2sk1058 mosfet amp

[tubem]

Hi this is my first thread, I have just completed a very nice version of Mark Houston 2sk1058 mosfet amplifier. It sounds excellent and looks real nice too. I hope to have pictures of it posted on the solid state projects page soon, that would be nice.

[doctortube]

Welcome to the forum .I am looking forward to viewing the images of your project .

[doctortube]

Thanks for the pics . Could you show the inside .

[larryldspkr]

I listened to this amp for about 9 hours, it sounded very nice...good dynamics...smooth...way bigger than its 5 watts!! It drove my Tannoy's with room to spare. I want one!!

[tubem]

inside pic as per your request.

[wabun]

can share the schematic ah ?

[taj]

What a curious amp. Can we see the schematic?

..Todd

[tubem]

It's Mark Houston's
Class-A 2SK1058 MOSFET Amplifier

[doctortube]

Nice amp tubem ! The choke looks as big as the tranny Nice point to point wiring .What are you going to build next ?

[ilimzn]

It has the classical error of misunderstanding maximum output swing.
In the positive direction, this would be (Vdd-Vq)Rl/(Rd+Rl)
In the negative direction, this is a bit more complex and depends on how far you want to go into saturation with the MOSFET, but it will be about Vq-2V,
where Vq is the quiscent voltage on the MOSFET drain (adjusted by the pot, this also changes idle current), Vdd is the power supply, i.e. 24V, Rd is the 15 ohm drain resistor and Rl is the load. Assuming an 8 ohm load, you get about 4.17V in the positive direction, and about 9-10V in the negative direction, which results in very asymertical clipping and quite serious reduction in maximum output power before clipping - only about 1W into 8 ohms.
Although it is possible to calculate maximum swing, it involves a compromise regarding distortion, so your best bet would be to measure with a scope, adjusting for symetrical clipping on a triangle waveform, while observing the linearity of the triangle. Themn listen, and fine-tune as needed.
In general, you will have to adjust a larger idle current, and Vq will be less than half Vdd, about 7-8V!
Keep in mind that this adjustment is heavily dependant on the intended load, so this is another thing that must be optimized for.
You ight also want to relocate the power resistors to the main heatsink. As it is, the amount of heat generated on them is exactly tehs ame as that on the MOSFET, so it is not logical to give them a smaller heatsink. In the output-swing optimized condition, the restsors develop more heat then the MOSFET, so the more logical it is to put them on the larger sink.