Soonthereafter, API released the "improved" 550A. A decade and a halfafter that came Paul Wolff's 4-band version, the 550B.
Like its vintagecounterpart, the BT50's filters are Proportional Q. Those who have had the pleasure of using the original 550's know that they arespecial.They have a meaty thickness to them that the rest of the familydoesn't have. The rest are still great, don't get me wrong but the originalgoods 550 is euphoric. The original 550 only had three frequencies on the high and low bands. The BT50have five frequencies found on a vintage 550A.
Splitted the "bandpass" filter so they canbe used individually. LP is 15kHz and HP is 50Hz. Cut/boost is via the upperclear concentric knob and frequency select is via the lower blue knob.The input is historically unbalanced. This can sometimes lead to a 6dB lossdepending on the output stage of the device driving the BT50. So there is ashunt jumper near the output transformer that will make up the 6dB, at theoutput stage. The module was originally designed to drive a 600 ohm load atunity gain. This will produce an approximate 1.3dB increase in gain whendriving a modern high Z load. A shunt jumper to reduce this gain is also placednear the output transformer.
API (and compatible) Lunchbox and VPR500 racking systems. These can be also build to order. If you are not certain please contact me first. If for any reason you are dissatisfied with the module(s) in the first 30 days after reception. Please include details, explanation, reasons.The item "CAPI Classic Audio Products of IL BT50 Litz" is in sale since Thursday, March 21, 2019. This item is in the category "Musical Instruments & Gear\Pro Audio Equipment\Preamps & Channel Strips". The seller is "bywaudio-com" and is located in Montreal, Quebec. This item can be shipped worldwide.