I've been experimenting with amplifying musical instruments with piezos.
I did all the normal experimentation & reading and discovered that piezos are very high impedance devices that need a buffer before being input to a guitar amp.
You can drive them straight into an amplifier & they usually work fine - but the sound is better with the impedance matched by a buffer.
The purpose of the buffer is:
- to allow the piezo to have a high impedance while talking to an amp of much lower impedance.
- and practically isolates the piezo input from the amplifier. Meaning the amplifier doesn't "load" or mess with the piezo.
So - I merrily built a little piezo buffer using a j201 jfet and all was well.
I even put it into a MerryPak tin can that looked quite cute.
Which had previously had my wood wax in it - so it even smells quite nice.
Except, in my application, I was needing 13 of these little piezo's - the application being the amplification of a 13 bar marimba.
So I just joyfully connected the piezos in parallel.
Reading my own explanation above a problem starts suggesting itself.
While the buffer circuit does a fabulous job of isolating a single piezo from an amplifier; conencting the piezos in parallel means they are all connected to each OTHER. Without any buffering.
And can mess with each other.
The signal of any one piezo is being sent to the amplifier (through the buffer) ... but also to all of the other parallel piezos WITHOUT going through any buffer.
What effect does that have?
Not really sure in theory - but in practice I can report that it's not good.
The strongest descriptors are "variable" and "unreliable".
Which are not good words to use for the output of musical instruments.
Especially when someone else is going to be playing them & trying to earn a living while doing so.
Some background - a piezo is a device that converts mechanical energy (e.g. vibration) into electrical energy.
= you whack it & it generates a current
And a hard whack can generate very significant voltages.
It also works in reverse - if you apply electrical energy to a piezo it generates movement.
If the signal is AC then the piezo buzzes.
So a piezo buzzer & a piezo pickup is the same thing.
Which is why cheap piezo buzzers make piezo pickups.
In short, the multiple parallel piezos don't work.
It's worse than that - they initially APPEAR to work.
So they tease you.
And you get excited.
And you record it & it sounds good & you send it to your friends.
And they get excited.
But then very strange things start to happen.
The odd effects include:
- a few of the piezos start sounding loud and others get soft
- and with use it seems to change. One piezo will work fine for a while ... then just go dead quiet. As if its soul is being stolen by the others
- all of them have lower outputs than when connected separately
- the piezos start failing after a while - are the energy spikes from some of the piezos frying the others? Are they just bad piezos that would have failed anyway?
It all seems a little of a Black Art with the interweb providing precious little guidance.
It seems that multiple concurrent piezo applications are very rare with very little international knowledge available.
An extreme measure would be to build a separate jfet buffer for each and every piezo (all 13 of them).
I have already done an obscene amount of soldering; and find my energy a little low right now to build 13 buffers on a whim that it may solve the problem.
As with all new stuff, the internet is full of guesswork suggestions - and it's difficult to separate the wild guesses which are presented with professor-like authority of truth, from the actual useful facts.
Some suggestions include using a series resistor to protect them (seems vaguely reasonable). With others suggesting with equally profound confidence that it's a stupid idea.
I even saw one person suggesting using a diode to isolate them. And everyone on this particular forum wildly agreeing with an imagined group nodding of heads.
The author clearly didn't understand that audio signals are AC sine waves and diodes only conduct DC.
There was a quiet comment later in the thread stating that the diode approach didn't work. The author seemed surprised.
I am beginning to understand why kksound has a starting price of $1900 to amplify marimba's with piezos; even though they are talking about many octave instruments. They also speak about very bespoke and special preamplifiers.
Alas I will not be defeated.
Even if I have to build 13 separate jfet buffers each with their own trimpots to balance the uneven piezo outputs ...
But ... I don't think I'll do this in the next week or two ...
I did all the normal experimentation & reading and discovered that piezos are very high impedance devices that need a buffer before being input to a guitar amp.
You can drive them straight into an amplifier & they usually work fine - but the sound is better with the impedance matched by a buffer.
The purpose of the buffer is:
- to allow the piezo to have a high impedance while talking to an amp of much lower impedance.
- and practically isolates the piezo input from the amplifier. Meaning the amplifier doesn't "load" or mess with the piezo.
So - I merrily built a little piezo buffer using a j201 jfet and all was well.
I even put it into a MerryPak tin can that looked quite cute.
Which had previously had my wood wax in it - so it even smells quite nice.
Except, in my application, I was needing 13 of these little piezo's - the application being the amplification of a 13 bar marimba.
So I just joyfully connected the piezos in parallel.
Reading my own explanation above a problem starts suggesting itself.
While the buffer circuit does a fabulous job of isolating a single piezo from an amplifier; conencting the piezos in parallel means they are all connected to each OTHER. Without any buffering.
And can mess with each other.
The signal of any one piezo is being sent to the amplifier (through the buffer) ... but also to all of the other parallel piezos WITHOUT going through any buffer.
What effect does that have?
Not really sure in theory - but in practice I can report that it's not good.
The strongest descriptors are "variable" and "unreliable".
Which are not good words to use for the output of musical instruments.
Especially when someone else is going to be playing them & trying to earn a living while doing so.
Some background - a piezo is a device that converts mechanical energy (e.g. vibration) into electrical energy.
= you whack it & it generates a current
And a hard whack can generate very significant voltages.
It also works in reverse - if you apply electrical energy to a piezo it generates movement.
If the signal is AC then the piezo buzzes.
So a piezo buzzer & a piezo pickup is the same thing.
Which is why cheap piezo buzzers make piezo pickups.
In short, the multiple parallel piezos don't work.
It's worse than that - they initially APPEAR to work.
So they tease you.
And you get excited.
And you record it & it sounds good & you send it to your friends.
And they get excited.
But then very strange things start to happen.
The odd effects include:
- a few of the piezos start sounding loud and others get soft
- and with use it seems to change. One piezo will work fine for a while ... then just go dead quiet. As if its soul is being stolen by the others
- all of them have lower outputs than when connected separately
- the piezos start failing after a while - are the energy spikes from some of the piezos frying the others? Are they just bad piezos that would have failed anyway?
It all seems a little of a Black Art with the interweb providing precious little guidance.
It seems that multiple concurrent piezo applications are very rare with very little international knowledge available.
An extreme measure would be to build a separate jfet buffer for each and every piezo (all 13 of them).
I have already done an obscene amount of soldering; and find my energy a little low right now to build 13 buffers on a whim that it may solve the problem.
As with all new stuff, the internet is full of guesswork suggestions - and it's difficult to separate the wild guesses which are presented with professor-like authority of truth, from the actual useful facts.
Some suggestions include using a series resistor to protect them (seems vaguely reasonable). With others suggesting with equally profound confidence that it's a stupid idea.
I even saw one person suggesting using a diode to isolate them. And everyone on this particular forum wildly agreeing with an imagined group nodding of heads.
The author clearly didn't understand that audio signals are AC sine waves and diodes only conduct DC.
There was a quiet comment later in the thread stating that the diode approach didn't work. The author seemed surprised.
I am beginning to understand why kksound has a starting price of $1900 to amplify marimba's with piezos; even though they are talking about many octave instruments. They also speak about very bespoke and special preamplifiers.
Alas I will not be defeated.
Even if I have to build 13 separate jfet buffers each with their own trimpots to balance the uneven piezo outputs ...
But ... I don't think I'll do this in the next week or two ...