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PostPosted: 22 Feb 2015, 05:09 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
My good friend Bill has some crazy expensive hifi gear. He has also bought some of my home grown goodies to supplement his gorgeous high-end stuff. Also he travels to NZ regularly and has some very classy high-end ear buds. BUT the plain's audio system fails to drive them to their best. CMoy to the rescue!

Bill gave me one solid, immovable mandate in two parts: Small and light. When checking out the specs of most OPAMP chips; LM833 and OPA2134 (my fav.) I discovered they will work down to +/- 2.5V. I'm running this fledgling on a single 9V battery with a differential resistive and capacitive network to give me +/-4.5V. OK not a lot of headroom but I'm working under tough conditions here.

A small Jaycar ABS enclosure will house all parts and battery required. I use prototype brds. I bought from Stiff Dick many years ago. When on the LED just glows to show some one is home. At 152gm with battery and being a little larger than the palm of your hand I think I have met all mandates. Not only that it sounds fine (short listen so far).

As you can see I work in 3D when it comes to cct. bds. The whole shebang is silver soldered and solid core fine copper wire hooks it all up. The two tone ABS enclosure is lined with bitumanised heavy Al foil for screening and resonance control. It will carry a "retro-thermionic" decal and will be delivered in a black velvet slim fitting bag. What a spoil!
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Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


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PostPosted: 24 Feb 2015, 12:34 
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Joined: 20 Feb 2015, 21:22
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Location: Central Scotland, UK
What impedance h/phones can it drive? I've got some lm833 and one of those little radio shack prototype boards. Do you have a schematic and / or a layout drawing?


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PostPosted: 24 Feb 2015, 18:09 
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gasboss775 wrote:
What impedance h/phones can it drive? I've got some lm833 and one of those little radio shack prototype boards. Do you have a schematic and / or a layout drawing?

The CMoy design is what I used.
http://diyaudioprojects.com/Chip/CMoy-G ... phone-Amp/

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Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


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PostPosted: 25 Feb 2015, 17:11 
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I have since discovered that the LM833 wants at least a +\-5V PS. Had to achieve with a single 9V battery. I going to change the chip to an OPA2134 which wil go as low as +\-2.5V. Pity because the HP amp sounded so good with this chip.

Also my Kiwi mate has 12ohm buds. They just distort. To fix this I'm adding a 22ohm resistor in each output leg. I have used my 33ohm phones with no problem.

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Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


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PostPosted: 26 Feb 2015, 08:26 
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Replaced the LM833 with an OPA2134. It drives those 12ohm phones well. No need for the resistor. Not only that it handles the low voltage PS much better.

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Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


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