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Experiments with Piezo Discs
Andyjr1515
Frets: 3128
Ask me what is the simplest and most natural sounding pickup system for acoustics and I would say K&K Pure Mini every time.
In fact, I am just about to fit one to my homebuilt dreadnought in preference to the Shadow Nano system presently installed.
And that is what I recommended to Tom, whose LAG Tramontane I'm sorting out for him. And that led to an interesting discussion. Although the Pure Mini is only £99, Tom asked why you couldn't simply use the small piezo discs that are as cheap as chips and use those - surely that's what's under the fancy epoxy covers of the K&K dots?
Decent question. Only one way of finding out - so £5.99 later I have myself 20 10mm discs:
In fact, I am just about to fit one to my homebuilt dreadnought in preference to the Shadow Nano system presently installed.
And that is what I recommended to Tom, whose LAG Tramontane I'm sorting out for him. And that led to an interesting discussion. Although the Pure Mini is only £99, Tom asked why you couldn't simply use the small piezo discs that are as cheap as chips and use those - surely that's what's under the fancy epoxy covers of the K&K dots?
Decent question. Only one way of finding out - so £5.99 later I have myself 20 10mm discs:
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Comments
1. Did you just connect them in parallel;
2. Did you replace the bare leads with screened cable; and
3. What are you running the output into?
1) parallel
2) no
3) DI box is a must (or a tu3)
I think what you're really paying for with the K&K is the R&D that's gone into making a product which has had all the bugs ironed out - number of sensors, placement, fitting method etc, the fitting jig itself, plus the jack and soldering done properly (not everyone can do this themselves) - rather than the cost of the pickup elements. For someone who isn't experienced at tinkering with bits and bobs and doesn't want to mess around inside their best guitar, it's still good value for money in my opinion.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Andrew told me to save my money and made one up for me…
Well, for starters: its simplicity; the naturalness of the sound it produces; the signal strength of the sound it produces.
This is where it is fitted - either fixed to the bridge plate with CA glue or two-sided tape:
The positioning of the dots is stated to be critical and the Pure Mini comes with a simple but effective kit for positioning the dots underneath in the hidden depths of the soundhole. The idea is that the dots are immediately below the saddle and spaced to add even coverage for each string position. So in this example, the left hand one will be sitting between the 1st and 2nd string, the middle one between the 3rd and 4th, etc..
What I've not found in any searches, is anyone doing comparisons of the sound if the the dots aren't quite where the instructions say they should be placed. Also, the epoxy cover over the piezo - does it simply protect the wiring or does it effect the piezo response? And are the K&K dots the 'standard' piezo discs or different?
Other features - which are certainly important - is they use shielded cable from the dot cables to the jack and the barrel jack is one of decent quality.
But his motivation - same reason I'm willing to spend a bit of time experimenting - is more curiosity and understanding better the boundaries and potential of piezos in acoustic and hybrid applications. Better to do that with £20 of bits than £99 of fancier bits
Actually, not quite. The reason is that K&K use the bridge pin holes to position the dots. And the LAG doesn't have bridge pins...
So I have to come up with a cunning plan of how to do that...
(And by the way, anyone who hasn't tried positioning something with either glue or sticky tape in your hand while that hand and forearm bent through a soundhole will have no idea just how difficult to stick it in the right place! Even letting go when it's in place is difficult
Luckily, I do indeed have a cunning plan. Just got to find out if it's going to work.
to give an idea of positioning… the bridge bolts are where the pearloid dots are…
https://music.apple.com/gb/album/the-flame/1601031181?i=1601031315
Stick a mobile phone in there and video call it from another... just like the heart surgeons do
And, there is an opportunity for these - it allows the larger piezo discs to be used because for a pinned bridge, there is limited space between the front edge of the bridge plate and the pins; too small for the larger piezos. I was talking to a electronics wizard, Geoff, yesterday who gave me some similar sized ones to try if I wanted. Here's the difference in size:
So - do I replicate the K&K with the smaller discs or do I use the larger discs?
Well - the logic probably goes that the larger discs give out a stronger signal and therefore less proportional 'noise' for the same amplified level as the smaller ones.
But my experiment is more about replicating the fitting recommendations and seeing if I get a decent natural sound at decent absolute noise levels - so at this stage I will use the small ones. If I find I do, indeed, get excess noise, then I will try again with the larger ones.
The other thing that @poopot 's pick shows is the epoxy covering. And that also ties in with @ICBM 's point whether the epoxy backing on the K&K's dots creates an audible difference.
I hadn't realised but Geoff has been fitting piezo discs for years - and some he's been asked to to epoxy backings and others not. His view is that there is no performance change - more that it's useful for protecting the solder joints. I don't have the time on this project to do the full A/B/C comparisons, but it's a topic to hang up for some future tinkering
That's a tone balloon - modern repros just don't have the same resonance.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
And so how to get the positioning right?
Well...the bridge plate (yellow) is sitting inside the X braces (blue) here:
And so, if I cut a piece of wood, just long enough to fit between the X braces, and just a touch deeper than the bridge plate, I know exactly where that piece of wood is in relation to the bridge. And if I put some two sided tape on it, I can also feel where it is to remove it when I need to:
And then, I could tape the piezos temporarily to the other side of the wood to the sticky tape. Trying with just one at first to test out the feasibility:
And - because the piece of wood is deeper than the bridge plate, even if the dots have CA or two sided tape on them, they are not going to stick until I press them down against the plate with my in-sound-chamber finger.
I tried it (no sticky at the moment)...
...it worked!
So, next step is to wire three piezos up, align them in their exact positions on this side, and then glue them in place on the inside. I might even use CA glue. Now there's misplaced confidence for you
I might be wrong, but I'm not sure that the K&K's are shielded between the buttons and the join point to the jack cable - I think the wires are a bit too thin. But as I say, I might be wrong. We have a fairly buzzy house - if it buzzes I'll have a rethink.