MCI 600 series console question re. faders and VCA´s

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API

Well-known member
Joined
Nov 25, 2005
Messages
869
Location
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Does anyone know if it is possible to remove the DBX VCA´s from the fader module of a 600 series MCI console and still have the fader working as a normal fader??
Is it only used for the VCA groups or is it in the actual audio chain??

Would be great if someone could give me a reply to this.

Regards,
Dennis
 
Hi I have one MCI 618 with vca faders, I think that you cant. The audio pass through vca's, the resistive fader serves to control the vca :sad:
I can try to found the schem if you need it...

Arnau
 
If it's like either of the JH636 I worked on, the fader generates a DC voltage which then controls the VCA. You need the VCA or the fader doesn't work.

If you have the automated system, the fader generates a DC voltage that goes into the big computer on the bottom, then the computer sends back a DC voltage to the VCA. If the automation computer dies, the faders won't work any more. It uses a 6502 processor, same as the Apple][.
 
Hi.

Thanks for the info.
To bad to hear this as I have faders without the VCA!

Is there a replacement for this VCA?
 
I'm no expert but I'm guessing the easiest way to check would be to look at the faders. If they are linear taper then they were used to control the VCA, if they are log taper then perhaps audio passed through them.

Cheers,
Ruairi
 
Actually Ruairi the faders are 'VCA law' which is neither linear nor log but a special characteristic to make interfacing easy with the VCA.
As to replacing the VCA (DBX202C), I guess you could use the THAT version that SSL use, or indeed cobble something together like the GSSL circuit where a THAT VCA and op-amp is used as a replacement for the 202.
 
there are fader packs without the automation option and without the vca, I think, direct replacements but with less options and you need to find them (blevins usually have them), the non automation faders looks very different, with big push buttons for the group allocations. If automation system dies you can still use the vca faders but in some desk versions you need to do a bridge on one of the fader connectors to work properly (easy fix). I see a MCI 636 that works with no problem with the automation PSU off... mine 618 not, mine is from 80's and the 636 that i talk about is from 70's

Arnau
 
There were 3 options for the 600 series desks:
The full automation fader - which had read, write etc. and was designed to work with their dreadful automation system.
VCA fader with grouping - which had the big pushbuttons next to the fader.
Normal fader - which was a straight 10k log fader.
There are several people here who have MCI 600 series desks.
Spares are a bit difficult to get hold of, especially the Clarostat pots which are non-standard values (and very expensive!)
 
[quote author="Apache5"]If automation system dies you can still use the vca faders but in some desk versions you need to do a bridge on one of the fader connectors to work properly (easy fix). I see a MCI 636 that works with no problem with the automation PSU off... mine 618 not, mine is from 80's and the 636 that i talk about is from 70's[/quote]

This one didn't. Some of them put in an automatic bypass in the fader module so if the automation was off, the fader voltage went right to the VCA. This one didn't do that.
 

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