Cgs synth

I only use mac so its a pian sometime for stuff other then audio

Try Osmond PCB

http://www.swcp.com/~jchavez/osmond.html

The basic version is free, if you register and pay then you can make
bigger boards and I guess get all sorts of other stuff.

I used to use the old maC OS9 version which was a bit buggy. The new
mac OS X version seems great - it hasn't fallen over once :-)

Mind you, I only use it for working out layouts for perfboard, I
haven't tried it's other features out yet....

Hope this helps.
cheers,

Dave

I basically have two questions about the CGS65.

Firstly, while I've heard some very nice demos of its waveshaping
abilities, I am curious how well it performs as a VCA. If the input
signal is kept below the level at which it distorts, how well does it
function as a VCA?? How well does it mute an incoming signal if no
envelope is applied?? Has anyone here used it as a conventional VCA??



Secondly, I am quite confused about the cathode circuitry. I do not
understand the inclusion of either the regular diodes (which are
described as optional) or the LED's (other than their ability to
illuminate the tube). I believe I understand why this circuit uses
the negative rail for the heater voltage instead of the specified
filament voltage of 1.2V -- since it uses a directly heated cathode,
doing so increases the potential between the cathode and plate to 30V.

Looking at this site: http://www.russiantubes.com/prop.php?t=12&p=7

it looks like the recommended heater current is ~13mA, so its
resistance would be ~100 Ohms. V/i=R 15/.011 = 1.4K 15/.015 = 1K
So I'm thinking a resistor between 900 Ohms and 1.3K is all that
would be needed to limit the current within its recommended range,
and the power dissipated by that resistor would be close to a 1/4W.

It says, "These LEDs are using waste power that would otherwise need
to be dissipated in the current-limiting resistors for the heater, so
even if you are hiding the tube, the LEDs must still be included."
I'm sorry, I don't understand that, than other than the change in
voltage due to the diode drop, how the diodes would effect the amount
of current running through the resistors. Could someone please
explain that??


Thanks :)

Check out Eagle. There is a free version you can use to lay out two
layer 80x100 mm boards. The free version can also be used as a reader
for layouts created with the more expensive versions...

http://www.cadsoftusa.com

Doug

http://www.analognotes.com
http://www.stoogepanels.com

>Firstly, while I've heard some very nice demos of its waveshaping
>abilities, I am curious how well it performs as a VCA. If the input
>signal is kept below the level at which it distorts, how well does it
>function as a VCA?? How well does it mute an incoming signal if no
>envelope is applied?? Has anyone here used it as a conventional VCA??

It works as one, yes, however if you want a "perfect" VCA, use the CGS64
instead. People chose tube designs when they add tonal color. A tube designe
that is "perfect" would be of little point as it would deliver the same
performance as a solid state one at a worse cost.

>Secondly, I am quite confused about the cathode circuitry. I do not
>understand the inclusion of either the regular diodes (which are
>described as optional) or the LED's (other than their ability to
>illuminate the tube).

There is a voltage drop required to power the heater. This power has to be
dissipated somewhere. A dirty great resistor could be used. Alternately, the
power could be dissipated as light, hence the LEDs. Besides, DIYers are
notorious for illuminating tubes with LEDs, so why not make it easy for them?

The redular diodes are to prevent the heater from being damaged in case
during experimentation/assembly a too high a voltage is applied to the
heater, e.g. via the installation of the wrong value current limiting
resistor, or a stray wire causing a short etc..

>it looks like the recommended heater current is ~13mA, so its
>resistance would be ~100 Ohms. V/i=R 15/.011 = 1.4K 15/.015 = 1K
>So I'm thinking a resistor between 900 Ohms and 1.3K is all that
>would be needed to limit the current within its recommended range,
>and the power dissipated by that resistor would be close to a 1/4W.

Never run a resistor at its rated dissipation - they die really quickly,
and/or burn the PCB around them.

>It says, "These LEDs are using waste power that would otherwise need
>to be dissipated in the current-limiting resistors for the heater, so
>even if you are hiding the tube, the LEDs must still be included."
>I'm sorry, I don't understand that, than other than the change in
>voltage due to the diode drop, how the diodes would effect the amount
>of current running through the resistors. Could someone please
>explain that??

If there is a 3.2 volt drop across the LEDs, it effectively reduces the
voltage across the current limiting resistor by 3.2 volts. It doesn't change
the current running through the resistors, but it DOES reuce the power they
need to dissipate: P = V x I.

_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

Here's the link to my demos again:

http://www.pugix.com/bottom-cabinet-lower.htm#tubevca

I find a very, very small output being passed when the Gain and CV pots
are at zero. I didn't try adjusting the trimpot, though, and this might
be why a small signal is passed. Initially I set the trimpot by ear.

