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TPA3255 Reference Design Class D Amp GB
TPA3255 Reference Design Class D Amp GB
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Old 2nd August 2019, 03:03 PM   #11
xrk971 is offline xrk971  United States
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TPA3255 Reference Design Class D Amp GB
Dr Mord,
For measurements of Class D amps, do you use an antialiasing filter on the measurement input lead? I was warned that applying usual techniques for measuring analog Class A and Class AB amps to Class D May have problems.

This is how I measure my amps:
Howto - Distortion Measurements with REW
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Old 2nd August 2019, 09:53 PM   #12
doctormord is offline doctormord  Germany
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I use Arta for this. No antialiasing-filter, no brickwall-filter at the output like the AES0025. Just don't ground any BTL output.
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Old 2nd August 2019, 11:23 PM   #13
xrk971 is offline xrk971  United States
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TPA3255 Reference Design Class D Amp GB
I am testing out a commercial TPA3255 amp at present and find that using a 35Ahr deep cycle gel cell battery for 12v to 51v conversion with DC-DC step up (800w) and homemade CLC filter (47uF and 10uH Coilcraft SER flat copper wire choke and 47u) the amp is silent with no source playing. It also isolates the amp from the Oscope’s (or other instrument) ground. Useful for measurement tools that are grounded.

This is turning out to be a pretty nice PSU for this amp actually.
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Old 2nd August 2019, 11:52 PM   #14
voltwide is offline voltwide  Ireland
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Quote:
Originally Posted by xrk971 View Post
Dr Mord,
For measurements of Class D amps, do you use an antialiasing filter on the measurement input lead? I was warned that applying usual techniques for measuring analog Class A and Class AB amps to Class D May have problems.

This is how I measure my amps:
Howto - Distortion Measurements with REW
like Doktor Mord I am doing these measurements with an USB-Soundcard (EMU-202) feeding its symmetrical line input via a symm resistor divider from the full bridged output of the class-d-amp to be tested.

There has been no need for filtering the clock residual for measurements - at least with my EMU interfaces.
And the DAC output of these interfaces is imho good enough so there is no need for extra low THD signal sources - with their fixed single operating frequency and restricted level stability.


16bit soundcards like the Behringer are restricted to 96dB dyn range, while 24bit soundcards usually play in the +110dB league.
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Last edited by voltwide; 2nd August 2019 at 11:55 PM.
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Old 3rd August 2019, 12:14 AM   #15
voltwide is offline voltwide  Ireland
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So I append a screenshot of a loopback measurement with EMU-202 operated by ARTA showing 1kHz THD vs level.
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File Type: png loopback_emu0202_outR2inL_steps_44khz1_24bit.png (29.8 KB, 514 views)
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Old 3rd August 2019, 12:23 AM   #16
xrk971 is offline xrk971  United States
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TPA3255 Reference Design Class D Amp GB
Ok. Good to know you guys don’t seem to have any issue or concern with aliasing. That was the warning I got from someone on my REW thread. They suggested a filter like this is needed to really stop the carrier from aliasing the results.

Click the image to open in full size.
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Old 11th August 2019, 06:02 AM   #17
JD2 is offline JD2  United States
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XRK,
This is a cool project. How is the initial build coming? Any timeframe for results?
JD0
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Old 11th August 2019, 07:20 AM   #18
xrk971 is offline xrk971  United States
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TPA3255 Reference Design Class D Amp GB
JPS64 is refining the layout still based on some comments we received in the prior posts. I am hoping to order the verification build boards this Monday.
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Old 11th August 2019, 11:09 AM   #19
Audio Mo is offline Audio Mo
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Interested
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Old 11th August 2019, 12:41 PM   #20
xrk971 is offline xrk971  United States
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TPA3255 Reference Design Class D Amp GB
Should we start a list then?

Vacuphile - 1 board - NL
JD2 - 1 board - USA
Audio Mo - 1 board - Country?
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