Difference In Level to Audio Groups Across Channels

[Matt Salazar]

When sending audio from the small fader to the routing matrix, the level sent to each group is off by as much as 6db. The variation in level varies by channel.

For example, if I send the output (via the small fader) of CH 9 to Group 1, and adjust the small fader so that the level sent to Group 1 is 0VU, and then do the same thing with CH 10 (outputting to Group 1 @ 0VU), then when I assign Channels 9 and 10 to Group 2, the level received by Group 2 from Channel 9 & 10 is different.

[radardoug]

I'm sure it would have come from the factory working. So you have some issues with group gain. From memory there is a group gain trim. Are they all set to the same position?
Otherwise you need to faultfind and correct the problem.

[Matt Salazar]

Group trims and all in there locked position (no attenuation) for all the channels.

That being said, my problem is with each channel sending different levels to each group. I'm assuming this is before the Group Trim on the channel strip (who's Group I am sending to) and is happening on the channel doing the sending. I'm just not sure where to start on the channel strips to fault find the issue.

Referencing the channel strip calibration procedure I do not see anything relating to individual Group send levels via the routing matrix, only the Group Card output level calibration.

[brewery]

are you measuring the actual ac voltage at the patchbay (group outputs) with an rms meter? this would rule out converter calibration/meters/wiring/normals issues.

are the routing switches in good shape? all the ribbons that carry the busses between buckets are clean and seated properly? (also s10 on the lower buss board, which feeds the group amps?)

the alignment very well adjusts that signal though.
in direct, the channel sends its output only into the last stage of the group amp.
once you use the routing matrix, the group busses are passively summed on the lower buss card, and each group amp takes that signal off their respective buss (with direct NOT engaged). the group trim knob attenuates this signal, the trim pot adjusts the overall output (group and direct).

hope this makes sense, your problem will be in there somewhere

[Matt Salazar]

Thanks brewery. Your answer does make perfect sense.

I haven't measured the actual AC voltage at the patchbay yet, although we recently calibrated the convertors (Avid HD IO) and when using an oscillator calibrated with an rms meter, the convertors are all functioning properly (-18dbFS = +4db in our case).

The routing switches "look" and feel OK, but I'm so new to poking around inside the console I wouldn't know how to spot a bad routing switch.

I'm guessing the problem is happening during the passive summing of the groups. Any thoughts on how best to clean the ribbons and connections on the bucket boards?

I've attached a few images for an example of the problem. Each image is a channel strip sending to groups 1-8 via the routing matrix. I have set the small fader of each channel so that the level outputting from Group 1 (which has been calibrated) is +4db (with corresponds to -18dbFS in Pro Tools).

As you can see, the level outputting to Pro Tools from Group 1 is -18dbFS from both channels, but the level from Group 2 is different between the two channels (-19.1 and -17.6 respectively) on Group 3, both channels are back at the same level (-16.7dbFS) and then at Group 4 they are off again.

[waltzingbear]

How to spot a "bad" routing switch

toggle it off and on, is the return level still the same? yes, switch fine/ no, clean switch.
repeat till its the same every time.

Cheers
Alan

[Matt Salazar]

all the ribbons that carry the busses between buckets are clean and seated properly? (also s10 on the lower buss board, which feeds the group amps?)

Are there ribbons to check on both the individual channels and bucket cards (s10?) that I should check?

[brewery]

there are a bunch of short ribbon cables connecting each bucket with the next one. the group busses are on the lower card, but just make sure they're all clean and seated properly while you're in there.

s10 is another short ribbon that sits on the bottom of the lower card. this one tells the bucket which 8 channels of the groups to tap into.

[Clip6]

Hey. Lucky your in LA just go see Bruce at Desk Doctor in Burbank.

So many techs in your area.