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To avoid massive build errors, make sure the BOM Revision you follow matches the Revision of the PCB you are building!! The 553F Rev B Entire Bundle is a kit comprised of every single part and component needed (sans opamp) to complete a 553F equalizer. This module is fully VPR compatible. The custom made full metal enclosure has a special notch at the rear to slip over the 18-pin connector in a 51x rack. So, no worries there and no modifications needed. The aluminum faceplate is wet painted and the custom steel frame/cover are clear-zinc plated. Following is a list of additional components that are required to complete this build: (1) 2520 style discrete operational amplifier PS: DOA's can be added to this kit at the bottom of this page. This kit ships with a EA2503 output transformer. Kits with Litz wire 2503's are also available here. This equalizer is basically a fairly faithful recreation of the vintage API 553. The 553 has always been know as a great sounding, limited featured equalizer. My original intention was creating the LC53A. In working on that, I had the skewed idea that simultaneously whipping up a simple 553 would be a breeze. Nothing is ever that easy especially when working on multiple modules at the same time. I decided it would be nice to add a HP and LP filter array in the same fashion as the Missing Link. While each filter has only 3 selectable frequencies, I have retained the handy -6dB/-12dB per octave switchable options. These filters are buffer by the simple 2 transistor discrete followers used in the original 550. The 3 equalizer bands are faithful to the vintage counterpart. Low band is shelving only at 100Hz. Mid band is a wide peaking filter at approximately 2.5kHz and the high band is shelving only at 10kHz. It would have been nice to add more flexibility by adding a few switchable frequencies. In order to keep the bandwidths consistent though, the inductance values would need to be changed along with the capacitance values. Things would get too complicated, expensive and move farther away from the original 553 not to mention, I am already doing this with the LC53A. New to the Rev B version are inductors from a new winder. The previous supplier jacked their prices up in a ridiculous manor. It took me quite a while to find suitable replacements hence why the 553F has been out of stock for so long. We actually beat the previous inductors with this new version. The have a slightly sweeter and more smooth tone with a little less edginess to them. They are wound in the USA and use the same euphoric sounding Molybdenum Permalloy Powder (MPP) cores. In a desire to keep the overall kit price low, I developed the DTO7 discrete opamp. This amp is used as the balanced receiver in the 553F Rev B which replaces a previously used 2520 style amp. Its a great sounding amp and super easy to build. You will see it being used in many other future CAPI projects. Special features: DTO7 discrete balanced receiver stage (no 6dB loss when driven electronically) Custom MPP core inductors wound in the USA 2503 stye output transformer wired 1:3 for 9.5dB of gain (in typical API EQ fashion) Full and complete zinc plated steel enclosure 100% VPR compatible ***This is a fairly simple build especially if the opamps are not kits. The most important thing is to follow my build instructions and DO NOT SOLDER THE BOURNS POTS DIRECTLY ON THE PCB!!! As always, I will have a build/support thread running at the GDIY forum.

Additional information and photos:

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