impressed to see the sustainer thread, though it’s demo tone is not very clean either.

A lot of distortion / harmonics is not a problem as soon as they are multiples of the one base frequency, it just changes timbre of a note.

Harmonics spoil the sound when all notes in a chord are mixed in 1 channel and then we add nonlinearity producing harmonics. We get harmonics of all base frequencies of a chord and all their sums and differences that makes a good white noise. So having 6 channels and uncontrolled nonlinear gain should not be so awfully sounding. May be even better than 1 channel with small distortion. So I started the thread asking for a sound sample of this machine. I bet sustain should be long for any real musical purpose (7-10 sec). Infinite sustain though is good to repel mosquitoes at night

See as just 3 equal amplitude harmonics produce almost square wave

http://en.wikipedia.org/wiki/Image:Synthesis_square.gif

Edited by grtvrm
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Thanks for info, Do you have a link for this?

I was really impressed to see the sustainer thread, though it’s demo tone is not very clean either.

A lot of distortion / harmonics is not a problem as soon as they are multiples of the one base frequency, it just changes timbre of a note.

Harmonics spoil the sound when all notes in a chord are mixed in 1 channel and then we add nonlinearity producing harmonics. We get harmonics of all base frequencies of a chord and all their sums and differences that makes a good white noise. So having 6 channels and uncontrolled nonlinear gain should not be so awfully sounding. May be even better than 1 channel with small distortion. So I started the thread asking for a sound sample of this machine. I bet sustain should be long for any real musical purpose (7-10 sec). Infinite sustain though is good to repel mosquitoes at night

See as just 3 equal amplitude harmonics produce almost square wave

http://en.wikipedia.org/wiki/Image:Synthesis_square.gif

The Anderton circuit is called the Tube Sound Fuzz, and it's described in his book Electronic Projects for Musicians. It just a basic fuzz circuit, but using a CMOS inverter for both the amplification and clipping. The transfer characteristic of the chip in that circuit is somewhat tube-like.

Anyway, I'm not sure whether you're referring to a polyphonic sustainer (something I have plans to eventually tackle) or just polyphonic distortion. Pete has, I believe, messed with polyphonic sustainers (right?). You add a lot of complication to the circuitry by going the polyphonic route -- 6 completely separate signal paths as opposed to one. That hex buffer probably won't help you too much. You still need output stages, and I don't think that chip has enough current capacity to drive a sustainer coil.

Polyphonic distortion for guitar has been around for quite some time now. It's actually very much like you describe, but the lack of intermodulation distortion makes for a somewhat strange (at least "un-guitar-like") sound. Sounds more like a synthesizer than a guitar when playing chords. The Anderton circuit would be worth a look if this is the route you're thinking of taking. The circuit uses two inverter stages and minimal supporting circuitry. So with a pair of hex buffers and about 40 resistors and caps, you could build a six-channel version.

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I was really impressed to see the sustainer thread, though it’s demo tone is not very clean either.

I really am not following this and similar threads at all. Are you talking about the links of the new tele sustainer?

If so, this has a circuit that has different levels of drive from clean and subtle to a max drive. In that demo, the more obvious sustainer is with the drive on max but was recorded with a half flat battery that would have improved headroom.

Also...maxing out the drive means that the string is being driven hard and bouncing on the frets particularly in fundumental mode. My sustainers are different from others in that they allow this kind of gain where as the commercial units sound a little less expressive and their range compressed. This has some of the ebows qualities...but it can do a lot of things.

Also bear in mind that this was also recorded in one take direct through headphones into a digital recorder and some of it may have been overdriving the digital converters. Through an amp, the extra drive tends to give a natural drive effect...or turn down the drive to 8 for a more natural sound.

If you want infinite polyphonic clean sustain...you want a keyboard. If you want controlled feedback guitar, you want a sustainer.

Pete has, I believe, messed with polyphonic sustainers (right?). You add a lot of complication to the circuitry by going the polyphonic route -- 6 completely separate signal paths as opposed to one. That hex buffer probably won't help you too much. You still need output stages, and I don't think that chip has enough current capacity to drive a sustainer coil.

Kind of...and potentially. I did make drivers with 6 tiny drive elements but I ran them in series. The intention was to optimize each for each string. They contained exotic materials and 12 magnets to get the separation necessary...but what happens if you bend the string out of alignment...etc. I could have run the same designs with 6 preamp, 6 poweramps and a hex pickup source...but it would require enough power to run a small city!

So...if you are sucked in by the promise of the moog thing, beware...they are very short on technical details. It is clever, but there is a lot of circuitry and a remote power box and circuitry box and power as well.

