i made an LA-2A

Get that song on tape! Errr... disk?
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i made an LA-2A

Post by øøøøøøø » Sun Jan 09, 2022 12:29 am

If anyone has any questions about the process, I'm happy to answer.

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JSett
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Re: i made an LA-2A

Post by JSett » Sun Jan 09, 2022 2:51 am

No questions, just came here to compliment that wiring.

*Chefs kiss*
Silly Rabbit, don't you know scooped mids are for kids?

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Re: i made an LA-2A

Post by Embenny » Sun Jan 09, 2022 7:18 am

That is an incredibly tight wiring job.

How much did that cost you? Does it sound like an original? How's the SNR?
The artist formerly known as mbene085.

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Re: i made an LA-2A

Post by øøøøøøø » Sun Jan 09, 2022 10:35 am

I have about $1500 in it all in, plus my time for assembly.

It's very quiet... impressively so.

As far as sounding like an original, I'm not sure yet. I'll have to use it for awhile to get a general sense of what it does for me. I've spent many many hours with three vintage originals at our NYC place, and all three are a little different from each other, so there's a bit of triangulation going on.

To be honest, it probably won't sound exactly like an old one because of some component changes I made based on my own preferences.

The originals used a 10µF Mallory electrolytic on the output, right before the output transformer. Electrolytics as coupling caps tends to "do something" to audio... I used a metallized polypropylene film cap in that location instead, which will probably leave fewer fingerprints on the signal.

Same for the Z5U ceramics the original used as coupling caps... this was an economical choice that I just couldn't bring myself to duplicate, opting for polypropylene film-and-foil instead. Class 2 ceramics are very distort-y in audio circuits, so it's likely that those old parts added some flavor as well. I just didn't want that particular flavor...

The original also used carbon comp resistors, and I opted for Dale CMF55 metal films. I've kind of lost my religion regarding carbon comp "magic" in tube circuits; these days I tend to go for the precise, reliable parts that just work and stay quiet.

So I've definitely evolved a few things, as opposed o a strict "vintage clone."

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Re: i made an LA-2A

Post by marqueemoon » Mon Jan 10, 2022 5:55 pm

That sure is pretty.

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Re: i made an LA-2A

Post by smjenkins » Mon Jan 10, 2022 8:50 pm

Amazing work. That's so tidy you could do heart surgery in there. I hope it sounds as good as it looks

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Re: i made an LA-2A

Post by alvinstraight » Mon Jan 10, 2022 11:14 pm

Very impressive!

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Re: i made an LA-2A

Post by DrQuasar » Wed Jan 12, 2022 2:12 pm

I have questions because I know nothing and if you're answering I'm going to take advantage.

1) What are the screw terminals on the back for? Do those ever actually get used?

2) How do you know when to use the limiter setting as opposed to the regular compression setting?

3) Is this from a kit? Where did you source parts? Particularly the faceplate and branded VU meter?

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Re: i made an LA-2A

Post by MattK » Wed Jan 12, 2022 3:16 pm

Sensational! Deep admiration for the craft and commitment.

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Re: i made an LA-2A

Post by øøøøøøø » Wed Jan 12, 2022 4:48 pm

DrQuasar wrote:
Wed Jan 12, 2022 2:12 pm
1) What are the screw terminals on the back for? Do those ever actually get used?
Originally, there were no XLR connectors on an LA2A, and you’d use these terminal strips to connect inputs and outputs using the screw terminals (like connecting speakers on an old home stereo).

There are so many because you can choose input and output impedances depending on your installation (before the 600 ohm standard was quite so standard).

The addition of XLR connectors is like a “mod” that I and most others include because it’s easier. The terminals are still functional if I ever wanted to connect it at 200 ohms or whatever for some bizarre reason.
2) How do you know when to use the limiter setting as opposed to the regular compression setting?
It’s just a choice. On an LA2A the difference isn’t really extreme… it’s fairly slow to attack since the EL panel has to turn on, and the transient is where you’d most hear the difference between ratios. Mine (and most) stay in “compress” most of the time.
3) Is this from a kit? Where did you source parts? Particularly the faceplate and branded VU meter?
Not from a kit, but a company in Germany makes the chassis (unbranded) and have a decently-thorough build guide and BOM.

Most people try to build these to be exactly like the original, including the shitty Class 2 ceramics as coupling caps and electrolytic DC blocking cap right at the output transformer, and the BOM reflects that.

