Classic Audio Products of Illinois – VP312



The preamp is essentially an exact recreation of the legendary API 312 preamp circuit that has become the benchmark for the API sound


Product Description

The VP312 preamp is essentially an exact recreation without compromise of the legendary API 312 preamp circuit that has become the benchmark for the API sound.  The love-hate relationship with the -20dB input pad is loyally carried out on this board. The simple voltage divider or U-pad resistor network follows the exact method used on the preamps in my vintage API console. This method is historically and mathematically correct, unlike many pads implemented into the 312 type circuits.  The mic input transformer is Ed Anderson’s EA 2622. This transformer mimics the inherent flaws of the vintage AP2622 that was found on the early 312 cards. A Zobel network  has been implemented exactly as the original API 312.  The discrete operational amplifier is the heart of this preamp. The industry standard 2520 footprint is utilized here.  For the balancing output transformer, the VP312 is designed with the Ed Anderson EA 2503 in mind. The circuit utilizes two of the secondary windings in series in standard API fashion. Although the 2503 is the most recognized output transformer for an API mic preamp, it should be noted that the console input modules made use of the smaller AP2623-1 for this duty, not the 2503. For those who prefer the 2623, we have the VP26 available.  A very nice and unique feature of the VP312, is the use of a Bourns custom, 600 ohm T-pad output attenuator. The 3-module attenuator gives the user the ability to drive the preamp harder, and simply turn down the output level. The insertion loss of the t-pad is very minimal with a near perfect transfer of power, from input to output. This is a very similar attenuator as used for the input of the popular 1176 compressor builds.



  • 60dB of gain provided by a 2520 style opamp.
  • -20dB Pad switch, polarity switch, and mute switch.
  • 48V Phantom power.
  • Output attenuator which allows you to drive the opamp and 2503 output transformer HARD and attenuate back down to digital safe levels (rarely implemented on Api style preamps, (increases the variety of tones).

Additional Information

Gain Control

Variable, Greyhill Rotary Switch [Add $20]

Discrete Op Amp

No Op-Amp, BA512 – Originally designed for the BBC as a drop-in replacement for the BA440 [Add $50], JE-990 – Clarity, true to the source [Add $50], Gar1731 – Modeled after the legendary Melcor 1731. [Add $60], Gar 2520 – Modeled after API’s legendary, mid ‘70’s, Studio Systems/Huntington era 2520. [Add $60], Gar918BC – Modeled after the legendary JE-918 using transistors from the Fairchild BC550 and BC560 family [Add $60], Gar918PN – Modeled after the legendary JE-918 using rare transistors PN2484 and PN4250A [Add $60], Inward Connections VF600 – From the highly regarded pro-audio designer, Steve Firlotte [Add $85]


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