Voltage levels and VU meters...

[Chris Crosskey]

Hi Folks.,..

I'm designing an external input pre-amp cum signal level meter panel for my
synth. I use Disgisound specs so it's 10V P-P audio and +/-15V supply. The
pre-amps will all be un-balanced single-sided things based on 1/4 of a TL074
probably, unless someone is willing to make a convincing case for using
something better/more expensive....What I need to know is what does a VU
meter expect to see?...is it DC or AC?...The one I'm planning on using has
an impedance of 250R and a 0dB deflection of 130uA (out of a maximum of
200uA)....so whatever it is expecting, 0dB is at 32.5mV at the meter....If
it is expecting AC then all I have to do is to put a resistance divider
between it and the the switch that selects between the pre-amps (three or
four pre-amps depends if I need an op-amp anywhere else in the
circuit)....that divider would have to be in the order of 1:300 or so
yes?....

If it needs DC then what do I do, if I rectify it with signal diodes, how do
I go about smoothing it when the signal might be anywhere between 20Hz and
20kHz?....I know that I'm unlikely to need the bottom octave of that or the
top two but I want it to be capable of the full range....


chrisc