API 550A Saul Walker Edition

This limited edition EQ is a continuation of the equalizers produced by API exactly as they were in the 1960’s, featuring hand-wired switches, the original circuit board design and API founder Saul Walker’s signature on the chassis.


The API 550A Saul Walker is a hand-wired limited edition re-issue of the original 3-band switchable API console EQ unit, for the 500-Series format.
Originally introduced in the late-60s, the API 550A Saul Walker is a faithful recreation of the classic console modules from API, or Automated Processes Inc, as they were then. Although the API 550A is still produced today according to the abiding principles, the API 550A Saul Walker comes to you hand-wired and built using the original 5 frequency centres of his first designs and signed by the designer himself.
Deceptively simple to operate, the API 550A Saul Walker uses a 3-band switchable EQ with overlapping frequencies and Proportional Q, which narrows the band chosen according to the amount of EQ being applied. The high and low frequencies are switchable between shelving and peak operation and a band-pass filter can be inserted independently.
By the time that the demand for rack-mounted outboard processing came along, the original 550As had long since vanished from the market, with only rare and pricey sightings occasionally occurring. With the 550A Saul Walker, API has rectified that imbalance and also made it fit into their innovative and much-copied Lunchbox – known as the 500 Series format in its larger, open-access form.
The 550A Saul Walker is an enticing and very desirable combination of musical, build and reputational quality.
API 550A Saul Walker Overview:

Hand-wired Limited Edition, signed by Saul Walker
Custom faceplate
3 bands of classic API equalization
Each band offers 5 API-selected frequency centers
Reciprocal and repeatable filtering
Maximum 12 dB of boost/cut per band
EQ Band 1 and 3 offer shelf/peak switching
“Proportional Q” narrows filter Q at extremes
Traditional API fully discrete circuit design
High headroom +30 dB clip level



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