Replies to This Discussion

Permalink Reply by Skeesix on November 14, 2010 at 7:11am

I've used 250k, which is the "darker" one. It doesn't seem to have much, if any, impact on the piezo sound. That was with a volume pot only.

If you use 2 piezos in parallel, it will halve the impedance and make it sound somewhat better.

In general, you can temporarily hook up the circuit with alligator clips and experiment to see what you like the best.

Permalink Reply by carverman on November 15, 2010 at 1:45am

Thanks Skeesix.

I have both 250k and 500K pots.

What range of tone caps do you use on these piezos?

Permalink Reply by KK Dirty Money on November 15, 2010 at 4:51am

This is a very interesting discussion, as I'm starting to learn about the ins and outs of wiring up CBGs.
Are these 250Ks and 500Ks used for volume, tone, or both?
Do people use tone knobs on CBGs very often? Does it matter that much with a piezo?
And finally, this is the first time I've heard mention of running two piezos parallel?
You say it makes them sound better. Is there any info on wiring schematics and other tips for using multiple piezos on a single instrument? If so, where?
thanks so much,
KK

Permalink Reply by Mark on November 15, 2010 at 9:49am

I've used pairs of piezos quite successfully. Someone whose work and views I respect greatly on this sort of subject is a guy called Bart Hopkin who is a mainstay of the Experimental Musical Instruments website. His interests cover all kinds of instruments - guitars being only an incidental part - but in amongst his writing is material that can provide insight to guitar builders.

Here are a couple of links to articles about use of multiple piezos:

http://windworld.com/tools-techniques-ideas/another-important-consi...
http://windworld.com/tools-techniques-ideas/piezo-film-pickups-how-...

Incidentally, two piezos in parallel don't necessarily have half the impedance. Although impedance is expressed in ohms, the same units as resistance, it is a more complicated phenomenon than resistance. When you are dealing with alternating currents - such as you get with pickups and other audio applications - you move into the territory of complex numbers when working out the effect of combined impedances.


KK Dirty Money said:

And finally, this is the first time I've heard mention of running two piezos parallel?
You say it makes them sound better. Is there any info on wiring schematics and other tips for using multiple piezos on a single instrument? If so, where?
thanks so much,
KK

Permalink Reply by MichaelS Country Boy Guitars on November 16, 2010 at 1:47am

I recently built one with 2 piezos in parallel, and a switch to turn one off. So now I can have a single or double pick-up. There is a definate sound difference. The single is sharper and the double is mellower. Both are very close in volume output. I prefer the double if I did not have the switch. For some handy schematics check out this thread by Wes Yates: http://www.cigarboxnation.com/group/cbgwiringelectronics/forum/topi...

Permalink Reply by carverman on November 17, 2010 at 8:37am

Thanks Mark. I've known about phasing on humbuckers and how they work and how some guys
flip bar magnets end over end 180 degrees to get the nasal out of phase sound on 2-wire humbuckers, but this phasing phenomena with disk piezos is new territory for me.
I've read and bookmarked the links you supplied.

I'm sure that if you could use a 440hz tuning fork on the acoustic
top with the piezos mounted and an cheap oscilloscope using a x-y lissajous figure, the
phasing of each piezo is easily seen and matched...but that requires a cheap audio scope
or facsimile to display the horizontal input and the vertical input.
http://www.jmargolin.com/mtest/LJfigs.htm



Mark aka. Junk Box Instruments said:

I've used pairs of piezos quite successfully. Someone whose work and views I respect greatly on this sort of subject is a guy called Bart Hopkin who is a mainstay of the Experimental Musical Instruments website. His interests cover all kinds of instruments - guitars being only an incidental part - but in amongst his writing is material that can provide insight to guitar builders.

Here are a couple of links to articles about use of multiple piezos:

http://windworld.com/tools-techniques-ideas/another-important-consi...
http://windworld.com/tools-techniques-ideas/piezo-film-pickups-how-...

Incidentally, two piezos in parallel don't necessarily have half the impedance. Although impedance is expressed in ohms, the same units as resistance, it is a more complicated phenomenon than resistance. When you are dealing with alternating currents - such as you get with pickups and other audio applications - you move into the territory of complex numbers when working out the effect of combined impedances.


KK Dirty Money said:

And finally, this is the first time I've heard mention of running two piezos parallel?
You say it makes them sound better. Is there any info on wiring schematics and other tips for using multiple piezos on a single instrument? If so, where?
thanks so much,
KK

Permalink Reply by Mark on November 18, 2010 at 9:49am

I don't think there's anything to be gained by testing piezos like that. It's one of those things that's so complex to analyse that there's probably little point. Wherever you put a pair of pickups there will probably be some notes where the predominant vibration modes are in-phase, some where they are exactly put of phase and some in between. I think the best practical approach is probably crude trial and error - before fixing pickups permanently in place try fixing them temporarily in various positions (eg. with tape) and see what sounds best.

carverman said:

Thanks Mark. I've known about phasing on humbuckers and how they work and how some guys flip bar magnets end over end 180 degrees to get the nasal out of phase sound on 2-wire humbuckers, but this phasing phenomena with disk piezos is new territory for me.
I've read and bookmarked the links you supplied.

