This is a 1960S audio testing instrument, used as a preamplifier for B&K measurement microphones. The sound is very warm and the frequency response is very wide. I compared it with the Telefunken v72. I found that it has greater gain and more power than the V72. but there is a slight motorboat noise. I modified it to meet the needs of professional recording. After the modification, it is quieter than the V72. I strengthened the shielding of the line, replaced it with a standard XLR interface, and added A JORGEN SCHOU input transformer to match the impedance of different microphones, and the filter input was modified so that I could plug in any filters and compressors in series internally.
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