Chinese TDA8920BTH bridge wiring - diyAudio
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Old 17th May 2011, 04:01 PM   #1
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Default Chinese TDA8920BTH bridge wiring

I'm building a new boombox & chose the TDA8920BTH for the amp because it was the right price & bridged it should provide plenty of power. The boombox is mono, with a single 10" mid/bass & a horn compression diver connected with a crossover. The amp is this more expensive of the 2x cheap TDA8920BTH boards on eBay, the blue one apposed to the red one that I've found a bit about here through searching.

I just got the amp in the mail today from Singapore & was expecting to just be able to wire it up bridged & start playing, but it looks like I need to do some soldering. But I don't understand what exactly it is that I'm supposed to do, so was wondering if anybody could shed some light on it?


Click the image to open in full size.

These are the instructions on the bottom of the PCB. I assume I'm meant to solder a wire between the two pairs of contacts marked by the 'Connect' lines? But the two contacts in the 'Cut' circle confuses me.
Click the image to open in full size.

This is the top of board that those contacts corresponds to. The 'Connect' lines would connect the yellow components (sorry I don't know what they are, they're labeled 470nJ 63) whilst the 'Cut' circle would cut one end of 2x of the 5.6k resistors.
Click the image to open in full size.

Does this make sense? Also, this may seem like an obvious question, but in bridge mode do I have to feed the amp a mono signal (down either left or right) or can I feed it a stereo signal & it will combine them for me?
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Old 17th May 2011, 05:47 PM   #2
Shaun is offline Shaun  South Africa
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Did the boards not come with instructions? What says the seller?
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Old 17th May 2011, 06:33 PM   #3
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No instructions at all, only what's printed on the bottom of the board. I've messaged the seller, but it will probably be a day or two until I get a response (I think it's night time in Singapore right now).

I've also discovered that I might not even be able to power it with the 2x 12v SLA I was planning on using Might have to shelf this one & buy a more appropriate one.
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Old 18th May 2011, 10:44 AM   #4
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Why won't the power work? I was considering this board.
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Old 18th May 2011, 10:56 AM   #5
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2 x 12V may not enough to power up the board, I am not sure how they lay the circuit or simply base on application note, but since most China DIY amplifier love to tune the circuit work at maximum voltage for highest power as seller point, it may not work at 2 x 12V.
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Old 18th May 2011, 02:04 PM   #6
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Quote:
Originally Posted by fraction View Post
Why won't the power work? I was considering this board.
The chip/board needs a symmetric power supply; where it says 24v that means you have to supply it with +24v as well as -24v (& ground obviously). Two 12v SLA batteries will give you +24v but you'll either need another two batteries to get the -24v (four batteries total) or alternatively use just two batteries but with something like a PT6650 to take some of the power from them & convert it into -24v (which would be inefficient & get hot).

I had no idea about this when I bought it, I thought 24v meant it would work on *either* +24v or -24v, not that it actually needs both!

I've already started another thread asking for recommendations for a more suitable amplifier that will run from just +24v & drive a mono 8ohm load to 50W & above.
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Old 18th May 2011, 02:08 PM   #7
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Ah, ok. Not heard of that either.

Hang on, can't you just use the same serial batteries to supply both?
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Old 18th May 2011, 02:17 PM   #8
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Quote:
Originally Posted by fraction View Post
Ah, ok. Not heard of that either.

Hang on, can't you just use the same serial batteries to supply both?
As I said, you could use two pairs of batteries (four batteries in total) with one pair supplying +24v & the second pair supplying -24v, or you could use just one pair of batteries but split the output so that one wire goes straight to the amp (+24v) & another goes to a PT6650 or similar to convert it to -24v & then to the amp. You can't connect +24v to both of the terminals if that's what you were thinking (I actually tried that before I understood what symmetric meant...).
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Old 18th May 2011, 02:24 PM   #9
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Hmm. I can't find any info on symmetric DC
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Old 18th May 2011, 04:36 PM   #10
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Originally Posted by fraction View Post
Hmm. I can't find any info on symmetric DC
AFAIK symmetric DC supplies aren't often used. The amp is more designed to powered by a centre tapped toroidal transformer, not batteries or an SMPS.

There's no point whatsoever putting symmetric DC through a bridge rectifier, because what you get out the other side will still be symmetric DC but with some voltage loss because of the diodes. It won't damage anything though, so the seller has marked & advertised the amp as being able to be powered by DC when in reality it only really makes sense to power it from an AC toroid.
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