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The CA-0252-DIY Single Kit is an all inclusive kit containing everything required to complete the CA-0252-DIY Discrete Operational Amplifier build. The CA-0252-DIY is not the same circuit as the gar2520. Gary's version is 9 transistors with a resistive current source for the input transistor long-tailed pair. The CA-0252-DIY is a 10 transistor circuit with a transistor current source for the long-tailed pair. You can see by comparing the BOM's that they differ in many other ways as well. The CA-0252-DIY is a pretty unique kit of parts. Such a version has never been realized before as far as I know. I am being as faithful as possible to the exact type of parts used in the early 1970's OG 2520s. I know this because I was gifted an unpotted 2520 from a friend a few years before we moved to Nashville. My friend got this amp from a trade show in the early 1970's. I looked at it a few times and thought "no way". After it living in a drawer of parts for years, I pulled it out in the fall of 2019 and jumped into the deep end. Interestingly, when the same friend saw on social media that I was finally working on it, he sent me 2 more unpotted amps and a few never populated PCBs. That said I had plenty of OG data to pull from! Input transistors The OG input transistor pair were BC414Cs. In researching these parts, I found BC237C to be the recommended replacement. So, due to supply issues, we chose to use BC237Cs for these. To our ears they were closer to the OG than the commonly used BC550C etc. Interstage NPNs The OG was TIS98 for these 3 transistors. We have been using Fairchild TIS97s for our BT50s so decided to stick with them for this situation. Since TIS97s are long out of print and very hard to find, we had them custom made by a US manufacturer. Its actually amazing that can still be done! Interstage PNPs The OG was 2N5087 for these 3 transistors. I was able to procure a mother-load of NOS National Semiconductor 2N5087s so that is what we are using. They definitely sound different than the more recent Fairchild or ON Semi stock. Output Transistors The OG output transistor pair were metal can TO-39s, specifically BC141-16 and BC161-16. These are unobtainium and have been for years. We tried the Multicomp version and found them lifeless so we had them custom manufactured like the TIS97s. They are outstanding parts and a very big part of the tone. The CA-0252-DIY only ships with the longer terminal pins so there is no issue in a 2500 etc that may have other components under the opamp footprint. These longer pins impose no issues when used in a situation with no components under the amp. Just leave them long. If you have an old school situation where the amps are soldered directly to the PCB, just solder them in and cut the pins off. Some of the applications the CA-0252-DIY DOA can be used for: Microphone Preamplifiers Line or Booster Amplifiers Lossless Combining Amplifiers Balanced Transformerless Amplifiers Equalizers and Compressors Additional features and specs: Industry standard 2520 footprint for plug-in or PC mount connections Low noise, high power output Low distortion Minimum load impedance is 75 ohms for full output voltage Power supply voltage is bi-polar +/- 12 VDC to +/- 20 VDC Includes all top quality parts and components The CA-0252-DIY Pictorial Build Guide can be found and reviewed here. The schematic for the CA-0252-DIY is not and will not be made public. The CA-0252-DIY is for use in DIY projects only. Commercial use is prohibited. We reserve the right to refuse service if we feel this restriction is being violated. If you want less than 10 kits then this product is for you. If want 10 or more kits, please see the CA-0252-DIY 10-Pack that features bulk sorted parts. ***Please note: This item is a complete parts kit and PCB bundle. Full and complete assembly is required. This kit is not for the beginner. Good assembly and solder skills are a must!

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