Difference between pages "CGS tube VCA and wave folder" and "CGS CV cluster (previous version)"

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[[File:cgs_photo_cgs27_tube1.jpg|thumb|center|300px|]]
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[[File:cgs_photo_cgs37_cv_cluster.jpg|thumb|center|600px|]]
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'''CGS37''' the '''CGS CV cluster''' is an unusual kind of mixer. It takes two input voltages - a base control voltage, and a modulating control voltage, and creates the sum and differences of them. These different voltages are the base voltage offset in a positive direction by the modulating voltage and the base voltage offset in a negative direction by the modulating voltage. A series of equal taps between these two points results in outputs that always maintain the base control voltage at its full amplitude, mixed with a differing amount of the modulating voltage. The center output has equal amounts of positive and negative modulation cancelling each other out, and thus behaves as a straight-through connection for the base input.
'''CGS27''' the '''CGS tube VCA wave folder''' circuit board was designed to allow for easier assembly of 7 pin tube based synthesizer circuits. Going on the number of requests I have had for a tube module that runs on +/- 15 volts, the first project I present using this board is exactly that. It is a simple VCA that doubles as a wave folder/distortion unit. There are no dangers in connecting this to solid state modules due to the voltages in use, and the fact that this is really a voltage controlled attenuator, and not an amplifier. There is about 50% signal level loss.
 
   
  +
While untested, the module should work on +/-12 volts.
== How to use this module ==
 
Connect a signal such as a VCO output to the signal input of the tube module. Feed the output to an amplifier or other signal processing module. Turn the LEVEL pot to maximum. This sets the gain to maximum. When fed an 8V peak to peak triangle wave, the first half of the travel of the DRIVE pot acts as an input level control. The second half of the travel sets the amount of overdrive/wave folding. A DC offset voltage can be added to the input signal via an external CD mixer to allow shifting of the fold point, animating the output signal.
 
   
 
== Some ideas on how to use this module ==
A control voltage can be used to control the output level, in which case the LEVEL pot controls the amount of effect the control voltage has. This signal needs to be above 0 volts to turn the VCA on, though negative voltages will not hurt it. put.
 
  +
Feed your 1/v octave input into the base input, and an envelope generator, LFO, sequencer etc. into the modulation input. Connect the outputs, starting with the center unmodulated output, and working both up and down, to a series of VCOs. While the modulation input remains at zero, all of the VCOs will track. As the modulation voltage increases, the VCOs connected to modulated outputs will shift in frequency away from the base, at an amount proportional to its position from the center output. For example, a small modulation voltage will de-tune the oscillators slightly, fattening the sound. A modulation CV of 5 volts will set each output 1 volt apart, setting the oscillators an octave apart.
  +
  +
An envelope generator connected to the modulation input creates in interesting effect.
  +
  +
It of course can be used with audio frequency signals too, and may prove interesting when driving a cluster of wave multipliers or similar. Two audio signals fed to it could produce interesting stereo effects.
  +
  +
Note: The sum and differences produced by this module are voltage differences, NOT frequency differences. It is NOT a ring modulator.
   
 
== A little on how it works ==
 
== A little on how it works ==
[[File:cgs_schem_cgs27_vca.gif|thumb|center|400px|The schematic of the VCA/Wave folder.]]
+
[[File:cgs_schem_cgs37_cv_cluster.gif|thumb|center|600px|The schematic of the CV Cluster.]]
  +
All four op-amps in the input structure are wired as unity gain voltage inverters or summers.
   
  +
The base input voltage is inverted by IC1a, and fed to the inverting summers built around IC1C and IC1B. The result, assuming no other input, will be the inversion of the inverted signal, thus restoring the signal to its original condition, but at two separate places. Between these two places there is a string of resistors forming a voltage divider. As both ends of this voltage divider are held at the same voltage, each tap will also be at that voltage.
The 1uF capacitor is to reduce any clicks caused though CV bleed-through. The 1M on pin 1 of the tune is really only needed if you do not include the DRIVE potentiometer. While I have specified 50k and 100k pots, the values are not critical. Anything between 20k and 100k would be fine. The tube is not really critical either, though pinouts will vary depending on the tube selected. I chose this tube simply because I have a lot of them.
 
