JFET as 1st stage in PLH

[Skorpio]

Nice...

I have 4 pcs. 2SK147 matched and there might fit well here...

I will use a lower power supply (20V secondary) and only on pair of output devices, giving a very simply amplifier.

10W will be enough....

[FYC]

4 pcs of 2SK147 will work fine, as in my case, with transconductance at about 80mA/V.
This device is really hard to find now and 2SK170 only has half of the transconductance.

At 20V power supply, are you sure you can get 10W? I have not done any calculation but at 40V power supply I believe I am getting 10W.

[EUVL]

You can use 2SK369 which has double the transconductance of 2SK170. Widely available in BL grade, which fits the application.


Patrick

[Skorpio]

Originally posted by FYC
4 pcs of 2SK147 will work fine, as in my case, with transconductance at about 80mA/V.
This device is really hard to find now and 2SK170 only has half of the transconductance.

At 20V power supply, are you sure you can get 10W? I have not done any calculation but at 40V power supply I believe I am getting 10W.

20V secondary will be 28V rectified and approx. 25V effective, this will just make 10W in 8 Ohm....

[FYC]

Originally posted by Skorpio


20V secondary will be 28V rectified and approx. 25V effective, this will just make 10W in 8 Ohm....

I am a bit doubtful on this. Assume you do get 25V as line voltage. The 2 MOSFETs are always conducting, so G-S voltage is about 4V. D-S voltage should be larger. Anyhow taking 4V drop across each device, you lost 8V already, leaving only 17V for max voltage swing. If you set your output DC level at mid point, you get 8.5V p-p, which is about 6V rms. So your output power into 8 Ohm load is about 4.5Watts, which might still be good enough if your speaker efficiency is high.