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Old 6th January 2012, 08:21 AM   #1
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Default haedphone amp. using 6418< NEED HELP

I would like to try the 6418 tube in headphone amp.

And if it is possible to run the headphone(32-44ohms) without an op amp. or just use transistor MOS or NPN??

THANKS


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Old 6th January 2012, 11:08 AM   #2
roline is offline roline  United States
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I did a tube-MOSFET hybrid amp, and ran the output Mosfet as a class A follower with a CCS biased at 12Volts across the stack at 200ma. I increased the output bias and it would drive a 8ohm speaker.... backed it down to 200ma for headphone use.
Verify the output current drive on the Opamp, you would want around a 8 volt swing at 125ma or more....
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Old 6th January 2012, 09:59 PM   #3
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Really thanks for sharing Roline < The amp looks really good at all, but i wanna to use 6418 to drive a headphone via transistor. The reason is that i wanted to use it in hand carry(out door) beside of indoor using.

6418 is a really small tube with a fm 1.25V and 0.01A, max. P is about 30V, 0.5mA


OR a tube 6519 fm 1.25V, 10mA max. P is about 30V, 0.6mA

Would you have some ideas in this too?< Hope you can help@@ THZ
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Old 7th January 2012, 04:22 AM   #4
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Quote:
Originally Posted by briansune View Post
Really thanks for sharing Roline < The amp looks really good at all, but i wanna to use 6418 to drive a headphone via transistor. The reason is that i wanted to use it in hand carry(out door) beside of indoor using.

6418 is a really small tube with a fm 1.25V and 0.01A, max. P is about 30V, 0.5mA


OR a tube 6519 fm 1.25V, 10mA max. P is about 30V, 0.6mA

Would you have some ideas in this too?< Hope you can help@@ THZ
That design does not look very good. At first glance R3 and R4 seem way too large. I don't think you can run two filaments from the same supply without getting a lot of crosstalk between the channels.

If you want to drive headphones with just a transistor take a look here HeadWize - Project: A Class A MOSFET Headphone Driver by Greg J. Szekeres
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Old 7th January 2012, 08:18 AM   #5
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Thanks astouffer< the site you posted can be used for an example.

The schematic is not my design, this is come from a kid, as you said some of the resistor might to high(This may be because the kid act the 6418 as pre-amp? and the op amp as the output?) So i am thinking use the 6418 tube as the op amp and replace the original pre-amp into transistor.

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Old 7th January 2012, 04:41 PM   #6
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That won't work either. The tubes have to drive the transistor, and the transistor drives the headphones.
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Old 7th January 2012, 04:50 PM   #7
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how about adding a small output transformer without the transistor driving?

Could you give the formula of the output gain?
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