  +
  +
The modulation CV is mixed directly with the inverted base signal in IC1B, and is thus inverted at the output of IC1B, and the bottom of the voltage divider, the result being the difference of the two voltages, specifically, the base CV minus the modulation CV. The modulation CV is also inverted by IC1D before being mixed with the inverted base signal in IC1C, the result being the sum of the base signal and the modulation signal.
  +
  +
These mixed points are fed to the top and bottom most output jacks. At the various taps of the voltage divider between these two points, there will be correspondingly less of the modulation signal present as the two differing voltages cancel each other out. At the center point they will cancel each other out perfectly. (Because of this, the base CV has been routed directly to the center output, rather than wasting another voltage follower to produce the same voltage.)
  +
  +
Each tap on the voltage divider is buffered by a voltage follower, the 1k output resistors providing current limiting and thus protection for the voltage followers in the event of short circuits, which are inevitable as patch cords using mini-jacks or 6.5mm jacks are plugged in.
   
 
== Construction ==
 
== Construction ==
[[File:cgs_pcb_cgs27_tubev2.gif|thumb|center|349px|The component overlay. As you can tell, it is rather generic.]]
+
[[File:cgs_pcb_cgs37_cv_cluster.gif|thumb|center|600px|The component overlay. Connections can be determined from the circuit diagram.]]
  +
I would recommend the use of hand matched 1% metal film resistors be used throughout this module.
  +
 
Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.
 
Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.
   
  +
When you are happy with the printed circuit board, construction can proceed as normal, starting with the resistors first, followed by the IC socket if used, then moving onto the taller components.
When happy with the board, use wire and parts placement as shown in the following diagrams.
 
   
  +
Take particular care with the orientation of the polarized components such as electrolytics, diodes, transistors and ICs.
[[File:cgs_wire_pcb_cgs27_tube1.gif|thumb|center|400px|Start by putting in the following links. Note that one wire runs under where the tube will be mounted. Test fit the tube socket. The holes may need enlarging, as may a few other holes around the board, depending on the components used.]]
 
[[File:cgs_wire_pcb_cgs27_tube2.gif|thumb|center|400px|After the wires are done, the components can be installed.]]
 
[[File:cgs_wire_pcb_cgs27_tube3.gif|thumb|center|400px|Wiring the board to the external components. On the connectors, SW is the switched terminal, SL is for the sleeve connection, and TP is for the tip connection. The pots are displayed as viewed from the front, with the shaft pointing towards you.]]
 
The tube heater can be powered from 5 to 6 volts DC, as is convenient. It is best if the heater 0 volt wire is not the same wire that is the signal ground, though they should be connected together back at the power supply.
 
   
  +
When inserting ICs into sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.
The resistors can all be 1/4 watt, and capacitors with a 50v rating will be quite adequate.
 
  +
[[File:cgs_photo_cgs27_tube.jpg|thumb|center|400px|Above view without the tube in the socket.]]
 
  +
There is a grey connection show on the circuit diagram between resistors of the divider. This is for if you wish to build a cluster with less outputs. Install a link in this position, and leave out IC3 and all associated components. Points X and Y are the connection points for expanding the CV cluster further if desired. The track will need to be cut between these pads.
[[File:cgs_photo_cgs27_tube2.jpg|thumb|center|300px|Above view with the tube in the socket.]]
 
  +
  +
A switch can be wired between points S and T. This will drop one resistor from the divider chain, the result being that the center "straight through" point is excluded from the voltage divider, giving and even spread of outputs (no null point) as distinct from an odd spread of outputs. Needless to say, the straight-through output continues to operate as normal, but the difference between it and the taps immediately above it and below it will only be half that of the difference between any other pair of taps. When operated in this mode, it is unlikely the center tap would be used.
   