I'm sure that if you could use a 440hz tuning fork on the acoustic
top with the piezos mounted and an cheap oscilloscope using a x-y lissajous figure, the
phasing of each piezo is easily seen and matched...but that requires a cheap audio scope
or facsimile to display the horizontal input and the vertical input.

Permalink Reply by carverman on November 18, 2010 at 3:15pm

Thanks Mark. I understand that the vibration sensing mode and resulting behaviour of
these devices to produce a/c waveforms is rather complex, since they don't seem to
follow any specific electrical theory rules like magnetic pickups.
Trial and error and using your ear as the final criteria is probably the
best way as you suggest.

Now the last question..is there any point to adding a tone control to these?
... and if so, what value of cap should I start off with?

I added a a tone control to a T-o-M piezo on one of my 6 string builds,and had to go through a range of caps from .01uf to .047uf and ended up with a value of .047uf to tame the sibilance.

Permalink Reply by carverman on December 8, 2010 at 1:23am

Sorry missed your question on tone pots.
I've made a custom semi-solid (semi-acoustic) LP and I wanted to install a fairly expensive
LR Baggs tune-o-matic bridge on it. Each saddle was a separate piezo pickup, so there
were 6of these which had to be tied together in a summing board, then either hooked
up to a 5 meg volume pot (supplied with the piezo), or directly into a 9v blend preamp.br />
Since I was also using 2 HBuckers, I decided to go with the preamp at first, but found
a big difference in volume between the hbuckers and the piezo bridge when
switching between sources. As well, the piezo seemed to have more "sibulance"
because of where it was located picking up string vibrations..right at the bridge.
Basically a wee bit too much treble! I installed the 5 meg volume
pot before the preamp, that helped with getting the levels between sources
balanced, but the piezo tone was not to my liking.

I ended up installing a 5 meg tone pot next to the 5 meg volume pot, then tried a range
of caps from .010 to .047 uf, eventually ended up using a .033uf to provide the treble
rolloff that I liked.

KK Dirty Money said:

This is a very interesting discussion, as I'm starting to learn about the ins and outs of wiring up CBGs.
Are these 250Ks and 500Ks used for volume, tone, or both?
Do people use tone knobs on CBGs very often? Does it matter that much with a piezo?
And finally, this is the first time I've heard mention of running two piezos parallel?
You say it makes them sound better. Is there any info on wiring schematics and other tips for using multiple piezos on a single instrument? If so, where?
thanks so much,
KK

Permalink Reply by carverman on December 20, 2010 at 3:13pm

I'm sure this question has been asked before, but...how do you affix the piezo disks to the CB top?

Do you use a hot glue gun or use a wooden brace to hold them in place against the top?

Permalink Reply by MichaelS Country Boy Guitars on December 22, 2010 at 3:30am

I have used thin doublestick mounting tape on some of mine, I also used some foam tape but the thin tape was louder. It also picked up more 'noise" (hand movement shirt rubbing etc.)

carverman said:

I'm sure this question has been asked before, but...how do you affix the piezo disks to the CB top?

Do you use a hot glue gun or use a wooden brace to hold them in place against the top?

Permalink Reply by carverman on December 22, 2010 at 6:25am

Thanls, I used titebond on the bottom of each piezo and a thin pine rib to hold them in place.

Got my wiring done this morning and now I've glued the CB to the neck.   Once that dries, I'll

take care of any gaps with some epoxy and wood strips.

 

I wired up the SC (CB Gitty) to a 3 way mini-toggle (ON-ON-ON) to replicate the 3 ways switch on

most of my guitars with a 250K volume and a 250K tone pot (.033uf cap) for starters.

On1 = neck Sc   center on = mix   On2 = piezos

I noticed through the tap test that the SC and piezo (in parallel) (center on),

 seems to drop down the volume a bit.

 

Do you or does anybody know, if I need to insert a series "isolation resistor" of 100K to try

and isolate the SC and piezos from loading down each other? 

MichaelS said:

I have used thin doublestick mounting tape on some of mine, I also used some foam tape but the thin tape was louder. It also picked up more 'noise" (hand movement shirt rubbing etc.)

carverman said:

I'm sure this question has been asked before, but...how do you affix the piezo disks to the CB top?

Do you use a hot glue gun or use a wooden brace to hold them in place against the top?

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