Measure the output of a bridged class D - diyAudio
 Measure the output of a bridged class D
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 Class D Switching Power Amplifiers and Power D/A conversion

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 13th April 2008, 09:44 PM #1 diyAudio Member   Join Date: Nov 2004 Location: sk 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
 18th April 2008, 11:32 AM #2 diyAudio Member   Join Date: Oct 2006 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.
 18th April 2008, 09:30 PM #3 diyAudio Member     Join Date: May 2001 Location: Canada 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
diyAudio Member

Join Date: May 2004
Location: Budapest
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.

diyAudio Member

Join Date: Nov 2004
Location: sk
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.

 20th April 2008, 07:12 PM #6 diyAudio Member     Join Date: Dec 2006 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 __________________ Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net spammer trap: spammers must die

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