Fader resistance--can I use 1k (or 10k) instead of 5k here?

[kakumei47]

I feel like this should be simple but I've read conflicting info about replacing faders with different values. I'm considering replacing the VCA section of my console channels (MCI528c) with proper audio faders and removing the VCA completely.  The master faders and channel faders on each IO use 5k.

I was hoping to essentially replace the VCA circuit with the channel circuit here on the attached pic.
Problem is, P&G isn't making the faders I need anymore and I can much more easily get 10k and 1k (1k is half the price so I'd prefer that). Could I use those here? Would anything else need to change? The 2003 opamp here is basically a 5534.

 

[ruffrecords]

What I cannot see is the circuit driving audio into the VCA. That is the one that would be loaded with the 1K pot . The pot output just goes into another op amp so that will be OK. The issue will be if the stage driving the pot can cope with 1K or not.

Cheers

Ian

 

[Khron]

The safer choice may well be going with a 10k.

 

[JohnRoberts]

+1 10k(audio taper) is typical fader value.

Maybe look for some other console with regular faders for typical termination and surrounding circuitry.

Typical post fader stages have 10 dB of gain and I often incorporate a differential to insure good fader kill and signal integrity between different local audio 0V. 

JR 

 

[madswitcher]

Hi there,

I did a similar excercise on a MCI 600 series console in removing the VCA and installing regular P&G faders.  If you chase the audio path back it is most likely driven by a 2003/2004 (low noise version of the 5534/5532).  This chip will quite happily drive a 600 ohm load, but may get a bit warm. 

Assuming that it is just driving the audio fader, the load on the output of the 2003 will be 1/4 of the fader value in parallel with whatever is after it.  So, as John said it is better to go for a 10K fader, but you could possibly get away with a 5K.

Kind regards

Mike

 

[kakumei47]

What I cannot see is the circuit driving audio into the VCA. That is the one that would be loaded with the 1K pot . The pot output just goes into another op amp so that will be OK. The issue will be if the stage driving the pot can cope with 1K or not.

Cheers

Ian

Thanks all.  Here's the rest of the circuit before the VCA (highlighted here). As you can see there really isn't any amp stage before the VCA (well the mic pre is switchable here with a 5534 in the normal mci500 swinging setup, but I can't see in my workflow really ever sending it to the big faders). There was a differential amp (again 5534) on the line in on the frame, but I since replaced those with B-series transformers (don't know the ratio but I'll try to find out).

 

[ruffrecords]

Assuming that it is just driving the audio fader, the load on the output of the 2003 will be 1/4 of the fader value in parallel with whatever is after it.  So, as John said it is better to go for a 10K fader, but you could possibly get away with a 5K.

Mike

How did you get 1/4 the fader value?

Cheers

Ian

 

[madswitcher]

Sorry - I got my source and load mixed up.  It is the circuit after the fader that will see the 1/4 of the fader value - scrub that post I don't know what came over me - in fact, utter crap - sorry.

Mike

 

[ruffrecords]

Sorry - I got my source and load mixed up.  It is the circuit after the fader that will see the 1/4 of the fader value - scrub that post I don't know what came over me - in fact, utter crap - sorry.

Mike

LOL. No problem. We all make mistakes. Time for an Xmas beer.

Cheers

Ian

 

[madswitcher]

LOL. No problem. We all make mistakes. Time for an Xmas beer.

Cheers

Ian

As they say in the cliche - I'll drink to that.  Happy Christmas to you Ian,

Cheers - literally,

Mike

 

[Brian Roth]

R306 is shown as 3k3 Ohms, which will be the load presented to the wiper of the pot.  That needs to be greatly increased.  You can see the very similar buffer circuit for the 5k MONITOR LEVEL pot loads the wiper with 100k (R1202).

Bri

 

[kakumei47]

Thanks a lot for the advice all! I have a better understanding of how the fader fits in. I was hoping to get the cheaper 1k ones but it seems 10k is the way to go.