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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Miguel Dahl on June 22, 2015, 10:42:57 AM

Title: Weird problem with D&B D12 amps and link between Input 2 and AES
Post by: Miguel Dahl on June 22, 2015, 10:42:57 AM
Hi!

Our amps are mounted in a rack, 2xD12 pr rack. there's a front panel where every input (four of them) leads to the input in the back of the amp (Input 1 = ch A on amp A, input 2 is ch B on amp A, input 3 is ch A on amp B, and input 4 is input B on amp B).. But we also have a link cable between the link connector of channel B and the AES input in the back of every amp. We have 4 speakon 4 outputs from each amp, and also one speakon 8, which bunches all the outputs together. In the examples further down the post only speakon 4 was used.

What's been happening lately is that people dont get a full range signal out of the speakon-connectors. The guys back at the warehouse are unable to reproduce the error.

It's happened 3 thimes lately which I'm aware of.
#1: Dual channel Q7, no highs, one Q7 on each channel. Happened on the B-channel
#2 M4 monitors, no highs. Happened on the B-channel
#3, Mixed mode, no sub (I don't know if Q-sub was channel A or B).

The culprit is the link-cable between Channel B on each amp. If we disconnect it it works as it should..

But why? I am stomped because as I said, the guys are the warehouse are unable to reproduce the error, and I myself can't find a cogical explenation. They've tried with the same amps to repdroducw the error.


Title: Re: Weird problem with D&B D12 amps and link between Input 2 and AES
Post by: Ade Stuart on June 22, 2015, 03:01:21 PM
Hi!

 But we also have a link cable between the link connector of channel B and the AES input in the back of every amp.

You need to explain this bit more clearly
Title: Re: Weird problem with D&B D12 amps and link between Input 2 and AES
Post by: brian maddox on June 22, 2015, 05:36:44 PM
You need to explain this bit more clearly

If i understand correctly, what he has done is to have a small jumper run from the 'feedthrough' male XLR on the analog B input into the AES input of that same amplifier.  The idea is that, if you wish to use the AES input, you can simply plug your EAS XLR into channel two on the front panel and it will jump through the passive analog split inside the amp on Analog channel B to the AES input.  Select Digital as your input source in the amp and you're golden.

Now, as to how well this works i can't attest.  I would not have done it this way, but i at least can understand the thought process...

Title: Weird problem with D&B D12 amps and link between Input 2 and AES
Post by: Michael Gorecki on June 22, 2015, 09:58:02 PM
Most amplifiers only run NL4 on the A channel of the amplifier. I would assume these are no different. And you've noted the issue on the B channel in 2 scenarios.
In a biamped configuration one ch does the high and one does the lows.

That's the most logical assumption I can come up with, assuming the boxes are biamped.


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Title: Re: Weird problem with D&B D12 amps and link between Input 2 and AES
Post by: andy craig on June 23, 2015, 12:05:07 AM
Hi!

Our amps are mounted in a rack, 2xD12 pr rack. there's a front panel where every input (four of them) leads to the input in the back of the amp (Input 1 = ch A on amp A, input 2 is ch B on amp A, input 3 is ch A on amp B, and input 4 is input B on amp B).. But we also have a link cable between the link connector of channel B and the AES input in the back of every amp. We have 4 speakon 4 outputs from each amp, and also one speakon 8, which bunches all the outputs together. In the examples further down the post only speakon 4 was used.

What's been happening lately is that people dont get a full range signal out of the speakon-connectors. The guys back at the warehouse are unable to reproduce the error.

It's happened 3 thimes lately which I'm aware of.
#1: Dual channel Q7, no highs, one Q7 on each channel. Happened on the B-channel
#2 M4 monitors, no highs. Happened on the B-channel
#3, Mixed mode, no sub (I don't know if Q-sub was channel A or B).

The culprit is the link-cable between Channel B on each amp. If we disconnect it it works as it should..

But why? I am stomped because as I said, the guys are the warehouse are unable to reproduce the error, and I myself can't find a cogical explenation. They've tried with the same amps to repdroducw the error.

The impedance of the analogue input XLR is 38k ohms.
The impedance of the digital XLR is 110 ohms.
That could be the problem right there, but I would have thought that it would be possible to reproduce this fault back in the shop.

Hopefully this helps.
Andy.