Tube headphone amplifier

RE: Tube headphone amplifier

jc2048 — Sun, 17 Jun 2018 10:52:29 GMT

Interesting circuit and a nice project built around it.

I can sort of understand the operation, indirectly, by substituting FETs for the tubes. The top tube is a

follower and the bottom one an active pull-down, driven by feedback from the anode of the top tube via C4 on your schematic (C3 on mine) leading to a low output impedance (for a valve

circuit without a matching transformer).

Couldn't resist trying it in the simulator. Here's a FET version that I've slapped together. (Important: this isn't a

properly designed circuit, so don't build it and expect it to be any good as a headphone amplifier. I might even be operating outside the spec for

the FETs. And, the equation for transconductance of a tube is more complicated than a FET, so the FET isn't quite an analogue of a tube and this

won't behave in quite the same way as the valve version.)

[View:/resized-image/__size/586x464/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-96e7da26-82cd-4fc8-82ee-44834d6dca1f/2630.contentimage_5F00_187567.jpg:586:464]

It does actually work (kind of works), though I can't persuade it to follow properly (so the pull-down might be a bit skewy) - I get a gain of about 0.8. It's

horribly inefficient - I've got a current of 30mA through the FETs and about 5mA peak into the load - but probably not as

inefficient as the tube version which I assume has a secondary use as a small room heater. Looks like there's a moderate

amount of distortion on the output too. All of that could probably be improved with proper design, though it's never going to

be that efficient because of the standing current through the FETs.

[View:/resized-image/__size/620x427/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-96e7da26-82cd-4fc8-82ee-44834d6dca1f/6763.contentimage_5F00_187568.jpg:620:427]

Frequency response is quite reasonable. Flat to 10MHz. Wonder how that compares to the valve version? Presumably the tubes do better because of lower parasitic capacitance.

[View:/resized-image/__size/620x243/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-96e7da26-82cd-4fc8-82ee-44834d6dca1f/2543.contentimage_5F00_187569.jpg:620:243]

RE: Tube headphone amplifier

neilk — Sat, 16 Jun 2018 16:02:23 GMT

Very nice job. [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-96e7da26-82cd-4fc8-82ee-44834d6dca1f/contentimage_5F00_1.png:16:16]

My first foray into electronics, in the early 60s, was to build a valve amplifier from a book of designs, published by the valve manufacturers Mullard. EF86, ECC83 and 2xEL84.

Neil

RE: Tube headphone amplifier

rachaelp — Mon, 11 Jun 2018 14:35:15 GMT

Very nice project! I used to have a valve amp as part of my hifi setup, maybe I will build one of these headphone amps one day just so I can have some excuse to mess with valves [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-96e7da26-82cd-4fc8-82ee-44834d6dca1f/contentimage_5F00_2516.png:16:16]

RE: Tube headphone amplifier

jw0752 — Mon, 11 Jun 2018 00:33:49 GMT

I like this. Nice job building it. By using the modern voltage boost technology you are illustrating how old and new technology can work together to make a unique device.

John

RE: Tube headphone amplifier

balearicdynamics — Sun, 10 Jun 2018 17:30:03 GMT

Nice! Super retro vintage

I hear no sound in the video. Is it normal?

RE: Tube headphone amplifier

DAB — Sun, 10 Jun 2018 17:19:41 GMT

Brings back memories.

I used to build these back in the 1960's.

DAB

RE: Tube headphone amplifier

genebren — Sun, 10 Jun 2018 14:29:16 GMT

Very cool and very retro!

Nice job.

Gene