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| Universal Audio LA-2A (hardware version) |
AudioScape’s T4B: A Nod to Vintage with Electroluminescent Magic
Enter AudioScape, whose Opto Compressor is winning hearts by nailing that vintage vibe. The secret? Their in-house-built T4B modules, crafted with the same electroluminescent (EL) panels that made the original LA-2A sing. The tube-powered support circuitry is fully balanced from input to output -- this is an important design difference from modern designs -- think of it like two, separate, parallel tube signal paths, one for the top half and one for the bottom half of the waveforms passing through. The LA-2A uses this "fully balanced", vacuum tube design to provide richer, full range tone.
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| T4B in Audioscape OPTO, click to enlarge |
Audioscape’s engineers have captured the sound that made the original such a cherished tool. They stuck to the classic schematics to endow their comp with that old-school gain reduction curve. The result? A compressor that feels like it rolled out of a ‘60s studio, with warmth and character to spare -- they call it "Sonic Truth". Whether you’re chasing the LA-2A’s magic or just love gear with soul, AudioScape’s EL-powered T4B is proof that vintage spirit can live on in modern builds.
LA-2A Teletronix vs Audioscape OPTO - A Brief Hands-On Comparison in the Studio
I bought my LA-2A back in 2002 and it has been a reliable friend in the studio — it lives, patched on channel 24 of my mixing console and it’s where I usually put the bass guitar when mixing. After years of experimenting and trying it on everything (guitar, bass, keyboards, percussion, vocals) this particular LA-2A unit provides a consistently great tone and punch on bass guitars.
I bought my Audioscape OPTO, (an LA-2A style clone), a little over a year ago, and for the very first time, I have an “optical” compressor I’m comfortable-with patched on a lead vocal track during a mix. Usually I have a sweet vari-mu compressor like the Weight Tank or the 14B (both from Locomotive Audio, reviews here on H.o.T.) on the lead vocal when I mix a song, due to the weight of the sound and the smooth, yet powerful gain-reduction these processors provide. The Audioscape OPTO is capable of getting me to that same happy place, it has the body and fullness I associate with the sound from variable mu type compressors. More importantly, this OPTO feels “fast enough” to catch odd peaks which my Teletronix LA-2A misses because its attack is too slow.
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| Tubes on the back of LA-2A, click to enlarge |
Installation Concerns — Comparing hardware designs
The original LA-2A had the tubes mounted to the exterior, rear panel — sticking out into the rack space behind the compressor chassis — this gets the tubes outside the box and all that hot air they generate, dissipated directly into the rack they’re mounted in.
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| Hinged front panel on LA-2A, I rarely ever open mine |
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| Who doesn't love a good gear photo, click to enlarge |
From the front, the AudioScape OPTO looks just like an original LA-2A, new users (with little or no hardware experience) like to stack them in the rack, just like those delicious gear photos from the old Oceanway recording operation.
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| Left: LA-2A by Universal Audio - Right: the OPTO by Audioscape |
Here is my concern, the AudioScape-OPTO has all the vacuum tubes inside the metal enclosure (not outside like the original LA-2A design), generating a LOT of heat, and the only place for all that heat to go is out the air vents in the top of the enclosure. WARNING, there needs to be an empty, open, air-space above this unit to allow the heat to escape. There are vent slots in the sides of the OPTO but they provide inadequate ventilation if the top of the enclosure is completely covered by the bottom of another unit mounted directly above it.
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| Audioscape OPTO |
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| Rear panel, inside view, Audioscape OPTO |
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| Found this online, someone did it right, air space above each processor |
Preemphasis
The original unit was not designed for recording studio use, it was a fortuitous situation that brought the LA-2A beasts into the recording studio, control room, for matching their smooth sound with lead vocals.
A huge AudioScape improvement over the original is making the Preemphasis control, a variable knob, it’s a BIG plus for the Audioscape OPTO — this variable side chain (preemphasis) control is right on the front panel and easily adjustable. It’s there on the LA-2A but there is no knob -- on the LA-2A it’s a short-shaft, locked-adjustment, with no label, Universal Audio clearly does not want you to adjust it ;-)
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| Preemphasis control labeled HF on Audioscape OPTO |
This preemphasis control is labeled HF on the AudioScape OPTO and they gave it a control, located in the same place as the vintage LA2A — that knob invites you to tweak it. The preemphasis control is a front-panel high-frequency trim pot that adjusts the compressor's sidechain response. By turning it counterclockwise, it increases resistance, filtering out low-frequency energy before it reaches the T4B opto-attenuator. This shifts the compression focus toward higher frequencies, enhancing versatility for controlling excessive low-end compression, making it ideal for vocals, acoustic guitars, and other sources requiring tailored dynamic processing. Instead of locking this knob, AudioScape made it adjustable because it won’t hurt the unit and it increases your flexibility dramatically.
