LA2A Compressor

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jctaudiodesigns
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LA2A Compressor

Post by jctaudiodesigns » Tue Apr 07, 2009 8:47 pm

Hey all, while you all are busy building guitar amps, I have been building gear for my studio. I started with an LA2A clone. This is an incredible compressor that can be used for vocals, bass, and guitar. (although I would prefer a 1176 on guitar) I built the first chassis by hand, what a pain, on the second I have a company building the basic chassis for me. The rest is all point to point just like a guitar amp. Too much fun!!!!!

Here are some pictures of the first one.
http://web.mac.com/JCTAUDIODESIGNS/JCT_ ... /LA2A.html" onclick="window.open(this.href);return false;

And here are pictures on the one I am building now.
http://web.mac.com/JCTAUDIODESIGNS/JCT_ ... A2A_2.html" onclick="window.open(this.href);return false;
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Re: LA2A Compressor

Post by VelvetGeorge » Tue Apr 07, 2009 10:05 pm

Awesome project! You may have inspired me to finally try this as well.

Is your chassis hinged on the front like originals? Also, where did you get your meter and T4?

george
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Re: LA2A Compressor

Post by jctaudiodesigns » Wed Apr 08, 2009 10:21 am

VelvetGeorge wrote:Awesome project! You may have inspired me to finally try this as well.

Is your chassis hinged on the front like originals? Also, where did you get your meter and T4?

george
Hi George,

My chassis is not hinged, but of course you could add that later if you want.

The meter I am getting from Instrument Meter Specialties. Its not the original meter, but I like it better. It's actually the same meter that was used in the old fairchild compressor. The funny thing is that what ever meter you use, if you are using a true vu meter, it will be the most expensive thing in this project. The lights on the meter are 12 volt LED's so I built a simple voltage doubler circuit to power it from the filament voltage.

The input and output transformers I am using are from Sowter. They sell clones of the original transformers.

The T4B I got from Universal Audio. They will sell you a maximum of 2 T4B modules. I have seen a company on E-bay that will also sell the original T4B modules from time to time. You can also get a clone of the T4B from dripelectronics.com. He also sells the LA2A printed circuit boards if you want to go that route. I chose to go point to point because as you say, thats what they did on the original. Well.........one other reason, when I do my clinic with my students, it will be easier for them doing point to point.

One thing I am changing is the position of control of the limiter response control. This was on the back and set from the factory depending on what the application. For recording studios it was set fully clockwise for flat frequency response. But the compressor was originally built for broadcast and due to the the pre-emphasis used, it was beneficial to compress the higher frequencies harder. So the limiter response control filters out low frequencies to the T4B module, so it will compress the low frequencies less. This can definitely be a cool thing and a very useful control, so I put it up front.

Jeff
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Re: LA2A Compressor

Post by NitroLiq » Wed Apr 08, 2009 10:29 am

George, if you want an easier route, there are a couple guys at Prodigy Pro offering fully-silk-screened chassis and PCB board/guide...it's basically the LA-2A with improvements.

http://www.prodigy-pro.com/diy/index.php?topic=30187.0" onclick="window.open(this.href);return false; (case/panel)
http://dripelectronics.com/la2pcb.html" onclick="window.open(this.href);return false; (PCB)
http://dripelectronics.com/t4b.html" onclick="window.open(this.href);return false; (T4B cells)

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Re: LA2A Compressor

Post by thousandshirts » Wed Apr 08, 2009 12:47 pm

Ahh, nice to see other folks here hang out on the Prodigy Pro boards, too.

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Re: LA2A Compressor

Post by jctaudiodesigns » Wed Apr 08, 2009 2:41 pm

NitroLiq wrote:George, if you want an easier route, there are a couple guys at Prodigy Pro offering fully-silk-screened chassis and PCB board/guide...it's basically the LA-2A with improvements.

http://www.prodigy-pro.com/diy/index.php?topic=30187.0" onclick="window.open(this.href);return false; (case/panel)
http://dripelectronics.com/la2pcb.html" onclick="window.open(this.href);return false; (PCB)
http://dripelectronics.com/t4b.html" onclick="window.open(this.href);return false; (T4B cells)
I have seen that chassis, it is very nice. I decided to go with the original because it works and it is better for the students to do point to point. I also don't care for the tubes to be mounted on the circuit board, especially the 6AQ5, that one does get really hot. By the way the chassis in the pictures is my prototype, the ones I will be getting for my students will also be silk screened.
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Re: LA2A Compressor

Post by NY Chief » Fri Apr 10, 2009 11:39 am

I have been looking at the re-issues of these units lately and I am a bit confused.

There is the LA2A, the LA610 and the 1176 which all appear to be pre/compressors. Then you have the 2 channel versions, the 2-LA-2, the 2610 the 21176 and all the offshoots the 6176, 1176AE, 1176LN.