You have raised a bunch of threads but seem to misunderstand some of the very basics and proposing "short cuts" like hex inverters. These are not designed for audio...they may be adapted to produce distortion through mis-application...but not for what you appear to be seeking (although I am confused...do you want an acoustic sound, do you want to run piezos without batteries...or do you now want to develop some kind of sustainer?)!

You also seem to have latched upon these components because they look like 6 inverting preamps...but that is not what they are designed to do. To get sustain, that's a whole different thing...you need a lot of power, perhaps a preamp into a poweramp of perhaps a watt and with individual strings, perhaps each...now we are getting well beyond battery power capabilities. Once you ditch batteries, you can go even further with a convenetional sustainer design...but it is a little impractical. You also have to consider that you are proposing six coils all putting out significant amounts of EMI...how are you going to keep that out of the pickups for your proposed ultra clean sound...or even prevent the inevitable self oscillation?

For the kind of sound you appear to be seeking...the way a roland synth does it or the use of a sampler or loop technology (a simple one would be the "hold" mode on my old DD2) which will loop the last preset seconds of whatever you play for as long as you like...so hold a note and step on the pedal and it will play continuously till you take your foot off...you can even play on top of the held chord or note if you want.

The thing is, these techniques are not organic like natural feedback from a sustainer...they sound "fake"...even though they are the exact looped real time sample or hold with a digital recording. A sustainer is supposed to be expressive, touch sensitive and mine at higher drive levels will easily overpower an amp. They are also pretty sensitive to an individual player...a good thing...so that it will sound different in another players hands...all you get to hear are bad direct sound of me playing.

I did put up the clip though of Dizzy's which has a much higher production value. Unlike mine, it is more like the fernandes and such with a lot of compensation circuitry. Also...Col presnted a more sophisticated circuitry and used a dual coil driver that developed my thing even further for more control, 4 modes and cleaner AGC control and published the circuit. It won't do the range that mine will though as it is intended to sound more restrained even in the highest drive settings.

Trying to make a polyphonic sustainer...or a sustainer per string...is not as easy nor produce the results you may think and certainly harder than you expect. For instance while with a bridge piezo you might get pretty good separation, there will be a lot of cross talk in any magnetic sustainer and the piezos will have significant phase differences that will require sophisticated compensation.

On this last point...although my designs look simple and are...they have been in development here since May 2003 and it took a few years to get the design formula to the consistency it is now. The big difference between my devices and any other sustainers is that I developed a driver that doesn't not require phase compensation and so can run on batteries, be compact and practical for DIY creation. Experience has shown that changing the formula means completely rethinking things...most have failed.

In short...don't knock it till you have tried it. And at least start with something that works before wanting more. It may be in fact that you are seeking more than you want or need or over complicating things for the sake of it.

Please try and spend some time to really dig deeper into the technologies of piezos, hex systems and sustainers before trying to create your own or propose things that are extremely impractical or even impossible.

I am happy to explain things...but really it needs to start at basics and you will need to understand how these things actually work and are intended to do and the limitiations of what can be done.

I have gotten a good sound from a single piezo mounted in the neck socket of a strat with a small preamp and battery that would last months and require very little modification...combines well with magnetic pickups and works for only a few bucks. Others have offered up similar things bridge mounted and such. Resorting to piezo lighters is "an idea" but not necessarily a good one. Not all piezos are the same...how do you propose to even solder to a piezo...I doubt that it has even the dual elements on there...but maybe...but for a few bucks you can get buzzer elements and cut them up. Most of the commercial things only sound any good at all through highly equalized preamps...look at any decent electro acoustic preamp for instance. Multiply by six for a true hex system...add six poweramps and six times the energy for a hex sustainer. You are definitely want something special to go to that much trouble and expense...but then it would take a few years to get it to even work...I spent a year on my hex drivers :D

Not that I want to put you off...but it may not be as easy as you think

pete

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PSW, thanks, for extended explanation.

Yes I am seeking for organ like sound or any other that’s different from what I have now; It may not be very clean and so not much sustained. I did not built many circuits, just read entry level electronics books. According to them one may build a good, low voltage, low current, amplifier with CMOS invertors (just use 3 of inverters), and 1-2, outside resistor and capacitors. Some chips designed to drive old TTL logic and have output current of 10mA, that’s more then enough.

The waveform of oscillating string is not pure sine wave. So even 10% of harmonics distortion will not spoil the sound that much. So it’s really feasible to build onboard “clean” amplifier with CMOS logic.