BUILD DESCRIPTION
AudioScape could have chosen to make their OPTO a 2RU design like other modern clones, but their formula for success has been based on close adherence to the original front-panel appearance, physical shape, layout and operational controls — of whatever processor they are cloning — so they stuck with the original LA-2A design as close as possible — same 3RU size, color and features. As an old-time gear user, I must admit I’m drawn to the vintage original appearance much more than either the Warm Audio or Klark Teknik modern versions.
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| No grommets on wire entries, click to enlarge |
I have a few other AudioScape products which are all built using a similar, 3RU metal chassis. This is basically a rectangular, metal box with the power supply transformer mounted externally on the rear. An unlabeled Cliff jack on the back panel provides stereo link capability. AudioScape metal work is always classy, nice paint job, no sharp edges, nothing garish or dangerous. Premium quality Neutrik XLR connectors are used on the back for input and output.
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| Note the large, squarish, silver colored metal enclosure for the input transformer |
Inside the AudioScape OPTO is a main fiberglass printed-circuit with all the tubes and their T4-opto cell (which is a plug-in device), on board. A custom input transformer and a large iron output transformer make the audio connections with the outside world. All the resisters and capacitors are old school, no surface mount components — the through-hole construction (which AudioScape uses) keeps their crew of human assemblers very busy and the results speak for themselves. I’ve ordered several pieces from the company and they’ve been consistently great. I just checked -- the delivery time for new OPTO orders placed today is currently shown to be four to six weeks — the good news is, they are accepting orders so they have the resources lined up to build a continuing stream of new OPTO units.
LIKES
- Affordable price
- Factory direct selling through internet
- Great sound right out of the box
- Adjustable knob on Preemphasis control
- Boutique build
- NOS tubes
- Stereo Link jack on the back - it’s not labeled though
- USA made, as much as humanly possible
DISLIKES
- Not enough ventilation, needs rear vents
- No audio specifications — no frequency response, distortion, headroom specs
- No 1/4” TRS connections — my patch bay destinations are TRS
- No grommets on transformer wire entries
- No manual
The thing that separates the LA-2A style compressor from a lot of the lower priced “optical” pretenders is the optical device used. Many cheap circuit designs use a simple, variable resister-cell with an inbuilt LED light source (marketed as VacTrol). The LA-2A uses a florescent panel to drive custom built light-variable resisters which do the heavy lifting, controlling the ballistics of the sound being processed through fully balanced tube stages. The turn-on attack and turn-off decay characteristics of the resistors is at the heart of shaping the output dynamics. There are lots of ways to try and work around limitations of using an LED as a light source but none I’ve had here in the studio, have ever sounded right to me (I’m looking you ART). The smooth rich, BIG sound produced by the AudioScape OPTO really lets you know why the enduring LA-2A design is still so popular -- so far, no modern optical-imitator has achieved similar performance.
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| New style input transformer in my OPTO |
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| Old style input transformer shown on Audioscape Web site |
There is a lot to love about the AudioScape OPTO. Not only does it sound good, it sounds right. If you patch it on a vocal channel it delivers a nice thickening characteristic and levels the track without flattening the dynamics. Be sure to twist that “Preemphasis” knob around, this control totally changes the character of this compressor, taking it from dark to bright and all points in between.
Sign up on the AudioScape website to receive their emails and you’ll be notified when the OPTO is on sale or when they have factory refurbished units available for big savings. If I could only have one optical compressor, it would be the AudioScape OPTO. It’s worth their asking price.
Thanks for reading High on Technology. Good Music To You!
©June 2025 by Mark King, it’s not ok to copy or quote without written permission from the author.
Go forth. . . . and create something beautiful. . . . .
ADDENDUM 1. I got my OPTO from AudioScape the same way everybody does, I waited until it was on sale, ordered and paid for it on their web site and waited a few weeks for it to arrive -- the wait is worth it!
ADDENDUM 2. Here's a teaser photo from an upcoming shootout between the Audioscape OPTO and the bargain priced Klark Teknik 2A-KT
