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Old 27th November 2007, 06:45 PM   #1
Faust3D is offline Faust3D  United States
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Question 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.
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Old 27th November 2007, 07:39 PM   #2
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Default Re: MOSFET or JFET

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
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Old 27th November 2007, 07:42 PM   #3
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Sorry I was going to put a diagram in previous post.
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Old 27th November 2007, 09:44 PM   #4
Faust3D is offline Faust3D  United States
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Thank you for the info.
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Old 28th November 2007, 08:28 PM   #5
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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
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Old 28th November 2007, 08:36 PM   #6
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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
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Old 28th November 2007, 09:15 PM   #7
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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
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Old 29th November 2007, 04:07 AM   #8
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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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Old 29th November 2007, 05:54 AM   #9
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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?
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Old 29th November 2007, 06:25 AM   #10
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