Bose Repair: 901 Series I Equalizer #31131

My workbench has been absolutely swamped lately, so I’ve been rather slow on writing up the projects I finish. I’ve finally had a little bit of time to put some of this down on paper and the first thing cleared off the bench is a Bose 901 Series I equalizer, serial number 31131 brought back to life!

The set’s owner reported it was giving him noise and distortion and definitely needed to be serviced. That’s pretty standard with these Series 1 equalizers, and many Series 2 – the parts are just so old they degrade and fail and can’t deliver the kind of performance the Bose 901 Series 1 speakers deserve.  He also requested I update the RCA jacks, as the old style jacks were spaced too closely together to support the high quality Monster cables.

This one came to me with some evidence of having been repaired at least twice over its lifetime. One of the 100 uF electrolytic capacitors was replaced, as were the two 500 uF primary filters. The two replacement main filters were actually a bit of an upgrade and were much newer, doubled capacity at 1000 uF each which will slightly lower the noise floor even further and provide better quality power.

It’s very easy to see with the original set of capacitors where the problem lies. The red capacitors are very clearly discolored, and spot-checking the resistors revealed they were badly drifted as well. Definitely time for a complete overhual.

Attention to detail and precision are key in refurbishing a 901 Equalizer. There are over 80 components which need to be replaced to restore the unit to complete functionality.

Finally, it was time for burn-in and listening test! I hooked this up to my Series 2 speakers. The Series 1 and 2 equalizers and speakers are compatible, so this provides a perfect live test. My listening lab is in transition right now, so I’m using them on a temporary setup but they still sound absolutely amazing.

After several hours of burn-in testing to ensure solid operation. I was satisfied this one was back to perfect shape. It’s actually in one of the best condition equalizers I’ve had the pleasure of working on – an exceptionally low noise floor, and perfectly operational switches. This one will really make the 901 speakers it’s attached to really sing.

If you need your Bose 901 Series 1, 2, 3 or 4 equalizer repaired, I can take care of that back to meeting or exceeding its factory specifications with precision manufactured components. Click through for more details!

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3 Responses to Bose Repair: 901 Series I Equalizer #31131

  1. Eli K. says:

    I have a pair of 901 series I speakers with no equalizer. Can i use them without it and, if so, what’s the difference in sound?


    • jwk says:

      Well, you can’t hurt it by not using the equalizer but you’re missing out on the best possible sound. The equalizer provides significant gain in the bass and treble regions and without it the speakers will sound dull and flat. You can use either a Series 1 or Series 2 equalizer with those speakers for identical performance.

  2. Pingback: Evidence of Past Repairs | KF7LZE's Blog

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