The CGS-65 really cannot do double duty as a regular VCA for a couple of
reasons. One is that a unity gain response is distorted for much over a
2 volt p-p input. You don't want any distortion for regular VCA use. A
second reason is that the control voltage feeds through significantly.
It thumps when there's an envelope but no input signal.

This demo starts and ends with a MOTM-190 VCA for comparison.

http://www.pugix.com/music/cgs-65-timbral-gate.mp3
<http://www.pugix.com/music/cgs-65-timbral-gate.mp3>

-Richard Brewster

Mark wrote:

On 3/24/07, Richard Brewster put forth:

>I find a very, very small output being passed when the Gain and CV pots
>are at zero. I didn't try adjusting the trimpot, though, and this might
>be why a small signal is passed. Initially I set the trimpot by ear.
>
>The CGS-65 really cannot do double duty as a regular VCA for a couple of
>reasons. One is that a unity gain response is distorted for much over a
>2 volt p-p input. You don't want any distortion for regular VCA use. A
>second reason is that the control voltage feeds through significantly.
>It thumps when there's an envelope but no input signal.

Thanks, that gives me a much better idea of what it can do. Although
2Vpp isn't that small of a signal. Perhaps I could try different
capacitor values in the LPF for the control voltage.

Have you tried sending it the inverted output of an envelope
follower?? It might make a nice sustain distortion unit.

I have been wondering why no tube compressors use pentodes as VCA's
or why I have never heard of a tube gate. Although it might be
possible to design a tube VCA where the control voltage is inaudible
using a pentode with a different configuration or with a tube with
more than three grids, I do not think anyone has ever done it.

On 3/25/07, sasami@... put forth:

>It works as one, yes, however if you want a "perfect" VCA, use the CGS64
>instead. People chose tube designs when they add tonal color. A tube designe
>that is "perfect" would be of little point as it would deliver the same
>performance as a solid state one at a worse cost.

Oh, I'm not looking for it to be a "perfect" VCA, I'm just trying to get a
better idea of what I can do with it. The amount of space and
modules I can build is limited.

> >it looks like the recommended heater current is ~13mA, so its
> >resistance would be ~100 Ohms. V/i=R 15/.011 = 1.4K 15/.015 = 1K
> >So I'm thinking a resistor between 900 Ohms and 1.3K is all that
> >would be needed to limit the current within its recommended range,
> >and the power dissipated by that resistor would be close to a 1/4W.
>
>Never run a resistor at its rated dissipation - they die really quickly,
>and/or burn the PCB around them.

Thanks, that is very good advice, considering that 1/2W and 1W
resistors are available in E24 values.

>If there is a 3.2 volt drop across the LEDs, it effectively reduces the
>voltage across the current limiting resistor by 3.2 volts. It doesn't change
>the current running through the resistors, but it DOES reuce the power they
>need to dissipate: P = V x I.

OK, with two 1K5 resistors in parallel and say another 100 Ohms for
the heater itself, V/R = i, 11.8/850 = .013mA

So if didn't use any diodes, and instead used two 2K or one 1K
resistor, V/R = i, 15/1100 = .013mA, P=iV, .013*15 = .195W, would
that work??


Has anyone tried adding a cathode bypass cap?? Admittedly, I have
very little knowledge and no experience when it comes to
directly-heated cathodes or using a "negative" cathode voltage, but
I guess I am just used to seeing them.


Also, as an aside, I'm guessing that these tubes use some sort of
coated tungsten, so their heater resistance would be only about 12
Ohms upon start-up, as tungsten filaments have only about 1/8 their
normal operating resistance when cold. While that difference is
negligible when using the resistance needed for 11.8V or 15V, for
anyone thinking of using a lower heater-cathode voltage with these
tubes, for example the 5A supply for their modular, the increased
power dissipation upon start-up might make a difference when choosing
resistors of the correct wattage.

>I have been wondering why no tube compressors use pentodes as VCA's
>or why I have never heard of a tube gate. Although it might be
>possible to design a tube VCA where the control voltage is inaudible
>using a pentode with a different configuration or with a tube with
>more than three grids, I do not think anyone has ever done it.

René Schmitz http://www.uni-bonn.de/~uzs159/ did a version which cancelled
out the CV by inverting the signal and feeding it through a second VCA,
re-inverting it and mixing it with the first, resuling in cancellation of
the control voltage.

>So if didn't use any diodes, and instead used two 2K or one 1K
>resistor, V/R = i, 15/1100 = .013mA, P=iV, .013*15 = .195W, would
>that work??

As long as the heater sees the same current, anything would be okay, so yes,
it would work.

_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>