Question regarding the 16 ohm 1500 HZ Mastering Labs Xover

[mogsailor]

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

[GM]

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 - - -

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.

[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.

[mogsailor]

@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

[Phil-G]

And hopfully this may help someone else.