Bose 901 series I active equalizer DIY

[rayma]

That is the circuit.

Unless someone wants to do a simulation, maybe using the published equalizer response curve would be
the easiest option. This is the last graph in the link. https://tvforfree.files.wordpress.com/2012/07/901-series-ii-frequency-response-normal.png
Simple enough, boost the lows at about 90Hz, and boost the highs at about 4200Hz, and also band limit
with a 30Hz bass high pass, and a 15kHz treble low pass. You could build the actual circuit on a breadboard
without too much trouble.

 

[srinath]

found this

Unless someone wants to do a simulation, maybe using the published equalizer response curve would be
the easiest option. This is the last graph in the link. https://tvforfree.files.wordpress.com/2012/07/901-series-ii-frequency-response-normal.png
Simple enough, boost the lows at about 90Hz, and boost the highs at about 4200Hz, and also band limit
with a 30Hz bass high pass, and a 15kHz treble low pass. You could build the actual circuit on a breadboard
without too much trouble.

I found this.

SEVENTIES STEREO: BOSE 901 Update.

I would prefer to use a homemade kit with Fet's in it, closet to the original, and I also have 1 series 1 eq with new caps in it, I can double up via tape monitor loop as well as compare the 2.

Thanks.
Srinath.

 

[bwaslo]

Someone may have mentioned this, if so, sorry, I didn't read the whole thread. But you could do this in about an hour and around $100 with a miniDSP 2x4 unit. Hook it up to your computer, tweak the parameterics till they match the curves in that article, load it, bam boom, you're done and with a decent case, too.

A practical problem with these speakers is that the scheme was designed when people were using receivers and the receivers had "tape monitor" loops. They don't anymore, so the EQ would have to be between a separate preamp and power amp. It may be difficult to find a customer who has such an arrangement and is still interested in old Bose speakers, but who knows you might find someone who has fond memories.

 

[srinath]

I got plenty of separates, as well as period amps these were built around. Pioneer sx1250, rotel 1203, Concept 12.0 as well as massive HT pre+pro sets and HT amps with 2 X tape monitor loops. I have 2 sets of 901's, a set of speaker lab clones with 901 drivers in it and a speaker lab clone with non 901 (sony I think) drivers with square magnets made from 1" thick plywood. Between all of those I have just 1 series 1 eq. However if I run an 8 speaker set up off a Yamaha dsp 3090 with 1 eq in tape monitor loop it will eq all 8 the same LOL.

The dsp 3090 wasn't fitted with a tape monitor loop for you to try to run 1 901 in the front. Trust me, I've tried, it makes all of them use the eq. The only way is to run one for every speaker - front and rear center all 901. Or speaker lab clones, which IMHO sound far too close to the 901's IMHO.

Cool.
Srinath.