[amphead]

Thats one mean looking case kklee! The sinister red glow belies its ballsy sonic capabilities!

Edit: Acrylic is one of the most transparent 92% solid material that currently exists, even more than window glass, crystal and diamond! Edit: Lexan is highly transparent and more crack resistant than acrylic.There are specialized optical glass with transparency of 98%

 

[amphead]

First rebias 10 minutes ago. Rebiased left channel, for left tube bias which drifted to 15.3 VDC and right channel tube bias did not drift and measured 13.7 VDC. DB bias did not drift at all from the 48mv left and right that I had them originally. I forgot that the Jensen bypass caps that were installed are 0.1uF. My evaluation on these caps are that they are neutral sounding, but 0.1uF versus 0.22uF moved the frequency response hump slightly towards treble, quite predictably. Eeexxtteennddeeddd Highs! Resolution is pronounced in the treble region. The saliva is quite audible on a singers lips! My next build will use 0.22uF bypass caps per the MAX spec.

 

[joneeboi]

That sounds great, amphead. Now you never mention if that extension is appreciated or not...

On another note, I thought I'd post my theory on why my earlier wallwart destructo-ed. The second one I ordered after my first busted included a little slip of paper I had not received in the first, "This power unit is intended to be correctly orientated in a vertical or floor mount position." Setting aside the various grammar goofs, I remember plugging this bad boy in upside down; that is, fat side away from the ground (err, the floor). One conclusion is that these bad boys shouldn't be plugged in this way. Then of course, we could spend pages debating what the real meaning is behind those cautionary words, or we could settle with a relatively safe assumption that these power supplies should be only used in a certain way. Again, I have no idea why that really makes any difference (plugging it in "normally" would make it seem as though it were plugged in upside down anyway since it's AC...right?), but my knowledge is limited. Perhaps someone can enlighten me. Anyway, that's my theory: I plugged it in with the wrong pin orientation.

 

[amphead]

The sound with extended highs is an apples and oranges situation. Both sound good. However imagine that you prefer oranges, and you have apples. he he ! On a more serious note: You did not destroy the walwart by installing it in the plug the way you did. The most likely cause of failure was that too much current burned the winding of the transformer open, or an internal fuse(not replaceable) located on the windings. If you really want to avoid problems, you can create your own power supply. It consists of five things 24VAC step-down transformer rated at 40VA, 2A fuse w/fuse holder, spst switch 3A at 250VAC and the input plug/output wiring. It should be mounted inside of a metal project box. This power supply will run forever.

 

[amphead]

Stop the presses! Some astute builder will notice that I biased my DBs for 48mv instead of 48ma. My true intention was to start with about 50ma~66mv. I have now biased the DBs for 66mv. Another evaluation is underway. Quick impression is: midrange boost!

 

[tomb]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif Stop the presses! Some astute builder will notice that I biased my DBs for 48mv instead of 48ma. My true intention was to start with about 50ma~66mv. I have now biased the DBs for 66mv. Another evaluation is underway. Quick impression is: midrange boost!

You're mixing millivolts and milliamps interchangeably.

E=IR, and the output resistors are 2.2 ohms. Therefore, "E" or in other words, "mV", equals 2.2 x milliamps. Like so: mV = 2.2 x ma. So, if you want 48ma, then you should adjust to measure 105.6mV on your meter (105.6mV = 2.2 x 48ma).

Some quick numbers you're referencing:

Meter voltage ............... ma Bias
..........48mV ................. 22ma bias
..........66mV ................. 30ma bias
......105.6mV ................. 48ma bias
.........110mV ................. 50ma bias

EDIT: Most likely, the DB's have barely kicked in at 22ma bias. Minimum is 66mV - 30ma bias, recommended is 110mV - 50ma bias.

 

[amphead]

You are absolutely right Tom! What I should have said was that I wanted to work my way up to 48ma in steps, starting at 66mv~30ma then after another 24 hours going to 106mv~48ma. I'm still over-cautious of the thermal runaway possibility, if there is such a thing as being over-cautious when it comes to biasing DBs. Edit: he he, I deserved the ohms law posting, what was I thinking? I was missing alot of sound with the weakly biased DBs. Now Its reeaally kicking in!

 

[amphead]

Slam, dynamic range, drums, guts! Thats what I now have, biased at 103mv left and right channels/DBs. That may be all I need. My head nearly bounces off the wall if you know what I mean!

 

[amphead]

Who's using V-caps in their MAX? Apparently they have a long burn-in, before they sound good. I was thinking that the V-caps could be mounted in a spare amp and allowed to burn-in before being installed in your primary listening amp. I know that teflon dielectrics are highly resistant to heat degradation, and are supposed to be superior sonically to other types. Dsavitsk?

 

[tomb]

Kklee was gracious enough to provide a complete web page with pics about constructing his Lexan see-thru case panels. I was able to add them to the MAX website today:

MAX Construction -> Casework -> Lexan see-thru Option

Many thanks to forum user Kklee.

 

[ruZZ.il]

x2!
I'd like to do use that stuff for my top panel.. on quiet a few things.
meanwhile, I didnt want to use the aluminum yet, so I decided to use some mdf wood that was just lying around.. it actually turned out kinda cool. will add pics.
I may even varnish it and stuff.. but I still like that lexan stuff. good stuff. respect.

 

[babbkutz@comcast]

as the bias of the DBs is adjusted upward from 70mv to 86mv I'm hearing more midrange grain....am I nuts?

 

[tomb]

Quote:

Originally Posted by babbkutz@comcast /img/forum/go_quote.gif as the bias of the DBs is adjusted upward from 70mv to 86mv I'm hearing more midrange grain....am I nuts?

No. As the DB's kick in with a higher bias, they'll reveal every shortcoming of your amp and system. Most likely, you will hear this if you haven't let the tubes warm up for at least a couple of hours. In some cases, it may never go away - those tubes just may not have a sweet midrange. In other cases, it may be your bypassing capacitors. It can be hard to pinpoint, but it gives you an idea why there is so much emphasis on boutique caps, quality sources, and even higher quality tubes in tube headphone amplifiers.

Also keep in mind - many people will never hear what you describe even with the most rudimentary components. 9 times out of 10 it's the tubes, anyway.

 

[odoe]

I've been listening to my MAX pretty consistently since I got it up and I've DB biased up to 100mv and tubes at 13.75v with PS at 27.5v. My music has a lot more clarity over my pimeta and I don't know the proper terminology, but the music is very "airy", not in a distorted sense, but almost like it has more breathing room. It's also like some of the bass is "blowing" at me. I like it a lot.

 

[tomb]

Nice going Odoe! Glad you solved your problems and that you've been sharing time for awhile now with a living MAX! Yes, a properly tuned MAX can be quite impressive and your terminology is just fine.