Altec A7 Refurbishment

[vottnut]

I am getting closer to finishing my Altec A7 refurbishment. This has been a 2 year project (on and off, mostly off).This pair of A7 was strip of its paint, re-braced both the lower woofer horn panel and bottom panels with 1 x 3 lumber. Two coats of primer follow by two coats of grey #5. The exteriors were finished off with new decals and stencils for the front panels. Both speakers were dampen with Ultra Touch Blue Denim insulation. I have some questions for my fellow Lansing enthuses. Should I do anything to the cross over units? They seem to be fairly clean. I hear folks talk about upgrading or changing the capacitors. There are suppose to be 2 pairs of capacitors per cross over, but I see only one pair in each. If so what are the cost? Where should I look? Parts-Express maybe, any part numbers anyone can help with? I also hear talk about changing the wire size and adding a felt pad on the inside cover of the HF driver. What should the ohm reading be for the HF and LF drivers? Where can I get a copy of the cross over specs?

I have added my Imgur link to share my progress. Altec A7 Refurbishing - Album on Imgur

Thank you all for your time,

[TerribleT]

Hi,
Congrats on your restoration. If possible, could you post some pictures of your cabinet bracing? I have a pair of 825 cabs in the garage waiting to be restored and I need ideas on how to tame some of their resonant behavior.
Regards,
David

[GM]

Should I do anything to the cross over units? They seem to be fairly clean. I hear folks talk about upgrading or changing the capacitors. There are suppose to be 2 pairs of capacitors per cross over, but I see only one pair in each. If so what are the cost? Where should I look? Parts-Express maybe, any part numbers anyone can help with? I also hear talk about changing the wire size and adding a felt pad on the inside cover of the HF driver. What should the ohm reading be for the HF and LF drivers?

Looking good!


First things first!


Your horns are 811/800 Hz, but your XO's are N501-8A/500 Hz for the 511 or other horns rated for 500 Hz, so best to not hook them up, even at low power! You can gut them and convert to N801-8A/800 Hz, though of course you can swap horns or XOs: https://i.pinimg.com/236x/4f/4c/60/4...stuff-kool.jpg


N501-8A schematic: Dropbox - Altec Pro Crossover Networks - Simplify your life

Better though to use one of the 'upgraded' XOs such as the M19's N1201or XO and best to use prosound/studio grade DSP for XOs, EQ, TD.


Without proper testing, generally best to upgrade caps this old, preferably to PIO if driven with tube gear. These are 'textbook' 2nd order Butterworth XOs, so one cap/driver and nothing special, so wherever caps are sold. No clue who's cheapest nowadays, probably Newark or similar if local.


PIO are relatively rare/expensive in small sizes such as Jensen, so likely will only be sold at high end boutique emporiums or can use big 'el cheapo' motor run caps outboard of the XO housing like the pioneers did.


Re wire size/type selection: there's so much misinformation/BS, you name it out in the 'wild' that all I'll say is that Altec followed good engineering practice, so if original, only need to replace with like if corroded and/or has any poor connections where audible changes can be heard.


Felt on the inside of the compression driver's rear cover is only required if there's no black bakelite loading cap sealing off the diaphragm.


Altec 8 ohm drivers over the decades range from ~6.5-7.5 ohms.


GM

[vottnut]

Thanks GM for all the fine pointers. I looked at the N1200-8A on GPA website. That will be my best option if I am going run the A7 straight but I also was considering going to run biamp. How do most people run biamp? Do they run a separate amp directly to the woofer as is or are there 2 way XO unit that is build for biamp option where the LF side and the HF of the XO unit can be split with the selection of the binding post.

[GM]

You're welcome! Some folks run the woofer wide open, so may want to try it, otherwise just split a standard XO, adding terminals for the woofer amp or use a separate bi-amp terminal cup with isolation straps: bi-amp terminal cup - Parts Express Ships Fast and Ships Free.

Don't recall any Altec bi-amp XO, just the poor performing integrated amp/XO for HF, LF: http://www.lansingheritage.org/image...-mi/page12.jpg

GM

[gearfreak]

Do they run a separate amp directly to the woofer as is or...

For 2 way stereo with selectable Xo freq and indep. channel levels, Altec 9442/4 A or SA amps, with Altec or EV Octal plug-in modules could be used.

e.g.



2x 9442/4 + 2x EV APX Octal crossovers

or

1x 9442/4 + 2x EV APX2 Octal crossovers + your HF amp


APX/APX2 selectable frequencies in your ballpark:
...
0500 hz
0630 hz
0800 hz
1000 hz
1250 hz
1600 hz
2000 hz
2500 hz
3150 hz
...


or subbing EV CX-1 (CX1) for APX2, :
0500 hz
0800 hz
('or user determined values')


AMCX1 appears to be the same thing, but YMMV.
See also Altec 15581A if you like.


Of course there's many ways to go 'active', but the Altec + Octal solution is flexible enough, and keeps it simple IMO.

Caveat Emptor wiring your drivers up directly, reading up on HF channel bypass caps etc. is prudent. I don't use them atm.

[Old Guy]

You're welcome! Some folks run the woofer wide open, so may want to try it, otherwise just split a standard XO, adding terminals for the woofer amp or use a separate bi-amp terminal cup with isolation straps: bi-amp terminal cup - Parts Express Ships Fast and Ships Free.

Don't recall any Altec bi-amp XO, just the poor performing integrated amp/XO for HF, LF: http://www.lansingheritage.org/image...-mi/page12.jpg

GM

Altec Lansing Model 1632A Electronic Crossover | #137131366

[FriendlyVolcano]

I bi-amp my A7/500s using a MiniDSP 2x4HD as the crossover. (McIntosh MC60s on top and McIntosh MC250 on bottom.) I put a protection resistor on the HF driver to limit any potential damage. I know the MiniDSP isn't analog, but it allows for any crossover point and parametric EQ, so I'm less concerned with analog purity than taming these beasts for the room they're in.

[Voice_of_the_Llama]

I'm a little late to the party but I'll chip in some experience. My primary music system has braced+tightened up A7's with 416A's/802C's/511B's and I've experimented with a multitude of different active and passive crossovers, and amp/bi-amp configurations over the years. The zenith was to use a slightly modified version of Jean Hiraga's A5 networks, with level controls on the HF output and the notch filter, and to drive the speakers with PIO capped MC30's. This configuration presents the most convincing timbre and biggest soundstage of anything I've tried.

FWIW every DSP/active crossover device I tested (miniDSP and others) sucked the realism out of any music I piped through, probably due to the A-D-A conversion process.