Replies to This Discussion

Permalink Reply by Mark on September 1, 2010 at 2:05am

I'd certainly be interested in hearing one of these if someone has made one work. I'm not sure about their use of a piezo attached to one of the regular pickups. I guess the results will be dependent on the way the main pickups are mounted and possibly also on other structural aspects of the guitar. I've read of systems that use piezo-type devices attached to other areas of the instrument including the headstock and the body.

I agree that, if it works, it is essentially a form of controlled feedback. I believe the same is true of the "infinite guitar" system developed by Michael Brook as well as the Sustainiac and various other commercial sustainer systems.

By coincidence I was thinking about building something similar into a CBG - although using a magnetic driver rather than a piezo. Your post has prompted me to do some background reading and I've turned up quite a lot of patents and other technical information that makes me think I've overlooked a few potential problems. I might put the build on hold while I figure out more details.

so I might put the build on hold for a while

Permalink Reply by Kevin Lawton on September 1, 2010 at 1:47pm

Does this actually work or is it just a theory ?
I can't really see how fixing a piezo to a magnetic pickup is going to send a signal back into the strings. The piezo will attempt to vibrate the magnetic pickup a minute amount, but this rather small amount of energy does not seem to have a way to get into the strings.
If the piezo was mounted under the bridge, creating a kind of 'servo bridge' then i think it might be in with a chance.

Permalink Reply by Naz Nomad on September 1, 2010 at 11:07pm

Kevin, I don't think it's meant to vibrate the strings. Like I said, it's not technically sustain, more like 'controlled feedback' from the pickup with the piezo attached.

But good call on yet another experiment for us to try ... dual piezo bridge ... one piezo as a pup, the other being driven by a preamp to excite the bridge ...might cause some funky noises.

Permalink Reply by Mark on September 2, 2010 at 5:04am

I think it's arguable that controlled feedback is one way to create sustain (the Sustainiac, Fernandes Sustainer and the Michael Brooks Infinite Guitar all use forms of controlled feedback).

I can also believe that mounting the piezo driver on a pickup might just work - although I think there are better places to mount it (as illustrated in various patents for sustain systems). The thing that any magnetic pickup detects is RELATIVE motion between the pickup and the strings. Usually this involves the strings moving and the pickup effectively staying still, however it could also include the pickup vibrating. On a hollow body guitar with a mag pickup mounted to the soundboard the pickup will vibrate slightly as the body of the guitar resonates, and that will contribute to the amplified sound.

I think one problem with mounting the piezo driver directly to the pickup is likely to be that most of the feedback will take a direct route from driver to pickup. I can see such an arrangement possibly just giving you a screaming howl, like uncontrolled feedback rather than controlled sustain. I'd reckon it would be much better if the feedback route involves the signal travelling through parts of the guitar which affect pitch or improve tone. In most of the commercially available sustainers the feedback is routed through the strings in some way, which allows the player to control the note by fretting and damping the strings. So, for example, if you have mag pickups mounted in the usual sort of positions you could put a piezo driver in the bridge. I believe one commercial system uses a driver attached to the headstock. Another way is to have a magnetic driver (essentially just a coil, like a pickup but without needing a magnet) in place of one of the pickups on a multi-pickup guitar (the Brooks Infinite Guitar was apparently based on a Tokai "strat" modified in this way). In this case the feedback route is from the driver into the string and then from the string back into the pickup. This allows you to control the sustained note by changing the ringing pitch of the string.

Putting a piezo driver into a bridge with a piezo pickup seems to me like another way to have too direct a route - I think it carries a big risk of sudden uncontrolled howl.

Nazzy 'Blind Boy' Nomad said:

Kevin, I don't think it's meant to vibrate the strings. Like I said, it's not technically sustain, more like 'controlled feedback' from the pickup with the piezo attached.
But good call on yet another experiment for us to try ... dual piezo bridge ... one piezo as a pup, the other being driven by a preamp to excite the bridge ...might cause some funky noises.

Permalink Reply by Mark on September 2, 2010 at 5:19am

One possibility I'm thinking about is essentially a basic CBG with a mag pickup and a piezo (the piezo attached in the usual way to the underside of the soundboard). Switches would allow either or both devices to be used as regular pickups, but I'd also arrange to be able to switch the piezo onto a separate circuit where, instead of being a pickup, it would act as a driver. The driver circuit will be based around an LM386. I think the real trick (or perhaps even black art) is in controlling gain and tone shaping in the driver circuit - I still have a way to go before feeling confident that I've got that aspect fully figured out.

Permalink Reply by Naz Nomad on September 2, 2010 at 5:38am

Good points ... I'm wondering if a huge (50mm / 2'') piezo might give a wider range of vibrations when driven? I know the different size piezos are rated at different frequencies (when used as sounders). Am I right to think the gain would simply alter the strength of vibration and NOT the frequency of it?

I''m quietly excited to see someone try this ... hehe.

Mark aka. Junk Box Instruments said:

One possibility I'm thinking about is essentially a basic CBG with a mag pickup and a piezo (the piezo attached in the usual way to the underside of the soundboard). Switches would allow either or both devices to be used as regular pickups, but I'd also arrange to be able to switch the piezo onto a separate circuit where, instead of being a pickup, it would act as a driver. The driver circuit will be based around an LM386. I think the real trick (or perhaps even black art) is in controlling gain and tone shaping in the driver circuit - I still have a way to go before feeling confident that I've got that aspect fully figured out.