L12-2 CFP OUTPUT AMP 120W*2 8R - diyAudio
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Old 7th September 2011, 06:12 AM   #1
ljm_ljm is offline ljm_ljm  China
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Default L12-2 CFP OUTPUT AMP 120W*2 8R

Each track used 2 to 3 will SA1186 2 SC2837 2.

LAPT power transistors, ultra-high frequency FT, solve the CFP switch distortion.

Tiny hand in the distortion + 0.6 V.
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Old 7th September 2011, 06:14 AM   #2
ljm_ljm is offline ljm_ljm  China
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AUDIO PRECISION SYS TWO TEST:
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Old 8th February 2012, 12:17 PM   #3
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Is this amp OK with 4 ohms?

Thanks
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Old 8th February 2012, 12:36 PM   #4
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Schematic?
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Old 13th February 2012, 04:46 PM   #5
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Bump
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Old 15th February 2013, 09:03 PM   #6
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Bump.

After running out of time with this project, I bought one of L12 kits on ebay. It's pre-assembled so all I had to do was connect a few wires from my power supply and mount it on heat sink. It works!

Below is the schematic from ebay. I checked the voltage across the resistors connected to output transistors (hope I've got it right) and they measure 12 mV at one and 10 mV at the other. There is no adjustable resistor for bias. Any thoughts on this?

I also posted the frequency response which I thought was interesting. Other amps I've measured show slight roll off at low frequency but this one has a bit of boost. FFT measurement of harmonics is very similar to what OP posted above which I expected for push-pull amp. Overall, I'm happy with the results from this $19 module.
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Old 16th February 2013, 06:42 AM   #7
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Harmonics measurement @ 1W 8 Ohm load.
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Old 16th February 2013, 09:46 AM   #8
Duco is offline Duco  Netherlands
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Very nice amplifiers boards! I have already build one amplifier with these boards and they sound fantastic .

I purchased a pair extra just in case and I'm planning to build a new amplifier using these boards and a regulated power supply. Just for the fun of it. I stumbled upon these kind of supplies: 48V 8 3A 400W DC Regulated Switching Power Supply CNC 400W | eBay. Can anyone help me to make a symmetrical power supply from these looking to me as non-symmetrical power supplies?

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Old 16th February 2013, 01:22 PM   #9
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Quote:
Originally Posted by Duco View Post
....Can anyone help me to make a symmetrical power supply from these looking to me as non-symmetrical power supplies?.....
In principle you can simply stack 2 supplies to get balanced polarity outputs. However, SMPS is not a simple safety issue and you should visit the power supply forum, search the topic and ask there. You don't see SMPS supplies encouraged here for a good reasons - it's not against rules to discuss them but the risks to newbs and DIYs generally, by being in contact with non-isolated wiring are much greater than with conventional, isolated supplies.

Active XP
The recommended 50V supply rails should be safe with 4R loads up to 150W. The 120W 8R capability suggests a stiff supply is being used at that voltage but I would not go much over a 300VA transformer in the power supply, just to ensure safety when the load drops below 4R as it likely will, on typical commercial speakers.

Those Sanken TO3P transistors are quite tough on audio as the SOA graph confirms. I can't understand though, why LJM's schematic shows them as Darlingtons.
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Old 16th February 2013, 04:19 PM   #10
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Originally Posted by Ian Finch View Post
Those Sanken TO3P transistors are quite tough on audio as the SOA graph confirms. I can't understand though, why LJM's schematic shows them as Darlingtons.
Mine came with Toshiba TTC5200 and TTA1943 even though the picture on ebay shows Sanken.

Last edited by Evenharmonics; 16th February 2013 at 04:25 PM.
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