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Class D Switching Power Amplifiers and Power D/A conversion

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Old 31st July 2005, 08:50 PM   #21
rjb is offline rjb  New Zealand
diyAudio Member
Join Date: Jun 2004
Location: Piha
I played with the original Sinclair "20 watt" class D amps in the late 60's. Sounded good at low powers. These fed the speakers direct with no output filter, so radiated EMF like crazy, right up past the AM broadcast band and aircraft beacon band, and even higher, with very significant power. For this reason I gave it up as too dangerous. The longer the speaker leads the worse it got.
Modern units with faster switching and higher powers will be even worse.
I strongly recommend not changing the manufacturer's output filter as this should be optimised to keep emf within the appropriate regulations.
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Old 1st August 2005, 01:02 AM   #22
jkeny is offline jkeny  Ireland
Join Date: Feb 2007
Location: Dublin
I have two questions:

Has anybody looked at the 5V regulation of the chip itself - I can't remember which pin it comes out of and feeds some pins on the input side - if it is not very clean, could this be substituted with an external clean regulated 5V supply? Any advantages?

I have tried replacing all input section with 2.2uF cap connected to 20K resistor on SI board (leaving out cap& res to ground as well as input inductor). In theory this should improve sound. Well bass is certainly better due to 2.2uF caps but midrange seems as if some life has been sucked out of it. I have tried this twice on another Si board also with the same result. When the 2.2uF cap is connected instead to the board with all the input circuitry still in circuit, midrange life returns. Has anybody else experienced this?

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Old 2nd August 2005, 06:52 PM   #23
jkeny is offline jkeny  Ireland
Join Date: Feb 2007
Location: Dublin
I connected the SI amp without inductors to my 15 ohm Rogers speakers as an experiment - the sound was not immediately better than with inductors although I didn't listen for very long ( see below).

The complex crossovers on the Rogers contain 3 ferrit core inductors and lots of caps & resistors. I have these mounted on outside of speakers and when running off SI amp without inductors I noticed that a couple of resistors became very hot - I disconnected after 5 mins playing. (These resistors commonly burn out on Rogers speakers if a lot of high freq signal is sent )

Just thought I report findings

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