[geom_tol]

Finally finished building my fourth headphone amp!

It's a multiloop amp with opa637 input and el2009 output stage, and a great dual ps that Voodoochile made. I had some 'amusing' mishaps while building it, first time I tried it, it didn't work (or so I thought) all I got was horribly distorted sound and overheating buffers. A week later I realized my test headphones were mono...

I also blew a electrolytic cap which I installed reversed, it took over a minute after powering on until it blew while I was measuring with a DMM on the board, I almost crapped myself...

I've only been running it for a couple hours, it's easily as good as my meta42 already (ad8620 opamps, el2008 buffers, dual battery ps).

I still have some stuff left to do, I'll do it in a couple months and it will be like a free 'upgrade'. Wire led, bias opamps into class a, add more caps, figure out the proper grounding scheme and rewire it. Possibly make two dual powersupplies so it can run dual mono.

Here's the pics:
(follow links at the bottom for the two non-pron pics, they're not nearly as exciting)

http://mysite.verizon.net/vze44bd6/iso-front.jpg
http://mysite.verizon.net/vze44bd6/iso-rear.jpg

 

[Budgie]

Who makes that volume pot? It looks like a nice one. Were did you get the circuit boards?

(edit-typos)

 

[geom_tol]

I op-amp rolled in ad843's this morning. Wow! Much better. The opa637's sound restrained and unlively in comparison.
It definately sounds better than my old meta42 now.

Budgie:
The pot is a Penny & Giles 100k audio pot. I pulled it from a Mod squad passive preamp that I'm not using anymore. The Mod squad is also the source of the isolated WBT RCA connectors and the knob.

I designed the pcb in Eagle and had it made when one of the pcb places had a "make three pcb's free" promo last spring.

 

[Budgie]

That is a very nice pot! And a very nice amp you have built for yourself, too. (You could smooth out that transformer shields shape, a little, though!

)

 

[Voodoochile]

Nice job! Very beefy looking chassis- attractive. The heatsinks look like they are a foot tall in that close-up!

What size was the cap that you set off, out of curiosity? Glad you survived to tell us about it. Are your ears still ringing?

Also, is the shield there 'just in case', or did you actually pick up some noise from the transformer?

Thanks for sharing. I also agree with Budgie on the pot, it's a beauty!

 

[xtreme4099]

cool you finally got use outta your el2009s ... here's my amp that was built with them ... cool stuff
http://www4.head-fi.org/forums/showt...ghlight=el2009

 

[geom_tol]

The cap that blew was a 470uF, 25V cerafine. A little cap, but the explosion was spectacular, loud bang and lots of smoke. It was positioned undeneath the pcb so the liquid was well contained.

The shield is 'just in case' I didn't realize how close the tranny would be to the inputs until I had everything in there so I put the shield in.

The amp has been on and driving my K501's for over 24 hours now. The heatsinks feel warm to the touch.

Xtreme4099:
Wow, that's a greatlooking amp. The wiring is incredibly neat!
Patience and a steady hand is needed for that kind of finish.

If I make another pcb all connections will be socketed. That would make wiring easier and then maybe I will be able to make an amp as neat looking as xtreme4099's.

The shielded cable I used in this amp was a pain to work with, it is too stiff. I think I'll use shielded microphone cable for my next project instead.

 

[london luke]

I like it. The copper shielding section,Does this have to earthed???
I have some great copper sections..and fancy doing this to my power supply.

Cheers


Luke

 

[jeffreyj]

Quote:

Originally posted by london luke I like it. The copper shielding section,Does this have to earthed??? ...

If you want the shielding to act as a shorted turn, to counteract stray magnetic flux, then it needs to be a continuous band of copper around the outside of the windings. If you want the shielding to reduce the coupling of (electrostatic) noise from primary to secondary, then the shield needs to be an almost continuous band of copper inbetween the primary and secondary windings, and grounded at one point only.

So, the little curtain of copper in the above pictures will do no good, but it won't harm anything, either. Furthermore, toroidal transformers radiate very little stray magnetic flux so there is no benefit from the shorted turn shield. They do benefit, greatly, from electrostatic shielding, though, but this is something which is not at all practical to add on later!

So, skip the shielding and, instead, rotate the toroid so that the wires exit from a point 90 degrees away from whatever might be sensitive to stray flux (the only significant source of stray flux in a toroid is the winding terminations).

 

[erix]

Spots for current sources, PS bypasses right next to the opamp, space for cap (if you need it...), nice and tight.

Good work!

ok,
erix

 

[geom_tol]

Jeffreyj:
Thanks for that info. The shield is there to shield from electromagnetic fields. I suspected it needed to be continuos.
Maybe I'll get a longer strip and solder it together.

 

[was ist los?]

Where can i get copper plate? BTW, nice amp!!