mattell starmaker guitar, with optical pickup system...

[anotherjim]

The simple relay drive for the sustainer was of course too simple. Because the coil drive is only one polarity, the pole piece magnetic remanence means it stays magnetised at one polarity somewhat and only pulls the string at the signal peaks. The drive polarity needs to reverse with the signal polarity to cure this. In fact, just like the magnetised pole pieces of a normal guitar pickup, it can actually act as a damper on the string if too close. Driving my sustain coil with a 386 like a speaker is an obvious next step but at least I know I have an electromagnet that should do the job.

The Opto definitely needs a cover. Trying it for the first time during the day, the heat of the winter sun was enough to cause it to cut out when it faced the window.

[anotherjim]

FYI, there was a stupid error in the Opto circuit I posted earlier. The signal out can't come from the opamp output because that is held at Vref on the +input, so it actually is taken from the emitter of the phototransistor. I've replaced the image.

The 386 drive for sustainer isn't strong enough. Even clipping, there isn't enough swing. It's quite a big coil with a DCR of 100ohms and of course, the impedance at signal frequencies is higher still. I can just about get it working with the coil at the mid string position. A bridge amp might be enough since that will bring a x4 power increase.

[amptramp]

FYI, there was a stupid error in the Opto circuit I posted earlier. The signal out can't come from the opamp output because that is held at Vref on the +input, so it actually is taken from the emitter of the phototransistor. I've replaced the image.

The 386 drive for sustainer isn't strong enough. Even clipping, there isn't enough swing. It's quite a big coil with a DCR of 100ohms and of course, the impedance at signal frequencies is higher still. I can just about get it working with the coil at the mid string position. A bridge amp might be enough since that will bring a x4 power increase.

As it is, you are applying a pull force on both the positive and negative excursions of the string.  You would need a polarized string to make this work.

When you apply a north magnetic pole on one half of the signal and a south pole on the other half of the signal, you get drive only for the even harmonics of the signal.  The drive cancels out for the odd harmonics, including the fundamental.  You may need push-pull drive coils with class B drivers that only drive one side at a time.  Think of it like the magnetic field inside a push-pull output transformer.

[pinkjimiphoton]

but do magnetic poles even matter in a case like this with the opto stuff?

[Ben N]

but do magnetic poles even matter in a case like this with the opto stuff?

Not for the pickup, for the drive.

[anotherjim]

Thanks Ron. That's given me a lot to think about. I'm going to play with some magnets!

Jimi, I want a Sustainiac type thing to excite the string. No speaker.

[pinkjimiphoton]

Thanks Ron. That's given me a lot to think about. I'm going to play with some magnets!

Jimi, I want a Sustainiac type thing to excite the string. No speaker.

jimmy, don't ya need a mag pickup for a sustainer to interact with? i never tried my ebow on an accoustic, i thought it needed the magnetic field of the stock pickup.

but i like where you're going with this

[anotherjim]

Yes, need magnet. Doesn't have be a pickup though....

[anotherjim]

Put a button magnet (one of those super strong molybollydenim tings) on the back of the coil pole piece and we have action with the basic 386 amp drive. Still has to be too close to the string for my liking and placed no further from the bridge that a neck pup would be. So probably still needs a stronger drive but the 100R coil is far too high a resistance really but it's the best I have. Some 5v coils are nearer 50R but that will probably still be weak.

Incidentally, if anyone out there does try hacking out a relay coil. Be careful of the fine winding wire as there's no bobbin - it's fitted directly on the steel pole piece. The steel "L" frame that is bent up to pivot the contact armature needs cutting off at its corner as it seems to divert the flux away from the top.

[anotherjim]

The bridge amp drive seems the way forward. Hooked up an NJM2073 as per the datasheet circuit. This chip is obsolete so if you're in the same position, a pair of LM386 may be the way to go. A TDA2822 might be easier to find as a pin for pin equivalent to the NJM2073 for this job. Just got to fit the sustainer now into the neck pup position.

