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Old 22nd August 2012, 04:01 PM   #1
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Default New idea for instrument pickups

I've occasionally thought of a new kind of instrument pickup system for metal strings that would use a high-frequency oscillator coil like a metal detector (changes frequency with proximity to metal), but demodulate it to get back the audio. Seems to me it might work well. So I thought I'd mention it here in case it's never been patented LOL now I have evidence I thought of it before this date.
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Old 22nd August 2012, 04:06 PM   #2
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One possible advantage might be nearly lossless transmission of the modulated signal to a remote demodulator (no guitar cable high-frequency losses). Some of the same advantages that make FM synths so much cleaner (less noise) and punchier (more dynamic range) than a simple Moog or ARP.
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Old 22nd August 2012, 04:19 PM   #3
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See if you can find some old Wurlitzer electric piano schems. They used an HF oscillator and a capacitive pickup..
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Old 23rd August 2012, 12:02 AM   #4
Simon B is offline Simon B  United Kingdom
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Nice idea cyclecamper,

To the best of my knowledge it's original too.

Wurlitzer electric pianos do use capacitive pickups, but I think they simply put a high voltage across the reed to the plate, fed through a big resistor, keeping the charge fairly constant:

" q = C V
"

The capacitance varies as the reed vibrates, so the voltage varies inversely. The varying voltage is then amplified directly, no oscillator and demodulation.

The Wurli sound is noted for hardening up very noticeably with more forceful playing, though this tends to break the reeds. Some of this change in sound is mechanical and some is due to the inherent non-linearity of the pickup.


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Old 23rd August 2012, 12:09 AM   #5
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Quote:
but I think they simply put a high voltage across the reed to the plate,
I can tell you that sticking your fingers in there will result in bad language, a loud zap in the speaker and a couple of broken reeds!
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Old 23rd August 2012, 01:19 AM   #6
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OK, next new idea for cool and unique giutar pickup......a magnet and a Hall effect sensor chip.....or six. I built one and it does work, but isn't quite right yet.

Somewhere on this forum about a year or two ago I detailed another one of my brain fart ideas. It seems to be all ofer the internet now as a "sustainer".

Wind the clock back about say 50 years. Motorola needed a method of generating, and detecting clean single frequency sine waves. They invented the Vibrasender, and the Vibrasponder.

These were plug in devices, each tuned to a specific frequency. Inside each one there was a vibrating reed, which looked very similar to the reeds in the Wurlitzer piano. There was a short arm fixed at one end and weighted at the other end with a steel weight. The weight was filed or ground to tune it to the exact frequency. Frequencies went from 67 Hz to about 1.5 KHz.

There was a coil mounted on either side of the weight. The coils were connected to an amplifier circuit to generate tones, one coil on the input, and one on the output, creating a feedback that only works at the frequency that the reed is tuned to.

For detecting tones transmitted over radio, one coil was connected to the receiver output, and the other to a detector circuit. The reed would vibrate only if the tone coming from the radio receiver was the same as the reeds resonant frequency.

What does this have to do with a guitar??????? Well we have coils, they are called pickups. We have a vibrating reed....or string, it does not matter. So wire it up just like Motorola did 50 years ago. Connect one pickup to the input of a small amp, and wire the other pickup to the output . Yes, it works.

I got a job at Motorola in 1973, and it took me about a week to find out that you could get tones out of a vibrasponder by smacking them. I just had to take one apart to see how it worked. Thus the guitar string idea was born. I think it was about 10 years before I actually built one. I have made several since, and I have learned a few things.

There are now commercial "sustainer" products. I haven't seen one or used one. From what I have seen on YouTube, they don't have enough energy to start up by themselves, but they will keep a plucked string playing.

There have been several homemade versions scattered across the internet. Most have the same flaw, they involve rewinding a pickup with a small number of turns using thicker wire so that it can be driven by a low impedance (8 ohm) chip amp. WRONG there is not enough inductance to get the fat strings singing. Use a high impedance driver like an opamp on 27 volts to feed a stock guitar pickup. Do NOT use a humbucker, the fields tend to cancel.

I got a new one working with a tube driver that really sings. Tune to an open E chord, pick up a glass slide and go at it. It plays itself!
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Old 23rd August 2012, 07:42 AM   #7
Enzo is offline Enzo  United States
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Wurlitzer did it in the 1950s with their Zenith Cobra record tone arm as used in their juke boxes. The input stage to the amp was an RF oscillator. The tone arm cartridge instead of a voltage generating crystal or coil and magnet was an inductor the stylus wiggled, the inductor was wired via shielded cabvle to the input stage where it changed the tuning on the oscillator. The signal then went through a detector to extract the audio from the varying RF.

