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Author Topic: MCI JH600 Auto Fader Packs  (Read 184 times)
Robomatic
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« on: February 27, 2017, 07:16:31 AM »

Hi All. There is a trimmer pot on the pc board on my auto faders packs in my JH636. Does anyone know exactly what that is for? Is there an easy procedure to adjust?

Thanks,

Rob
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Harrison
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« Reply #1 on: February 27, 2017, 08:22:56 AM »

Distortion trim for the VCA. There are no other adjustments.
What do you want to adjust?
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Robomatic
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« Reply #2 on: March 03, 2017, 08:53:15 PM »

Wanted to check them. Is there an easy way to do this?
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Harrison
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« Reply #3 on: March 04, 2017, 05:44:41 PM »

You did not answer the question.
The pot is a distortion trim for the VCA. ie a trim for a minimum.

The old best way is with SMPTE IMD, although some will prefer THD.
And then there's the discussion as to where the fader is when you set this value. MCI used the Crown/Amcron IMD analyser with the fader at the top and measure at the following 2003/5534.

BUT, since we rarely use the fader at the top, would it not be better to optimise the trim at fader zero as opposed to VCA zero. ie you get different results depending on which position you choose.

In the absence of any test gear, you could do this adding 2 out of phase signals together. 2 identical line in, but one has fader flip. Set both to the same gain and to the same left or right. phase change one.
Adjust one of them to really null out signal, then adjust distortion trim to improve that nulling

The point being that the one with the rotary pot will be slightly cleaner than the one with VCA. (If you've got black 202s, this is really obvious), and what you can't null out is the remaining VCA artefact.

But of choice, some form of distortion measurement, please.

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