Head-Fi.org › Forums › Equipment Forums › Headphone Amps (full-size) › Crack;Bottlehead OTL
New Posts  All Forums:Forum Nav:

Crack;Bottlehead OTL - Page 5

post #61 of 5826
Thread Starter 
Quote:
Originally Posted by roger_s View Post
Great looking amp and I'm glad to learn that it sounds great as well. How'd you polish the top plate? And how'd you polish it so fast? Mine's primed and painted.
Unfortunately, I have lots of experience in fine finishing from working on hardwoods mostly.
I try not to waste any time and start very aggressively.
Of course, wear ear, eye and breathing protection.

I started by mowing off the wire brush scratches with some "Sandblaster" 120 grit (I think it's a 3M product) on a palm sander. That stuff is hell on wheels and if you used it on wood, it could gouge in an instant but for removing some mil's on metal, it's great.
It does leave major swirl marks so I then went down to 150 grit aluminum oxide then 320 grit. All that took me about 1.5 hours. The last sandpaper I used was some more 320 grit that I rubbed against each other and that makes it closer to 1000 grit.
With each grit, stop after a few minutes, wipe off the surface with a rag and look to see what "new" swirl marks you're making and what you're getting rid of. It doesn't pay to go any further than the grit will allow.

After the sandpaper, I cut up some rags into squares and put them on the sander. I smear "Mother's Aluminum and Mag Polish" (at your auto parts store) and polish it till most of the sanding swirls are gone. This means every 10 minutes or so, you need to clean off the polish and take a soft clean rag and polish. You'll be able to see when most of the sandpaper swirls are gone and just the very fine polishing swirls are being created now.

When you get to the point that you aren't making any progress, take a foam car wax applicator (I like Meguires), apply a light coating of the Mag polish and using a very light touch in circular motions, get rid of as much of the swirling as you can.
Polish it with clean, soft cloths and wash with 409/fantastic type cleaners and water. Examine closely at every angle.
If you weren't super careful, you may find marks from earlier sandings. In this case, it's better to just give up and go back to that point in the polishing rather than wear your arm off trying to get it with too light a finishing stage.

I then put clear gloss lacquer to protect the polishing (it'll scratch by just looking at it if you don't). If it's a flat surface like this plate, I flood it on in one coat (just short of dripping off the edges). Of course, keeping everything totally clean and dust free is key to the final finish you'll get.
Wear a respirator if you value your brain cells too.

I guess I spent about 3.5 hours doing this and painting the transformer bell.

This process won't yield a totally mirror finish but this isn't silver we're working with. You can totally remove any swirls by using the compounds that are used to polish the mirrors in reflecting telescope kits (Edmund Scientific) but I don't think it's worth the extra time.
post #62 of 5826
wow so how long did it take to build it minus the metal finishing?
post #63 of 5826
Thread Starter 
Hmm, I guess if I'd worked on nothing but the Crack amp,.. ,maybe 6-7 hours.
Unfortunately, between watching TV, fooling with another amp, cooking dinner, doing some sketches of the base design and daydreaming about sex, it's kinda tough to get an exact figure.

A couple of things that I found handy was, a pair of lineman's pliers to hold and trim stuff (one of the terminal bases butted up against a tube socket so I could clip off the end a bit). I have a cheap one I got at Home Depot that comes in handy for all kinds of stuff,.. it's the blunt end of the stick.
I double stick taped a ruler to my desk so I didn't have to search for it for the gazillion wire cuts you have to make.
A small file set. The power switch hole was very tight (maybe all that lacquer?) so a few swipes with a file helped.

