Plate Reverb pre EQ Issue

[deveng]

Thanks!

I actually was looking at that one as well.  But that 1Gig ohm output impedance would best be handled by an amplifier very close to the piezo.  That's one of my considerations for going with the integrated amplifier and 100 ohm output impedance.  If someone already has the pickup amp designed for high impedance piezo's that may be a good choice and I'd be interested to see how it compares.  I really don't know how much the 0.3 ounce piezo would effect the plate vibration.    Experimenting with these fairly expensive piezos could get costly. 

I've also designed a PIC controlled stepper motor system for the damper mechanism.  It will store calibrated reverb positions, has the stepper ramps, end of travel stops and will work with a remote!  After I get the drive/receive electronics dialed in I'll build the mechanicals for the damper.  The PIC program with LCD display and 4x4 keypad and stepper motor has been bread boarded and works.  I've got the pcb for controller designed but have not fabbed it yet. 

Regards,
Jeff

 

[Bo Deadly]

But that 1Gig ohm output impedance would best be handled by an amplifier very close to the piezo.

That makes sense but the cables that come with them look pretty long. The cable needs to be above average for sure. I don't think there's anything particularly special about a "charge amplifier". It's probably just a JFET common emitter not entirely unlike what you might find in an LDC mic. It's not like you need a 100dB noise floor. Putting the whole Enchilada into an insulated enclosure would make a much bigger difference in noise performance.

But it looks like you're on the right track to me. I'm just being pedantic at this point.

 

[deveng]

In the early stages of my plate I had built a pair of high impedance JFET pickup amps.  In fact it was one of the first things I built.  I just never got around to applying it to the plate since I got the Isotrons.  If I ever need to go back to it, its ready to go! 

One thing I noticed during the initial testing of the Isotrons, very quiet.  My problem with the sound appeared to be plate tension and the driver (an old Acoustic coneless driver).  It was distorting a bit on transients so drum hit attacks were not good.  Could be I was driving it too hard as that's a common issue.  I managed to get my hands on an original EMT driver magnet with the wide gap.  I purchased a 3/4" voice coil and fashioned a bullet head on it so its very much like the original EMT coil.  I need to get my plate properly tensioned first then I can drill and mount the bullet coil.    Only then will I know if I'm on the right track!

Regards,
Jeff