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Simple tube/mosfet headphone amp.
Simple tube/mosfet headphone amp.
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Old 17th July 2019, 05:47 PM   #1
nigelwright7557 is offline nigelwright7557  United Kingdom
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Default Simple tube/mosfet headphone amp.

Found a little simple headphone amp circuit.
Its a 12au7 gain stage into a mosfet source follower.
The mosfet has a lm317 current source.

Didn't work to start with but then found a dry joint on the tube socket.
Then found a 2k2 pot in place of the 22k pot which killed the gain.
Got there in the end.
Click the image to open in full size.
Click the image to open in full size.
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Last edited by nigelwright7557; 19th July 2019 at 01:50 PM.
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Old 17th July 2019, 07:03 PM   #2
Sodacose is offline Sodacose  United States
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I built something really similar not long ago using a 7370 tube (1/2 per channel) and a 48Vdc supply. Sounds very good for how simple it is.

Is the 12AU7 grid leak biased at this low voltage?
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Old 17th July 2019, 07:12 PM   #3
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Sodacose View Post
I built something really similar not long ago using a 7370 tube (1/2 per channel) and a 48Vdc supply. Sounds very good for how simple it is.

Is the 12AU7 grid leak biased at this low voltage?
The cathode resistor is only 150r so not far off grid leak biased.
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Old 17th July 2019, 09:01 PM   #4
Fredenando is offline Fredenando
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Hi,

I was thinking to build this, that is very similar and include some improvements as a delay on/off but I don't know wich is the better and most simply building.

NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier

What do you thing??
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Old 17th July 2019, 09:12 PM   #5
nigelwright7557 is offline nigelwright7557  United Kingdom
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Its the same circuit as mine.
I was pleasantly surprised with how good it sounds.
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Old 19th July 2019, 02:41 AM   #6
nigelwright7557 is offline nigelwright7557  United Kingdom
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A short youtube video showing head phone amp.
YouTube
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Old 19th July 2019, 05:27 AM   #7
aardvarkash10 is offline aardvarkash10  New Zealand
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pcb seems quite large for a headphone amp ;-)

Mods, surely the forum can limit the size of images placed in the threads?
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Old 19th July 2019, 01:49 PM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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I found my amplifier doesn't work well with all 12ax7's.
I suspect 12 volts is a little too low for it.
I found an article where someone had the same problem and they found making the grid a bit more positive helped.
I have a 100k grid resistor so added a 1 meg pull up resistor and the amp works much better with marginal valves.
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Old 20th July 2019, 06:38 PM   #9
PRR is offline PRR  United States
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Quote:
Originally Posted by aardvarkash10 View Post
....Mods, surely the forum can limit the size of images placed in the threads?
It tries. Does not always work. Especially on external images.

If you click on the image it shrinks to fit your screen. (At least on my FireFox Win7 PC.) Yes, that is counter-intuitive.

If you Refresh the page (F5), it tries to re-size the images. On this thread I had to do it twice; some threads take more F5 beating, some just never fit.

The current forum software is VERY old. The plan is to replace it with new software "soon". In the meantime we live with little annoyances. Any attempt to change the old software would be time-consuming, time better spent in preparation for moving to new software.
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Old 20th July 2019, 07:08 PM   #10
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by PRR View Post
It tries. Does not always work. Especially on external images.

If you click on the image it shrinks to fit your screen. (At least on my FireFox Win7 PC.) Yes, that is counter-intuitive.

If you Refresh the page (F5), it tries to re-size the images. On this thread I had to do it twice; some threads take more F5 beating, some just never fit.
.
Sorry I keep forgetting my digital camera creates huge pictures.
I have resizing software but keep forgetting to use it.
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