MOSFET or JFET

Faust3D · 27th November 2007, 06:45 PM

Can you recommend good current production low power (2-3 watts) MOSFET or JFET transistors with tube like characteristics? I am looking for good transistors that would be used in a hybrid headphone amp.

Thanks in advance.

Nico Ras · 27th November 2007, 07:39 PM

Quote:

Originally posted by Faust3D
Can you recommend good current production low power (2-3 watts) MOSFET or JFET transistors with tube like characteristics? I am looking for good transistors that would be used in a hybrid headphone amp.

Thanks in advance.

I used both IRFP150 as well as 2SK1058 with SE valve hybrid. Worked well and sounded good.

Regards

Nico

Nico Ras · 27th November 2007, 07:42 PM

Sorry I was going to put a diagram in previous post.

Faust3D · 27th November 2007, 09:44 PM

Thank you for the info.

Nico Ras · 28th November 2007, 08:28 PM

Quote:

Originally posted by Faust3D
Thank you for the info.

Sorry mate, I don't know what happened with the last post, the values got left off. Here it is again.

Kindest regards

Nico

Nico Ras · 28th November 2007, 08:36 PM

Quote:

Originally posted by Nico Ras

Sorry mate, I don't know what happened with the last post, the values got left off. Here it is again.

Kindest regards

Nico

Oops there is a mistake somewhere. Ignore this let me check my archives.

Nico

Nico Ras · 28th November 2007, 09:15 PM

Here is the original simulation with CCS. I think I screwed up with some calculations above because the amplifier turned out to be an attenuator.

Cheers

Charles Hansen · 29th November 2007, 04:07 AM

You should change many things on this circuit:

a) The tube does not need an input coupling cap.

b) If you put the coupling cap on the input of the MOSFET instead of the output, you can get away with a value around 0.22 uF (polystyrene is best, polypropylene is OK). This will sound much better than any electrolytic you put at the output.

c) You show a 1.5 amp CCS. This is huge overkill and will place great demands on everything. Assuming the MOSFET is biased halfway between the rails, it will be dissipating 18 watts. This will require a large transistor (100 watts or more) mounted on a very large heatsink.

Go back to the drawing board and try again. It will help if you know the impedance and sensitivity of the headphones you will be using. In any case, I can't imagine that you will need more than 1 watt of class A power. I also can't imagine that you will need more than +/- 6 volts of rails (12 volts total). I'd say 250 mA of idle current will be way more than enough. That will put you in class A up to 1 watt with 8 ohm headphones. If you have 300 ohm headphones, that is enough current to give 35 watts of class A (if the rails would swing that much, which they won't).

roender · 29th November 2007, 05:54 AM

Quote:

Originally posted by Charles Hansen
I'd say 250 mA of idle current will be way more than enough. That will put you in class A up to 1 watt with 8 ohm headphones. If you have 300 ohm headphones, that is enough current to give 35 watts of class A (if the rails would swing that much, which they won't).

1W rms?
35W rms?

jacco vermeulen · 29th November 2007, 06:25 AM

slip of the PP.

27th November 2007, 06:45 PM	#1
Faust3D diyAudio Member Join Date: Jul 2007	MOSFET or JFET Can you recommend good current production low power (2-3 watts) MOSFET or JFET transistors with tube like characteristics? I am looking for good transistors that would be used in a hybrid headphone amp. Thanks in advance.

29th November 2007, 06:25 AM	#10
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	slip of the PP. __________________ Looks like Sponge Bob has killed another thread.

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27th November 2007, 09:44 PM	#4
Faust3D diyAudio Member Join Date: Jul 2007	Thank you for the info.

29th November 2007, 04:07 AM	#8
Charles Hansen diyAudio Member Join Date: May 2003 Location: Colorado	You should change many things on this circuit: a) The tube does not need an input coupling cap. b) If you put the coupling cap on the input of the MOSFET instead of the output, you can get away with a value around 0.22 uF (polystyrene is best, polypropylene is OK). This will sound much better than any electrolytic you put at the output. c) You show a 1.5 amp CCS. This is huge overkill and will place great demands on everything. Assuming the MOSFET is biased halfway between the rails, it will be dissipating 18 watts. This will require a large transistor (100 watts or more) mounted on a very large heatsink. Go back to the drawing board and try again. It will help if you know the impedance and sensitivity of the headphones you will be using. In any case, I can't imagine that you will need more than 1 watt of class A power. I also can't imagine that you will need more than +/- 6 volts of rails (12 volts total). I'd say 250 mA of idle current will be way more than enough. That will put you in class A up to 1 watt with 8 ohm headphones. If you have 300 ohm headphones, that is enough current to give 35 watts of class A (if the rails would swing that much, which they won't).

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