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Zenith Allegros: Guts and All

My folks had an Allegro system back in 72 or so, came on a metal rack, eight track tape player, phono and AM/FM. The speakers were the 3000's I think. I thought the whole thing sounded great! Of course I was maybe 10 at the time..... I remember it had a series of red and green lights that would light up with the beat of the music, very "1970's".
 
grateful said:
I have a pair of the 3000s and I have to go against the groupthink here. I find them to be boomy in the bass with horrible honky midrange and no real high end. They sound sort of like jukebox speakers to me. I can't see why anyone would waste their time on them when there are so many superior cheap vintage speakers made by Advent, AR, EPI etc.
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I agree. I wouldn't even pick up a free pair from CL if they were down the street. They usually violate 2 of my rules for speakers: can't remove the grill, or it has its own wire or RCA jack.
 
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The 3000's were the set I had and I was surprised how many other speakers they booted to the curb using a Pioneer SX-750. Still not sure if it was the paper pleated woofer or the Foster Horn that made these sound good but I did reuse the horn in my first speaker building project.

The woofers varied and mine had the Carbonneau woofer.
The codes on the woofers were:

Carbonneau - 719 (square Alnico magnet)
Rola - 285 (huge round magnet)
Mcgregor - 789
Zenith - 343
 
I picked a pair of Zenith Allegro 3000's out of a recycling trailer. They are a little beat up and I got the grills off far enough to see that the speakers were in good condition. (with a mechanic's mirror)
These sound great and to me the louder they are the better they sound.
I think I will cut the grills off to see everything and then use velcro to reattach them.

Mark

 
So I went and cut the grills off with my utility knife and this is what I found.
The grills are now held on in place with velcro.
The Allegro emblem is spring loaded and if you pull it out you can change it's position.



I tried to unscrew the woofer and of course there are nuts on the buck so now I need to get the back of the speaker cabinet off which is glued and stapled.
No easy task. I ended up cutting the backs and then chiselling the edges off that were glued and this is what I found inside.
The cabinet is made out of MDF but the front and back are plywood.
I will have to make new backs as the old ones are junk now but I'm not sure what I am going to do with the cabinets. They are in rough shape and I am contemplating either making new cabinets myself or having my Dad make the cabinets (he has all the woodworking equipment to do that and also is retired)

Mark



 
If it's not too much trouble, could you measure those cabinets?

I have the drivers (tossed the cabinets years ago) and am looking at building some decent cabs. I don't know that I'll use exactly those dimensions (need to consult with Mr Thiele and Small on that) but it would be good to know as a starting point.

Thinking of going with an aperiodic vent...
 
The cabinets are 24 3/4" tall by 15 1/2" wide and 10" deep.

The woofer center is in the middle of the speaker cabinet for width and 9 1/4" center from the bottom of the cabinet

The tweeter center is 5 5/8" from the left hand side of the cabinet and 7 1/2" from the top.

The square hole for the vent is 2 5/8" from the right hand side of the cabinet and 2 7/8"from the top of the cabinet. These two measurements are for the side and top of the square hole, not the center like I did with the speakers.

Hope this helps and I wouldn't mind reading up on some information about speaker enclosures and the sizes and effects either.

Mark
 
I think the Allegros were designed using Thiele/Small parameters (and Ken Kantor may object to my use of the term, but I've forgotten what the more accurate term is -- small signal something), so I think that probably the easiest path to a nice sounding speaker is to replicate what was the original size. Stouter enclosures or bracing might be an improvement, as might damping of some sort, but probably the size is pretty optimal.
 
Wolfe64 said:
The cabinets are 24 3/4" tall by 15 1/2" wide and 10" deep.

The woofer center is in the middle of the speaker cabinet for width and 9 1/4" center from the bottom of the cabinet

The tweeter center is 5 5/8" from the left hand side of the cabinet and 7 1/2" from the top.

The square hole for the vent is 2 5/8" from the right hand side of the cabinet and 2 7/8"from the top of the cabinet. These two measurements are for the side and top of the square hole, not the center like I did with the speakers.

Hope this helps and I wouldn't mind reading up on some information about speaker enclosures and the sizes and effects either.

Mark
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Thanks! This will be a good staring point. As I said, I'm investigation aperiodic venting which will alter the enclosure size a bit. Also I'm not so concerned about efficiency (the original design assumed a ~15 WPC amp) as I have many 100+ wpc amps around, so compromises can be made there also.
 
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Bose Interaudio 4000 and Infinity SM100 cabinets are roughly the same size as the original Allegro.
I found a set of JVC cabinets and changed the woofer to a Goldwood GW-10PC-8
Those Foster horns are still singing... oh, and I still have the WEDGE console these came with.

 
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Do the drivers handle enough power to survive a switch to lower efficiency/higher power at the volumes you favor? I suppose there is one way to find out...
 
The orginal woofers lasted years using a 50 w.p.c. Pioneer SX-750 and I drove them harder than I should have on many occasions. The woofers finally bit the dust when I was testing a Sansui AU-D11 (120 w.p.c.) and got a little carried away.

The horns need something rolled off on the top end to avoid fatigue. The SX-750 was the best match I found. The Kenwood KA-9100 was also a good solid state match followed by the Scott 233 tube integrated. Switching to tubes it lost the bottom end and the bass seemed slow. :thmbsp:

I finally hooked these up to a Harman Kardon 730 twin and I plan on keeping this setup.
 
Nat said:
Do the drivers handle enough power to survive a switch to lower efficiency/higher power at the volumes you favor? I suppose there is one way to find out...
Click to expand...

I don't play music at high SPL, and I've never blown a driver of any sort in 40 years of messing with this stuff. I obey the 'if it sounds bad, turn it down' law.

So far, so good.
 
i have a pair of 4000's that i picked up recently. I will add pics to this thread for information purposes. They sound similar (not the exact same but similar) to my HPM's.
 
here you go...i still have to get the vacuum on the woofer. One day i will open them up to compare the woofer and mid to the pioneer units..
allegro.JPG allegro2.JPG allegro3.JPG
 
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