The INTEGRA III SYSTEMS Compressor/Microphone Preamplifiers are designed for professional audio applications. There are six different models, 3 single channel models, and 3 dual channel models. Dual channel cards have two identical channels constructed on one printed circuit board assembly. The INTEGRA III SYSTEM Compressor/Microphone Preamplifiers come in two different models, a single channel model, and a dual channel model. Both models have low impedance transformer isolated inputs. A push-on jumper supplies 15VDC phantom power on each channel. The gain, and threshold level, of each model is adjustable, via trimpots mounted on the on the backplane assembly. The output section on all models is balanced, transformer-isolated.