JLM Audio LA500A Opto Compressor

Projects > JLM Audio LA500 Opto Compressor > JLM Audio LA500A Opto Compressor

The LA500A is JLM’s take on an LA2A/LA3A-type optical compressor for the API 500-series format.  The “A” unit is identical to JLM’s earlier LA500 unit, except that it adds a “slow attack” functionality that can be accessed through a pull-out switch on the Threshold pot.  The unit also adds an indicator light to show when the unit is set to “stereo link” mode with an adjacent unit.

Instead of cloning the original design, Joe Malone and co. have reworked the original circuit to improve signal to noise ratio and add additional control features. These include new side-chain filtering options and compression ratios. The circuit features the “JLM Sound” throughout, with their JLM99v discreet opamp and JLM111DC output transformer. JLM currently offers complete kits with everything needed to complete the compressor.

When purchased two at a time, JLM includes matched pairs of NSL-32 opto components to facilitate stereo operation.



  • Electronically balanced input
  • JLM1111DC output transformer
  • JLM99v Discrete Opamp
  • 3:1, 5:1, and 10:1 compression ratios
  • “FLAT,” 100Hz, and 200Hz sidechain high pass filters
  • Mix bus output for Radial Workhorse rack
  • Same compression circuitry as LA2A/LA3A

Price: $449 AUD for full kit; $749 AUD assembled

Purchasing and more info: Available from the JLM Audio store.


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