Quilla333 Posted March 25, 2022 Report Share Posted March 25, 2022 What are the Factory OP Amps for the 901 series IV equalizer ? And your sugestión if they are obsolete. Thanks Quote Link to comment Share on other sites More sharing options...
CYNR Posted March 26, 2022 Report Share Posted March 26, 2022 Quoted from the RetroVoltage web page... One interesting thing to note is this Active Equalizer came with IC sockets fitted from the factory, which were still populated with the original National LF 353 op-amp chips. These chips are a big, known problem in Series IV Active Equalizers. So much so that in January 1983, Bose® issued a product service bulletin describing their unusually high tendency to exhibit high noise or fail completely due to lead contamination in the manufacturing process. The factory recommended using the TL072, or RC4558 or RC4559 op-amp instead, and that all op-amp chips be changed if a unit came in for service. Quote Link to comment Share on other sites More sharing options...
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