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Sustainiac And Piezos


FerretallicA
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I am going through the motions of getting my ideal realistic ( :D ) custom guitar design together. At the moment I'm leaning heavily towards having no magnetic pickups at all (Variax-style) and just having a Ghost setup for the bridge. I'm quite happy with the sound of a GK2 pickup into a VG8EX (it's just the tracking which disappoints) so I can't see why I wouldn't be at least equally happy with a better pickup and a VG99. Being able to plug into a normal rig "just in case" is of absolutely no interest, if I want to do that I'll use a standard guitar.

The first catch is that I am also very keen on a Sustainiac thrown into the mix. You supposedly need a separate pickup to feed the sustain driver with the most common (see: only) suggestion being to use a standard magnetic bridge pickup. If I absolutely have to install a bridge pickup to make it happen then fair enough but I'd much prefer not to. The Sustainiac web site has the following in their FAQ:

COMPATIBILITY WITH PIEZO-ELECTRIC PICKUPS You can operate the Sustainiac if you select your piezo as the guitar output. Piezo pickups, on the other hand, don't provide a good input signal for the sustainer. Piezos and digital modelled pickups, etc. produce phase shift in the signal which alters the performance of electromagnetic sustainers. So, you must provide a conventional MAGNETIC PICKUP INPUT to the sustainer. But, you can use piezos while the Sustainiac is on, and they don't interfere with each other. Same thing for guitars having hexaphonic pickups such as the Roland GK-2a for synths etc.

The haven't updated that in quite some time... I'm pretty sure it said the exact same thing when I was tearing my hear out trying to make a similar idea happen only in 7-string form (no prizes for working out where that went and how much hair I pulled out in the process). That was years ago so I'm wondering if that was just based on generic piezos like you get in acoustic pickups. Has anyone tried using decent modern hexaphonic piezo based systems to feed a Sustainiac (or home made sustain driver for that matter)? Failing that, any educated guesses as to what I could expect? I tried emailing Sustainiac but that was a couple weeks ago and I still haven't gotten a response.

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I suspect that sustainiac know what they are talking about there, although, some "tests" have indicated the DIY version works on an electro acoustic with only piezo pickups on it.

There would definitely be a problem with anything that has tracking problems and potentially with modeling systems like the Variax which has to go through the digital analog conversion which causes a very small delay but big enough to create definite and to an extent unpredictable phase differences.

Using a bridge pickup (seems happier with an HB) like a rail just to drive the sustainer may be the easiest solution...obviously you then have the option of having that output as yet another signal from the guitar. The stealth driver on the sustainiac also operates as an active neck pickup when off.

The driver will work with piezos and hex synth drivers for sure...but getting the piezo to drive it is highly experimental. If you were prepared to test all systems on a guinea pig guitar (something I have been known to do) then you may be able to develop something that works but I would not stake a custom design on you being successful.

Some have suggested that the moog guitar uses the piezos to drive hex drivers but I suspect not personally and there is no details available. They do however most likely use the hex piezos to create a canceling muting effect...all of it is guess work...

Good Luck...

pete

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The Sustainiac probably compensates for the phase shift introduced by a magnetic pickup (in fact, their patent claims a phase compensation network as part of the driver circuitry). So it may not work as well with piezo pickups. You could certainly add a magnetic bridge pickup for use with the Sustainiac, but it doesn't really seem to be what you're looking for. I would suggest that this is the perfect project for building your own sustainer. Since you're using piezos, you won't have problems with direct feedback from the driver to the pickups. I've been meaning to do a full calculation of the phase between the string displacement and the resulting output voltages for piezo and magnetic pickups, but I just haven't gotten around to it yet (need to pull out some old notes from my transducers class). That would be a handy thing to know, so I'll be sure to post it when I get it done.

There would definitely be a problem with anything that has tracking problems and potentially with modeling systems like the Variax which has to go through the digital analog conversion which causes a very small delay but big enough to create definite and to an extent unpredictable phase differences.

The delay caused by the Variax system is orders of magnitude greater than the period of the frequencies we're interested in. Feeding a sustainer driver with the post-Variax signal would be a very dodgy proposition. It is, however, entirely possible to grab the signals from the piezos directly before they hit the Variax circuit. In fact, I'm planning to do this on my Variax guitar (which is currently being refinished after gathering dust on a shelf for about a year). You could to the same thing with a piezo-to-midi guitar. In fact, the Graphtech preamp allows easy access to buffered output from the piezos and midi output at the same time.

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