LA502 Optical Compressor for 500 series - DIY Analog Pro Audio
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  • LA502 Optical Compressor for 500 series - DIY Analog Pro Audio
  • LA502 Optical Compressor for 500 series - DIY Analog Pro Audio

LA502 Optical Compressor for 500 series

$299.00
$299.00 VAT incl.
$299.00 VAT excl.

The LA502 is a soft knee, electro-optical compressor based on the LA2A/LA3A design, which we have adapted to the '500' series format of API*.

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LA502

Bootstrap Image Preview


The LA502 is a soft knee, electro-optical compressor based on the LA2A/LA3A design, which we have adapted to the '500' series format.

It delivers the vintage compression and warmth of its ancestor thanks to the optical coupler response, side chain and transformers.

It shines on vocals, bass and drums.

The LA502 adds a few features to the original such as a new ratio of 6, two high-pass filter in the side chain and two slower attacks of 10 and 20 ms.

Install it in your API* compatible LunchboxTM rack and start working.


Highlights

    • Based on the LA2A/LA3A compressor,
    • Transformers on input and output,
    • Extremely simple to use, never sounds bad,
    • True RMS compression,
    • Program dependent attack, release and ratio makes it very transparent sounding,
    • More than 40dB of gain reduction,
    • 3 ratios : 3 (LA2A Compress), 20 (LA2A Limit) and one additional ratio 6.
    • Optional High pass filter in the sidechain @100 & 200 Hz,
    • 3 Attack times : 5mS (LA2A), 10mS and 20mS,
    • Can be linked for stereo,
    • Hardware relay bypass,
    • Available assembled or as a full kit.

Controls





Bootstrap Image Preview

1: PEAK Sets the amount of compression from zero to more than 40 dB of gain reduction. It defines the threshold at which the compression appears.

2: RATIO 3 positions switch that set the compression ratio.

  • Ratio 3 (left): This is the COMPRESS setting in the LA2A. The actual ratio value is program dependent and changes with the level.
  • Ratio 20 (center): This is the LIMIT setting in the LA2A. With this setting the LA502 works like a limiter.
  • Ratio 6 (right): This is an additional intermediary setting.

3: HPF This switch inserts a high-pass filter in the sidechain which produces a fat sound and eliminates bass driven pumping.

  • 0 (left): No filter, works like the original LA2A,
  • 100Hz (center): 100Hz high pass,
  • 200Hz (right): 200Hz high pass.

4: ATTK Sets the attack time of the compressor.

  • 5mS (left): This is the attack time of the LA2A.
  • 10mS (center): We have added a delay in the sidechain allowing percussive sound to pass through less affected.
  • 20mS (right): The delay is further increased.

5: BYP

  • BYP (left): Hardware relay bypass,
  • IN (center): Compressor active,
  • STER. (right): Compressor active and stereo link connected for stereo operations.

6: GAIN This potentiometer sets the output level of the compressor.

7: Meter Shows the gain reduction from -3dB to -20dB.


What's in the kit?

Absolutely everything!

  • Passive components (resistors, capacitors, inductors),
  • Transformers
  • Active components (diodes, transistors, LED's, Opto-coupler, IC's),
  • Control elements (switches, potentiometers, knobs),
  • Connectors, relay,
  • PCB's,
  • Front panel and side panel,
  • All hardware.

You bring the solder (use good quality solder, 1mm diameter max) and the Lunchbox.

Difficulty level

The LA502 kit is an easy kit. It can be undertaken by everyone who is able to make a clean solder joint.

The setup is simple. It only requires a decent quality AC voltmeter.

ard DC voltmeter.
PK014

Specific References


Technical specifications

Measure Conditions Value
Idle supply current No input signal V+ : +65mA
V- : -60 mA
Input impedance f=1kHz 14 kΩ
Maximum input level defined by input transformer > +25 dBu
Maximum output level before clip f=1kHz +28 dBu
Minimum gain - ∞
Maximum gain +40 dB
Frequency response Deviation=+/-1dB 10 Hz - 20 kHz
Attack time from 5 to 20 ms
Release time

60mS for 50% release

1s or more for 100% release

Reviews

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Quality

Alex S
 03/17/2025

Perfect Introduction to DIY 500 Series Gear

For starters, I don't know that I'd recommend this as your *very first* soldering project. It is not a difficult build at all, but personally I'm glad I tried my hand at something even simpler (like a Fuzz Face-style pedal) first to "iron" out the kinks in my soldering technique. My first pedal build did have some issues, which were not hard to trace out and fix in that tiny circuit.. This circuit is nothing crazy but it is definitely more complex than a Fuzz Face! Just food for thought.

That said, I don't have a ton of experience beyond a handful of pedal builds and a whole lot of cable assembly, and it went very smoothly, testing out as expected on first power up. All in all, the build was finished and tested about a day and a half after the parts arrived, probably ~5-6 hours total, moving at a leisurely pace. Also it arrived lightning fast, being on a different continent (US) I didn't assume I'd have the parts within a week of ordering, let alone have the whole thing built, but sure enough it arrived only five days after ordering, mad props to Sound Skulptor for that.

Lastly and most importantly, the quality - this thing sounds phenomenal. Optos are my favorite style of compressor and I'll admit I was highly skeptical $300 would build me anything all that special, but I was wrong. Almost bummed I have no need for all those LA-2A plugins I've got now... This is all I'll need, at least until I find a good tube-based opto build to add to the collection! Even then, I have no doubt this will be getting used heavily for a very, very long time. Especially love it on a bass track, no surprise there as that's always been one of my favorite uses for an opto. I also have no doubt that I will be ordering many more kits from Sound Skulptor, if their other units live up to this experience then I can't imagine there being a better value on the market.

Grade 
Quality

Reinhard M
 02/14/2025

I love it

The LA502 is my first, but definitely not my last Sound Skulptor module. The kit is very well sorted and the instructions are excellent. There are numerous Youtube videos in which Sound Skulptor modules are assembled. If you prepare yourself, you will also learn some tricks on how to solder better.
I took my time with the assembly and worked carefully. As a result, everything worked right away.
And the sound of the compressor? Fantastic! I love it on vocal tracks.
Many thanks to the Sound Skulptor team

Grade 
Quality

Alex Harmer
 11/09/2024

WONDERFUL-sounding compressors!

These compressors were a very easy build, with fewer components than other Sound Skulptor kits.
This is a nice payoff, because you get a phenomenal sound for quite a small effort.
VERY glad I purchased. They are installed next to my CP4500, and my two CP554s.

Grade 
Paul Tietze
 01/13/2023

Excellent Compressor!

I bought this unit already assembled on Reverb. This a very musical sounding comp. I use it mainly on Bass but it works great on all kind of sources. You can dial in a quite heavy compression without it being too obvious. It does not color too much. This is a professional Hi End compressor. I like it a lot!

Grade 
Cesar
 01/24/2022

Reminds me a lot of the LA3A

The extra functions in sidechaind are very useful. Premium quality in all components and the great sound reminds me a lot of the LA3A.

Grade 
ZMFG
 08/01/2018

Silky Smooth

For the record, I had never soldered before I bought my first Sound Skulptor kit (CP5176). I have had this compressor for a few months now, and I am in love with what it does to vocals and bass. I use it on everything though... [insert shrugging emoticon]. Tuning the LED's was a little tedious and time consuming, but everything else about the build was easy. Highly recommend if you want some creamy vocals and thick punch bass!

Write your review

LA502 Optical Compressor for 500 series

The LA502 is a soft knee, electro-optical compressor based on the LA2A/LA3A design, which we have adapted to the '500' series format of API*.

Write your review

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