I guess I was on kind of a mission but if I'd spread it over more than one day, it would've been a relaxed easy job.
post #64 of 5826
Quote:
Originally Posted by roger_s View Post
Great looking amp and I'm glad to learn that it sounds great as well. How'd you polish the top plate? And how'd you polish it so fast? Mine's primed and painted.
It looks great.
Primed & painted mine today. Kind of sorry now.
post #65 of 5826
Thread Starter 
Viva la difference!
I've seen some fantastic looking Bottlehead plates that are painted and what I did certainly isn't the easy way. I've just done it enough so each time it gets a little easier and the finishes are a little better.
There's a lot of iffy results behind me.
post #66 of 5826
Looks very nice, ironbut.

Just wondering how it compares with your other amps?
post #67 of 5826
Thread Starter 
Quote:
Originally Posted by Lil' Knight View Post

Just wondering how it compares with your other amps?
Any real comparisons are a long way off I think. Aside from burn in time, my other amps (currently in use at least) have the advantage of finding just the right combo of tubes and cables to optimize them for a particular headphone (for the most part, I only use one headphone per amp or set up).
I do have a couple of amps in my gear list that I don't really use very often (ASL Mg Head OTL and Eddie Current EC-01). Having the Crack will keep me from ever using them again.
post #68 of 5826
Quote:
Originally Posted by ironbut View Post
Any real comparisons are a long way off I think. Aside from burn in time, my other amps (currently in use at least) have the advantage of finding just the right combo of tubes and cables to optimize them for a particular headphone (for the most part, I only use one headphone per amp or set up).
I do have a couple of amps in my gear list that I don't really use very often (ASL Mg Head OTL and Eddie Current EC-01). Having the Crack will keep me from ever using them again.
I would like to know how the crack sounds with your DT880. I am planning to build one and will either use it with my DT880 (250 ohm) or maybe get an HD600 again.
post #69 of 5826
Thread Starter 
I won't be home tomorrow but I'll give the DT880's a listen on Monday and post something then.
I have a feeling from the way they sounded with my AD2000's that it should be a really nice pairing.
post #70 of 5826
Great work ironbut on the Crack. It looks awesome. Would you mind to take some pics of the soldering work inside, thanks?
post #71 of 5826
Thanks for the detailed reply! I'll have to give polishing a try on whatever my next Bottlehead project is.
post #72 of 5826
Thread Starter 
Just to emphasize the point (it was kinda low in my other post), there are a couple of typo's in the first run of the assembly cd. Doc knows and will be doing corrections on these Monday but if you're hot and heavy into assembly already, you should check out this thread on the Bottlehead forum.

BTW the resistance checks won't pass without the corrections and it should be needless to say, don't do the voltage checks if the the ohms don't jive.

I swear baby, this has never happened before (please help me, Crack won't work)
post #73 of 5826
After fixing those 2 wiring mistakes the Crack is running.

Played for about an hour tonight and it sounds pretty good (HD-650).
Even though it uses the same 6080 tube that the Wheatfield HA-2 I used to own does, it sounds cleaner & more detailed than the HA-2, but not quite as rich.

I'll try to see if I can get picts of my build progress up tomorrow sometime.
post #74 of 5826
Thread Starter 

Link to manual typos

As usual, Doc hopped on getting out the manual corrections as soon as the office was open. Great customer service!

Crack Manual - corrections for the kits shipped the week of 4/19

I did get a chance to listen to my DT880's this morning. I think this amp has given them the bass that I always felt was somewhat lacking. Needless to say, the Crack had no problem driving these to ear shattering levels with my laptop>Metric Halo. The highs were a little edgy but there's lots of burning in still to do not to mention a world of upgrades that should clean those up with very little cash.
I'm still totally shocked by what this ultra simple circuit will do!
Kudos to Paul Birkeland and the rest of the Bottlehead design team. With this amp, I don't see any reason why new headphone fans can't have a great sounding rig right off the bat.


Edited by ironbut - 5/7/10 at 1:57am
post #75 of 5826
Todd, will you be getting the upgrades that are being planned for the Crack?
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Headphone Amps (full-size)
Head-Fi.org › Forums › Equipment Forums › Headphone Amps (full-size) › Crack;Bottlehead OTL