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Old 7th December 2012, 11:55 PM   #1
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Default Using an old Yamaha receiver to build a chip amp.

I have an old Yamaha HTR-5730 that no longer works. I've spent some time diagnosing it and can't really track down its issue. I doubt I'd mind sacrificing it in order to make my own.

This will be my first chip amp. I've done a ton of reading, have some experience building circuits, tons of soldering experience, zero experience with audio amp ICs. I really don't have a clue, but am will to learn by trying.

Here's my plan. I'd love to get some feedback:

I have 3 LM4780's sitting here, samples from Texas Instruments - I'm thinking I could use one or two of them to make a simple stereo amp for a pair of 4ohm speaks from a Tivoli system (broken as well, $5 at a garage sale), using the power supply from the Yamaha. I have the schematics for that power supply:

Click the image to open in full size.

I was thinking I could power the LM4780's by pulling power from the point where it says 23.2 and -23.9 - right before it's changed to 12.1 and -12.2. As far as I know, with 4ohm speakers my target voltage should be around 18v.

Beyond the power supply I was considering this single chip circuit:

2 x 60 W audio amplifier circuit - Electronic Circuits and Diagram-Electronics Projects and Design

I'm still on the hunt for a simple 2 chip circuit.

So, questions:

Is 23v too high?
Is it a good idea to use the Yamaha power supply?
Anyone know of any simple 2 chip circuits?
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Old 8th December 2012, 08:56 AM   #2
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Datasheet of LM4780 should be answering all your questions. If i were you, i will rebuild the receive amplifier using dicrete transistors. In this forum you can find very simple 6 transistor 100W design which easy enough for you to build. The space inside the yamaha receiver is definately large for you to accomodate self made pcb assy.
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Old 8th December 2012, 09:41 AM   #3
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I doubt the lower voltage taps from the transformer can source much current, likely they are just designed to drive DSP and pre-amp stages. You'd need to use a new PSU run from the 36V taps, giving you 36x1.41= 50V rails, much too high for a chipamp.
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Old 8th December 2012, 12:18 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

You could use each 50V voltage rail for single rail chip amplifier circuits.
Bridging two single rails can eliminate the output coupling capacitors.

Note that the Tivoli speakers are actively EQ'd and won't sound good
directly driven by a flat amplifier. They might also have some form of
bass excursion control in the design, again not in a flat amplifier.

rgds, sreten.

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