RED-25 Discrete Opamp Kit


This kit contains all components necessary to build a RED-25 opamp. This is without a doubt the simplest discrete opamp kit available on the market today. All the heavy lifting is done for you, courtesy of the pre-mounted SMT components.

The RED-25 is Whistle Rock Audio's version of the sought-after Huntington era AP2520 from API.

Although a mostly SMT discrete opamp may seem unorthodox, you can be assured that all the components in the RED-25 have been carefully selected with a no-compromise approach. Throughout the prototyping stage, no less than three different manufacturers of equivalent SMT transistors were evaluated. It goes without saying that only the very best were chosen for the RED-25. In fact, performance measurements of the opamp show that the RED-25 is on par with its through-hole counterpart.

All surface-mount resistors are Susumu thin-film resistors and all capacitors are Murata C0G/NP0 types for the lowest noise and distortion achievable.

The RED-25 sounds large and impressive. The low-end alone is worth making it a part of your tone arsenal.


  • Supply voltage: +/-12 to +/-18V
  • Matched input transistors
  • Quiescent current draw: +/-30mA @ +/-16V
  • Dimensions (LxW): 1.1"x1.1"
  • Height: 0.95" from the tip of pins to top of output transistors / 0.625 from lowest solder joint to top of output transistors
  • Gold finished pins
  • Standard 990 / 2520 footprint
  • High current output
  • Carefully selected quality components throughout

    Customer Reviews

    Based on 8 reviews
    Marcelo Navia
    Great sound

    Easy to assemble, great warm sound.

    Marlon Mehr
    Sounds Great! Quick and Easy Build

    I was hesitant to use the Red-25 version because of some of the SMD components and my ignorance of their sound capabilities. Having said that, the OpAmp sounds great, so good, that I now feel comfortable to sell my remaining API 312s, 500A eq’s, etc.

    The build time is really amazing, almost completed right out of the box.


    Very easy to build, works perfectly in the side chain of my Api 525

    Luke Robinson
    Hands down the best.

    The fact that you had the part and got it to me so quickly was one thing, but how it works in my API is just amazing. Thank God for y’all.

    John Keith
    Voltage Rails

    I would not go any higher than +- 17V, any higher the current gets so high (Over 40mA) the output transistors will need a heat sink..+- 16 seems ideal..IMHO

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