Bose® 901 Series IV Active Equalizer #509052

From Rain City Audio:

This Bose® 901 Series IV Active Equalizer, #509052, was just purchased and sent to Rain City Audio for an overhaul.






This unit was originally a 220V model but had already been converted to 110V on a previous repair. The op-amps had been replaced as had a couple of electrolytic capacitors.



Unfortunately, the pads and traces on the bottom of the unit were badly damaged around the op-amps. Ultimately, it ended up being too risky to replace them, but since they had already been replaced with reliable models this wasn’t a major loss.


New electrolytic capacitors, and silver solder later, and this one works and sounds good as new.

This entry was posted in Audio, Bose, Electronics and tagged , , , . Bookmark the permalink.

2 Responses to Bose® 901 Series IV Active Equalizer #509052

  1. Ian Bos says:

    Do you know what voltage the transformator has on this model?
    My transformator is broken and i can’t find the specifications anywhere. And i can’t test the voltage because it’s broken.

    • jwk says:

      I think it’s a 15-0-15V transformer, and very low amps. Output ~19V DC after the rectifier, before the dropper resistors to 15V for the op-amps.

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