It worked, though I can't claim it was superior in any way. Then stereo happened and that killed it. To this day, I have a small Cobra tone arm mounted on a hunk of plywood, just for servicing old Wurly amps of the Cobra era. Without the tone arm, the oscillator stage wouldn't oscillate.

I know it was a Zenith idea, but the only place I myself ever saw them was in the jukeboxes.
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Old 12th January 2014, 07:50 PM   #8
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I vote "or six". Because there are experiments worth trying
that might be simpler with separate pickups for each string.

I for one, would like to bend the scale from 12TET to 19 or
BP, and implement automatic tuning and intonation training.
The right pitch shift for any individual string is totally wrong
for any other, so the need for individual pickups.

And a fret to string contact matrix to know the player's other
hand. Yeah, that's an extra wire to each fret, and there might
be some problems with aliasing... Open to suggestions...

I figure you tap a "Fix it!" button only when you finger the
strings in some normal way, no deliberate bend. It would
never try to self train or correct intentional string bends
in play... Train twice, once low and once high, and the
intonation should be good too.

And then there is IMD. Distortion adds very musical low order
harmonics, and is fine with single strings and chords that share
a simple low order harmonic relationship. But awful with some
complex chords that sound fine on a clean setting.

The problem IMD mixes up irrelevant tones in the process.
If you distort strings individually before summing them, IMD
does not need to occur unless you choose to distort again
later in the chain.

I don't care optical, hall, piezo, or even coils. If there is a way
to keep them separate, or buck out cross-talk from neighbors?
To some extent, the body of the guitar will couple them all,
even if individual string pickups were completely isolated...

Ohyeah, and "Formant Modelling" per each string and fret
position. Make sound like single coil or humbucker, bridge
or neck. They both will have the same fundamentals and
harmonic frequencies, but equalized differently per string
and fret. If you got it all broke down to six individual strings
in the frequency domain, and know the fret position thus far:
Its no big extra to fudge those formant envelopes to make
sound like any famous brand's pickup arrangement.

Last edited by kenpeter; 12th January 2014 at 08:18 PM.
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Old 13th January 2014, 01:53 PM   #9
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Quote:
Distortion adds very musical low order harmonics, and is fine with single strings and chords that share a simple low order harmonic relationship. But awful with some complex chords that sound fine on a clean setting.......The problem IMD mixes up irrelevant tones in the process
This is why you can't crank an amp to 12 and play unrestricted chords without creating ugly noise. Power chords are simple two or three note chords constructed such that the IMD products are musically relevant, but the amps bandwidth must be restricted a bit to avoid sounding like......

Quote:
I don't care optical, hall, piezo, or even coils. If there is a way to keep them separate, or buck out cross-talk from neighbors?
There are hex magnetic pickups designed for MIDI interfaces, and there is the Ghost Pickup piezo system from Graphtech that will give you an individual output for each string. I have experimented with both, and I have wound some of my own individual string pickups. The piezo's need a very high impedance buffer, and the hex pickups have rather low output since you can only wrap so much wire around a single pole piece. The solution to both is opamps or tubes inside the guitar.

Quote:
If you distort strings individually before summing them, IMD does not need to occur unless you choose to distort again later in the chain.
The IMD will occur later in the chain if anything gets nonlinear (including the speaker), which it WILL since all real guitar players will turn it up past 11. I decided that you need.....a seperate amp and speaker for each string.

So, I made a crude setup with a Ghost Pickup system in the bridge and a home made six coil setup in the neck position with wires running to 3 Tubelab SPP boards and 6 seperate speakers. You can crank this thing past eleven without any obvious IMD except what's created inside your head when your ears go nonlinear....yes it happens. I have not found cross coupling inside the guitar to be a problem since it is at a rather low level.

I'm now believing that 6 seperate amps is overkill. It looks like the two bass strings can share the same amp and speaker. Maybe some others can be combined too. I like the seperate volume control for each string, as well as different speaker sizes.

My current setup is a crude experiment with a Fender Strat neck and a fixed (no vibrato) Strat bridge mounted to a rectangular pine board. There are no opamps on board yet, just twisted pairs to a breadboard about 3 feet away, so there is some hum. My lab is currently being boxed up for a move, so there will be no more progress for a while. I am still trying to complete a real electric guitar body before woodshop class ends forever.
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