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Old 16th December 2013, 04:46 PM   #1
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Default Generating a 1 KHz sine at 10mvrms

I need this signal to inject in an amp to set the bias. I have a B&K 3022 generator, but I can't quite figure out how to get such a low signal. Is there easy way to get this done?
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Old 16th December 2013, 04:54 PM   #2
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Originally Posted by DreadPirate View Post
I need this signal to inject in an amp to set the bias. I have a B&K 3022 generator, but I can't quite figure out how to get such a low signal. Is there easy way to get this done?
It is easily done with 2 resistors, say a 10K in series with a 10R. The generator is set to 10V and this divider will have an output of 10mV (1000:1).

The output impedance will be 10R, which is usually no problem with any reasonable load. 1% resistors are usually quite good enough.

Adjust values / amplitude to get other results.
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Old 16th December 2013, 04:56 PM   #3
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If the output of the generator will not go down that low you could build a simple attenuator to get what you need. Here is where a way to measure AC RMS volts would be most handy, like a scope or a good RMS voltmeter. I poked around a bit and it looks like the manual is available. If you have it check for the minimum output level and report back.
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Old 16th December 2013, 04:56 PM   #4
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Yea what cliff said.
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Old 16th December 2013, 06:08 PM   #5
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I measure from .065VAC to 7.260VAC on the output of the 3022 via a Fluke 77 (an older one) which is not rms. So I guess what I need to do is attenuate this range down and feed into an oscilloscope? Now to figure out how to do that, I have a Tek 2245.

Can I also just set it to read 28.29mv (the Vpp of the rms value)? Is the Fluke reading peak to peak or must I halve that value?
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Old 16th December 2013, 06:17 PM   #6
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Why do you need audio into the amplifier to set bias?
Bias is usually adjusted with no audio.
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Old 16th December 2013, 06:33 PM   #7
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Quote:
Originally Posted by cliffforrest View Post
It is easily done with 2 resistors, say a 10K in series with a 10R. The generator is set to 10V and this divider will have an output of 10mV (1000:1).

The output impedance will be 10R, which is usually no problem with any reasonable load. 1% resistors are usually quite good enough.

Adjust values / amplitude to get other results.
Would that impedance be adequate into an audio amplifier?
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Old 16th December 2013, 06:36 PM   #8
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Quote:
Originally Posted by Frank Berry View Post
Why do you need audio into the amplifier to set bias?
Bias is usually adjusted with no audio.
See here:

German Translation Needed: Bias Setting for Denon PMA-520
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Old 16th December 2013, 07:00 PM   #9
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In looking at that old thread, there appears to be a discrepancy between the adjustment procedure and some notes near the optical biasing device, procedure says 100mvrms input and at device 10mvrms input, perhaps that is why getting this adjustment to work has not been smooth for me, nor the individual in this thread:

Trouble with Denon PMA-520 bias adjustment

I wonder if the actual value is 10mvrms. Does 10mvrms seem like a more reasonable input from a source (ie cd player) than 100mvrms?
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Old 16th December 2013, 07:23 PM   #10
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OK, the manual has line input sensitivity at 150mv, so an input of 100mv seems reasonable to set the bias.

By the way, it appears Nelson Pass has a patent on this optical biasing approach used in the Denon products of that time.
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