I went a different way on most things. I’ve spent a fair amount of time around the 3 originals at the NYC studio where I’m a partner, and I’m not nearly so superstitious about supposed magical benefits from shitty parts. I’m open to changing my opinion about that as I get to know this unit (which uses better quality parts). It’s entirely possible that the distortion imparted by those cheap capacitors (it would be mostly second harmonic) is the source of some kind of magic… but I’m skeptical.

The branded meter and repro logo came from a German reseller, Don-Audio, who sells these chassis kits. The chassis kit comes unbranded, but for a few Euro you can have them do a “custom logo” for you, which for most people means the original Teletronix logo.

I used AMI UT10 and UT24 transformers, which are a better match for the originals than the Sowters that are suggested in the build guide. I’d have sourced old UTCs (as I have for projects in the past) but they’re just too expensive now. People are getting 600 bucks or more for an A10 now, it’s crazy.

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Re: i made an LA-2A

Post by DrQuasar » Thu Jan 13, 2022 10:38 am

Thank you so much for answering. I always greatly appreciate your insights. I saw you in that 5G commercial playing Get Back with Brittany Howard. Pretty darn cool! Was that the space sparkle Les Paul?

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Re: i made an LA-2A

Post by øøøøøøø » Thu Jan 13, 2022 10:46 am

DrQuasar wrote:
Thu Jan 13, 2022 10:38 am
Thank you so much for answering. I always greatly appreciate your insights. I saw you in that 5G commercial playing Get Back with Brittany Howard. Pretty darn cool! Was that the space sparkle Les Paul?
Oh wow, I didn't realize that was airing yet!

Yeah, that's the '92 Les Paul Studio I had refinished in metal flake several years ago

One other thing I forgot to mention is that I used the Kenetek T4B photocell

The T4B is kind of the "heart' of this compressor as it's where the actual gain reduction action takes place.

The way these compressors work is that input signal is split off into a separate amp that lights up an electroluminescent (EL) panel. If you remember the old Timex Indiglo watches it's sort of a similar kind of light-up technology... they have been used in aircraft displays for a long time now (in fact, the guy who designed the LA2A had an aerospace background)

So anyway, the EL panel lights up and shines light on a couple of photoresistors (one to do the actual compressing and one to register that compression on the meter).

The T4B contains both the EL panel and the photoresistors, so it's a pretty important part.

Part of what makes an LA2A special is the way the release time works, and this is entirely a function of EL panel behavior. The EL panels (at least the old ones) aren't "instant off." The light kind of has to slowly die out. And how long the light takes to decay is, to some degree, a function of how long it had been lit before being turned off.

So a momentary burst of audio that lights it up for a second will recover pretty quickly. But if it's hanging out doing -5dB of gain reduction for several seconds (or more), the EL panel will dim quite a bit fairly quickly, but then it might take several seconds for the last little bit of light to die away.

This creates kind of a two-stage release on consistent loud signals, and for whatever reason this sounds incredibly natural on many sources (not least vocal and bass)

The deal is... manufacturers of EL panels have "improved" their products over the past half a century, so the new stuff doesn't really work the same... it's much closer to the "instant-off" theoretical ideal, which messes up the cool variable-release characteristic that makes an LA2A an LA2A.

Kenetek has sourced/commissioned some panels that behave very much like the old ones, and many people consider them the only "proper" T4B that's currently being made.

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Re: i made an LA-2A

Post by postboredom » Thu Apr 07, 2022 5:19 am

that wiring! :?
well done

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Re: i made an LA-2A

Post by TadejMihelic » Sun Apr 23, 2023 2:12 pm

øøøøøøø wrote:
Sun Jan 09, 2022 12:29 am
If anyone has any questions about the process, I'm happy to answer.
Hello! Great work!!
I'm in the process of building mine as well. :)

I would like to ask you, what wires did you use? 18 awg? 20 awg? Solid-core?

Tnx!

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Re: i made an LA-2A

Post by øøøøøøø » Sun Apr 23, 2023 2:47 pm

TadejMihelic wrote:
Sun Apr 23, 2023 2:12 pm
øøøøøøø wrote:
Sun Jan 09, 2022 12:29 am
If anyone has any questions about the process, I'm happy to answer.
Hello! Great work!!
I'm in the process of building mine as well. :)

I would like to ask you, what wires did you use? 18 awg? 20 awg? Solid-core?

Tnx!
18 awg for tube heaters, 20-24 for everything else

I used solid core for the things that don’t move, stranded for anything that connects to the hinged front panel.

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