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Realistic Optimus-10's: fixing an oldie

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  • Realistic Optimus-10's: fixing an oldie

    Back in the late '70s I worked at local Radio Shacks. At the time I had to set up their audio equipment to demo. There was a nice mid-sized speaker called an Optimus 10, which featured a 3.25" tweeter, an 8" woofer with a 1 pound magnet, and a 10" passive radiator. It could handle 75 watts RMS with a frequency response of 42-20K, +/- 3dB. I remember that the speaker sounded pretty good, but not as good as my Altec Lansing Model 6's. ;-)

    A couple of years ago I managed to get five of these from my employer. Most were pretty beat-up; I mixed/matched parts to make the best pair I could get and scrapped the rest. The foam surrounds on the 8" and 10" were shot, so I invested some money in rebuild kits and rebuilt them.

    When I hooked them up to an amp and turned them on I was underwhelmed. The tweeters worked but the speakers just didn't have the high end I remembered. Overall the speakers sound like a wet blanket is over them.

    I opened them back up and took a closer look. The"crossover" is a 100 volt, 4 uF NPO electrolytic. This is inline with a 30K ohm wirewound pot (unknown power rating) that connects to the tweeter for a "brilliance" control.

    I thought I might try putting a real crossover into the unit but I have no idea what the frequency range of the original speakers are. Add the passive radiator into the mix and I'm completely befuddled. If my calculations are correct the speaker has an internal measurement of 1.51 cubic feet.

    So, other than scrapping them (as I'm sure some would suggest), what would be the best path for me to try and restore these to usability? I'd like to keep the original drivers since I rebuilt the woofer and P.R., but a 1-pound magnet on the woofer is pretty small...

    Any input appreciated!

  • #2
    Re: Realistic Optimus-10's: fixing an oldie

    Originally posted by Harbinger View Post
    Back in the late '70s I worked at local Radio Shacks. At the time I had to set up their audio equipment to demo. There was a nice mid-sized speaker called an Optimus 10, which featured a 3.25" tweeter, an 8" woofer with a 1 pound magnet, and a 10" passive radiator. It could handle 75 watts RMS with a frequency response of 42-20K, +/- 3dB. I remember that the speaker sounded pretty good, but not as good as my Altec Lansing Model 6's. ;-)

    A couple of years ago I managed to get five of these from my employer. Most were pretty beat-up; I mixed/matched parts to make the best pair I could get and scrapped the rest. The foam surrounds on the 8" and 10" were shot, so I invested some money in rebuild kits and rebuilt them.

    When I hooked them up to an amp and turned them on I was underwhelmed. The tweeters worked but the speakers just didn't have the high end I remembered. Overall the speakers sound like a wet blanket is over them.

    I opened them back up and took a closer look. The"crossover" is a 100 volt, 4 uF NPO electrolytic. This is inline with a 30K ohm wirewound pot (unknown power rating) that connects to the tweeter for a "brilliance" control.

    I thought I might try putting a real crossover into the unit but I have no idea what the frequency range of the original speakers are. Add the passive radiator into the mix and I'm completely befuddled. If my calculations are correct the speaker has an internal measurement of 1.51 cubic feet.

    So, other than scrapping them (as I'm sure some would suggest), what would be the best path for me to try and restore these to usability? I'd like to keep the original drivers since I rebuilt the woofer and P.R., but a 1-pound magnet on the woofer is pretty small...

    Any input appreciated!
    I recently had the chance to do something similar, only in my case, the gentleman had already replaced the woofers with something else. Tweeters were the originals, and well, underwhelming was a very good choice of terms.

    If the high end is lacking, and you've tried completely bypassing the volume pot, you're at a dead end, and have to think about replacing the tweeter.
    R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio

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    • #3
      Re: Realistic Optimus-10's: fixing an oldie

      That "brilliance" control works from 10-20 khz according to the '78 Radioshack cat. With that cap my guess it would cross that tweeter @ 5000. Being a novice myself that will be the extent of my help? Best of luck.

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      • #4
        Re: Realistic Optimus-10's: fixing an oldie

        You could take a quick trip through e-bay electronic's! Ever so often someone pops up with reworked Optimus speakers! Might be a source for some tips or help....Could also just try an engine search on reworked/repaired optimus speakers and see what comes up.....

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