82E149 card input calibration >>SOLVED<<

[oyanliz]

Hi all,

I have some 82E149 transformerless amp cards with +-0.6dB of input signal. These cards does not have any trimmer for adjusting the input signal. In my other channel strips, I have the same cards and they have +-0.05dB of input. How can be fixed the input signal? Are there any speciffic condensers of the card wich affects to this issue?

I have readen sometime somewhere some information about it, but I am trying to search the info with the searcher without succes.

Thanks to all in advance.

Regards.

Oihan

[oyanliz]

Hi all,

I was prety sure that my transformerless input cards were wrong, but they are not. I have swapped 2 of them with input cards of other channel strips and the problem remains in the strip, so... Could be line pot issue? Is it possible to fix it? or I should acept as they are? Could someone give me any idea?

Thanks in advance.

Regards

Oihan

[waltzingbear]

it is entirely unclear what you are talking about. Do you mean differences in level or differences in freq response?

If it is differences in level, these are totally in spec numbers. This is not digital where you can adjust it to 0.01db and have it the same every time all day long. This is a complex analog console that has small variations between channels. The number of parts and the usage of 1% parts still leaves this amount of error. ITS NORMAL. 

You do note that the numbers are the same each time you check them. Stability is what is important. You are using this to mix right? The basic instruction is to adjust by ear.

Alan

[oyanliz]

Hi Alan,

Thanks for answering. I know this is not digital world, so I asume that differences between channel strips it is normal. The issue is that I have 20 mono channels with +-0.05dB level of input (measured with NTI with 1000Hz signal). And I have 4 strips with +-0.6dB level input. I was asking if someone knows if is any  "gain trimmer" or any way to adjust the input level. In my case, all of my channels have 82E149 transformerless amp cards, but the "very small deviation" is not caused for the 82E149 card, so maybe there is a way to adjust the input to +-0.05dB.

This is not an issue for me , I am asking this becouse I would like to reach to know the console as far as I could.

If someone know about any trimmer or trick for adjusting the input level, I would apreciate the information, but if there is nothing for adjusting the input level or it is a line input potentiometer issue or so... I would like to know it, for knowing more about the console.

Thanks in advance once more.

Best regards.

Oihan

[walrus]

At what point in the channels signal path are you measuring?

[waltzingbear]

and again I say, what are you measuring?

there is no input level that is specified as +-.1db.

levels are specified as a specific level, such as +0.12 dbu, or -0.1 dbV. A specific number and reference. Saying something is +-0.1 db is nonsensical. That is a range, of plus and minus 0.1 db, it says nothing about the level.

a db is a relative measure, it has no value. It must be measured against a value. dbu is a number that is relative to the old dbm voltage in a non-power loaded transmission system. dbV is relative to 1V. there are others. So, yes, this is 0.1 db greater than that, but not, this is +0.1 db.

So, what are you measuring. 

[Chris Simon]

Let's assume the original poster is measuring levels as in the calibration procedure; i.e. line input level of +4dBu and measuring a would-be level of 0dBu at the insert send. I generally see a variation of +/- 0.2 dBu measured here. Any greater discrepancy I've found might be due to a slightly dirty line input pot, and I always exercise it by turning it fully clockwise and counter-clockwise several times. There's no level calibration in this path, so a level of 0.6dBu is a little puzzling, but as Alan says, hardly cause for major concern.

[waltzingbear]

I believe it was Glenn Meadows that tells the story of the SSL they had at Masterfonics.

There was some belief that some of the channels sounded "better" than other channels. They took several month to go through and trim the board so that all levels were identical. This involved trimming resistors mostly in the circuits so that the gain staging was identical from one end to the other, not trivial. This was with a professional service department on staff.

At the end they determined that the better channels were those that had slightly higher "0" gain structure. So yet again, the louder one was "winning", because once they were done, all the channels sounded the same.

Cheers
Alan

[oyanliz]

Hi all,

Thank you so much for your answers!

I am so sorry because I did not explain prepertly what I was doing/measuring.

I was injecting 1KHz/+4dBu signal to each channel for checking all of my channels. I measure the signal from each channel insert out with my NTI Minilyzer ML1 device (where 4dBu are drop at this point).

On 20 channels of my console y get measurements like: +0.01/+0.05/-0.02/-0.01... as I have defined as +-0.05dBu (all the measurements are betweeen -0.05dBu and +0.05dBu), the balance is correct in every channel and the signal frequency is detected correctly (1000Hz); so everything is fine.

There are 4 channels, where the balance and signal frecuency detection is correct but the measurements are these: +0.64dBu/+0.46dBu/-0.58dBu/-0.39dBu

I was asking if would be any trimmer or any way to fix this issue, I knew that the deviation was caused by the mother board, line pot or other thing, instead of the 82E149 card (because I swap the card between channels and the problem remained in the channel, so...)

Now, I know that the issue is regarded to the dirty line pot (thanks Chris). As I have mentioned, it is not a big issue for me, but I was not sure if there it was any way to trim the input signal as in the 82E291 card and as I try to learn everything about the console...

Thanks to all for answering, I will try aplying EML lube and try turning the pot several times in both directions. Maybe I would be able o reduce the deviation, but if not... does not matter.

Thanks to all once more.

Best regards.

Oihan