Hex phonic sound is really cool thing that should be simple with CMOS chips and minimalistic circuitry. As it was noted by fookgub the problem is inter modulaton of string notes. As I build few power amps I know its a problem. And one channel circuits have this inherent – the inter modulation, as soon a there is nonlinearity in the signal channel or compressor pedal or somewhere.

Seems I am from another school of guitar builders, I really do not see beauty of 1 channel (and even 6 channel) sustainers.

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So...your interest here is in sustainers, not so much the piezo thing?

Some chips designed to drive old TTL logic and have output current of 10mA, that’s more then enough.

Not nearly enough to drive a string I suspect...the output impedance alone will necessitate a coil of some difficult (read...exhaustive testing and advanced knowledge) calculation...and geting into the 1omm space between strings while not affecting of being affected by the equally strong driver right next to it will be something to behold.

The waveform of oscillating string is not pure sine wave. So even 10% of harmonics distortion will not spoil the sound that much.

No...a string isn't vibrating at a sine wave, but a complex pattern. The amplifier should aim to reproduce this as accurately as possible...distortion of any type (including filtering and phase or delay effects of the circuit or the intrinsic nature of electromagnetic coils) will corrupt that and so not accurately reflect the strings vibration and cause varying amounts of inefficiencies...the result will be anything from failure to sustain or even damping of vibration, harmonic generation (as in the 180 phase technique I use). or simple distortion of the actual string vibration...which sounds like "distortion"...

Hex phonic sound is really cool thing that should be simple with CMOS chips and minimalistic circuitry. As it was noted by fookgub the problem is inter modulaton of string notes. As I build few power amps I know its a problem. And one channel circuits have this inherent – the inter modulation, as soon a there is nonlinearity in the signal channel or compressor pedal or somewhere.

Depending what you mean by Hex of course. True Hex sound is very rarely heard as you would need not only six outputs with separate preamps...but separate amplifiers and speakers...and even then the room and resultant sound will be mixed in our ears back into a single signal.

If you mean Hex as in polyphonic...my sustainers and the commecial units (barring the ebow) are fully polyphonic...although a more even response where the lower strings don't predominate is a worthy pursuit perhaps.

Seems I am from another school of guitar builders, I really do not see beauty of 1 channel (and even 6 channel) sustainers.

Well...many people don't see any need for sustainers at all...some actively hate the sound. Personally, the guitar sound is something I enjoy and the sustainer is an addition to the conventional guitar, not a total redesign of the instrument. There is immense beauty in the natural sustain and decay of a guitar.

As for "channels", I really don't follow. My assumptions are contradicted in the above sentence. You see no "beauty" in a single channel sustainer...I take that to mean as in a conventional sustainer that sends a monophonic combined signal of what ever is played to all the strings and let the resonances of the strings sort out the drive of each of them...and yet no "beauty" in a 6 channel system. Surely....a 6 channel system would be a hex system?

It is analogous to an acoustic guitar. All six strings are connected to the same top...the result is a combination of vibrations amalgamated into the tops vibration by the combination of string vibrations...you still hear every string and "beauty" in that surely. So, with a sustainer...a single electromagnetic coil sends a combined signal to all the strings...is this not simply the reverse of the process. Presumably you would feel that a conventional pickup has no beauty as this is exactly the same principle a single (or noise canceling pair).... or in a monophonic guitar amplifier...where all the strings are being transferred to a single paper speaker cone by the use of magnets and electromagnetic coils?

If there is a school of guitar builders that build acoustics with separate tops for each string...I'd like to see such a thing compete with a conventional acoustic in a "beauty" contest!

What you appear to be striving for is a synth controller...unlimited sustain and realistic organ or similar type effects through entirely electronic means. A sustainer can only ever be a sustain of the guitar's sound...it can emulate some of the attributes of other instruments that are blown or bowed or electronic like organs or synths.

I am sorry if I come off a bit catty...but I suspect that there are some misunderstandings and a little naivity about sustainers, how they work and what to expect from them...or at the very least the problems associated with what you may be trying to achieve...on the other hand, I may not be fully understanding...

In my pursuit of hexophonic drivers...like this one...

CP9xHEX.jpg

and many others like them built in the early part of the thread...I learned that many of my preconceptions about exactly the kind of things you are suggesting were false or impractical. Like you, I too was attracted to Hex inverters and have a few here still that I don't quite know what to do with. But...there are some fundumental practical problems with these designs and it took a lot of effort, expense and ingenuity to come up with even devices like the above (a true hexophonic driver...as in six completely separate driver elements) to prove that there were flaws in my thinking about them

That is not to say that I am committed to my designs...I recently went back to a bridge driver concept on a bass that had 4 separate elements and multiple magnetic field arrays like the above. Nothing would please me more if someone were to experiment and achieve even more out of the device.

