CAPI FC526 XFMR Litz Wire

The FC526-XFMR is a somewhat unique compressor/limiter module based on commonly used circuit blocks. The audio path is comprised of a CA2622 input transformer, a two transistor voltage follower, a DTO5 five transistor opamp, one 2520 style opamp and one 2623-1 output transformer. The receiver stage is the CA2622 input transformer and the two transistor voltage follower. The input stage can be hit with a +28dBu signal before clipping occurs. The 2nd opamp is known as the signal preamp. This is the stage where the audio signal is detected, rectified and then used to reduce the audio signal level, aka gain reduction. The final opamp is the output amplifier, which is followed by a 1:2 balancing transformer. This part of the circuit is very much the same as the 2nd stage of a VP28 or ML2. The output stage also clips just beyond +28dBu. The red front panel peak LED indicates clipping of the output stage and/or the signal preamp opamp.

The FC526-XFMR uses a common FET gain reduction method. This FET hangs just after the input amp and is employed as a voltage variable shunt resistor aka VVR, very much similar to the legendary 1176. The control voltage for this FET is a product of the FET’s bias voltage and a rectified DC signal of the output of the signal preamp. By definition, this is a “feedback” style peak limiter. The sidechain detection circuit is a mash-up of an 1176 and an 1178 using two amps from a quad IC opamp to rectify the audio’s AC to DC. This DCV is then mixed with the FET’s bias voltage, varying the resistance of the shunt FET in a manor that is proportional to the incoming audio signal.
• 1176 style controls, in a compact footprint
• API style opamp, input, and output transformers
• massive gain reduction without pumping
• switchable sidechain high pass filter
• gain reduction bypass switch for adding the API tone without compressing
• Attack Time: ~20 microseconds adjustable to 800 microseconds
• Release Time: 50 milliseconds adjustable to 1.1 seconds
• Current Draw: Less than 118mA per bipolar 16V rail

API (and compatible) Lunchbox and VPR500 racking systems.
Fully built to perfection in Canada with a 1 year warranty.
These can be also build to order.