Bose® 901 Series IV Active Equalizer #253288 Overhaul

This Bose® 901 Series IV Active Equalizer came through the shop for a full overhaul. Inevitably over the years, various parts wear out and degrade and can make the equalizer sound bad – or not work at all. Without the Active Equalizer, your 901 Direct/Reflecting speaker system won’t sound good at all! Fortunately, it’s a straightforward fix.

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Inside the lid, there’s a pretty visible patch of outgassing from when the electrolytic capacitors went bad. That’d explain the problem!

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The construction on these equalizers varies a bit from unit to unit. In this case, the op-amps are socketed from the factory instead of directly soldered and it still had the original LF353N op-amp chips which were the subject of a factory service bulletin recommending their removal and replacement due to a high defect rate. Interesting!

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The power lamp on this one had also failed and was replaced. These use neon bulbs for the power indicator and they can occasionally leak their gas and fail to light after 30 years or so, but replacement are readily available.

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Quite a few replaced parts! After service, this equalizer was back to peak performance and should serve faithfully for many years to come.

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