Opinion wanted on this QE VU Buffer Amp

[nwsoundman]

I finally figured out the Vcc+ and - for this circuit. It uses a cheesy zener setup to get a +/- 9 VDC. If this circuit looks ok I will replace the diode pwr supply with a +/- 15 VDC supply. PRR gave a VU buffer amp drawing but if these cards are good to use I will use these instead. They mount right on the meter out of the way. Forgive my amature drawing. I did it left handed in MS Paint. Can't wait for my right hand to heal up.

http://home.earthlink.net/~nwsoundman/id11.html

I didn't include the cap values.

NWSM

 

[NewYorkDave]

Looks good to me if you don't need a floating input. This is conceptually very similar to the buffer design PRR posted a little while ago.

Actually, PRR's figure 2 (with its "quasi instrumentation amp" arrangement) is better in that it offers an easy means to vary the gain with only one resistor.
http://headfonz.rutgers.edu/VU-buff-gain.gif

I would suggest a hybrid of PRR's circuit with the resistors and trimpot around the VU meter as shown in the Q.E. design. A 2.2k trim would give you finer control than the 4.7k shown on the Q.E. schematic.

 

[nwsoundman]

If one of the inputs is tied to ground when the meter is looking at a unbalanced line will it work? That would leave one input for signal and the other grounded, not floating. I will have the meter bridged across pins 2 and 3 on the out XLR and when I am bypassing the eq the output signal will be balanced and when the eq is "in" the output will go unbalanced and pins 1 and 3 will be shorted. I am learning from these questions and a bit stubborn to use the QE parts.

NWSM

 

[nwsoundman]

I think it is working fine. I built a test jig and everything seems ok running the QE design balanced or unbalanced. If anyone sees a reason for me not to use as explained in my post above let me know please.

Thank you New York Dave and PRR.

NWSM