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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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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Very nice amplifiers boards! I have already build one amplifier with these boards and they sound fantastic :D.

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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....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.

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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. :confused:
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Mine came with Toshiba TTC5200 and TTA1943 even though the picture on ebay shows Sanken.

Hmm ...I thought the advertised LAPT Sankens were too good to be true. Well, that's HK Ebay stores.
I've had a look at old threads and tried to find data sheets for those TT prefix equivalents to 2SC5200/A1943.
'Can't see anything credible yet, other than that they are indeed Toshiba products - perhaps not made
to the same process as in the Thai plant.

They should be up to the task though, given the rating and larger case for better dissipation.
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Doing a small amount of digging, it seems from Toshiba's own website references, that TT prefix parts identify Chinese production.
Officially, there is no need for concern there.
There are a few suppliers of kits and built-up L12-2 modules. One of them, Zoe_Tsang, shows pics of original On-semi ss transistor
packaging and Sanken output transistors. I think they are trying to tell us something there.
This is the schematic they post on the web. You can see it is not screwed up like that above in #6 :

Dear Ian Finch

I tottaly agred with you.
This schematic is very similar with Yamaha small amplifier and it have extra compenents like the transistor like diode in position Q17 and Q19(i suppose). When you see the PCB there is one TO92 TR missing.
Worth by the price offer.

Doing a small amount of digging, it seems from Toshiba's own website references,
Very interesting amp!

One of the few that I have seen around with double output CFP. Once I had published here a simple design (http://www.diyaudio.com/forums/solid-state/188412-jas-just-another-sziklai.html) in such way (it is still under very slow development, ( I have recently modified the VAS but it come up one day...)
Some people here and elsewhere argue that such kind of output is almost impossible to stabilize, so the fact that it is around with a mixed choice of outputs is somehow reassuring.
From my few tests , it is not so.
Thermal stabilty is rock solid (never really had a problem in such sense with a CFP in general), high frequency stability can be an issue, but if the PCB routing is done well and you do not get too extreme compensation values, it is easily working. My impression on prototype listening is that those amps sound really "fast" , i.e. with cristal crear highs and well controlled bass. Ideal for soprano voices, let´s say.
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May be in the future if I have more free time to play around with it.

On mine, the voltage across R13 and R20 measure 12mV and 10mv. What do you think?
That should be around 40-50 mA. That´s perfect for my taste, but you migh hear different opinions. I follow the current of thinking that CFP should be biased low, at the limit of the crossover distortion. People more skilled than me have given some physics about that, but I cannot reacall who, at the momement.