I'm scanning your online catalog and seeing 20mm/27mm and 41mm piezo sizes. What are
the differences..are there any differences tonewise?
Also..you show a 250K pot and a 500K pot. I have used a piezo tune-o-matic bridge on my homemade
Les Paul types and the volume control supplied by LR Baggs is 5 meg ohm. Piezos are high impedance
devices according to my understanding and tube amps have typically 1 megohm input impedance.
Now a 500k for a humbucker pickup or 250k for a SC (single coil) sounds right, but I would think
that if the piezos are wired directly into a volume control, it should be around 1megohm at least.
Am I correct in this assumption?
What about wiring the two piezo's in parallel. Someone stated that two piezos will sound louder than
1 piezo or two wired in series. Again this appears to be the result of the transducer's very high
input impedance.
Replies
Thanks for the quasi-scientific explanation on piezos. I already wired mine up in parallel and even included
a tone cap/pot..although the tone pot is for the SC more than the piezos, even if they are switched
through the 3 way.
Basically, they sound ok with 250k volume control..which I decided to use because of the SC and the fact
that Fender uses 250K vol pots on their SC, although Gibson (I believe) uses 500k pots on their P-90 SC.
I agree that the piezos lack bottom end and are basically "fair to middlin" as far as frequency response.
The piezo electric effect can be summed up in a nut shell. The voltage output is determined by the pressure applied (sound waves) on its surface area with a fiddle factor of the piezo electric effect.
So, as the most piezos are made of the same material the fiddle factor is constant. Also the sound waves pressure are constant across choice of piezos its the size or surface area that will affect the choice. 20 and 27mm wouldn't really make much difference in the scheme of things. The 41mm piezo should be louder but there is the volume pot and the impedance matching between guitar and amp. The resonant frequency will change over the sizes but I find all piezos to be biased to the treble end compare to magnetic pick ups.
When dealing with audio there is never a linear response. Often there is an exponential response when falling in impedance, 1M to 500K appears to be 'half' the actual response may only 10% different.Whereas 100k to 1K may be as much of 60% difference in volume. Actual responses may be difference but the principal is as you approach a low impedance the effect is greater.
When dealing with parallel pick ups/piezos, I fear of going in to Kirchhoff, Thevenin and ac theorys and deep mathematics to resolve the ultimate sweet spot for whats sounds good and gives best signal transmission from ac sources (pick up/piezo) to amplifiers, effects pedals or mixing desks etc.
I think the best way to look at this, transducers in parallel will not give a louder signal than a single one if you got a volume pot over a high impedance say 250K. However that said there are reactance of capactive and inductive elements (including wires and leads) which will change over the frequency range of said tranducers.
By adding parallel transducers and the positions of the transducers you introduce phase shifts and even more possibilities for tuning to specific frequency response curves. This starts getting into mega-deep calculus and material worthy of a good Phd.
What I use is a simple rule of thumb. I never go below 47K pots for volume because the impedance mismatch of guitar output to amplifier input starts to affect the signal strength and you start getting a quieter guitar.At the end of the day I turn my volume pot to a point that sounds good for what I want at the time and if the tone is a or volume is a bit low I'll use the controls on my amp.
Turkish said:
What you say is true..but Gibson, and other guitar makers, have traditionaly used LINEAR resistive element taper
in vol pots and Audio (logrithmic) taper in the tone pots. It may have something to do
with the pickup combining switch and the way the controls were wired up, though.
Don Thompson said:
So what value of volume pots have you used on your builds?
I know from past experience with the piezo tuna-matic bridge, that the piezos seem
to be sensitive to pot values. LR Baggs supplied a 5 megohm vol pot with their piezo t-o-m
bridge and I thought that was rather high..but after installing it, I found out that the pot
would work up to a point,d then cut out completely about 1/4 of way down to zero.
Now, it may have something to do with the o/ps of the individual saddles which were
then summed together on a printed circuit summing board.
It just wasn't as smooth an audio taper or even a linear taper, as I had expected,
so I had to add a 100k resistor to prevent the pot from going to "zero" accidently.
Does the disc style piezo(s) and the 500K pot have a nice smooth tapered volume response?
C. B. Gitty (Ben) said:
Thanks CB...I think I will go that route and order one through your shop along with some
other things. The preamp is priced right and until I get it in and working, I really won't
know for sure..BUT..and here's the beauty of getting CBG supplies..you are not paying
hundreds for Fishman or Schatten or LR Baggs piezo transducer/preamps.
I went that route one of my LP customs and the T-o-M bridge (from Stew-Mac)
sounded very thin to me, because the individual saddles were the peizos.
I had to add a tone control/tone caps and a preamp to tame the sibulence.
It took some experimentation..as it general does with
these kinds of mods..but I'm going to go for one of your preamps shortly.
Roy Alderman said:
For a 3 + 3 tuner arrangement, you need a minimum of 6.5 inches of headstock from the nut.
If you want some kind of emblem or decal to personalize it, sometimes it's better to have
an extra 1/2 inch of headstock as well, but most often the emblem will fit between the
rows of tuners.
Regarding -
" still need space for the volume/tone for the P-90 pickup, and a mini-selector switch"
It depends upon if you want separate controls for the P-90. If not you could run the piezo and P-90 via a 3 way switch and the output from this to your preamp.
I did this for a CBG with 2 minihumbuckers and disc piezos using a 5 way switch.
Video link is here http://www.cigarboxnation.com/video/comparing-cbg-pickups
When I get around to it I still plan to add a preamp bypass so I can use it if the battery goes flat.
If you prefer piezo discs rather than a rod you can get the 2.5mm connectors off ebay which plug into these preamps (if it is the same as the ones I have come across) and wire the disc to that.
Regards,
David
As for the pre-amp and feasibility... I can't guarantee that it will give you the exact sound you are looking for, but it should sound pretty good! When it comes to stuff like that, about the best advice I can give is to try it and see!
It appears that my response to your response got buried in the response exchange,
MY SPECIFIC QUESTION TO YOU is in the form of this comment. (See below)
Ok..I've looked at the different sizes of piezos and their resonant freq response.
Now whether
that makes any difference in tone, I don't know..but after dealing with a very thin sounding
Piezo t-o-m (on one of my previous projects) and having to fine tune it with a tone control,
I'm leaning more now towards
just getting the EQ-7545R preamp,
even if it takes a battery and you need a large
opening (3.75 x 1 9/16) in the top side.
I still need space for the volume/tone for
the P-90 pickup, and a mini-selector switch, so it may be a tight squeeze, but I could always
put the volume/tone selector on the bottom side with only 1 grommet
and the
preamp and another grommet on the top side for balance.
Does this sound like it's feasible?
Oh and..how does the rod piezo mount? lengthwise underneath the bridge?
C. B. Gitty (Ben) said:
Oh and..how does the rod piezo mount? lengthwise underneath the bridge?
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