[sdiy]Stereo plasma VUmeter demos...

[m.bareille at free.fr]

Hello Larry ,

> Will these run directly off of the 10v p-p (+/-5v) of many modular synths?
> If not, what modifications might be necessary to make them work that way.

Yes ! Under the basic configuration , the VU-meter plot -20 to +20 db. I have
plugged it many times during testsspe directly on my modular VCOs/VCF and VCAs.
No, problem at all even at lower freqs.

About input calibration options : the input stage is set by default at unity
gain = the 'calibrated mode'.

On the pcb i have managed an optional 'gain' trimmer/pot footprint to increase
the input stage gain up to +25dB to set the Vu to work full range with low input
signals. It shift the 0dB point to the top of the tube. This trimmer/pot can be
mounted on the panel with a switch as desired.

In a similar way it is possible to add an attenuator pot before the VU-meter
input to calm down any heavy signal of more than +20dB and to shift the 0db
point to the bottom of the tube... It is also possible to combine both systems
gain and attenuator , variable and /or fixed...


> I'm thinking that a really neat 'retro' module could be made that would show
> the CV or Audio synth signal patched in, with '0' being in the middle, -5v
> at the bottom, and +5v at the top.

The VU is sized to monitor LF or BF signals, not really DC... There is a
capacitor to block DC voltage before the RMS detector. I let you compute the cut
off frequency ;) This can be adjusted too ...

If you want to monitor only DC voltages the best it is to shunt the RMS detector
stage and to wire ( with a switch..) the incoming DC signal directly into the
LM358 driver stage. Add a voltage divider or an attenuator pot to scale the
input eventualy... My schematic/pcb is generical, up to you to wire it as
desired to fit your need. It is quite simple in most of the case...


Well, to be clear my goal was to build an audio VU-meter with the IN-13/IN-9
tubes, a thing that nobody seems to have done before... My idea was to make +/-
a hombrewed RTW equivalent but without the RTW cost !

Please do not fire me,  but at the price of the panel surface square meter of
most modulars, specialy MOTM ones, i deeply prefear to put useful functions here
rather than decorative things... I understand howeverthat many of you like to
transform their modular into a Christmas tree ...I am a little bit like this if
i do not take care ;)

Anyway i have many other module ideas using the IN-13/IN-9 tubes but with much
more interest for the average synthesist than a simple VU/voltmeter... They are
ones i will build in 5U MOTM format ... More to come, stay tuned :)

Cheers,

Marc B.