Bose 901 Series III Equalizer #181986 Repaired

Cross-posted from the Rain City Audio Repair Blog:

Bose 901 Series III Active Equalizers are uncommon compared with the other series, but I did have one through the shop just recently. The Series III design – while a great performer when in good condition – was susceptible to reliability problems with the somewhat more complex circuit design. The Series III was the last generation Active Equalizer to use discrete transistors; while functionally interchangeable, the later Series IV used op-amp chips.

This one originally came from Europe and was fitted with a 220V plug. Voltage conversions aren’t generally possible with later series, but the Series I, II and III were easily convertible by just removing a couple of parts and changing the plug end.

Starting with the Series III, Bose used high quality resistors which don’t drift, and good film capacitors – but like most other electronics, it’s the electrolytics which cause the problems. In this case, the owner also requested an upgrade to audiophile-quality film output capacitors.

This equalizer got a full set of new Nichicon capacitors, including Nichicon Fine Gold capacitors in the signal path, and top of the line ERSE PulseX film capacitors with excellent transient response and a vanishingly low dissipation factor for the best clarity possible in the output signal path.

That’s a few parts pulled out! The new replacements are all up-rated and will provide many years of reliable service to come.

Do you need your active equalizer repaired? Rain City Audio can help!

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

1 Response to Bose 901 Series III Equalizer #181986 Repaired

  1. Frank says:

    Good day, Is the Bose equalizer serie III for sale?

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