So I've never seen the inside of one of these old crossovers & decided to open mine up and see what's inside.
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So I've never seen the inside of one of these old crossovers & decided to open mine up and see what's inside.
Well I think I figured out the schematic. I did the drawing as if viewing the crossover's top plastic terminal plate from above. the only marking on my crossover are the "HF", "LF", and "INPUT". The 1,2,3,4 output numbering and B (black) and R (red) input labelling was applied to later crossovers that had the same ternminal layout. So there are 3 L/C components in each signal path which I believe makes this a 3rd order 18db/octave crossover.
The HF part of the network also includes a wire wound resistor network of 3 sections wound on the same flat form that is attached directly to back of the terminals. The short resistor sections at the ends of the form are the ones in series with the HF output, the longer section in the middle connects the junction of the two short sections to ground. It was kind of neat to be able to see the relative resistance values by the length of the windings.
I haven't seen capacitors like these before, rectangular about 1 inch x 4 inches x 5/8 inch thick, about the size of a box of staples or a harmonica. They look like they might have been wrapped in green paper before the had that black tar-stuff poured over them. There were (at least) two of them stacked under the input terminals, and one more laying on top of the row of three transformer like inductors under the outpput terminals. The middle inductor was rotated 90 degrees relative to the outer two inductors.
Some of the hookup wire was solid core, and some was stranded all had the old cloth insulation. Connections were wrapped in what looked like plain old paper masking tape, and some of them seemed to pushed into a dollop of tar, presuambly to immobilize them.
Take a look at my crude schematic and ruff drawing of the parts layout, not fancy but I think they tell the story;
Always a pleasure to see some "investigative reporting." Thanks for sharing this perspective, and especially for taking the time to do the drawing.
When I look at the old techniques and parts, I'm amazed that it worked as well as it did, though it's easy to see why it lasted so long.
This is very thoughtfull Glen and thanks for sharing it with us.
I do wish there was more of this info contained in the threads for future posterity.
I am fascinated by how they made this stuff way back and how it worked and now as a collector of Vintage Altecs and builder of clones I find myself constantly searching for info on how to upgrade or make old style XOs with new electronics of today.
Have to wonder how the speakers this XO was intended for would sound today with the upgrades of new Caps and some nice Air Coils installed.
I am trying to find this exact info on the Altec Model 19 XOs or the 1201-8As right now to no avail.
I could show the picture of the 19 XO but don't have the tech skills to disect it as you have.
Nice going!
Gary
Glen,Quote:
Originally Posted by Titanium Dome
Any information of the value / voltage ratings of the capacitors (C1-C3) or are they covered in black tar? I wouldn't be surprised if they needed replacing after 55+ years.
Thanks!
Howe
Glen, thanks so much for your fine work. You have become a tremendous Lansing Heritage resource.
We found photographs in the JBL archives of eight sketchpad drawings and figures that were apparently from Jim Lansing's hand. Three of them involve crossover design. They are up on this site and can be found here:
http://www.audioheritage.org/html/hi...ng/the_man.htm
One of these pages depicts a crossover schematic that is almost identical to your schematic of the N-1000. Could this be the very page on which Jim calculated this crossover? Perhaps someone with crossover design skills or a simulation program can run these numbers to see if they add up to an 18dB/octave crossover for 16 ohm drivers centered at 1,200Hz.
http://www.audioheritage.org/images/jbl/notes/page6.jpg
The N-1000 network is decribed on this Van Nuys era catalog page:
http://www.lansingheritage.org/image...1948/page7.jpg
Yep, they're all covered in tar, only one capacitor that was resting on top of the inductors was moveable and it was also covered in tar except for the corner where the wires emerged, there I could see some faded green paper. The capacitors looked as if they might have been dipped in a separate pot of tar before being placed in the crossover housing.Quote:
Originally Posted by Howe
The inductors were not completely covered in tar, but were set solidly into it in the bottom of the crossover case. They were also pretty closely placed (I gave the parts a little more room in my "x-ray" drawing), so I really couldn't make out any printing on them.
I expect the wire-wound resistor on the flat form was custom made and did not seem to have any printed values I could see.
I wouldn't be surprised either, but I'd probably run a test signal through it (as you planned for your own crossovers) before I started replacing parts. I look forward to seeing the test results of your N1000 and N1200 in your restoration thread. If you do have to replace some parts please take lots of pictures!Quote:
Originally Posted by Howe
Wow Steve you nailed it!Quote:
Originally Posted by Steve Schell
That schematic at the top of page6 IS the same as the one I drew, mine was just a slightly diffferent arrangement.
Thanks also for your kind words, I'll try to live up to them.