A7-500

[SD-50]

Hello All
Been sitting here on the sidelines for a year or two enjoying all the friendly ******r on all things Altec. Well the time has come for me to ask for some help in up grading the x-overs on a pair of A7s that I picked up at a garage this summer. While they sound mighty impressive, i've had a nagging suspion that I'm not geeting the full benifit of the A7s because the x-over is not from Altec. The proper x-over was stolen some time ago from the previous owner and replaced with one from Macauley sound.
What I need is a modern/updated x-over for the drivers, 416-A, 808. Can anyone help me with this project, schematics most welcomed.
Cheers

[bfish]

The original Altec XOs for A7-500 ( with 16 ohm 416A and 802D on 511 horn) were the N500D, E, and G. Later versions of the A7-500 using 8 ohm components (416-8A and 808-8A on 511 horn) used a N501-8A. These XOs are commonly available on eBay at resonable prices, and perform very well with no modification. As in our earlier discussion, just make sure all your components are either 8 ohms, or all 16. The 802 and 808 are equivalent drivers, and both can be fitted with either 8 or 16 ohm diaphragms as desired, regardless of model number (the only difference originally was the use of different diaphragms.) To be sure what you have, either check the diaphragm part number, or measure with an ohmmeter, 8 ohm units read around 6 ohms DCR, while 16s measure around 11 ohms.

Also, make sure you have 511 horns, which XO at 500hz, and work with the above-mentioned XOs. If you have the smaller 811 horns, you'll need to XO at 800hz, and use an N800D-G (16 ohms) or N801-8A (8 ohms).

Clear as mud?

[SD-50]

Thanks bfish, I have the 416-8A with 808-8A /511 horn combo. There's a bit of shout in the mid-range that should be correctable with a tweaked x-over. What I want to do is create an updated version of the x-over with Solen inductors, oil caps with either Caddock or Vishay resistors that address some of the problems with the stock x-over.
I know some people think its crazy to pay $6 or more bucks for a single resistor, but I'm willing to spend to get the best out of the drivers.
Thanks, Gus

[bfish]

I'm the wrong guy for XO design, but there are others here that are plenty capable. While I firmly believe in quality components in all respects, I do feel many have been over-rated as having magical properties which just ain't so. Classics became such because they excelled, as-is. Without advocating "blind faith", I really don't think you'll outdo a pair of N501-8As for your app., but if you do, please share the results with the rest of us.

A low-cost possible solution for the "shout" you refer to, is to remove and discard the plastic loading caps from the diaphragms, and add a 1/4-inch-thick, self adhesive felt pad to cover the inside rear of the 808s rear covers. (You can find the felt padding in 4"x6" sheets at **gasp** W--Mart, near the furniture glides). Just be careful on reassembly that nothing contacts the exposed dome.

Also, the 511 is notorious for resonances, or "ringing" at certain frequencies, which can have a similar effect. Search previous threads for many methods of damping the 511 to cure it. The factory solution was to cut through the center welds of the sectoral "fins", leaving an 1/8" gap that was filled with rubberized adhesive. No crossover design will cure this, or for that matter, the previous item.

If your current XOs don't have a HF attenuator (the N501-8As do), you might also experiment with adding some series R to the HF side to tone it down a little.

[bfish]

A quick pass through the Mccauley site bought to light that most, if not all of their crossovers are designed for 4 or 8 ohm LF, and 16 ohm HF drivers, and (as all well-designed XOs), are tailored to THEIR drivers....soooo......

If you're running an 8 ohm HF driver on a 16 ohm XO branch, your 808s will effectively produce DOUBLE their intended output.....very shouty indeed!

Also, the Mc units I checked had an XO point of 1Khz, or 1.2Khz, which could cause problems with a 416 in the LF horn.

If such is the case in your situation, and you're judging your A7-500 performance based on this, you're in for a MAJOR (but pleasant) surprise, by simply using the right XO for the app.

[bfish]

If you're interested in trying a pair of N501-8As, and will pay the freight both ways, I'll loan you a pair for a week or two, but it would be only a loan, as I'll need them in the near future. Email me the details if you're interested, shipping from and to 72714.

If you accept my offer, but don't return them promptly,......let's just say a hillbilly fueled by anger and corn liquor, and bent on vengeance is NOT a pretty thing to find on your doorstep.....

[dgwojo]

Bfish, that's a nice offer for him but he's up in the Great White North, you know, that country north of the USA!! It'd cost a fortune in air mailing, tons of time in customs, etc., probably not worth the hassle. My next A7-500-8 pair will be built around a re-capped set of these 18/12db crossovers from Eminence, the 1600hz versions work excellent with my 604's, I'll report back how they sound in the future, Dave.
EMINENCE pxb2-500 2-WAY CROSSOVER BOARD 500 Hz

[Carl Bill]

I have a pair of extra 500hz Altec crossovers from A7's that I would sell at a reasonable price. It may be a good place to start even if you plan on upgrading caps. Let me know if you are interested. I will see if I can figure out which box they are in out in the barn!

I am not exactly sure which model, but I do know they are 500hz. If you are interested, I will try and find them and get you the exact model number.

[GM]

Greets!

The stock N501-8A is a textbook Butterworth with 28uF caps/3.6mH inductors. FWIW, the caps in mine are PIO, though I recommend them regardless. That said, after >35 yrs, they need replacing, so unless you just want 'stock looking for any potential increase in re-sale price, I recommend 'rolling your own'. I don't recommend using pots other than for set-up, then replacing the shelving ckt. with fixed value components and a bypass cap to tonally balance it out to at least 16 kHz if a matching impedance amp isn't used. If you go with a stock XO, then wire the bypass cap across the pot if need be.

Assuming these are for a HI-FI app and the 808s still have their stock Symbiotic diaphragms, then swap them out with GP's replacements, and as bfish noted, if a 500 Hz XO is used then finish converting them to 802D spec (which will remove most of the 'shout', with proper shelving/HF bypass correcting virtually all the rest) and damp at least the len's bell modes regardless of the XO used, though of course I recommend all the tweaks me and others have previously posted. The downside to doing them all is that most of the distinctive Altec 'sound' (highly 'colored') gets damped away, so as always YMMV.

WRT using different XO slopes, this is a personal choice as to what sounds best in-room since the horn can be positioned as required to get a decent summation at the XO point.

GM

[bfish]

Originally posted by dgwojo:
Bfish, that's a nice offer for him but he's up in the Great White North, you know, that country north of the USA!! It'd cost a fortune in air mailing, tons of time in customs, etc., probably not worth the hassle. My next A7-500-8 pair will be built around a re-capped set of these 18/12db crossovers from Eminence, the 1600hz versions work excellent with my 604's,

<font size="2" face="Verdana, Helvetica, sans-serif">Great White North, AY (EH)? Whatever happened to those two kooks (or should I say tukes)?

Yeah, Dave, I noticed the loc., but the offer still stands. (I'm a die-hard when it comes to proving a point).

The Em. XOs look great, I've been very pleased with my (limited) experience with their products. The 'finished' models look like they might even fit the cutout made for an Altec XO. It's been a long time since I've seen anyone using incandescants for current-limiting, just proves again some of the old dogs' tricks are still valid. Before I got hold of a cherry Sprague TO-6, I still used the old 60W bulb bulb method to re-form electrolytics.

C.B., where's that barn at?