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Class A headphone amp - novel design


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Old 19-10-2013, 21:15
Phil Dodd
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Anyone who dabbles in constructing gadgets might like to look at a design just published on the "Instructables" website. It is for a class A stereo headphone amp, using a double triode valve feeding FETs !

He claims that it gives exceptional audio quality, although is not very portable thanks to a hefty lead-acid battery ! But even the valve works from 12 volts !

I must admit, the best amp that I ever built quality-wise was a class-A headphone amp, using a single VN67AF V-FET per channel. Great sound, especially the bass. It even used to drive a pair of Leak sandwich speakers, again with reasonable bass. It did run quite hot, but FETs are resiliant to thermal runaway. The battery ran hot too !

So this guy's along the right lines to have a hefty battery linked up.

Anyway, if headphone amps are your thing, the project is at :

http://www.instructables.com/id/Clas...Headphone-Amp/

Happy listening ! Phil
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Old 19-10-2013, 21:22
jjne
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This forum's resident expert will be with us shortly to rubbish the idea of using triodes in modern electronics, I'm sure.
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Old 19-10-2013, 22:49
Orbitalzone
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This forum's resident expert will be with us shortly to rubbish the idea of using triodes in modern electronics, I'm sure.
gosh, controversial!
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Old 20-10-2013, 11:47
Nigel Goodwin
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Notice there's no specifications included - best not to measure the distortion

Still at least he's honest about his reasoning for doing, they glow
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Old 20-10-2013, 12:56
chrisjr
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Not so sure I'd wire the volume control pot up as shown in that circuit diagram either. The way it's shown with the volume at zero you'll be shorting the input source to ground! More conventional to wire the input source to the top of the pot and feed the rest of the circuit from the wiper.
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Old 20-10-2013, 13:20
Nigel Goodwin
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Not so sure I'd wire the volume control pot up as shown in that circuit diagram either. The way it's shown with the volume at zero you'll be shorting the input source to ground! More conventional to wire the input source to the top of the pot and feed the rest of the circuit from the wiper.
Yes, I've always absolutely hated that wrong way of wiring a volume control - and can't ever see any reason for doing it?.
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Old 20-10-2013, 13:46
chrisjr
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Yes, I've always absolutely hated that wrong way of wiring a volume control - and can't ever see any reason for doing it?.
Can't say I've seen any kit wired that way. I've certainly never used that method in anything I've designed or built over the last 30 years or so.

And like you can't see any compelling reason to do it that way either.
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Old 21-10-2013, 17:03
spiney2
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with current energy prices, I dont see how anyone can afford to run a triode in class A ......... suggest not heating the cathode .......
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Old 21-10-2013, 17:35
stvn758
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I have just bought a Little Dot MKIII Valve Amp, I find the yellow glow of it's four triodes quite pleasing. I also have a pair of Grado headphones, sound great but horrible to wear.
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