Difference between pages "Digital signal processing" and "CGS gate sequencer CV adapter"

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(Created page with "== Introduction == === Continuous vs Discrete === In order to understand the benefits and limitations of Digital Signal Processing (DSP) it is important to understand the dist...")
 
(Created page with "<!-- file missing thumb|center|600px| --> '''CGS42''' the '''CGS gate sequencer CV adapter''' is an addition to the obsolete CGS07 CG...")
 
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== Introduction ==
 
  +
'''CGS42''' the '''CGS gate sequencer CV adapter''' is an addition to the obsolete CGS07 [[CGS gate sequencer (obsolete)|gate sequencer]], (superseded by the CGS89 [[CGS gate sequencer|gate sequencer]]), converting it to a traditional eight-step control voltage sequencer.
=== Continuous vs Discrete ===
 
In order to understand the benefits and limitations of Digital Signal Processing (DSP) it is important to understand the distinction between '''Continuous''' and '''Discrete''' signal representations. In the Synth DIY world, much use is made of the terms '''Analog''' and '''Digital''' without any clear explanation of the very different assumptions that underpin those terms.
 
   
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It simply adds a single channel no-nonsense 8 step analog output. Additional boards can be added to increase the number of channels as desired. The pots are assigned to a particular step during construction, so the board can be mounted either vertically or horizontally as required.
A ''signal'' can be defined as any function that conveys information about the state of a physical system. This is usually represented as a variation of values over time or space. Signals are represented mathematically as functions of one or more independent variables.
 
   
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All clocking, sequence length and reset functions etc. are handled by the main gate sequencer board.
''Continuous-time'' signals are defined across a continuum of time and reflect a continuously variable value. So, for example
 
: '''f(t) = sin(2wt)'''
 
is continuously defined for any and all values of '''t'''.
 
   
  +
While untested, the module should work on +/-12 volts.
''Discrete-time'' signals are only defined at specific times and the independent variables can therefore only take on discrete values. Discrete-time signals are represented by a sequence of discrete values. In the context of Synth applications, the specific times at which the signals are defined are regular and evenly spaced.
 
   
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== A little on how it works ==
In real world applications, the values a signal takes on as it varies usually represents an amplitude. The signal amplitude can also be either ''continuous'' or ''discrete''.
 
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[[File:cgs_schem_cgs42_cv_adapter.gif|thumb|center|500px|The schematic of the core of the CV Adapter.]]
  +
To avoid overloading them, each of the column drives from the Gate Sequencer is buffered by a general purpose NPN transistor such as a BC547 or 2N3904 wired as an emitter follower. The buffered column drives are used to apply a voltage across each of the pots in sequence. The wiper of each pot picks up the reduced voltage, which is then fed into a non-inverting mixer based around a dual op-amp.
   
  +
As only one put has a voltage across it at any time, only one voltage is fed into the mixer. The remaining inputs are all at 0 volts, and as such have no effect on the summed output.
When we talk about an ''analog'' signal, we are usually referring to a signal that is both a ''continuous-time'' and ''continuous-amplitude'' signal. A ''digital'' signal is both a ''discrete-time'' and ''discrete-amplitude'' signal, which translates into the reality that it is both sampled (discrete-time) and quantised (discrete-amplitude).
 
   
  +
This board could of course be connected to other signal sources if desired, or even used as a small mixer, if the transistors were omitted and the input signals were fed directly into the pots.
This all sounds very academic, of course, but is important to understand the fundamental differences between the two domains when making design decisions around sample rates, bit resolution and cost when selecting components for implementing DSP hardware.
 