I haven't spent a lot of time on the engineering side in the studio but I have seen and heard any and all versions of these tools but I'm confused. Which circuit is considered grail or do they just have different flavors for different applications? If I wanted to add one to my system which one? I'm cornfused....
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Re: LA2A Compressor

Post by NitroLiq » Fri Apr 10, 2009 2:44 pm

It's basically like choosing which year plexi to build...they're more or less the same with small changes to the circuit or components used. The 1176 has revision numbers, hence D or E or what have you. This may confuse you more but it's a good read:

http://www.geocities.com/m_natsume/1176.html" onclick="window.open(this.href);return false;

Purple Audio makes a great 1176 clone.
http://www.purpleaudio.com/Product/MC77.html" onclick="window.open(this.href);return false;

Here's a good LA-2A read:

http://www.recproaudio.com/diy_pro_audi ... x_la2a.htm" onclick="window.open(this.href);return false;

The Grail items would be the standard 60's LA-2A and 1176 compressors. No preamp. No dual-channel. The 1176 is Fet; the LA-2A is iso-optical (IIRC). LA-2A is fantastic in a vocal chain. 1176 is fantastic on guitars,...you can use them on whatever you want but in general that's how I've used them in the past.

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Re: LA2A Compressor

Post by NY Chief » Fri Apr 10, 2009 4:30 pm

NitroLiq wrote:It's basically like choosing which year plexi to build....
I thought as much. Thanks for the links, Pete! I'll check 'em out.
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Re: LA2A Compressor

Post by jctaudiodesigns » Fri Apr 10, 2009 9:00 pm

NitroLiq wrote: The Grail items would be the standard 60's LA-2A and 1176 compressors. No preamp. No dual-channel. The 1176 is Fet; the LA-2A is iso-optical (IIRC). LA-2A is fantastic in a vocal chain. 1176 is fantastic on guitars,...you can use them on whatever you want but in general that's how I've used them in the past.
I will agree with these statements completely, LA-2A is also the Holy Grail on bass although a 1176 is not too bad on bass either.
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Re: LA2A Compressor

Post by thousandshirts » Sat Apr 11, 2009 1:50 am

What about recording a drumkit? Lets say two overheads, a bass, a snare top, snare bottom, hi-hat, and three toms (eight mics). Does a guy need eight LA-2A's? I don't play drums, but one of these days I'll get the time to finish making up a decent recording setup. Maybe some Neve clones for preamps, or some REDD 47s, or I-know-not-what. Probably be years from now. But while we're on it - what parts of a kit (even sometimes) need a decent compressor, and, if so, when, and, which compressor would you choose? Why? LA-2A's for overheads? 1176 for kick? Very curious. . . That Pultec EQ looks nice, too.

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Re: LA2A Compressor

Post by jctaudiodesigns » Sat Apr 11, 2009 3:11 am

thousandshirts wrote:What about recording a drumkit? Lets say two overheads, a bass, a snare top, snare bottom, hi-hat, and three toms (eight mics). Does a guy need eight LA-2A's? I don't play drums, but one of these days I'll get the time to finish making up a decent recording setup. Maybe some Neve clones for preamps, or some REDD 47s, or I-know-not-what. Probably be years from now. But while we're on it - what parts of a kit (even sometimes) need a decent compressor, and, if so, when, and, which compressor would you choose? Why? LA-2A's for overheads? 1176 for kick? Very curious. . . That Pultec EQ looks nice, too.
For drums, 1176's hands down! Neve clones are also going to be great on drums especially kick and snare. The pultec would also be great for kick, snare, and especially overheads.
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Re: LA2A Compressor

Post by jctaudiodesigns » Sun Apr 12, 2009 10:58 pm

Just finished the second one. Check out the pictures.
http://web.mac.com/JCTAUDIODESIGNS/JCT_ ... A2A_2.html" onclick="window.open(this.href);return false;
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Re: LA2A Compressor

Post by thousandshirts » Sat Apr 25, 2009 7:41 pm

Out of curiosity, what might a good compressor for radio broadcasting be? The local University station has got me on board as a consultant for equipment. Building them some tube phono stages, stuff like that. They seem dead set on a tube compressor, though. I'm not sure that they need one. In any case my Ham radio experience doesn't deal with anything like a stereo music broadcast compressor. Any ideas? I guess this might be something like a mixdown or mastering compressor.

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Re: LA2A Compressor

Post by Herec » Wed Jun 10, 2009 1:12 am

I've used the LA-2A (well, an approximation of it with a Distressor), and even with minimal compression, just running a signal through it seems to improve that signal. I'd go for the LA-2A, but that's with my limited knowledge/experience. I do know there is alot of DIY help for them.

And where's the magic in the 1176? Any key components that have to be a special something? Like the LA2A with the T4b?

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