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Panasonic SA-AK340 high freq on audio output.

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danielsoy

New Member
Dear ppl.

My panasonic audio box has its class D amplifier, that show HF signal (370khz), on the
speakers output. Sound is OK.

Amplifier IC is TDA8920BJ.(200mv-2useg div)

Audio out:


Is that signal right?
 

spec

Well-Known Member
Most Helpful Member
Yes, that is fairly normal with class D. The speaker is effectively used as a filter and does not respond to the class D switching waveform.

spec
 

danielsoy

New Member
Thanks spec for your answer.

200 mv is the voltage per vertical division in my scope, so I ve got 800 mv peak to peak, with +30vdc -30vdc
power supply for the amplifier.

what do u think now?
 
Last edited:

spec

Well-Known Member
Most Helpful Member
Thanks spec for your answer.

200 mv is the voltage per vertical division in my scope, so I ve got 800 mv peat to peak, with +30vdc -30vdc
power supply for the amplifier.

what do u think now?
That is a bit on the high side, but not wildly so. You can only hear 20K Hz max and most speakers roll off around 10KHz to 15Khz, unless you are talking HiFi speakers. In case you are interested there is a breed of class D chips that are called 'filterless' that for economy rely on the inductance/resistance and frequency response of the speaker and leads to effectively filter the class D switching signal.

I did get the scope reading :). Although the signal may seem high, have no fear, it will not damage your speakers- you want to see the switching signal on our TV and and my laptop.:arghh:

spec
 
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audioguru

Well-Known Member
Most Helpful Member
The 370kHz at a level of 0.3V RMS produces a whopping high power of 0.01W in an 8 ohm resistor but since most speakers are inductive then the power in a speaker is much less. Nothing to be worried about.
 
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