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== Construction ==
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[[File:cgs_pcb_cgs42_cv_adapter.gif|thumb|center|400px|The component overlay. Connections can be determined from the circuit diagram.]]
  +
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. (Note that on the first run of PCBs a corner hole is missing. I don't know why - it was on the artwork.)
  +
  +
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.
  +
  +
The order the pots will be sequenced is indicated by a small number in the middle of the overlay for each pot. It follows left to right, with no consideration for the vertical offset. This way, each gate sequencer column can be represented by a vertical line. If you would prefer a different arrangement, the wires connecting the "C" pads on this board to the main gate sequencer can be shuffled as required.
  +
  +
There is no power input jack on this board, as it is designed to be jumpered directly to the host gate sequencer board. You will find you need to run a negative feed to the gate sequencer board if one is not already present.
  +
[[File:cgs_wire_cgs42_cv_adapter.gif|thumb|center|350px|An example of hard wiring the CV Adapter to the gate sequencer board.]]
  +
  +
== Parts list ==
  +
This is a guide only. Parts needed will vary with individual constructor's needs.
  +
  +
{| style="border:1px solid #BBB;"
  +
| Part||align=right|Quantity
  +
|-
  +
! colspan="2" align=center|Capacitors
  +
|-
  +
| 100n||align=right|1
  +
|-
  +
| 10uF Tant||align=right|1
  +
|-
  +
! colspan="2" align=center|Resistors
  +
|-
  +
| 1k||align=right|1
  +
|-
  +
| 33k||align=right|1
  +
|-
  +
| 100k||align=right|10
  +
|-
  +
| 10k lin pot||align=right|8
  +
|-
  +
! colspan="2" align=center|Semi's
  +
|-
  +
| TL072||align=right|1
  +
|-
  +
| BC547||align=right|8
  +
|-
  +
! colspan="2" align=center|Misc
  +
|-
  +
| CGS42 PCB||align=right|1
  +
|}
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=== Notes ===
  +
* PCB is 3.8" x 2.3" with 3mm mounting holes 0.15" in from the edges.
  +
  +
== See also ==
  +
* [[:File:cgs42holeguide.zip|CGS42 panel hole drilling guide, print at 300dpi.]]
  +
* [[CatGirl_Synth#The_CGS_modules|The CGS modules]]
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* [[CGS parts FAQ]]
  +
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== References ==
  +
* ''[https://web.archive.org/web/20180209234737fw_/http://www.CGS.synth.net:80/modules/CGS42_cv_adapter.html Gate Sequencer CV Adapter for music synthesizers.]'' (archived) by Ken Stone, 2001, with permission of the author
  +
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== External links ==
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* [http://groups.yahoo.com/group/cgs_synth CGS Synth discussion group], for discussion of locating parts, modifications and corrections etc.
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  +
[[Category:CGS modular]]

Revision as of 21:23, 10 December 2018

CGS42 the CGS gate sequencer CV adapter is an addition to the obsolete CGS07 gate sequencer, (superseded by the CGS89 gate sequencer), converting it to a traditional eight-step control voltage sequencer.

It simply adds a single channel no-nonsense 8 step analog output. Additional boards can be added to increase the number of channels as desired. The pots are assigned to a particular step during construction, so the board can be mounted either vertically or horizontally as required.

All clocking, sequence length and reset functions etc. are handled by the main gate sequencer board.

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

A little on how it works

The schematic of the core of the CV Adapter.

To avoid overloading them, each of the column drives from the Gate Sequencer is buffered by a general purpose NPN transistor such as a BC547 or 2N3904 wired as an emitter follower. The buffered column drives are used to apply a voltage across each of the pots in sequence. The wiper of each pot picks up the reduced voltage, which is then fed into a non-inverting mixer based around a dual op-amp.

As only one put has a voltage across it at any time, only one voltage is fed into the mixer. The remaining inputs are all at 0 volts, and as such have no effect on the summed output.

This board could of course be connected to other signal sources if desired, or even used as a small mixer, if the transistors were omitted and the input signals were fed directly into the pots.

Construction

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

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. (Note that on the first run of PCBs a corner hole is missing. I don't know why - it was on the artwork.)

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.

The order the pots will be sequenced is indicated by a small number in the middle of the overlay for each pot. It follows left to right, with no consideration for the vertical offset. This way, each gate sequencer column can be represented by a vertical line. If you would prefer a different arrangement, the wires connecting the "C" pads on this board to the main gate sequencer can be shuffled as required.

There is no power input jack on this board, as it is designed to be jumpered directly to the host gate sequencer board. You will find you need to run a negative feed to the gate sequencer board if one is not already present.

An example of hard wiring the CV Adapter to the gate sequencer board.

Parts list

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

Part Quantity
Capacitors
100n 1
10uF Tant 1
Resistors
1k 1
33k 1
100k 10
10k lin pot 8
Semi's
TL072 1
BC547 8
Misc
CGS42 PCB 1

Notes

  • PCB is 3.8" x 2.3" with 3mm mounting holes 0.15" in from the edges.

See also

References

External links