Check out Mix magazine's review of the EQ500 Combo from the October 1997 issue.

The microphone preamplifier section of this unit is based on fully differential topology with its known propensity for cancelling out even-order harmonic distortion components. We teamed this superb and full-featured microphone preamp with the famous EQ 500 passive EQ circuitry coupled to a second differential line-amp to make a stunning combination for field recording or direct-to-tape tracking for which we also provide built-in illuminated VU metering as well as an Insert point for flexible operation with other outboard effect units. (And yes, the Mic Pre and the Equalizer sections can be used completely independently.) 

Up to 55dB of total gain is available through the whole unit, structured as 46dB from the Mic Pre section plus up to 9dB more from the EQ/Line amplifier. All inputs and outputs are balanced transformer coupled. The EQ section is a refreshing revival of one of the most musical passive EQ’s from the past– the "heart" section having been designed by Art Davis who seems to have worked for many (or is it most?) of the historic companies: Altec Lansing, Cinema Products, Universal Recording, and of course, Langevin... always taking his seminal design along with him.

The complexity of the 2dB stepped switching (using gold-contact custom built Grayhill switches in our reincarnation) is solely for the purpose of having no more than 3 components, (1 R, 1 L, 1 C) in the signal path at any given moment for maximum signal purity. We cleverly added to this historic passive EQ circuit the choice of either PEAK or SHELF modes for each band giving sufficient flexibility within the confines of musical, accurate tonality. Similar to the Variable Mu’s topology, the MIC/EQ 500 uses our exclusive differential circuitry, renowned for preserving delicate imaging information. 

The output attenuator allows the overall gain to be kept constant while boosting or cutting and, more importantly, provides for optimization of noise levels especially when used in conjunction with the Mic Input Level control which functions as a variable input pad. Another sometimes desirable trick is to push the tubes into distortion by turning up the Mic Input Level while turning down the Line Output Level control in order to flavor the sound with a bit of grunge and overdrive.