 
== Parts list ==
 
== Parts list ==
Line 31: Line 45:
   
 
{| style="border:1px solid #BBB;"
 
{| style="border:1px solid #BBB;"
| Part||align=right|Quantity
+
| Part ||align=right| Quantity
 
|-
 
|-
 
! colspan="2" align=center|Capacitors
 
! colspan="2" align=center|Capacitors
 
|-
 
|-
| 220n||align=right|1
+
| 100n||align=right|4
 
|-
 
|-
| 1uF||align=right|1
+
| 10uF 25V||align=right|2
|-
 
| 22uF 25V electro||align=right|1
 
 
|-
 
|-
 
! colspan="2" align=center|Resistors
 
! colspan="2" align=center|Resistors
 
|-
 
|-
| 2k2||align=right|1
+
| 1k 1%||align=right|10
 
|-
 
|-
| 10k||align=right|2
+
| 10k 1% matched||align=right|10
 
|-
 
|-
| 39k||align=right|1
+
| 100k 1% matched||align=right|10
 
|-
 
|-
| 47k||align=right|1
+
! colspan="2" align=center|Semi's
 
|-
 
|-
| 680k||align=right|1
+
| TL074||align=right|3
|-
 
| 1M||align=right|1
 
|-
 
! colspan="2" align=center| '''Tubes'''
 
|-
 
| CV4014 or 6064||align=right|1
 
 
|-
 
|-
 
! colspan="2" align=center|Misc
 
! colspan="2" align=center|Misc
 
|-
 
|-
| PP-ST7-195 tube socket||align=right|1
+
| Ferrite bead (or 10R resistor)||align=right|2
 
|-
 
|-
| CGS27 PCB||align=right|1
+
| 0.156 4 pin connector||align=right|1
 
|-
 
| CGS37 PCB||align=right|1
 
|}
 
|}
  +
  +
=== Notes ===
  +
* A 10 to 22 ohm resistor can be used instead of the ferrite beads. If you don't care about power-rail noise, just use a link instead.
  +
* PCB is 6" x 1" with 3mm mounting holes 0.15" in from the edges.
   
 
== See also ==
 
== See also ==
  +
* [[CGS CV cluster]] for the latest version.
 
* [[CatGirl_Synth#The_CGS_modules|The CGS modules]]
 
* [[CatGirl_Synth#The_CGS_modules|The CGS modules]]
 
* [[CGS parts FAQ]]
 
* [[CGS parts FAQ]]
   
 
== References ==
 
== References ==
* ''[https://web.archive.org/web/20180209234737f/http://www.cgs.synth.net:80/modules/cgs27_tube.html Tube experimenter board for music synthesizers.]'' (archived) by Ken Stone, 2001, with permission of the author
+
* ''[https://web.archive.org/web/20180209234737f/http://www.CGS.synth.net:80/modules/CGS37v10_cv_cluster.html CV Cluster for music synthesizers.]'' (archived) by Ken Stone, 2001, with permission of the author
   
 
== External links ==
 
== External links ==
 
* [http://groups.yahoo.com/group/CGS_synth CGS Synth discussion group], for discussion of locating parts, modifications and corrections etc.
* ''[https://web.archive.org/web/20170614003708/http://cgs.synth.net/tube/index.html Audio Synthesis via Vacuum Tubes]'' by Eric Barbour, 1997, for a more detailed discussion on how a tube VCA works.
 
* [http://groups.yahoo.com/group/cgs_synth CGS Synth discussion group], for discussion of locating parts, modifications and corrections etc.
 
   
 
[[Category:CGS modular]]
 
[[Category:CGS modular]]

Revision as of 18:40, 3 June 2019

Cgs photo cgs37 cv cluster.jpg

CGS37 the CGS CV cluster is an unusual kind of mixer. It takes two input voltages - a base control voltage, and a modulating control voltage, and creates the sum and differences of them. These different voltages are the base voltage offset in a positive direction by the modulating voltage and the base voltage offset in a negative direction by the modulating voltage. A series of equal taps between these two points results in outputs that always maintain the base control voltage at its full amplitude, mixed with a differing amount of the modulating voltage. The center output has equal amounts of positive and negative modulation cancelling each other out, and thus behaves as a straight-through connection for the base input.

