Altec N-1600-A crossover schematic.

**jmarkwart** · December 16th, 2012, 08:36 PM

Originally Posted by 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?

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** · December 19th, 2012, 06:28 PM

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** · December 19th, 2012, 07:57 PM

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

**cradeldorf** · December 22nd, 2012, 02:59 AM

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** · December 22nd, 2012, 03:41 AM

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.

**cradeldorf** · December 22nd, 2012, 06:31 PM

The High frequency wasn't lacking, it was more of a mid frequency honk/sharpness. At 5 am I had the cabs open and was adding carpet to the back side of the baffle, It cured what I was after, the sharpness disappeared. I used that thin black stuff that's on the walls. I also put it across the ports and replaced that saggy cloth that was on there. It is very porous and doesn't appear to have altered the ability of the port to do it's job.

**cradeldorf** · December 22nd, 2012, 07:24 PM

Originally Posted by 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.

They sound like this. This is before adding the carpet to the back side of the baffle.
DSCN6256_WMV V9 | Flickr - Photo Sharing!

**cradeldorf** · December 26th, 2012, 07:16 PM

Listening to my speakers last night and I could swear I heard the HF dropping out on the right side. So I removed the cover and checked everything. Found that the lead in wire where it was connected to the loop for the phram screw was hanging on by 3 strands. That made them sound a little better. Also realized that without the loading caps, the screws I was using were steel where the original ones won't stick to a magnet. so I put the loading caps back in. They must be stainless or something. Not sure if that was affecting their operation but I feel better about it now.