Question regarding the 16 ohm 1500 HZ Mastering Labs Xover

I asked this question over a year ago on a different forum but it was never answered so I'll ask it here:

I have a pair of these which apparently were originally used in the "Super Red" version of the "Big Red" monitor. Why do I think this? In addition to the 4 connections required for hookup to the 604E driver, it has another pair of connectors. My guess is that these extra two connectors were for the supplementary 15" woofer in the bottom of the "Super Red" cabinet. However, they don't connect into the crossover circuitry at the same locations as the primary woofer connector leading to the 604 driver's LF section. Perhaps the two EQ adjusting controls do not affect the lower woofer.

I have one unit installed and I'm listening to it now. The extra connections are unterminated - simply unconnected and separated from each other. The speaker sounds fine to me.

My question is: Is it electrically safe to simply ignore this extra connection and not connect it? Or, should a resistor be connected across the connectors to simulate a speaker load?

Thanks in advance for any answers or advice!

Best to all you Altec enthusiasts out there!

Fred

is there any marks by the terminals?

Quote:

---

Originally Posted by mogsailor

I asked this question over a year ago on a different forum but it was never answered so I'll ask it here:

I have a pair of these which apparently were originally used in the "Super Red" version of the "Big Red" monitor. Why do I think this? In addition to the 4 connections required for hookup to the 604E driver, it has another pair of connectors. My guess is that these extra two connectors were for the supplementary 15" woofer in the bottom of the "Super Red" cabinet. However, they don't connect into the crossover circuitry at the same locations as the primary woofer connector leading to the 604 driver's LF section. Perhaps the two EQ adjusting controls do not affect the lower woofer.

I have one unit installed and I'm listening to it now. The extra connections are unterminated - simply unconnected and separated from each other. The speaker sounds fine to me.

My question is: Is it electrically safe to simply ignore this extra connection and not connect it? Or, should a resistor be connected across the connectors to simulate a speaker load?

Thanks in advance for any answers or advice!

Best to all you Altec enthusiasts out there!

Fred

---

Quote:

---

Originally Posted by Phil-G

is there any marks by the terminals?

---

Hi Phil,

No markings for these extra wires.

They look like part of the original crossover in that they are similar to the 4 primary wires leading to the 604E driver itself. They even are sheathed with the same grey tubing as the primary wires. It's my opinion that the crossovers were originally constructed this way. It's also my opinion that they were, at some point, original equipment on a Super Red speaker
system.

My question is, how to I deal with these extra wires since, in my system, they are not used? What I have done is to protect the bare ends with tape, coil this separate "harness", and secure it with plastic ties.

My other question is, since they are unterminated, what, if any, are the electrical implications? The crossovers seem to operate just fine judged simply by listening.

Thanks for answering,

Fred

Forgot to say - the extra wires are color coded, black & red. The main harness includes red, green, white, and black wires, which match the diagram on the case.

Did you try to see if the Black wires are common? Likewise the Red wires?

Good question.

I didn't test with a meter but when I opened the case, I did notice that the leads for the 2nd woofer did not terminate at the same locations in the circuit as the leads to the main woofer of the 604E. There is no chassis used in this unit which uses a plastic (or Bakelite) case, so the grounding is sort of a bus type with all ground wires leading to it.

Unfortunately, the schematic I have for the ML Xovers does not show this later modification as used in the Super Red version of the monitor.

Perhaps an owner and current user of a Super Red system might have already looked into this and notice this thread.

I'm confident that using not these extra leads will not hurt anything but there are much better heads on this site than mine. Perhaps there is an impedance issue here.

Fred

Quote:

---

Originally Posted by mogsailor

Perhaps an owner and current user of a Super Red system might have already looked into this and notice this thread.

I'm confident that using not these extra leads will not hurt anything but there are much better heads on this site than mine. Perhaps there is an impedance issue here.

Fred

---

I know there's at least one person on this site that has a super red or knows the crossover.
have you tried the search Altec user board.

https://www.hostboard.com/forums/f70...+Red+crossover

No, Phil, I haven't done such a search. I'm an old guy somewhat new in the forum world. I've looked for a long time but rarely participated.

I'll try a search as you suggest.

Tks, Fred

604e UREI horn mod?

