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World Audio HD83 Headphone Amplifier Kit

post #1 of 4
Thread Starter 
I am a "returnee" to the field of electronics. About twenty-five years ago I worked as an electronic technician,
mostly high voltage, high current amplifiers and electromechanical circuits. The things I worked on were mostly tube
based. I got into another profession and have just tinkered on the outskirts of electronics through PC's and such.
Recently I have been working on some small DIY project, a couple of swithch boxes, some digital interconnect cables, and
some audio interconnect cables. Through these projects I have re-aquired most of the basic tools to do DIY projects.

I now have three solid state headphone amps (Corda HA-1, Creek OB11-SE, Total Airhead) and would like to give a tube amp
a try. I saw some posts on the World Audio HD83 on this forum and went to their web site and read all the material that was available
there. From what I read there this amp seemed like the perfect amp for me, it would let me experiece the "tube" sound and
fufill my craving for a more challenging DIY project. All of the tube electronics I worked on before were kind of brute
force technology, you wired resistors between pins of tubes, used cloth covered wire, and anything that had to be wired in
was wired to bakelite or plastic terminal strips. I think by building this amp I could learn a little about circuit boards
and maybe gain experience enough to move into the wonderful world of opamps and transistors.

I would like to ask anybody who has owned, built, knows anything about this amp, or would just like to comment a few questions:

1: Am I folling myself? Would I have a chance in hell of building this thing without to much frustration, or am I going
to have a $300 paper weight?

2. From what I have read you have a choice of four impedance settings with this amp. Is there any way a switch could be
added to pick what impedance you wanted. The schematics seem to show that this would be pretty hard to do, but it is
easier to tell if you've actually seen the physical parts. If it is possible any suggestions on how or what switch to
use?

3. If a switch is not possible (and I think it probably would require extensive rewiring) which impedance setting would
you suggest? I have Senn HD600, Senn HD580, Grado RS1 and Akg 501 phones. I would like to be able to drive all to
their fullest, but know that is not possible, so would favor the Senns' since I use them about 90% of the time.

4. From what I can see you can pick you voltage by wiring up the power transformer in different ways. Is this correct or
do you need to special order for US power?

I think I would really like to try to build this amp and even if I screw it up I can leave it to my heirs and they can take
it to Antiques Roadshow fifty years from know and find out that it is folk art and worth fifty grand.

Any help would be appreciated. Thanks in advance.
post #2 of 4
Hello,

1. I have heard people who are very happy with this particular design, but these guys use speakers. This definitely won't be 300 USD paper weight.

2. Impedance adjustment is sometimes good idea. Generally this is done by switching thru couple outputs of OPT. I believe this is done in HD83 with plastic jumpers. Note you can use switches for this instead. But you must use NON-SHORTING switches. I would use a NON-SHORTING rotary switch if there are indeed 4 choices.

3. The standard output impedance for headphone is 1/10 of the headphone impedance. ECL86/6BM8 can output like 2.5W. So given that you can lower impedance down to 10~50ohms, you might be able to drive Gradoes too. However, there is NO garrantees that performance will be maximal for all headphones.

4. It is true that sometimes power transformers come to accomodate both 120V and 220V. However, this is not true all the time. Please contact World Audio and get explicit instructions.

Tomo
post #3 of 4
Tomo has already answered a couple so I'll just add some encouragement - get this amp. It sounds great, I have it on my desk at work with the HD580s.

1. Sure you could build this, it's simple.

4. The power transformer has twin primary windings. If your power is 240V you use the windings in parallel, if it is 110V you use the windings in series. Easy enough to change if you move.

(I did not like the circuit board and built it on an IAG twin-tube prototyping board I got from www.hndme.com, but followed the same circuit.)
post #4 of 4
Thread Starter 
Thank you very much for your comments, Tomo and Aeberbach. I went ahead and ordered the amp. They haven't got back to me yet, but I should have it before December holidays. Think I'll ust build it stock to start out with.
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