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Mods for the FC 3

  • Microphone PartsMicrophone Parts
    The “Linear 87” modification kit for the Apex 480 / GAP FC3 replaces the 2-stage “emitter follower” circuit and low-ratio transformer with a new audio circuit based on vintage designs. This is not an upgrade, but rather a wholesale replacement of the audio circuit with a single-stage JFET design and 10:1 output transformer, both created by Samar Audio exclusively for

OmnidirectionalCardioidBidirectionalGolden Age Project FC 3

Multi-Pattern Condenser Microphone

The FC 3 is a side-address, 3-pattern FET condenser with a transformer-coupled output circuit.

Although previously reported here (based on statements from GAP) to use a 34mm, 3-micron capsule, the sample FC3 microphone we purchased contained a 32mm capsule. This capsule almost certainly has a 6-micron diaphragm. It is a center-terminated K67 type.

Three switches on the mic body enable pattern selection (Cardioid, Omni, Figure-8), a switchable pad (-10dB), and a switchable high-pass filter (cutoff at ~80Hz).

FC 3 PCB and circuitThe circuit is a two-stage transistor design, with an emitter follower driving a low-ratio output transformer. This circuit is linear — it does not apply any frequency-dependent corrective filtering to the capsule’s signal, unless the high-pass filter is engaged.

The DC circuit board contains a voltage multiplier that is capable of polarizing the capsule at +60VDC. Individual samples we’ve seen vary from 50–63VDC. Note that in Figure-8, the rear diaphragm is at double this voltage (+120V), while the backplate is at +60.

The FC3 is nearly identical to the CAD GXL3000, although the GXL3000 comes with a higher-quality, larger capsule (35mm O.D., 6 micron diaphragms).

The Golden Age Project FC 3 is also known as: FC 3.


Pickup Patterns Pads & Filters
Omnidirectional (14.5 mV/Pa; 20 - 20,000 Hz)
Cardioid (14.5 mV/Pa; 20 - 20,000 Hz)
Bidirectional (14.5 mV/Pa; 20 - 20,000 Hz)
  • Pad: -10dB (Via Switch)
  • Filter: HPF @ 80Hz (Via Switch)
Capsule Dimensions Impedance SPL/Noise
Diaphragm diameter: 25mm
Capsule diameter: 32mm
Diaphragm gauge: 6 microns
250 Ohms (Low) Max SPL: 140 dB
Self-noise: 17.0 dB(A)
Weight Length Max Diameter Interface(s)
470g (16.58oz) 190mm (7.48'') 50mm (1.97'')
  • 3-pin XLR male (1)
Power Specifications
  • Requires phantom power
  • Phantom voltage: 48v

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