[anotherjim]

With the coil fitted in and clamped sustain is much more reliable. Like an Ebow the polarity matters. One way excites fundamentals and the other way excites harmonics.

There's none of the frequency doubling effects (at least not that's musically useful) we theorized earlier in this thread. If the string moves too far out of the optical "axis" it makes a very broken scratchy noise. I think this is because the string doesn't vibrate in a consistent up or down or side to side manner but kind of rotates with it.

I used an old guitar string that when tuned to what feels like the right tension actually turns out to be E6 tuning. The string measured at about .041". For non-musicians reading this, string gauge numbers are thousandths of an inch even in metric land.

Anyway, it seems I've made a one-string cello. Rather than frets, I'll hunt around for a suitable fingerboard material. I'll probably go quiet on this now while I do some luthiering to make it some kind of presentable instrument.

How to make something pitched up in something like the violin range? I think the type of Opto I'm using isn't the best choice, although a shorter scale will help, but I think it needs a different kind of sensor that can see a thinner string.

[amptramp]

One way to get sustain is to run a current proportional to the output along the string with a crossed magnetic field.  After all, that's how a speaker works.  Whether you can tolerate the voltage on your fingers is up for debate but based on people having no problem touching 9 volt batteries, I doubt it will be an issue.  Why bother having an amplifier to speaker interface then the mechanical speaker to string interface when you can have a direct amplifier to string interface?

[duck_arse]

How to make something pitched up in something like the violin range? I think the type of Opto I'm using isn't the best choice, although a shorter scale will help, but I think it needs a different kind of sensor that can see a thinner string.

the mouse sensor. dual elements, use both at the same time, the aperture is "right" for a string. if only we could find a datasheet for one of that type.

[anotherjim]

I've ordered some TCRT5000 reflective sensors to play with. I'm not expecting too much difference, but it might be more tolerant and easier to fit multi-string. The Opto I currently have would only suit bass string spacing and then they'd have to be staggered to overlap the screw lugs although they do have a simple mounting method.

Those Willcox Guitars optical pickups could well have dual detectors. They don't give much away (probably a patent we could search for) but the setup instructions say...

First, adjust the highest string; then the lowest; and then go back and re-trim the highest string. This can be done by ear, or using the visual indication of the centering LED on the Motherboard in the electronics cavity.

Centering LED it says, so maybe this refers to getting a balance between two detectors?

[pinkjimiphoton]

maybe we can find some info in this stuff

https://www.manualslib.com/manual/341207/Yamaha-G10.html?page=7#manual

https://www.soundonsound.com/forum/viewtopic.php?f=24&t=64216

https://patentimages.storage.googleapis.com/8f/33/7c/d9a010f0ef97e9/US4723468.pdf

http://synthmanuals.com/manuals/yamaha/g10/owners_manual/

https://usa.yamaha.com/files/download/other_assets/7/320087/G10E.PDF

this is all stuff related to the yamaha g10 guitar synth system, but the reason i post it is cuz it used the optical pickup apparently as a VIBRATO sensor.

[anotherjim]

It's interesting that the Willcox system has an optional GR synth output. Maybe my log can drive a PLL frequency doubler better than a normal guitar can?

[anotherjim]

Well now, the Yamaha system is plain crazy clever but uses no optoelectronics. It pings the string length sonar/radar style with an ultrasonic pulse and measures the time it takes to echo back and calculates the fret position from the timing. All strings have to be tuned to the same F#.

[pinkjimiphoton]

guess i was mistaken, thought when i restored mine it talked about using optos to sense the vibrato or something like that. mah bad!

[anotherjim]

There might be opto but not for pitch. There's what looks like a magnetic pickup for velocity but a 3rd thing looks for string bends.

[anotherjim]

https://www.chuckwhite.com/photonmidicontroller/photon-reverse-engineering.html
Photon huh. Coincidence.