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Old 13th April 2008, 09:44 PM   #1
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Question Measure the output of a bridged class D

I have been trying to measure the output of my Sonic Impact 5066 amplifer. I find the voltage will vary when my other class AB amp will be constant to 4 digits. I am not sure why but is there a way around that?

I have tested other amps through the soundcard but am unsure how with a bridged amplifer.

Frequency Voltage out
500_________3.9 to 4.2
100_________3.8 to 4.1
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Old 18th April 2008, 11:32 AM   #2
acid_k2 is offline acid_k2  Italy
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hi ocool_15
I'm not an expert, but your amp is not a linear amp, and has a lot of HF residual at output.
Your sound card probably has some sensitivity upon 20 Khz, and it's able to measure the fluctuation of that residual.
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Old 18th April 2008, 09:30 PM   #3
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Hi,

You have to use 1kHz as the input signal and hook up the required load 4 ohm or 8 ohm, just connect your scope at the output with a differential probe since this is a bridge connection and crank the input signal up to the max available output into the chosen load just before clipping. This is how it is done.

Regards,
Eric
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Old 19th April 2008, 07:04 AM   #4
Pafi is offline Pafi  Hungary
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Quote:
I have been trying to measure the output of my Sonic Impact 5066 amplifer.
How?

Quote:
the voltage will vary
Depending on what?

Quote:
am unsure how with a bridged amplifer.
Eg.: build a differential amplifier! This has a differential input and a single output wich can be connected to soundcard input.
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Old 19th April 2008, 03:43 PM   #5
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Quote:
Originally posted by Pafi


How?



Depending on what?



Eg.: build a differential amplifier! This has a differential input and a single output wich can be connected to soundcard input.

I have tried measuring with a voltmeter and sending the amp a tone. I intended to measure the frequency response by this way. I tried measuring just the + output and signal ground through the PC.

The voltage out would be fluctuating when the amp was sent a tone. I would be surprised if my voltmeter could pick up that much HF noise from the amp as my meter reading is down more then half by 20k. For the initial test I had no load placed on either amp.


I'm mostly interesting in lowering the F3 down to ~30-50Hz and calibrating the gains then the actual output power as thats well documented here:Michael Mardis T-amps

I will look into setting up a differential amplifier.
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Old 20th April 2008, 07:12 PM   #6
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a diff measurement is simple with a dual trace scope. ch2 is set to INVERT, and vertcal mode is set to ADD. both channels are set to the same (such as 10V/div) gain. ch1 probe goes to the +amp output, ch2 goes to the inverted (-amp) output
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