A couple tips and a quick review

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A couple tips and a quick review

Postby nate-o » Mon Jan 19, 2009 11:02 pm

Just completed an A12. It would have been a very simple, easy build if I had taken my time to do it right.

I had one issue where I didn't check the schematic and I ended up putting a capacitor in the wrong place. This wouldn't be a big deal, except I hadn't ever de-soldered something from a pcb, and I ended up ruining my solder pads, and almost ruining the board. So practice de-soldering before you try it on the A12 board, if you need to remove any components. Or better yet just put them in right the first time.

Also, the + end of the cap goes to the - terminal on the board. This seems kind of obvious, but I had to think about it when I was stuffing the board.

Get a tap for the XLR connectors. I tapped one with the screw, and it sucked. Got a tap, and it worked great, just remember to take out the metal tab. In one of the connectors there was a metal tab in the screw hole that got caught up in my tap and I ended up breaking the tap.

The DC offset was a bit of a pain. My multi-meter isn't really good enough to do the job properly. On the lowest voltage setting it jumped around and didn't give good readings, so I just kinda guessed on the DC offset. I don't think it mattered too much, because the unit worked fine.

The preamp is not nearly as "colored" as I thought it would be. I compared it to my Mackie Onyx pre, which is regarded as a "neutral" pre. I just did a quick acoustic guitar recording with identical mics placed side-by-side.

At low gain settings there was a very subtle difference in the midrange, with the A12 being a bit more forward, but honestly it was hard for me to tell the difference. According to my frequency analyzer plugin, there wasn't more than 1dB difference at any particular frequency, it was more a tonal difference in the midrange..

At higher gain settings, the A12 smoothed out a bit and sounded a tiny bit warmer. I never noticed this before, but the Onyx has a sort of tinny sound, slightly hollow at high gain. It was kind of like it picked up a little bit more reverb, in a bad way. The A12 sounded smooth and clear.

I was surprised by how it sounded. I expected a thicker transformer sound and a bigger midrange, but I didn't get that. It just sounded good, in a way that could be used on any source.
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Postby lynyrd » Wed Jan 21, 2009 10:40 pm

I think you might want to grab up an N72, they have a nice big fat sound. My SCA preamps are my favourite pieces of gear and I love the A12 and the N72.
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Postby nate-o » Thu Jan 22, 2009 7:29 am

N72 is next on my list, time/money willing.
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Postby stevens » Fri Jan 23, 2009 9:24 pm

Wow, what a difference a tap makes!! Seriously, I made two models without it, and tapping with the screw was hands down the WORST part about the whole project! In fact, it was the ONLY part that I really considered to be a pain in the ass! It sucked, and I didn't even go in all the way, because I just couldn't get the screws in past a certain point! (and yes, I went in 1/2 turn and out 1/4, used oil, and backed out all the way sometimes to clean out shavings):evil:

After reading this post, I went out and spent less than 10 bucks at Home Depot and with my new tap, cut the threads on a new connector like butter! When it was all the way through I said "that's it??"
:)
Anyway, nate-o is totally right! If you want to save yourself a lot of trouble, just go get a tap and handle! My next two modules are gonna be a lot more fun!
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Re: A couple tips and a quick review

Postby dkatz42 » Sun Jan 25, 2009 10:46 am

nate-o \$m[1]:Also, the + end of the cap goes to the - terminal on the board. This seems kind of obvious, but I had to think about it when I was stuffing the board.

Um, no, this is not the case.

You may be fooled by the fact that a bunch of the electrolytics have the negative end marked rather than the positive, but the plusses and minusses need to match between the component and the board.
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Postby nate-o » Tue Jan 27, 2009 6:52 pm

Yeah, you're right. Just goes to show you have to check, and double check your caps to make sure they don't explode.
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Re: A couple tips and a quick review

Postby Todzilla » Tue Mar 31, 2009 4:06 am

nate-o \$m[1]:Also, the + end of the cap goes to the - terminal on the board. This seems kind of obvious, but I had to think about it when I was stuffing the board.


You're kidding!?!?

This may be the clue to why my A12 isn't working. I put all the + ends of caps into the + terminals on the board. I figured that was how it worked.

Did I do any damage if every polarized component is put in backwards?
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Postby tpryan » Tue Mar 31, 2009 7:24 am

the + end of the cap goes to the - terminal on the board


No, no, no!
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Postby Todzilla » Tue Mar 31, 2009 8:41 am

tpryan \$m[1]:
the + end of the cap goes to the - terminal on the board


No, no, no!


Thanks for the clarification Tim. I was scared that matching the component polarities to the polarities on the board was wrong.
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Postby Dean Roddey » Sun May 17, 2009 2:58 pm

Since I'm just about to start down this path, just as a sanity check the tap you got is the one recommended in the docs?

T-Handle wrench and 4-40 tap (Hanson 12001 and 8012)
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www.charmedquark.com
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Postby mmarton » Sun May 17, 2009 3:24 pm

YES, absolutely tap the connectors first. I just did 2 N72's this weekend and it's a small bit of work that makes a huge difference. 4-40NC tap does the job!
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Postby Dean Roddey » Sun May 17, 2009 5:44 pm

OK, I ordered the tap, and I got a 1/2 inch knockout punch and stepped drill bit for some other DIY work (LA-2A.) So I'm full locked and loaded now I think.
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www.charmedquark.com
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