Altec N-1600-A crossover schematic.

[jmarkwart]

cradledorf,

Thanks for posting the N-1600-A. It's one of the few Altec duplex crossovers I never had the opportunity to open up and examine. It's a series crossover, as you suspected, using first-order filters and taps on the inductor for HF attenuation steps. You could recreate it with mutiple inductors, or substitute a continously variable resistor shelving control instead like the N-1500-A used later on with the 604E.

Jeff

[cradeldorf]

Thanks Jeff, I used the sketch I made as I was dissecting it and the Altec 604E schematic you have on your site to put it all together. Hopefully it helps others because a N-1600-A schematic on the net is pretty much non existent. Since were on the subject, I understand the variable resistor on the "E" crossover (R2) but what purpose does the other resistor have (R1)? Considering the size I would be tempted to assume it's an attempt at a zobel?

[Earl K]

I have no idea, It's a series crossover I think. I don't really get how it works. They used the inductor to attenuate the HF. I was thinking of building a pair but I wouldn't be able to do the taps on the inductors. All I would be able to do is build an un-attenable one. I wonder if I could use another small inductor to imitate the original attenuation or if it wouldn't work because it has to be part of the LF inductor?

- Here's a calculator ( from LHF ) that might help you build your own autotransformer ( though , I've never used it ).

- Ostensibly, your coils should be kept together so that they are working as a single, unified inductor / but the problem with that, is that Mutual Inductance of all the coils together gives a final inductance figure that is larger than the sums ( of the individual coils ) .

- ie; One can't simply add a .75mH coil onto a 2.25mH coil and expect the resulting coils inductance will be 3 mH ( assuming you stack the coils in their proper orientation & that they are wired in series the result will be larger than 3 mH ) .



- Running one example ( to find the winding ratio for the -6 db point ) is; power of 10^(-6/20) = .5012

- Running another ( to find the winding ratio for the -3 db point ) is; power of 10^(-3/20) = .708

[Panomaniac]

It's not a series crossover as far as I can see. Normal 2nd order low pass with variable L on the woofer, 1st order high pass (cap) on the tweeter. Unless I don't understand the drawing. Is the horn connected into the spiral switchy thing?

[rontec]

To me it seems to be a 2nd order (12db slope). The 16uf cap and the .92mh coil are doing double duty.
The 16uf cap is bypassing HF to the tweeter but also shunting HF from the woofer. Same is true of the
.92mh coil. It's shunting LF away from the tweeter and bypassing LF to the woofer.That's how it looks to me
anyway , but I'm sure the experts here will clarify!

[jmarkwart]

Thanks Jeff, I used the sketch I made as I was dissecting it and the Altec 604E schematic you have on your site to put it all together. Hopefully it helps others because a N-1600-A schematic on the net is pretty much non existent. Since were on the subject, I understand the variable resistor on the "E" crossover (R2) but what purpose does the other resistor have (R1)? Considering the size I would be tempted to assume it's an attempt at a zobel?

cradledorf,

You're right about N-1600A references being hard to find on the net.

R1 & R2 on the N-1500A crossover provide a voltage divider to selectively shunt part of the HF energy going to the HF driver. This is a simple type of "tone control" that does not have constant impedance like an L pad attenuator, but is pretty close to the desired impedance when adjusted to the "normal" listening level. When adjusted, it varies from constant impedance a bit more. Simple but effective.

Jeff

[Alien_Shore]

Nice post, Cradeldorf! This is the kind of stuff I like to see. Disect these old pieces of engineering excellence and see what makes them tick. I think in many cases, there are some great things to be learned by studying how Altec did what they did.

[cradeldorf]

It's nice to be able to provide something back to the group. Were all in this together.

[cradeldorf]

This is my final crossover for the 604C's They sound as good as their gonna get I think.
http://www.flickr.com/photos/8281241...in/photostream

[rontec]

I've got to hear a 604 one of these days. If the HF is lacking you could try a 1uf-2uf bypass around your 3 ohm 10w resistor. And if that's not enough increase your 3ohm resistor to 6 ohms. It works for me with 811's/511's but may not apply to 604's , may be too much a different animal.