While I have conceived of a "sustainer" instrument my work has always been towards realizing a practical device that does not compromise the instrument as it is and what it does...but is an addition to it. I have even gone so far, unlike previous sustainers....not to have a driver that replaces the conventional passive pickups and choice on a guitar. In the main I work on modifying the neck pickup or in a surface mounted driver as on my new tele. Neither concepts require any permanent modification and add little (in the case of the tele) or no extra magnetic pull on the strings.

Still...beauty is in those who hear it, and what you can make of the resources at hand. Moog have done something like what you are considering I suspect...but as there appears to be no patent detail and they are suspiciously coy (they have a switch to make it work like mine does kind of)...exactly what they have achieved and how well it does it is completely conjecture. Obviously it has required enormous power and circuitry requirements and expensive pickup systems to drive the thing. For the type of effect I think we would both like to see, I suspect that they future really lies with modeling guitars like the Variax in 3 or 4 more generations and advancements in digital sampling rates and synth technology merging with it.

pete

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Just found the sound I was looking for, cool, esp. first 2 chords

http://matthias.grob.org/pMusic/ppSound/PolyDemo.mp3

and nice article on that, quote below

In '79, I understood, that the ordinary monophonic distortion limits the rock musicality. In order to keep the interference harmonics of the distortion within the harmony of the music, the rock guitarist mainly uses 5th and octave intervals. With separate distortion of each string, any chord can be played fully distorted and each note is clearly audible - no dirt.

end quote

Edited by grtvrm
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Cool link...nice sounds I agree...

But what you have there is essentially is early guitar synth technology similar to that of the GR500 and GR300 and such. Fantastic units...Pat Metheny makes good use of such things still today...check out "offramp" for that classic sound.

Now we have switched again from piezos to sustainers to hex pickups to analogue synthesis (distortion and filtering effects being the key to this type of thing)...A hex system of this type is essentially 6 mono effects...so you can use things like analogue octave dividers and ring modulator type things that can't cope with multiple signals to produce complex and rich sounds.

I see like many others this guy has "patented" the hex piezo bridge...hmmm...LINK

Did you know that the real early roland and similar synths actually used tape heads for the hex pickup elements...essentially the technology has not changed to this day.

One of the reasons I have never revealed my own unique "hex" driver technology is because it also functions in reverse as a hex pickup and probably has more value in that mode fitted into a bridge or something over a driver as in that position it would not be affected by string deflection in bending.

All the same, these, piezo and electromagnetic mini pickups like tape heads do require significant preamplification and tone shaping to sound "good"...at least compared to a conventional pickup.

Now, if this kind of polyphonic distortion is what you are really after, well there are a whole lot of different approaches to making polyphonic pickups. Typically, string deflection is an issue so they are mounted as close to or actually in the bridge (as with piezos)...a hex inverter may be of use here, but far more could be done with conventional audio op-amps...the TL071 series for instance is a standard, easy to use and tailor gain and filter stages and comes up to 4 per chip...most importantly, designed for audio applications.

One of the problems with hex pickups is trying to get a clear independant signal. If mounted away from the bridge, obviously string bending can become an issue. But regardless, with magnetic systems...there is usually some cross talk. Piezo's too suffer from this to some degree as they will pickup any vibration, not just from the pressure of the string directly from it. Completely independant bridge elements can help but even the vibrations from the guitar wood will be picked up and confuse many of these kinds of polyphonic effects.

SO...this would be an interesting project...but one that would require quite a bit of work...some of it has been superseded since the 70's by newer guitar synth and even digital modeling technology. A lot of work is already fast happening in this area with fender bringing out the V strat for instance with multiple pitchshift tunings. It is only a matter of time before these new instruments start exploiting still further their hex capabilities in this direct. Roland has far exceeded this already...I recently went to a demo of their latest guitar synths for instance...infinite sustain, infrared control, digital synthesis like a keyboard, extremely realistic sample triggered sounds of real instruments...pretty amazing capabilities but at a cost of course!

DIY though sounds like a daunting task. There is a diy synth like thing about that uses hex inverters...just can't think exactly where it is, but might make an interesting effect with a bank of them on a hex guitar...

pete

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granted i haven't tried a hex preamp with it however if you want a smaller package to work with. you can try this dual version for all the tweakers out there. i found a nifty little idea if you take one of these and flip it upside down its roughly the same pinout as a dual opamp. with a secondary card and a couple of spare parts you can mod a tubescreamer with one of these.

little bit of creative liscensing though

have fun.

ed

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