Class D amp with unloaded output

Feb 08, 2015 9 Replies
P

I have some experience designing and building conventional (Class A & AB) audio amplifiers, both with ICs and with discretes, but I'm new to Class D. I'm thinking of experimenting with one of those pre-assembled medium power modules from China. Here's an example:

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Putting other considerations aside for the moment, what I want to ask others with more experience is this: Most of the modules are



2-channel types. If I were to use only one channel and ground the input of the unused channel, does leaving the output open pose any potential problem? Bridging the two channels is not an option since each channel is already bridged.

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J

On a sunny day (Sun, 8 Feb 2015 21:31:55 +0530) it happened "Pimpom" wrote in :

That is cool, I just ordered one myself :-) Will use it to drive my cryo cooler. As to 'un-used channel', looking at the chip datasheet why not put the outputs in parallel? Either at the chip leads or after the low-pass? That is what I will try, need more than 50 W. Will let you know if it lives...

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B

Why not run the two output stages in parallel? Halve the load resistance and then you get double the power. It says the thing is capable of 100 watts into 4 ohms mono down at the bottom of the ebay listing.

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B

10 dollars for that module including heat sink is a pretty crazy price!
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J

No problem.

John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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P

They have higher-powered modules and more crazy prices at their eBay counterpart

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Most products are available with free shipping if you can wait for up to 2 months. I've just ordered, among other things, a pack of 8500 SMD resistors - 50 pcs each of 170 values in E24 series from 0 to 10 Megs for US$20 inclusive of shipping. Try that with Digikey, eh?

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J

I just designed a class-D thingie but not for audio. I connect and disconnect the load at will, without problems.

Regards, Joerg http://www.analogconsultants.com/
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J

OK, it arrived, connected a big 80 W 8 Ohm speaker. First tested one channel, about 10 mV 35 us period time RF remains.

Then put the output of the 2 channels in parallel. Now I get 100 mV RF!!!

So it seems putting the filter output in parallel changes the frequency, and the RF attenuation decreases. I have no problem with that with what I use it for, but it may or may not be undesirable for audio.

I have not run at full power yet out of compassion for the neighborhood. But the amps works, what more can you want for that money.

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