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 4 reviews
    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

    John Keith JMK Audio
    Very easy build, about 7 minutes.

    Easy build, I do prefer to solder pins next to last, they get in the way of soldering..
    Draws a moderate amount of current (32mA) which I like..
    Still testing, like it so far, clean and quiet..

    Eddie R.
    Assemble Carefully!

    Be sure to not mix up the NPN and PNP transistors...otherwise you will fry the board!

    Glenn B
    Cleaner than a GAR2520

    I've used these in a couple of Classic API preamps, and they are a great, affordable opamp. Generally, they seem to have a little more detail and clarity, than the GAR2520. If you really want that vintage sound, the GAR2520s are where it's at, but these opamps are perfect, if that VP26 is just a little too wooly for your taste. Also, add these opamps' crispness to a VP25, and your kick drum will hit hard.

    Related Products

    Liquid error: Could not find asset snippets/iStock-notify-me.liquid