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Old 3rd September 2003, 04:28 AM   #1
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Default Yet another boring tube headphone amp

A few years ago I designed a solid state headphone amp for my Grado's, but I've always wanted to try my hand at a good sounding tube amp for them. The rub is that the Grado's are 32 ohm loads. With my penchant for over-engineering, I decided to use a 6AS7 (6080) tube as an output tube. I use one half of it for each channel, and I'm driving it with a 12AT7 (one half for each channel) which is direct coupled to the 6080. I'm using a bit of feedback around the amp to lower the output impedance a bit more and decrease distortion. The really sleazy part is the power supply. I'm using a telema toroid from digikey (all the parts are from digikey except the tubes and sockets). The two 7 volt secondaries form the heater supply, for the 3 amps of heater current needed, and one of the pair of primary windings is used for the b+. Nothing special about the power supply, it's a several stage RC filtered full wave rectified supply.

The downside to OTL amps like this is that the headphones are driven through a big (electrolytic) capacitor. The other downside is efficiency, if the input (wall) power is compared to the power delivered to the headphones (at clipping) the amp is about 0.05% efficient.

But it does sound quite good.

Here's a picture...

http://www.quadesl.com/madisound/tube_headphone_amp.jpg


Sheldon
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Old 3rd September 2003, 05:39 AM   #2
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Ack, a PCB! And to add insult to injury you used a 12AT7, the worst of the 12A_7 series, even worse I'm told than the absolutely horrible 12AU7!!!!!!! How the heck can it sound good!?!?

Hehe glad you like it. Now put a case over that ugly PCB

BTW you forgot that it's not power consumption that matters, but weight. You were supposed to mount that stuff in a 1/2" thick lead chassis.

Tim
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Old 3rd September 2003, 06:09 AM   #3
Duo is offline Duo  Canada
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There's exactly what I have to build, except with two tubes so that I can direct couple with the headphones. My headphones are 8ohm so they'll be a good load for a pair of 6as7Gs. I'll have to do mine in a chrome chassis and point to point wiring to boot.

Gotta use enough junk in there to make it look and weigh like a power amp for normal speakers!!!!


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Old 3rd September 2003, 06:16 AM   #4
Variac is offline Variac  United States
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Please send me your horrible amp. I will give it a decent
burial. I certainly won't hook it up to my heaphones and boogie down at work - really. For being so horrible it actually looks real cool to my apparently warped eye.
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Old 3rd September 2003, 07:02 AM   #5
SHiFTY is offline SHiFTY  New Zealand
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Have you got a schematic? I have a couple of 6080s hangin around, looking lonely...
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Old 3rd September 2003, 05:32 PM   #6
moe29 is offline moe29  United States
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looks nice as usual Sheldon

i'd like to hear it!
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Old 4th September 2003, 03:40 AM   #7
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PCB's are bad...No Comment...

Here's the schematic, simple and boring:
Attached Images
File Type: gif sds_headphone_amp.gif (6.4 KB, 589 views)
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Old 6th September 2003, 05:12 AM   #8
karma is offline karma  Canada
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Default .

thanks
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