Classic Audio VC528 "Missing Link 2"

After a long cold winter the VC528's have finally come out of hibernation, and they are better than ever before. Each filter has an added frequency, the fader switch has tighter tolerances for better matching between units, the mute switch has been replaced with a relay-based hard bypass, and an additional discrete buffer has been added to reduce interaction between the LPF and the fader section for flatter frequency response.


The VC528 was designed by Jeff Steiger of Classic Audio Products of Illinois to replicate a single channel from a vintage API console.  A pair are excellent on the 2 buss, and with 12dB of gain they are great for boosting signal level after a summing mixer.  The VC528 also gives you high and low pass filters, each with 6 frequencies switchable between 6 and 12dB per octave slopes.  These prove very handy for thickening and tidying up sounds between preamps and A/D.  All of the controls are stepped, and the main fader is adjustable in .5db steps throught the majoity of it's range.  The new Elma 24 position switches are made with extremely high tolerance resistors for great matching between any unit, negating the need for ordering them in pairs to get good matching.


Description of the 528 Version 1, From CAPI-gear.com:


"The overall goal of the VC528 is to achieve the complete and lovely sound of a vintage API console channel without the cost of the rest of the console. It is definitely a little something different for the 500/51x format. Basically, it is a two stage console channel with the vintage circuitry of my API board.

The first stage is a balanced, transformerless receiver. Everything is true to the original console circuit. This entire first stage can be bypassed with shunt jumpers or simply left of the build if one desires.

Next in the block diagram comes the fader. Due to space constraints and a request from a friend, I have chosen to use a 24 position Elma with a 1K overall value. Original faders in my board were 600ohm. The fader has 12dB of gain in hand to keep with the vintage API norm. Since the majority of the upper range gain steps are in 2dB increments, I have used a stepped Grayhill for a fader trim that is in .5dB increments.

Next in line is a 6 position stepped LP filter. This filter was not in my board. I have however implemented the same passive philosophy that they used for the HP filter that was in my board. Since it was easy to implement, I have added a switch to select 6dB or 12dB per octave for the filters. Very smooth and natural sounding, by the way.

I follow this filter stage with a 3 transistor discrete voltage follower using 5087/5088’s. This buffer circuit is very reminiscence of the buffer amp used 4 times in the 550a. Very handy indeed.

Next is a 6 position stepped HP filter. This filter can also be switched between a 6dB or 12dB slope per octave. Again, the overall philosophy is the very same that was used in my old board.

The last stage is the post fader booster amp. Again, the same circuit as found in the vintage console. I have modified the feedback R and C to provide unity gain when using the entire VC528 circuit.

The VC528 modules have been given a few nicknames by some happy users. They have been referred to as “Audio Bacon” as well as “The Missing Link"


Check out these Gearslutz threads:
Preliminary Mixing Experiments with "the Missing Link" thread started by drBill

Classic Audio Products, VC528 ST2+ thread started Klauth


Price: $700

I build VC528 V2's on a per order basis. Lead time is usually around 1 to 2 weeks, but depends on parts availability.  For a time estimate or to place an order please contact me

Back to Products