Phil, for the life of me, I have no idea where that came from or how it got into my reply!

I told you I was an old guy but hopefully not yet senile. :confused:

Pretty sure you're right, but if you have an otherwise complete schematic (trace it to be sure), then trace/add these extra wires and post it. :)

Good afternoon, GM,

With your extensive background with Altec pro gear, I would guess that you must have seen inside a ML crossover. A lot of stuff packed into a smallish case with most of the space being occupied by three immense air-core inductors and the 2 large variable resistors used in the HF and MF circuits. Sorta hard to tell what is what. Also seems to violate a lot of "rules" for inductor placement in a circuit! :)

However, your advice is good as always and of course, logical. I have the schematic and will do as you suggest the next time I have the crossovers out of service - I'm listening to them now.

I also have two other crossover pairs, the OEM N-1500As which are like new, and another pair that I built from a schematic that Bill H. at GPA kindly sent me. These were designed by his friend, Jerry Hubbard, who was a acoustics engineer at Altec back in the day. I will no doubt be swapping in my DIY pair sometime soon.

Thanks, Fred

Quote:

---

Originally Posted by mogsailor

604e UREI horn mod?

Phil, for the life of me, I have no idea where that came from or how it got into my reply!

I told you I was an old guy but hopefully not yet senile. :confused:

---

I found the UREI Horn mod in the search. A couple pages in they had something about the Big Red crossover Schematics. truth be told i really didn't read very far into it. but they were comparing the two.
i figured if we kept the post live long enough one of the big hitters would eventually check in with pertinent info. :)

Quote:

---

Originally Posted by mogsailor

With your extensive background with Altec pro gear, I would guess that you must have seen inside a ML crossover.

---

Greets!

Actually, IIRC, no, just a copy of it someone I designed some huge studio monitors sent along with some other info, which sadly is locked up in two damaged HDs along with lots of other Altec info either no longer on the net or never uploaded TTBOMK and for a variety of reasons wasn't even aware of the 'Red' monitor series till I got online in '96.

- - - Updated - - -

Quote:

---

Originally Posted by mogsailor

604e UREI horn mod?

---

This brings back frustrating memories! During my high school years I was nearly daily seduced by an A6 minus riser, so later on every time there were rumors of upgrades, new 604 designs, me n' some other locals would be 'campaigning like Southern Diplomats' to go back to the original big horn or at least a WG variant, but never happened during my active Altec based DIY audio 'career', again only learning about Urei when I got online.

@mogsailor

RE; LF termination

If that "helper-woofer" circuit only has a single inline ( series ) inductor-coil on it > then you're good-to-go with leaving it un-terminated.

OTOH, if there's a capacitor following the inductor placed across the two wires then you should terminate those two wires with something like a 40 watt resistive load .
- I think the helper woofer was actually 4 ohms to help keep-up with the rest of the system > therefore 4 paralleled 16ohm ( 10 watt ) resistors would fit the bill.

:)

Quote:

---

Originally Posted by Earl K

@mogsailor

RE; LF termination

If that "helper-woofer" circuit only has a single inline ( series ) inductor-coil on it > then you're good-to-go with leaving it un-terminated.

OTOH, if there's a capacitor following the inductor placed across the two wires then you should terminate those two wires with something like a 40 watt resistive load .
- I think the helper woofer was actually 4 ohms to help keep-up with the rest of the system > therefore 4 paralleled 16ohm ( 10 watt ) resistors would fit the bill.

:)

---

Thank you Earl K. That seems like an excellent recommendation.

I have another pair of speakers on the way so, quite soon I'll be pulling these 604Es out of the system for a while. This will allow me to take one of my Mastering Labs Xovers out of its case and see for certain where these extra woofer leads originate in the circuit. Once I do that, I'll scan the ML schematic and add the extra leads in a contrasting color or linestyle. Then perhaps I can send it here for analysis to make sure I'm correct. Then this revised schematic could be somehow put in an archive along with the older one-woofer version.

I can't be the only person who has this later version of the ML Xover. I believe Urei developed their own phase coherent Xover for their 2-woofer monitor. So, maybe, not many of the Altec/Audio Techniques Super Red monitors were made and I would hope that those that still exist, remain whole.

Thanks again,

Fred

And hopfully this may help someone else. :)