The Plasma VU-meter display audio levels on Russian bargraph
gaz discharge tubes IN-13
or IN-9.
Features:
- Balanced/unbalanced
Inputs
-
Cal/Uncal levels ( +4dBU/-10dBV)
- -20dBU
to +20dBU (If calibrated to 0dB)
- 40 dB range
over 10Hz up to 25kHz bandpass
- True RMS
Levels
- CV output
to use as an enveloppe follower
- Compatible
with IN-9 and IN-13 bargraph tubes
- Stackable
pcb for stereo or multi-track displays
- Integrated
hi-voltage transformless PSU ( pcb v2.1 for IN13 only)
- Module powered
by +/-15V or +/-12Vdc ( pcb v2.1 only )
Circuit
overview
The
true- RMS converter stage is inspired from a diy project published into the french electronic
magazine Radio Plans (now disapeared since many years).
A
THAT2252 chip convert audio levels ( dBs ) into a linear control
voltage ( Volts DC ) to
drive an IN-13 (or IN-9 ) gaz discharge bargraph tubes ...
The
THAT2252 is set to provide almost 0V on the output at -20dBu
input level and 2.50V at +20dBu.
An adapted RC time constant set the up/down
raise time to imitate classic vu-meter balistics, The IN-13/IN-9
driver stage is
based on a common LM358 and a hi-voltage power transistor. The full
range display is set by a trimmer.
All
audio circuits are powered under +/-15V . To simplify the
integration of the VU meter into various devices, a high
voltage DC to DC converter has been included. It transform
the +15Vdc into a clean +150Vdc at approx 10mA. The high
voltage converter is a minimalistic switched psu based on
a 555 and a mosfet transistor. This cheap and secure solution
provide an independant power supply for each tubes. It is
ideal for multiples Vu-meters displays.
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Please be aware this schematic work with
potentialy lethal DC voltages !
Use at your own risk !!!
I
am not responsible in any cases or situations of
any damages or destructions of devices or humans
resulting of the use of informations provided into
this page.
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Schematic
, bom, pcbs & co...
Here is the Plasma VU-meter prototype v1.0 ...It
require a well regulated external hi-voltage
power supply. This old version is not advised for
stereo /multitrack displays ...
Download
the Plasma VU-Meter schematic v1.0 (pdf )
Here are pictures of the VU-meter v1.0 fitted with IN-9 ( purple ) tubes,
both powered with an external hi-voltage psu
bellow it is the same... but with IN-13 tubes.
Much more stable and it require at least 2 time less current on the hv-psu
Clic
on pictures to view in big
The
Plasma Vu-Meter revision 2.1 ...
Here are
now pictures of the most recent Plasma VU-meter pcb,
the revision 2.1
- Designed to hold IN-13 or IN-9 tubes
- Stackable
- Based
on an optimised schematic
- only one trimmer for full
range display , hardware calibration
- Include
the high voltage transformless psu 150V @ 10mA ( on the left on
the picture)
- Powered
under +/-15V dc ( or +/-12V) only
Download
the Plasma VU-Meter BOM v2.1 (txt )
Download
the Plasma VU-Meter schematic v2.1 (pdf )
Please notice the plasma VU-meter pcb v2.1 integrated hi-voltage psu is only to drive IN-13 tubes. This psu is not powerful enough to drive IN-9 tubes !
For IN-9 afficionados : The IN-9 require at least 12mA but many tubes need up to 50mA for tube pre-polarisation during a short time period to be able to reach the full range at 12mA ...However it is still possible to use the RMS detector+ tube driver holded by the pcb v2.1and to supply the IN-9 tube with a more powerful external hi-voltage psu. Be aware that 50mA is for one IN-9 tube so for a stereo version you will need at least 100mA under 140V dc ...
To build an accurate VU-Meter the IN-13 is the best choice :
- It is very stabe
- it start glowing at the bottom of the tube
- it consume less curent : 5mA full range, ideal for multi-tracks displays
- it have increased length ...
The
revision 2.1 pcb is perfect to build mono , stereo or multitrack
displays
Here
is a stereo Vu-meter with IN-13 made with two rev 2.1 boards stacked...Ready
to work !
The
stereo version with IN-13 and revision 2.1 pcbs in action
on YouTube !
