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Pics of my new amp!

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Hi guys!

I finally got a chance to go to a friend's house and get some pics of my DIY 6922/6DJ8 headphone amp; the circuit's the Optimized Morgan Jones as can be found at headwize.com though the PS is different.

Other pics of this amp will be posted later today at http://home.earthlink.net/~shidenkai/index.html along with pics of some of my other projects which are already there.

All the wood and metalwork was done at home with simple hand tools.

Morse
 

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Thanks for the compliments guys!

Hi King 30; hope I don't put you to sleep with the answer!! ;)

The chassis was made from a single 48" long plank of 3/4" thick cherry, 3-1/2" wide. The aluminium is 1/8" thick extruded stock that was purchased in a 36" length, 2" wide. The overall dimensions of the chassis are 8-1/2" x 8-1/2" x 3-1/2" plus 1/2" for the rubber feet.

The tools were a cheap mitre saw ($80 from the local home improvement store), a 15" 15point hand saw for the aluminium, and a cheapie Black and Decker drill for the holes (I did use the drill press at work for the 3/4" tube socket holes though, since I don't have a 3/4" bit yet). Also I used an ordinary plate joiner to biscuit all the joins.

For the aluminium I just cut off the appropriate length using the hand saw in a mitre box, then marked the positions for the holes using a ***** punch and hand pressure. All corners were radiused with a pair of files - a bastard file to get started, then a fine cut triangle file (for sharpening 15 point saw blades) to put a nice 45 degree corner cut on the top edges as well as to clean up the corners. The finishing is just sanding with 400grit paper initially, followed with a LOT of work with a soft cloth and MAAS metal polish. If you're lazy and happy with a matte look, you can call it quits at this point.

For the cherry, a mitre saw is a must along with a sharp blade - the 10-1/2 saw I have cut it like butter and gave nice clean 90 degree edges so that a good box could be made. For fitting it up I used four corner clamps along with a pair of larger clamps to assure it would be square.

Finishing involves sanding in stages - first with 220 grit and a finish sander. Then, when it's got a nice gloss to it I applied the first coat of tung oil (natural finish from Minwax). After about 5 minutes I wiped off the excess and let it dry overnight. After drying, I gently hand sanded it with 400 grit wet/dry paper to knock down the grain that the first coat of oil raised. Next, another coat of oil (same as before) and another very gentle hand sanding the following day to remove any 'gummies' that started to show up in the finish. Then yet another coat of tung oil with the excess removed after about 2-3 minutes (as you go on, you want each successive coat of oil to be thinner).

After this, it gets dicey - if it's 'mirror gloss' enough for you, you're done. If not, it's time to get out the 600 grit paper and VERY VERY GENTLY work the surface by hand to remove any imperfections WITHOUT GOING THROUGH THE FINISH YOU'VE BUILT UP. It takes practice though so don't get too upset if you have to work at it a little.

At that point I called it quits on this one and rubbed it down with a final polishing of Flitz metal/fibreglass polish (which has a wax in it to protect the metal from corrosion and gives a sheen to the wood) and a soft cloth. If you're more obsessive/compulsive than I am you can keep going on up to 1500 grit automotive fine finishing paper and even more thin coats of tung oil....

Hope this helps,
Morse
 

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Great Job on the case!!!!...looks very clean....a little tip on working with the aluminum....."Scotch Brite" made by 3M is the best for polishing up....I would never use sandpaper....the scotch brite comes in different grades so you can achieve a brushed to a mirror look.


Cheers!!The DIRT®
 
Hi Joe, and thanks;

Scotchbright, hmmm? I'll give it a try on my next one - right now I just finished polishing the metalwork for my 6BM8 that's in the works to go with the 6DJ8/6922 that's pictured (identical chassis design and wood but the metalwork's a little different to accomodate 2 rather than 3 valves, no headphone jack, and more fittings on the backside).

Oh well, time for me to get back to work! ;)

All the best,
Morse
 
Hi King 30;

>>>...Do you have a shot of the bottom?<<<

Sorry, but those are the only 2 pics we had time to snap - the bottom's a piece of .028" thick scrap aluminium I had lying about the place. I cut it with metal shears and rounded the edges, then drilled it for 8 holes - 4 of which are for the rubber feet and the other 4 of which are for phillips headed sheet metal screws.

It doesn't seem to generate much in the way of heat (there's about 4.3 watts of waste heat generated in there, but it's a big chassis....) or I would have put in a small 12V fan running at reduced RPM's off the heater windings.

Oh, some things I should have mentioned earlier -

1. If you're new to drilling sheet metal, be wary of the drill bit 'catching' and trying to screw it's way through the metal. It's easy to lose control of the work piece if that happens. Usually I clamp the work piece to the bench and put a piece of scrap wood behind it.

2. Also, be aware that you really should predrill any holes in hardwood. It's not soft pine where you can just drive a wood screw in anywhere without cracking!

3. For square holes in aluminium, if you don't have access to an end mill, you can just drill a series of small holes adjacent to each other (like a postage stamp). Then you can go to a larger bit and make the webbing between holes small enough that you can chisel it out with a cold chisel and a hammer. You do need to make the hole undersize though and do the final work with a bastard file. It takes me about an hour to put in the square hole for an IEC connector to put it into perspective.

Good luck!!

Hi EC8010;

>>>...Hey, this is a family forum!<<<

LOL!! :)

I felt a little bad when I saw that my post was apparently automatically censored to omit the type of punch I used though! FWIW, anyone reading this can also use a 'centre punch' though it's harder to accurately scribe lines than with a 'pr**k punch' because the angle of the tip is different.

All the best,
Morse
 
Ex-Moderator
Joined 2003
The easy way

IECs are a so-and-so. But the way to do irregular holes is with an "Abrafile" blade in in a hacksaw frame. It's a coarse round file about 1/16" in diameter, and works like a saw, but cuts in any direction, an IEC socket can be cut then trimmed in 15 minutes...
 
If you can get a jig saw table you can make square holes even faster. I build musical instruments, and one of the instruments I make is the hurdy-gurdy. It has fourty eight rectangular holes in it, each around 1/4 inch x 3/8 inch. By drilling each hole out with a smaller drill bit, I then place each holeonto the jig saw table with the blade in the hole. I can move the wood back and forth while the edge of the blade cuts the side of the hole flat. I do all fourty eight holes in less then two hours, with a little touch up work with a file after that. Total time would be about 2 1/2 hours.
Untill someone invents a sguare drill bit, this is the most efficient way I have been able to figure out how to make square/rectangular holes. I wish someone would invent one, though, to make it even easier. :nod:
Dave:)
 
Hi EC8010;

Thanks for the tip on the 'abrafile' blade - do you know if they're available anywhere on this side of the pond?

Hi Hurdy Gurdyman;

I always said that there's a lot that hifi afficionados can learn from the musical instrument makers, and you've proven it again! Thanks!

Hi Tim;

>>>...But I'm still a metal man...<<<

No problem there :) - one of these days I'd love to get time on a milling machine and have the money for a big billet of 6061 T6 so I could build a Zen SS amp into the hollows of a one piece chassis/heat sink. I have most of the parts sourced, save the PS caps and the PS trafo. $$ are the problem at the moment though, *sigh*.

For valve kit I still like the 'pseudo Victorian' look (to quote one of my friends description).

What I'd really love to do if I could just get a good stock of nixies, is to build my own CD player with a wooden chassis, nice big bat handled momentary switches as the controls, valves for the audio stage, and nixies for the display.... But as usual, $$ are a limit.

All the best,
Morse
 
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