Tag Archives: Active Equalizer

Everything to Know about Bose 901 Series I and Series II Active Equalizer Repair & Speaker Systems (and the 800, too!)

Posted on June 12, 2026 by retrovoltage

A deep dive into the tips and tricks for repairing the Bose 901 Series I and II, plus the Bose 800 Series I and II, along with a discussion of their history and variations, sourced from direct experience repairing more than 500 examples. Includes schematics and parts lists. Continue reading →

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Bose® 402E Active Equalizer #102853 Repaired

Posted on November 30, 2015 by retrovoltage

The first Bose® 402E Active Equalizer, for the Panaray speaker system, just came through the shop. It’s a small speaker array system, designed around similar drivers in the 901, and uses an Active Equalizer for the same effect. They’re designed … Continue reading →

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Bose® 901 Series VI Active Equalizer #199732 Repaired

Posted on February 20, 2015 by retrovoltage

A first for my shop, I recently worked on a Bose® 901 Series VI Active Equalizer! These are considerably newer than the Series I-IV that typically come through the shop, although they’re still getting to be 25+ years old at … Continue reading →

Posted in Audio, Bose, Electronics, Projects, Vintage | Tagged , , , , , | 1 Comment

The Speaker Spotter – Speakers of Craigslist – March 14th, 2014

Posted on March 14, 2014 by retrovoltage

There’s always something interesting for sale on Craigslist, especially in Seattle. Here’s a selection of especially notable vintage speakers and other audio products for sale on the local Craigslist. I’m not affiliated with any of these sales, but if you’re interested, you … Continue reading →

Posted in Audio, Collections, Photos, Speakers, Stereo, Vintage | Tagged , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , | 2 Comments

Bose 901 Series I Active Equalizer #50911 Repaired

Posted on December 3, 2013 by retrovoltage

I recently had this Bose 901 Series I Active Equalizer, serial number 50911, in the shop for repair. These are a lot of fun to work on and very rewarding for the great sound they produce when they’re working properly. … Continue reading →

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Mailbag: Is The Bose 901 Equalizer Really Necessary?

Posted on October 21, 2013 by retrovoltage

I take questions from readers often, but they don’t always make it to a Mailbag segment. I’ve got this one a few times lately, though, so I figured I’d answer this one publicly. Jim from Ohio writes, I bought a … Continue reading →

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First Ever Bose 901 Series 1 Active Equalizer Repair

Posted on July 25, 2012 by retrovoltage

This post is almost 15 years old! Check out this much more recent round-up of Bose 901 Series I and II Active Equalizer repair tips and tricks, and leave a comment if you have any feedback. This post was one … Continue reading →

Posted in Electronics, Projects, Speakers, Vintage | Tagged , , , , , , , , , , , , , , , , | 37 Comments

Identifying Your Bose 901 Series 1 Equalizer

Posted on July 11, 2012 by retrovoltage

Bose 901 Series I Active Equalizers came in two varieties, which can be used interchangeably, but have fairly different circuit designs. It’s simple to tell them apart for ordering parts for a repair with a quick inspection of the inside. Both … Continue reading →

Posted in Electronics, Projects, Vintage | Tagged , , , , , , , , , , , | 4 Comments