4K G-Series / Crackling Noise on the Centre Buss

[marcmozart]

Something I noticed from when I first installed the console, but now becomes a real problem is a crackling noise I get on the Centre Bus (my console has Film panning, the Centre Bus is equivalent to the RL Buss on Quad Consoles).

In Stereo Mode the Console is very clean, but the Centre Buss is very noisy + makes random crackling noises.

The first thing I tried was swapping the 4 "026" Quad Buss Mix Amp Cards to find out if the problem moves to another Buss by swapping them.
The problem stayed with Centre Buss which happens before the signal hits the Mix Amp Cards.

Any ideas?

[Showcase]

So for example, if you take away every channels from the mix bus with FLAT, it still there?

[marcmozart]

Yes, even if I cut every channel.

So for example, if you take away every channels from the mix bus with FLAT, it still there?

[walrus]

Sounds like the noise is coming from one of the channels on the virtual earth summing buss for the Centre. Try turning off one bank of channels at a time until the fault stops, then pull the channels in that bank until you find the culprit.

[Showcase]

Yes, even if I cut every channel.

So for example, if you take away every channels from the mix bus with FLAT, it still there?

CUT will not help, you need to push FLOAT on every channel to exclude them from the mixbus, walrus tip could also work

[marcmozart]

Thanks!
I tried your method and found 4 channels across the console that induced noise into different busses. I removed them for now.
I actually went and removed ALL channels to double-check which ones would cause problems.

Interesting side-notes:
1. These channels would still add noise to the summing buss, even if their bucket was switched off.
2. When floated, a channel adds less noise to the summing buss compared to being CUT.

Sounds like the noise is coming from one of the channels on the virtual earth summing buss for the Centre. Try turning off one bank of channels at a time until the fault stops, then pull the channels in that bank until you find the culprit.

[Showcase]

2. When floated, a channel adds less noise to the summing buss compared to being CUT.

Yes, as I said, CUT will not help, if everything else is ok w console, you can put these channels back and hit FLOAT and it will exclude them from the summing/mix (not less noise, NO noise)

[marcmozart]

You never stop learning! 

Makes me wonder - what is the difference of sending a VCA signal directly to the quad buss verses floating it and then sending it via routing matrix (LF RF) to the quad buss?

2. When floated, a channel adds less noise to the summing buss compared to being CUT.

Yes, as I said, CUT will not help, if everything else is ok w console, you can put these channels back and hit FLOAT and it will exclude them from the summing/mix (not less noise, NO noise)

[sintech]

Floating the channel uses the monitor (small fader) path and buffer, rather than the quad pan buffer.

[sintech]

If LF and RF are sounding good and Centre (LB?) not, the fault must be on the Film Pan card.

It's very handy to have the abillity to fire a module up on the bench with a test Jig, as it keeps the console working whilst you sort problems out.

Scope the output of the Quad Fader Buffer (Group card Pin 44) and chase forward.

If you don't have a scope, you can make an Audio Probe and use it with a cheap powered speaker. (I use this combo more than the scope)

[marcmozart]

Found out that these noises are usually coming from the 281 Film Pan Card MKII. Moving the pan pot will reveal the condition of the card. I had noise or crackling on more than 10 of my 48 modules.

I need to start refurbishing all of these, they look very messy, contradicting to the rest of my consoles condition, with corrosion around resistors, lots of dust etc. Will start a new thread about the Film Pan Card soon and report my findings.

I have two modules that have the first version of the Film Pan Card. These are super quiet and when measuring the frequency response running through the pan-card, these have a better freq.response in the low-end.

Will find out if that gets better after recapping.