Vacuum Tube Analog Synthesizer
Tube VCO,VCF, VCA, Magic-Eye
Solid State design for modulation modules:
interface for VCOs and VCF. Tuned by Sysex
paths are 100% tube and "on air" wired
3U 19' alu rack with transparent plexyglass
X2TS is a prototype ...
Not for sale !!!
VCO & VCA modules
schematics are from Eric Barbour,
Metasonix Schematics are working very well ! I have 6AU6
penthodes for the VCA. Other tubes are OB2 regulators,2D21
Thyratrons and 12AU7 dual triodes. The VCO ouptut signals
are attenuated with a resistor divider network to attenuate
signal at the VCF input . The VCF is very sensitive to the
volume of incoming signals and it is very easy to ovearload
it with a couple of VCOs...
VCF is a Salen&Key filter as implemented in Synths'r'us
site by René Schmitz. I have modified this schematics
to add CV control for VCF Cutoff and resonance. Builded with
6AU6 and 6U8 tubes plus a 220V/24V transformer for feedback.
LDR cells are coming from an old measurement tool and are
fast and accurate. All optical parts of the filter are enclosed
in a metal box to avoid ligth and electronic interferences.
It is possible to use the VCF/VCA module independently with
noise module only or an external audio jack. A little line
preamp +20db ( aop) is integrated to the modulation pcb.
here to view more pictures of the X2TS internal assembly ,VCO,
Magic Eye is
an EM81 wired as a basic peak meter, plugged on VCA output.
Another pin compatible Magic Eye with different look is the
Modulation pcb contain a pair of ADSR ( asm1),homemade
LFO (tri,sqr,rnd) + CV adders/scalers, glide, noise.
X2TS Modulation schematic (pdf)
PSU is builded with a PC386 PSU (on top) modified to deliver
6V@5A for tube filaments and 14V@1A for the MIDI3CV.There
is a couple of 2x15V @1.5A transformers mounted under the
PC psu to produce the +/- 150V for tubes modules and a classic
7815/7915 psu for modulation pcb. There are switches for both
VCO on rear panel to disconnect unused modules if i plan to
play with one VCO or with the filter/vca module only. The
little trouble i have with the power supply is that when tubes
are cold, i need to remove 1 tube to start the synth , else
the PC386 unit fall down until i remove it ... It is another
reason why i have implemented modules On/Off switches...There
is no problem when tubes are hot.
X2TS Power supply schematic (pdf)
Box and mechanics in the X2TS are 100% recycled materials.
The box is a 19U rack with smoked plexyglass. It is a "inside
modular" unit where everything can be reach by removing
3 screw max from front panel to rear top and bottom..... Tubes
modules are asssembled on Alu bars with ceramic isolators
for parts and a 12 pin connector is provided for each ot them..
This way i can remove or replace any module very quickly and
it is perfect for experiment, test, modifs... As many other
tubes based devices, the mechanical work was a bit complicated
and has required a lot of time and energy!.There is a big
cooler between PSU and tube modules placed here because it
good look and not really used as a cooler.... The entire psu
unit stay relatively "cold" and do not require fan
or particular cooling. 6AU6 tubes in VCF and VCA are shielded,
this is not really a need , but as i had some 8 pins sockets
with shields to use ... All I/O jacks ( 6.35) , MIDI and PSU
plugs are on rear panel
of the X2TS internal assembly ,modules and pcb.
The front panel
is a couple of aluminium panels, placed behind the plexyglass.
The front has been printed on an adhesive sheet for laser
printers.This film has been glued on metal parts who are fixed
by pots and switches.Knobs are Rean's for 3.18 mm potentiometers
(Sfernice and Spectrol cermets). The green power switch is
recycled from an old dead measurement tool ...I really love
recycling this kind of good parts !
Panel part 1 VCO -VCF (gif)
Front Panel part 2 Modulation (gif)
drive VCOs and the VCF cutoff . It is a MIDI3CV interface,
the ancestor of my "MCV series"
with a special firmware of 2 table of 28notes to tune each
VCO independently. The interface is controled by the same
PC config software i use for basic versions of the MIDI3CV.
All this work rather well, but the MIDI3CV is an 8 bits interface
and a bit short in precision to reach perfect tuning with
unmatched Thyratrons tubes. Both VCO delivers a lot of signal
and good tuning is obtained only when they are hot and only
for a defined position of tune knobs, else the interface must
be retuned. The best way to avoid VCO beating on every notes
is finaly the Sync switch ! I have in mind to build another
MIDI interface with a larger PIC and a 12bit DAC or a multiplexed
one, to reach a more precise control. At this time, the 8
bit interface is good enough and allow to a scale of 2octaves
(quite) well tuned.
of the X2TS were taken with a VHS camera acquired with
a cheap video card on PC. Also i have assembled a little
AVI file of the X2TS at work, without any pretention.It
shows the magic eye in action but there is no sound coming
with. This file is encoded with DivX 5.02 codec to reduce
the size as much as possible. The quality of this video
is very low...
the "X2TS at work" DivX file (547ko)
are sounds produced by the X2TS "summer 2002"
version , recorded with the synth plugged directly into
the PC sound card....