One of the true gems in the sea of DIY recording equipment is the GAR2520 discrete opamp designed by Gary Barnett. These are sold in kit form by Classic Audio Products of Illinois. They are also available fully assembled and tested as an add-on option for CAPI's preamp kits.
This opamp circuit is a modern component interpretation of API's mid 1970's Huntington era 2520 and operates on bi-polar +/- 12VDC to +/- 20VDC power supply voltages. For my studio, this righteously priced kit has been an absolute life saver due to the sheer number of opamps required for the various preamps, EQ's, and other outboard audio equipment we utilize. While I have never been hands-on with a vintage Huntington 2520, many people who are intimately familiar with the vintage opamp feel the GAR2520 is sonically "hair-splittingly close" to the original that it is modeled after. What I can say is in my experience, this opamp has sounded gorgeous in every device I have tried it in, and as such, it is my go-to baseline opamp for the many API-family devices I build for the studio. There are many fine pre-built options currently available, and people often equate high cost to high performance, but make no mistake, a properly built GAR2520 is capable of holding its own when compared to any of the other top tier API-type opamps available. Slight sonic variations and colors aside, the pedigree of this device is on par with the rest of the field.
For this article, I will build 2 complete GAR2520 kits to the best of my abilities.
The first step is to pull the Milmax pins from the kits.
I find it easiest to use a preamp or other device that utilizes the 2520 footprint to align the pins for soldering to the opamp's tiny PCB. This positions the pins perfectly for soldering and also loosens up the sockets if the device is a new build. The Milmax sockets can be extremely stiff the first time an opamp is inserted. It is much easier to insert the pins one at a time like this. The pictured device is a CAPI VP28 dual stage preamp that utilizes 2 opamps.
Place the GAR2520 PCB's onto the pins and solder in place.
Pins are perfectly aligned and the op-amps are ready to be populated. The assembly PDF documentation provided with the GAR2520's is VERY thorough and walks you step-by-step through the process. A steady hand and an eye toward detail are required.
and opamps complete.
If all went well, like these 2 copies, the opamps should be ready to roll. My only complaint about the GAR2520 kit is full schematics are not provided with the kit, so trouble-shooting a non-functioning opamp is somewhat difficult. But, this deficiency is easily superseded in my opinion by the low cost of these kits, and for that, the DIY audio community owes a great debt to Gary Barnett.
For more detailed information and a good read, please visit the official support thread for this opamp.
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