Aphex J PRE 500 Jensen Transformer-Coupled Mic Preamp 500 Series Module

Heritage Audio 73 JR 73JR Junior 500-Series Module Mic Preamp - Used

Empress Effects ECM-519 500 Series compressors (6 total)

FMR Audio RNLA500 Compressor Leveller - 500 series

Alctron 500 Series Chassis + Fredenstein Preamp and Compressor Modules

Fredenstein F600A 500 Series Compressor

Trident Audio Developments 80B 500 Series Mic Preamp

Aphex 228 8 Channel Professional Audio Input Balancer