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-   -   Simple tube/mosfet headphone amp. (https://www.diyaudio.com/forums/tubes-valves/340352-simple-tube-mosfet-headphone-amp.html)

nigelwright7557 17th July 2019 06:47 PM

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.
https://i.ibb.co/t4g94RH/headphone.png
https://i.ibb.co/D9yM2zL/100-0188.jpg

Sodacose 17th July 2019 08:03 PM

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?

nigelwright7557 17th July 2019 08:12 PM

Quote:

Originally Posted by Sodacose (https://www.diyaudio.com/forums/tubes-valves/340352-simple-tube-mosfet-headphone-amp-post5855048.html#post5855048)
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.

Fredenando 17th July 2019 10:01 PM

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??

nigelwright7557 17th July 2019 10:12 PM

Its the same circuit as mine.
I was pleasantly surprised with how good it sounds.

nigelwright7557 19th July 2019 03:41 AM

A short youtube video showing head phone amp.
YouTube

aardvarkash10 19th July 2019 06:27 AM

pcb seems quite large for a headphone amp ;-)

Mods, surely the forum can limit the size of images placed in the threads?

nigelwright7557 19th July 2019 02:49 PM

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.

PRR 20th July 2019 07:38 PM

Quote:

Originally Posted by aardvarkash10 (https://www.diyaudio.com/forums/tubes-valves/340352-simple-tube-mosfet-headphone-amp-post5856426.html#post5856426)
....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.

nigelwright7557 20th July 2019 08:08 PM

Quote:

Originally Posted by PRR (https://www.diyaudio.com/forums/tubes-valves/340352-simple-tube-mosfet-headphone-amp-post5858021.html#post5858021)
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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