While untested, the module should work on +/-12 volts.

Some ideas on how to use this module

Feed your 1/v octave input into the base input, and an envelope generator, LFO, sequencer etc. into the modulation input. Connect the outputs, starting with the center unmodulated output, and working both up and down, to a series of VCOs. While the modulation input remains at zero, all of the VCOs will track. As the modulation voltage increases, the VCOs connected to modulated outputs will shift in frequency away from the base, at an amount proportional to its position from the center output. For example, a small modulation voltage will de-tune the oscillators slightly, fattening the sound. A modulation CV of 5 volts will set each output 1 volt apart, setting the oscillators an octave apart.

An envelope generator connected to the modulation input creates in interesting effect.

It of course can be used with audio frequency signals too, and may prove interesting when driving a cluster of wave multipliers or similar. Two audio signals fed to it could produce interesting stereo effects.

Note: The sum and differences produced by this module are voltage differences, NOT frequency differences. It is NOT a ring modulator.

A little on how it works

The schematic of the CV Cluster.

All four op-amps in the input structure are wired as unity gain voltage inverters or summers.

The base input voltage is inverted by IC1a, and fed to the inverting summers built around IC1C and IC1B. The result, assuming no other input, will be the inversion of the inverted signal, thus restoring the signal to its original condition, but at two separate places. Between these two places there is a string of resistors forming a voltage divider. As both ends of this voltage divider are held at the same voltage, each tap will also be at that voltage.

The modulation CV is mixed directly with the inverted base signal in IC1B, and is thus inverted at the output of IC1B, and the bottom of the voltage divider, the result being the difference of the two voltages, specifically, the base CV minus the modulation CV. The modulation CV is also inverted by IC1D before being mixed with the inverted base signal in IC1C, the result being the sum of the base signal and the modulation signal.

These mixed points are fed to the top and bottom most output jacks. At the various taps of the voltage divider between these two points, there will be correspondingly less of the modulation signal present as the two differing voltages cancel each other out. At the center point they will cancel each other out perfectly. (Because of this, the base CV has been routed directly to the center output, rather than wasting another voltage follower to produce the same voltage.)

Each tap on the voltage divider is buffered by a voltage follower, the 1k output resistors providing current limiting and thus protection for the voltage followers in the event of short circuits, which are inevitable as patch cords using mini-jacks or 6.5mm jacks are plugged in.

Construction

The component overlay. Connections can be determined from the circuit diagram.

I would recommend the use of hand matched 1% metal film resistors be used throughout this module.

Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.

When you are happy with the printed circuit board, construction can proceed as normal, starting with the resistors first, followed by the IC socket if used, then moving onto the taller components.

Take particular care with the orientation of the polarized components such as electrolytics, diodes, transistors and ICs.

When inserting ICs into sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.

There is a grey connection show on the circuit diagram between resistors of the divider. This is for if you wish to build a cluster with less outputs. Install a link in this position, and leave out IC3 and all associated components. Points X and Y are the connection points for expanding the CV cluster further if desired. The track will need to be cut between these pads.

A switch can be wired between points S and T. This will drop one resistor from the divider chain, the result being that the center "straight through" point is excluded from the voltage divider, giving and even spread of outputs (no null point) as distinct from an odd spread of outputs. Needless to say, the straight-through output continues to operate as normal, but the difference between it and the taps immediately above it and below it will only be half that of the difference between any other pair of taps. When operated in this mode, it is unlikely the center tap would be used.

Parts list

This is a guide only. Parts needed will vary with individual constructor's needs.

Part Quantity
Capacitors
100n 4
10uF 25V 2
Resistors
1k 1% 10
10k 1% matched 10
100k 1% matched 10
Semi's
TL074 3
Misc
Ferrite bead (or 10R resistor) 2
0.156 4 pin connector 1
CGS37 PCB 1

Notes

  • A 10 to 22 ohm resistor can be used instead of the ferrite beads. If you don't care about power-rail noise, just use a link instead.
  • PCB is 6" x 1" with 3mm mounting holes 0.15" in from the edges.

See also

References

External links