Discussion in 'Music Corner' started by Steve Hoffman, Jul 18, 2018.
It is nice vintage stuff still holds very well over decades.
Many people still have no idea what this machine does. For me, it fleshes out thin, mean mixes, makes them more 3D lifelike sounding. Occasionally I’ll use it for its true purpose, but not often.
I never use it like that, don’t worry.
Here's your chance everyone one day left!!!!
UREI Teletronix LA-2A pair Vintage Leveling Compressor/Amplifier - Not UA | eBay
I vaguely remember reading a post of yours where you stated the audio needed to be run through multiple times through such a unit to add life and that tube magic. Is that right or is my memory wrong?
Once is enough.
Cool, love seeing stuff like this! Thanks for sharing.
Here's a link to an early Teletronix manual from the Library of Congress:
http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Teletronix Model LA-2A Leveling Amplifier.pdf
There's a schematic in the back...
Note that schematic in the LOC PDF:
differs a bit from the UREI schematics:
Note the redlined switch in the LOC schematic for setting between compression and limiting functions - just shunts out the 2.7K resistor in the photocell circuit... The UREI schematic incorporates that redline.
Supposedly the T4A's can no longer be manufactured:
Teletronix T4A T4B T4C Electro-Opto-Attenuator Info
Not sure which T4 is in Steve's unit.
There's a $25.00 documentation package available at Gearsluts:
Teletronix LA-2A Secrets - The most complete information [LA-2A-SECRETS] - $23.99 : Welcome to the GearSlut Store, Lots of cool toys for recording engineers, producers and musicians
For those that are not familiar with an opto compressor, photocells (one in the audio path at the gain pot) and one on the meter circuit) are driven by an EL light source. The light source was coupled to photocells.
Not unusual to use optical things like light bulbs - directly or indirectly - for current limit. The UREI studio monitor crossovers used them:
The UREI 813's used them - when you'd crank the control room vol, you'd see them glow. A while ago, repaired a bass guitar speaker cab for a local club (the Birchmere) that used old style dome lights for protection. I typically use polyfuses in designs I do.
As to more modern version of opto driven compressor/limiters, we still design audio stuff using these:
NSL-32SR2 Advanced Photonix | Isolators | DigiKey
Just did a design last month using these...
But believe me, they don't sound like an LA-2A. I don't think anything does. They've tried with various DAW plugins. Not so much...
EL nightlight - https://www.amazon.com/GE-55507-Electroluminescent-Night-Light/dp/B0017C7YRM
Similar, larger version of the EL is in the T4's
If you're an IEEE member:
An Improved Method of Audio Level Control for Broadcasting and Recording - SMPTE Journals & Magazine
On that webpage they mention the LA-4. We used those to drive broadcast loops to transmitter sites over equalized phone lines. The thing was that the output transistors for the 600 ohm output were similar if not the same as those used in the Advent 300 receiver's power amp used to drive speakers.
Lots of headroom and drive. UREI always made silly amazing overbuilt gear.
Another interesting use for LDR's is for bringing bias up on a pro audio multitrack - it keeps ir from causing a pop when punching in. Scully's used them...
And that sucks.... I posted a rant somewhere on the gen discussion forum about the Village Voice that mentions why I think that happened:
I buil a drip audio LA2A clone. Sounds amazing, especially on guitar and vocals.
So you know lil' Rocket Man? I hear he's a hoot....
I heard he's into flatt and scruggs type stuff.
There was a remake on utube:
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