Oy, what's all this, then?

[J. Frum]

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.

 

[TubeHiFiNut]

Looks like this will be a fun project.

 

[prime minister]

Lots of parts there!

 

[mhardy6647]

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

 

[marantzfan]

Looks like fun. I’ll happily come along for the ride.

 

[rusomon]

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.

 

[J. Frum]

Do you know if your tweeters are Atlas's take on the Jensen RP-302?

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!

 

[J. Frum]

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.

 

[rusomon]

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?

 

[J. Frum]

Through trick of fate, I've found myself listening to the unaltered Sansui SP-80 in my main rig, and have found them wanting. This restuffing project is finally moving along. Pics tomorrow or the next day.

I was able to dig up my Dayton Audio DATS for the first time in years, and have been having all kinds of fun testing drivers.

This evening, I tested all four of my Trusonic 80FR drivers. The two Stephens drivers are fairly close in serial number, but have led different lives, with 13375 appearing to have had the more pampered existence. The two Utah drivers have been together since the factory.

Clearly, the extra goop on the Utah surrounds is having an effect, adding mass and driving down fs and sensitivity dramatically.

 

[J. Frum]

I wound up using my older pair of 80FR.

Last night, I listened to them by themselves in the Sansui cabs, and quickly decided I liked them better in these small boxes with the ports plugged with space-age elastic/cotton blend. Pretty great, but in need of woofer and tweeter, IMHO.

Today, I knocked together a second-order highpass with L-pads for the Atlas tweeters. Still playing with levels, but getting ready to bust out the mic.



Y'all like clip leads, right?

 

[Opa1]

I wound up using my older pair of 80FR.

Y'all like clip leads, right?

View attachment 10796

That's the preferred method around here! LOL

 

[mhardy6647]

a best practice, as far as I am concerned.

 

[J. Frum]

I'm still a USB cable away from REWing up a storm.

As far as the highpass goes, I've been using the L-pad and playing around with component values, 1st and 2nd order crossovers, bypass caps, and phase inversion.

So far, the big eureka moment came from ripping out the whole mess of clip leads and L-pads, and starting over with a simple 1uF cap on the tweeter. A little more expermentation, and I'm heavily favoring a bundle of caps totaling 0.79uF.

That probably won't raise a lot of eyebrows around here, but it surprised the hell out of me.

This combo is shaping up to be a winner.

 

[mhardy6647]

Maybe first order's like... you know... Class A.
Class A is... umm... class A.

And first order is... ahhhhm... first.

 

[TubeHiFiNut]

I wound up using my older pair of 80FR.

Last night, I listened to them by themselves in the Sansui cabs, and quickly decided I liked them better in these small boxes with the ports plugged with space-age elastic/cotton blend. Pretty great, but in need of woofer and tweeter, IMHO.

Today, I knocked together a second-order highpass with L-pads for the Atlas tweeters. Still playing with levels, but getting ready to bust out the mic.

View attachment 10797

Y'all like clip leads, right?

View attachment 10796

Not just any clip leads, mind you. We only use @mhardy6647 approved clip leads.

 

[J. Frum]

I've been driving myself mad listening to different cap combinations, and today got around to making some measurements.

Here, mic'd from about a foot away, you see the Stephens Trusonic 80FR in blue, and the green line includes the Atlas SA-264 rolled in with a .68uF PIO cap (about the best compromise I could come to).

Most of the frequency response nasties are endemic to the 80FR (that 1.3K suckout!), and the Atlas tweeter drops like a stone after 13K. Still quite listenable.

 

[mhardy6647]

looks pretty darned comely to me.

 

[JimPA]

I've been driving myself mad listening to different cap combinations, and today got around to making some measurements.

Here, mic'd from about a foot away, you see the Stephens Trusonic 80FR in blue, and the green line includes the Atlas SA-264 rolled in with a .68uF PIO cap (about the best compromise I could come to).

Most of the frequency response nasties are endemic to the 80FR (that 1.3K suckout!), and the Atlas tweeter drops like a stone after 13K. Still quite listenable.

View attachment 11235

John I wish you could show us a schematic of the tweeter crossover.
If you are using a resistor on the tweeter have you tried paralleling a cap with the resistor say around 2mfd with the tweeter?
This will raise the high end a little by lowering the frequencies above tweeter resonance.
It will take some trial and error and may not give the desired results.

 

[J. Frum]

John I wish you could show us a schematic of the tweeter crossover.
If you are using a resistor on the tweeter have you tried paralleling a cap with the resistor say around 2mfd with the tweeter?
This will raise the high end a little by lowering the frequencies above tweeter resonance.
It will take some trial and error and may not give the desired results.

No resistor, just a single .68uF cap.