haedphone amp. using 6418< NEED HELP

briansune · 6th January 2012, 08:21 AM

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

roline · 11:10 AM

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....

briansune · 6th January 2012, 09:59 PM

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

astouffer · 7th January 2012, 04:22 AM

Quote:

Originally Posted by briansune

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

briansune · 7th January 2012, 08:18 AM

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.

astouffer · 7th January 2012, 04:41 PM

That won't work either. The tubes have to drive the transistor, and the transistor drives the headphones.

briansune · 7th January 2012, 04:50 PM

how about adding a small output transformer without the transistor driving?

Could you give the formula of the output gain?

6th January 2012, 08:21 AM	#1
briansune diyAudio Member Join Date: Sep 2011	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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6th January 2012, 09:59 PM	#3
briansune diyAudio Member Join Date: Sep 2011	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

7th January 2012, 08:18 AM	#5
briansune diyAudio Member Join Date: Sep 2011	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.

7th January 2012, 04:41 PM	#6
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	That won't work either. The tubes have to drive the transistor, and the transistor drives the headphones.

7th January 2012, 04:50 PM	#7
briansune diyAudio Member Join Date: Sep 2011	how about adding a small output transformer without the transistor driving? Could you give the formula of the output gain?

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