Oy, what's all this, then?

Discussion in 'Speakers' started by John Frum, Apr 15, 2018.

  1. John Frum

    John Frum Junior Member


    Folks, you're looking at my next project.

    Telling people on the internet obligates you to actually get started, right?

    In short, my plan is to upgrade the stock Coral drivers in the Sansui SP-50 with Trusonic 80FR and Atlas SA-264.

    I want to suss out a simple high-pass for the Atlas tweeter, and along the way learn a thing or three about measurement, modeling, and how objective data relates to my subjective preferences.

    These cabs are smaller than the Trusonic drivers call for, but the ultimate plan is for these speakers to serve only as mid/high cabs. In the meantime, I'll get by without learning how low the 80FR can go.

    Hope y'all are into coming along for the ride.
    rusomon, airdronian, Audionut and 3 others like this.
  2. TubeHiFiNut

    TubeHiFiNut Administrator Staff Member

    Looks like this will be a fun project. :)
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  3. Prime Minister

    Prime Minister Site Owner Staff Member

    Lots of parts there! :)
    John Frum likes this.
  4. mhardy6647

    mhardy6647 Señor Member

    I thought that the SP-50 was a pretty nice sounding little loudspeaker, FWIW. Utterly guileless, but very pleasant and tuneful.
    John Frum likes this.
  5. marantzfan

    marantzfan Administrator Staff Member

    Looks like fun. I’ll happily come along for the ride.
    John Frum likes this.
  6. Do you know if your tweeters are Atlas's take on the Jensen RP-302? (I know Atlas made a clone of these, just can't remember the model number.) From what I can see they sure look like they could be. Whatever they are, they're substantial looking buggers, aren't they? Pretty sure they'll be an upgrade to the RP-103 clones crossed over to 80FRs in my Wattersons-- and the Wattersons aren't half bad as they are. But with a better tweeter, who knows?

    Depending on what you sort out here I might end up wanting to try something along the same lines as what you're doing. (Unfortunately, there's only one RP-302 in the audio closet at the moment.) In any event, I'll definitely be watching your progress with interest. Consider yourself the canary down the coal mine.

    Good luck.
    John Frum likes this.
  7. John Frum

    John Frum Junior Member

    Good eye.

    The Atlas tweeters are often traded online as the "Atlas RP302" and represented as being produced in cooperation or agreement with Jensen. The Atlas tweeters generally bring $300-400 for a nice pair, or about half the value of their Jensen counterparts.


    I'm pleased, for the first time on the internet, to tell the real story, and give the drivers back their identity as the Atlas Sound SA-264:

    Allen Organ Company famously used Acrosound TO-series ultralinear output transformers in their amplifiers, but also contracted out exacting copies by other leading manufacturers such as Saratoga and Stancor. These tweeters have a similar origin.

    In 1965, Atlas Sound was commissioned by Allen Organ to produce a direct replacement for the Jensen RP-302, which was used in some Allen organs and Gyrophonic speaker cabinets. The reasons why this happened are lost to the mists of time, but we can imagine that it came down to cost or availability.

    Design of the Atlas SA-264 was strictly an in-house affair, and it was loosely based on the earlier Atlas HR-3 tweeter.

    Many thanks to AtlasIED Vice President Steve Alban, who was very gracious to dig into the company archives for information on a 50+ year-old OEM product. THAT'S customer service!
    Last edited: Apr 16, 2018
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  8. John Frum

    John Frum Junior Member

    The Stephens Trusonic Free Cone series was designed under Bert Berlant in 1958, and originally consisted of the 80FR, 120FR, and 150FR.

    Twelve-odd years and two corporate owners later, my green-frame pair was apparently made in the Utah plant in Huntington, Indiana.


    I never understood the prejudice against the green-frame (Utah) Trusonic speakers. Sure, Utah sent the Trusonic nameplate to hell with speakers indistinguishable from the main Utah line, but why hold that against perfectly respectable drivers like the 80FR?


    Now, with a pair in my possession, I have an inkling as to why some people turn their noses up. The fit and finish (in earlier examples, on par with JBL or Altec) is just shittier. The paint job on the frame isn't as good. The glue on the dustcap and voicecoil leads seems heavy-handed, and the surround treatment, absent in the original version, looks sloppy. Utah also dispensed with serial numbers and the Stephens name.


    I've got a single earlier 80FR to compare this pair to, and I'm keen to see if the manufacturing differences will translate into measurably or audibly poorer performance.

    I've got a pair of green-frame 150FR in the same cabs these 80FR came from. They have serial numbers, and were apparently made in California. I haven't pulled them yet, but it'll be interesting to see which way the build quality leans.
    Last edited: Apr 17, 2018
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  9. Really interesting background on the Atlas SA-264. Thanks for that.

    Great close-up of your 80FRs. What a lot of different iterations of 80FRs there seem to be. Green baskets, green magnets; black baskets, black magnets; gray baskets, gray magnets; black baskets, unpainted magnets; unpainted baskets, unpainted magnets; magnets with a foil wrap, magnets without a foil wrap; spring terminals, solder tabs; 16 ohm, 8 ohm; Stephens Trusonic labels, Trusonic labels, Ampex labels. And this isn't even touching on cones and surrounds. (Kinda mind boggling, ain't it?) However, in that most of these differences are superficial I'd expect them all to sound more or less the same, but this is just a guess. Not an expert, trust me on this. I'll be interested in hearing about your comparison, for sure.

    Like you I also have a single 80FR on my hands. Unfortunately, the dust cap on mine is a little dimpled. Still sounds OK, though. Can't remember if it's 8 or 16 ohm. What's your single?
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