Minimalistic piezo buffer for passive blending?

[Rob Strand]

What kind of impedance do regular single-coils have anyway? I've seen vastly different values quoted.

The problem is they *are* all over the place and they are quite variable over the frequency range.

I'd probably put and average value around 22k but I wouldn't batter an eyelid over say 15k to 33k.   An overall average simply doesn't exist.

So this plot for a Fender Jazz is quite useful but it's hard to read the impedance values accurately.
Maybe 15k ohm average upto 2kHz and 50k ohm upto 4kHz.

http://davel.datatruck.com/Fender%20Jazz%20Bass%20Pickup%20Repair.htm



You can see some more graphs for guitar pickups here.   Watch out trying to eyeball the average on these graphs as the frequency axis is linear which weights the eyeballed impedance in the high frequencies.  Maybe just eyeball upto 2kHz or so,
http://www2.ece.rochester.edu/courses/ECE140/resources/Guitar-Project/Electric_Guitar_Pickup_Measurements.pdf

Two pickups in parallel with be lower!

[vin97]

Ok, then I guess the Richter preamp could work quite nicely.


One question regarding the trim pots: When put behind the individual buffers, do they have to be "proper" grounded volume pots (voltage dividers) or would it also work if they are merely introducing series resistance (unground)?

[amptramp]

Ok, then I guess the Richter preamp could work quite nicely.


One question regarding the trim pots: When put behind the individual buffers, do they have to be "proper" grounded volume pots (voltage dividers) or would it also work if they are merely introducing series resistance (unground)?

Designers prefer to use a low output impedance and a high input impedance to ensure stompboxes can be connected together without interacting to much extent.  Since the input impedance is high, a series resistance would have to be higher to achieve acceptable attenuation and this would result in excessive resistive noise.  The buffers should have proper grounded pots as voltage dividers.

[vin97]

And this also applies when there is a grounded master volume pot at the end of the circuit?

[amptramp]

^^^

Correct, this is how it is implemented.

[vin97]

I have been talking with Andreas Richter and he is currently building a custom version of the PPX Piezo Preamp for me.
He is still trying different things to get the best sound and mixing behaviour. He also said that it is not as straightforward as putting a resistor behind the output as this will make the sound very dull.