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Old 28th March 2010, 02:44 PM   #1
Mywing is offline Mywing  Italy
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Default Bias adjusting on Threshold SA4/e

I finally managed to buy a SA4/e used and in excellent condition. I only have a small problem: the temperature of the two heatsinks differ by about 4 degrees: 49 to 54 left and right sides. I should probably adjust the bias but the instruction manual in my possession does not say how ...
Among other things I do not know at what point precisely measure the temperature ... I did that in the screw holes of the top cover; would be right?

All the advices about the exact procedure of bias adjusting will be welcome.
Thank you
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Old 28th March 2010, 06:34 PM   #2
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Screw holes in the top, 50 deg.

There are a couple of potentiometers on the front end board,
one controls the bias, the other controls the offset. It won't
take long for you to figure out which.

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Old 28th March 2010, 07:17 PM   #3
Mywing is offline Mywing  Italy
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Thanks,
...but if the potentiometer to bias adjusting is unique for both channels, how can I remedy the temperature difference between left and right channel?
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Old 28th March 2010, 07:27 PM   #4
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I would not adjust the channel which is at 49 deg. You would
probably want to reduce the bias of the other channel slightly.

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Old 29th March 2010, 03:21 PM   #5
Mywing is offline Mywing  Italy
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I think I have identified them.
Should be two small blue trimmers one for each channel.
I would not be wrong, but to decrease the temperature I should UNSCREW, right?

Thanks again
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Old 29th March 2010, 05:15 PM   #6
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You should not touch either pot unless you are monitoring
the current draw. Usually counter-clockwise will reduce the
bias, but don't assume anything.

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Old 30th March 2010, 01:18 PM   #7
Mywing is offline Mywing  Italy
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I thought it was enough to decrease the bias of the channel with the warmer heatsink...
Btw, what is the correct procedure of bias adjusting? My owner manual does not say that.
Also does anyone know where I can find a more comprehensive manual?

Thanks again
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Old 30th March 2010, 07:08 PM   #8
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There is a lengthy procedure, but it is simple enough to put
a voltmeter on the power Emitter resistors (one for each output)
on the channel and look at the DC voltage across it. You want to
turn it down slightly and then wait a couple hours with the lid on to
see what temperature you get. When you get 50 deg for a
room temp of 25, you are done.

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Old 30th March 2010, 07:39 PM   #9
Mywing is offline Mywing  Italy
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Ok,
which voltage value I would see on the voltmeter?
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Old 31st March 2010, 02:05 AM   #10
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Quote:
Originally Posted by Mywing View Post
Ok,
which voltage value I would see on the voltmeter?
That which gives you 50 degrees.......
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