[sdiy]'plasma' vu-meter

[m.bareille at free.fr]

Hi Joe,

>
>      Would anyone be interested in a PCB set for this thing? If Marc
> is okay with me doing a layout, I'd love the chance to layout
> something like this.


I think it is not only one pcb but many to be designed around this
schematic...Draw one if you want to :)

It is very simple to add an A/D stage with a 'cv-output'amp+jack in parallel of
the Tube driver by ( pick up the signal at R4/D1/R3 point on the schematic )to
get a 'true-rms envelope follower with plasma vumeter'  I must find a shorter
name for this module ... I have a schematic ready for this too , not yet inline
, one thing at time :)

I thought about it last night and came up with
> the idea of splitting the design into two PCBs: A power supply board
> and a VU meter board.

I think it is more secure to not carry the +150Vdc through external connectors
...

One of the most frequently  config of this Vu meter for 'audio' application will
be a stereo version, probably boxed into a Rack 1U , a console module (RTW style
) may be some MOTM style like panels, and in the most designed case like those
nixies clocks enclosed into a transparent plexi box ...

In all those cases, the integrated psu seem to be the most secure.
Just keep the 'HT' transfo onboard ... The first transformer is then an AC
(wall) transformer and psu connection to pcb is secured...There is no need of a
lot of power for just 2 tubes: in the worst case they eat around 5mA at 150V
each...

The tolerance of IN13 ( and probably IN9 too) are quite wide, check the
datasheet , as usual with tubes... I have not tested yet but it is problale the
IN13 will need to be matched for stereo applications too... I have not yet
tested the calibration /linearity of tubes too...

I also think a regulated +150V with separated lines/caps for each IN will be
necessary , when the bargraph value change quickly , it drop drow the +150V
 voltage violently! I guess the C8 capacitor won't survive a long time at this
regime...

>That way if one wanted to do multiple channels,
> one PSU board plus NxVU boards could be used.

Take care with Hi-voltage DC distribution ... It is dangerous voltages...


I'd add on a
> differential receiver to the VU board so it could handle both balanced
> and unbalanced signals,

This is seem obvious for audio apps. Now if my proto is unbalanced it can be
balanced the cheapest way with two resistors added to U3A...Matching all U3A
resistors is then a good idea too... Another possible solution is chips like
INA134 & co.



Cheers,

Marc B.






>
> Best Regards,
>
> Joe Grisso
> Detachment 3 Engineering
>