C|24 Analogue levels way out??

[justinhill]

I'm integrating the analogue side of my new old C|24 and the first thing I noticed was the control room output seemed lower than I expected, and the headphone output was too low to use for detail editing. This being a bit subjective, I looked instead at the cue input/output, which is line-level.

If I send a sig gen signal from a pair of Pro Tools outputs to the C|24 cue in connection and then return the signal from C|24 cue out to a pair of inputs on Pro Tools, I find a level difference of -16dBFS with the C|24 cue level knob at the 'nominal' 2 o'clock position, and still -10dBFS even with the knob flat out.

I haven't done a similar check with the control room i/o but to my ears the difference is probably the same.

Is this a fault with my C|24 or something endemic to the product? It seems completely weird that there should be such a massive level drop going into the unit and it totally disrupts my plans for how to use the thing.

[justinhill]

I should have mentioned - I did get Pro Tools to update the C:24 firmware to the most recent version, and I did reset 'analog routes' and 'monitor gains' to default.

I've just checked the studio LS output and it's even lower than the cue output.

[its2loud]

Sounds like your monitor section outputs are trimmed down.

Check out page 65 of the manual

https://cdn-www.avid.com/-/media/avi...uide_41362.pdf

Assuming the levels from your Pro Tools interface are correct. No info was provided from you on that part.

[justinhill]

Originally Posted by its2loud

Sounds like your monitor section outputs are trimmed down.

Check out page 65 of the manual

https://cdn-www.avid.com/-/media/avi...uide_41362.pdf

Thanks for your reply. I reset all the trims, in fact I set the whole desk back to factory default. In any case, there is no trim function for cue out...

[its2loud]

Originally Posted by justinhill

Thanks for your reply. I reset all the trims, in fact I set the whole desk back to factory default. In any case, there is no trim function for cue out...

And you’re positive that the actual analog signal coming into the C24 is correct levelfrom the interface?

Do you have some way to measure it? Route it back into Pro Tools? -20 going out = -20 going back in

[justinhill]

Originally Posted by its2loud

And you’re positive that the actual analog signal coming into the C24 is correct levelfrom the interface?

Yes of course I should have made that clear. I've checked my interface on numerous occasions and I'm confident it's working within specs. I know the multicore I'm using to perform the tests is good because I tore it out of a working part of the studio. I know my Pro Tools session is set up right because I can plug the test output straight round to the test input and see unity.

I read the C|24 front to back several times before buying the desk. I did notice it has no specifications for any of the analogue sections. Gawd knows what I'll find when I decide to check out the line mixer and mic pres...

[its2loud]

Sorry to hear that. Probably not something you were hoping to hear but it least it’s a fix.

[justinhill]

My problem is now fixed. I realise the DUC isn't really the place for technical details but I"m posting this here in case one day another C|24 owner finds it useful.

The first replacement board shipped to me didn't work; in fact the input/output routing was completely garbled. I returned it and had another shipped to me. In the meantime the first board was re-checked by the Avid service guy and found to be fine. It turned out that while dismantling the desk one of the ribbon cable headers (which are glued into place!) had become intermittent. A new ribbon cable fixed the problem.

The monitor board is hard to diagnose because, although it's an analogue board, all its levels and routing are digitally controlled. The bad ribbon cable was running to the monitor board from the "com" board - which appears to be the hub for scanning all the buttons and encoders. So this ribbon was 'telling' the monitor board where to send its signals at at what level.

Also worthy of note is that the actual problem with the original board may have been overheating. There are six voltage regulators on the board: +/-18, +/-9 and +/-5, and all three boards I looked at had scorch marks on the PCB around these regulators. In fact, both the replacement boards from Avid had had at least one of these regulators replaced. The original board had low output from two of these regulators and in hindsight I imagine I might have solved my problem by just installing new regulators - but I wasn't to know that at the time, and I'll never know if that was the only thing wrong with the original board. Still, it's worth checking this if your monitor board is playing up.

Judging by the scratch marks on the bottom panel screws, I suspect the original owner of my desk had it installed with at least two of the four feet 'off the edge' of the surface it was standing on. Since there's two huge ventilation grills under the desk, this may have contributed to the overheating.

All 8 main outputs (surround and alt. out) on my desk are now much closer to the input - about 2 - 2.5dB down, which according to the Avid service guy is about as good as it gets. Cue Out is still 10dB lower than Cue In so this seems to be endemic to the design - and that's a disappointment since it's probably the output I most wanted to be at unity.

Oh, and - you have to remove EIGHTY-FOUR screws just to get the bottom panel off!