Replacement for old 600Ohm faders

[alphadept]

Hello everybody!

i'm considering to put a moving fader automation on my old Cadac (one of the first series, g228 channel with inductors).
the problem is that it's impossible to find a moving fader auto with 600ohm faders. ti can find 5k or 10K faders.

somebody can help me to understand if 5 or 10k faders will work instead of those old 600ohm?
to consider that on some point the singnal (unbalanced) goes from the patch directly into the fader, to it should work with new and old equipment too...

thanks so much to anybody will help me!

f.

[Radardoug]

It depends on what circuit follows the fader. If it is high impedance then you could use a 10K fader. Check to see if the fader feeds a buffer, and what its input resistance is.

[MrMegaEli]

First of all, what mixer?

Are you replacing constant impedance faders, or just slide potentiometers (probably followed by a buffer).

[Transform]

Here's what's behind it

******//www.gearslutz.com/board/attac...e-228-copy.jpg

btw does anyone know of any source for a 44v power supply for these boards?

[alphadept]

hey thaks for the replies!

To MrMegaEli: My console is an old Cadac built in '72 (schematics from '69 actually). moduels are G228, G232, G233...
the faders are normal slide potentiometers, made by SEYDEL Electronic, Berlin in the late '60. they are Danner size. Nominal 600ohm but i mesure them, they are between 700ohm and 1kohm.

the signal from the fader is going into the G232 module.
inside the G232 there are 4 amplifier, two C113 for the panpot, one C114 for the echo send and one C114 for the foldback send.
the fader is always feeding the two C113.
the C114's are fed just in case the FB and ehco sends are switched post fader.
i've attached the schematichs of the amplifiers.
somebody can tell form these schematics what is the input impedance, and if is possible substitute the fader with a 5 or 10k one?

to Transform: this is the second Cadac that i own, the PSU is made by Farnell and i remeber the other one was made by coutant. Both are simple but very powerfull. i think they can go up to 50Ampere at 44V!

thanks guys!
f.

[Radardoug]

The easy way to determine input impedance.
Take a variable resistor. Wire it in series with your input.
Feed the free end of the variable resistor with an oscillator.
Set the variable resistor to zero ohms, and monitor the output of the amolifier with a meter. Adjust oscillator so meter reads zero.
Now adjust variable resistor till the meter reads -6 dB.
Measure the value of the variable resistor. This is your input impedance.
Those circuits will probably be not very high impedance.

[alphadept]

Ok,
i never knew that!
but the impedence is frequency variable.
so which freq i have to set the osc to?
1K?

thanks

[Bill Wilson]

Looking at the amplifier schematics I believe you can likely use a 5k unit. Try hooking up both a 5k & 10k rotary pot in place of the 600 ohm fader on one input & see if there is any change in the quality of the signal. That should give you your answer.

[Transform]

Hi-
I am still looking for info to help me cobble together a supply and am wondering if you have any more data about yours. Model number, photo, or schematic?

[mjrippe]

You should be able to buy a 48v linear power supply from Power One or other manufacturers. These have a voltage adjustment trim pot that will let you drop it to 44v.