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12AU7 / IRF612 Headphone Amp - Update
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Author:  Gio [ 02 Nov 2008, 08:07 ]
Post subject:  Re: 12AU7/IRF612 update

Did you notice a change in the gain when you added Ck?

Author:  roggom [ 03 Nov 2008, 00:46 ]
Post subject:  Re: 12AU7/IRF612 update

Most definitely, I have seen this used in many amps, but I haven't studied tubes in over 20 years. So to brush up I am redoing the US Navy NEETS module http://www.tpub.com/content/neets/14178/ and it is in the first chapter of tube theory. Good stuff. I even capped the low voltage version as well. Of course this is old knowledge for you tube guys.



I had to bump up the capacitance of the inter stage cap to get a flatter response on the low end. It is noticeable on certain formats, but sure looks better on the scope.

Author:  roggom [ 12 Nov 2008, 13:33 ]
Post subject:  Re: 12AU7/IRF612 update

Just like a kid with a new guitar and playing smoke on the water over and over, I have another version of the same circuit. I used a 6AS7G and for now 120 B+ and 24vdc on the mosfet follower stage. Since there aren't any Tina models for this tube, I did all of the plate curves and Resistor values by hand using the plate graph and ohms law. This tube has a lower Rp so I ended up with 3k for RL and 1K for Rk. I got a magnatek VPS-12-2000 for the filament transformer (4A) because the tube is a little pig for filament current. It is still a work in progress but I am happy with how it looks so far. The base used to be pot holder with a ceramic tile in the middle, used a drywall patch kit for the metal base (fit perfectly). More pics to follow.

Author:  Gio [ 12 Nov 2008, 19:41 ]
Post subject:  Re: 12AU7/IRF612 update

Hey Rogers, that is great work!

Can you share some details about the enclosure construction. How is the aluminum plate held in place?

Cheers

Author:  roggom [ 12 Nov 2008, 20:53 ]
Post subject:  Re: 12AU7/IRF612 update

Gio,
Since this is a headamp it doesn't put out too much heat underneath. The tube is raised from the chassis by the octal receptacle. The metal is a very thin sheet of stainless steel from a drywall patch kit, similar to this. http://www.homedepot.ca/wcsstore/HomeDe ... .DP8_4.jpg it has an adhesive side that is stuck to the fiber board (the mesh is removed). I have a hole knock out kit and made the holes for the tube, and caps and drilled the fiberboard.
Here are some more pics, under the hood and a finished one. The whole project was under $50 USD, of course it was built around the items I could find locally.

Author:  RiGuy [ 12 Nov 2008, 22:39 ]
Post subject:  Re: 12AU7/IRF612 update

I really like it Roger. Simple and nice looking. One defiant tube just announcing "you HAVE to listen to THIS!!"
Ri

Author:  Gio [ 12 Nov 2008, 22:46 ]
Post subject:  Re: 12AU7/IRF612 update

Is the box a picture box or did you make it using molding?

Author:  roggom [ 13 Nov 2008, 00:54 ]
Post subject:  Re: 12AU7/IRF612 update

I believe they are picture box's of some sort.I picked them up at a thrift. There are four pieces of 5/8" x 1 3/8" pine and some molding on top, with a 1/4" piece of fiberboard for stability. The insert used to hold a 6 x6 ceramic tile. There are no nails so I think it was some old school craft project.

I have another box that holds the main power and mosfet power supplies it stand off to the side and is connected with a din plug.

I had many choices with this project, but I wanted to make it simple and aesthetically pleasing. Novels are nice and sound great as well , but you cant beat the look of this tube type. The best part is they are still plentiful on the bay for around $5 each.

Author:  Gio [ 13 Nov 2008, 19:38 ]
Post subject:  6AS7G Output TransformerLess (OTL) tube amps

Yes, it is a great looking tube. These tubes are a popular choice for making Output TransformerLess (OTL) tube amps.

Cheers

Author:  crackerkorean [ 03 Dec 2008, 14:45 ]
Post subject:  Re: 12AU7/IRF612 update

I am planning to build the revised headphone amp and had a question about the power supply that I was going to build for it.

I was going to do a simple linear power supply (regulated with a 7812 , thanks gmilitano).
I was wondering what size caps would I need for this?

I know i can use a walwart but wanted to try building the ps my self. I am also going to try a battery out for kicks,

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