Altec N1209-8A Network

[Alien_Shore]

I've noticed that there isn't a schematic online for the N1209-8A network.
It's essentially the same as the N1201 that is used in the Model 19's, but it has some differences, the main being a zobel added.
I'm in the process of refurbing my 1209s so I figured I'd contribute to the collective by putting a schematic up.

Here's a picture that is quite helpful for starters. I salvaged this off of audio heritage, and made a couple of updates:


And then here's the schematic I've drawn up. I numbered the components to match the old picture:

[Altec Best]

Nice Work ! Thank You for your contribution ! What program did you use to draw up the diagram ? The layout looks the same as the 1201/M19 Crossover except for the zobel.But all the values seem to be different so not really the same.Interested to know the readings of the coils when you get them.

Very,Very Nice Thanks Again ! We want to put all the schematics in one place for easy retrieval.

[Alien_Shore]

Finally getting around to refurb on my 1209s, so I yanked out the coils and measured them.
The schematic now is updated with the values. These measurements are only the averages from one unit that I've worked on so far. Will continue to perform tests on the other three I have and then update again if the average values move as the sample size increases.

I can tell from these values that I still have a lot to learn about these filters. They're pretty complicated. At first, I thought that L2 and C2 were essentially the 2nd order low pass, and that L3/C3 were the 2nd order high pass, but it's not that simple apparently...

[RonSSS]

It would be interesting to power one from a nice SS amp, load it with 8 ohm resistors and measure the response. Do the same for the 1201 and see what the diff is.
A project I could tackle in the winter.
Ron

[Alien_Shore]

It would be interesting to power one from a nice SS amp, load it with 8 ohm resistors and measure the response. Do the same for the 1201 and see what the diff is.
A project I could tackle in the winter.
Ron

Good call - that will be some useful info.
I am waiting for parts to come in from PE, so in the meantime, I re-worked the schematic drawing to make it a bit more intuitive to look at, and added some specs.

[Alien_Shore]

I finished re-furbing my 1209s today. As you'd expect, the sound is better. I'm noticing much clearer definition (particularly in mid bass), and the sound is cleaner (not as muddy) at the crossover point. The horns blend with the woofers better now. All in all, I completely re-wired two of the networks, and checked the inductor values on three units.

I won't bore everyone with another "crossover rebuild" thread, but here are a couple of things that may be of interest.

First, I gutted the network, leaving only the L-Pads and coils (which look and test out fine):


Then, I rewired with all new components:


The parts used (each crossover) were:

(2) MILLS 2 OHM 12W NON-INDUCTIVE RESISTOR
(2) DAYTON 7.5 OHM 10W PRECISION AUDIO GRADE RESISTOR
(1) ERSE 6.0μF 250v PulseX - Metallized Polypropylene Film Capacitor
(1) DAYTON 10.0 UF 250V POLYPROPYLENE CAPACITOR
(2) DAYTON 18.0 UF 250V POLYPROPYLENE CAPACITOR

I also tested all the rest of the inductors. The values posted in the schematic above are pretty much representative of the average across all three of the 1209's that I pulled apart. I tested each inductor five times and took the average of all the tests. Here is a shot of a typical test for L3 (the coil in the high-pass filter section):


Fun project, and the garage is sounding better all the time.

[RonSSS]

Nice work Mike! I love to see folks dig in and make some solder smoke!

I'm watching Tower Of Power's 40 anniversary concert on AXS through the A7's powered by 8 screaming watts of modified Heath W5M PP DHT power.

It jams!

Ron

[aditya]

Many thanks Alien_Shore (Mike) for the posts...
I really like these types of threads.

Congrats

[Altec Best]

That's what I told Mike.They are never boring ! They are all different in some way... Keep those threads a coming guys.

[Alien_Shore]

Tonight I did a bit more focused listening tests of the crossovers.
After a few cold IPAs from the beer fridge, I decided to let the big 816s out for a run.
Man, the old 416a are really, really nice drivers. I push them and those big bass horns just sound so incredibly good.
The 802-8gs on the 511s are another matter. Even with the big L-Pads in these crossovers, it is really hard to tame them down. I think I need to whip out the active XO and play around a bit with some bi-amping and see if it is just mismatching in terms of the wattage, or need to make some changes to the crossover itself.

Again, I don't know much about the original intent of the N1209 - it seems more like a general purpose XO for pro sound reinforcement (PA maybe?) And to be fair, I don't have them loaded correctly. The 416a is a 16ohm driver, so I probably need to just start over with some custom XO design for my garage I definitely am thinking that the 816/416 combo is a winner for sure.