Mastering Labs xover for 16 ohm Big Reds and driver tune up

Hi guys,

Getting back into audio after a number of years absence and am going to start restoring/dialing in my Big Reds. They are bone stock with M/L xovers on the back. My version uses the 604-16LN, not too common from what I can find. One thing I have noticed is the highs aren't really there as I think they should be, could be my aging ears but there just isn't a lot of sparkle to them. I noticed a little trash on the throat screens..perhaps a cleaning is in order .

I haven't pulled the xovers apart again but I am now wondering about different versions to accommodate the 16 ohm 604. I have only seen one schematic published for the M/L xover and it isn't mentioned what the impedance is. I'll attach the drawing I have and a few pics of the driver.

I haven't ever taken one of these apart, is there anything to watch out for in dismantling the 604? Will I be able to get to the throat screen?

Thanks all, I hope I can get the highs back, after all, they were used as studio monitors for many years.

cheers

PS could someone please confirm if the attached schematic is for the 16 ohm xover? From what I read, I think there WAS just the 16, but want to make sure. thx


Attachment 4393Attachment 4394Attachment 4395Attachment 4396

Greets!

What's a 604-16LN? Only 'oddballs' I've seen are -168x, -16xx.

Quote:

---

Originally Posted by GM

Greets!

What's a 604-16LN? Only 'oddballs' I've seen are -168x, -16xx.

---

Exactly. maybe Low Noise :D

I'm guessing they are old enough to be Alnico, but not sure how to tell without dismantling. Are there any special instructions for taking these apart or do I just start removing screws layer by layer?

Cheers

LN = Less network
HPLN = High Power Less Network

Les Nesman?

Quote:

---

Originally Posted by Phil-G

Les Nesman?

---

I'd rather have Lonnie Nanderson

Quote:

---

Originally Posted by kilohertz

I noticed a little trash on the throat screens..perhaps a cleaning is in order .

I haven't pulled the xovers apart again but I am now wondering about different versions to accommodate the 16R 604. I have only seen one schematic published for the M/L xover and it isn't mentioned what the impedance is. I'll attach the drawing I have and a few pics of the driver.

I haven't ever taken one of these apart, is there anything to watch out for in dismantling the 604? Will I be able to get to the throat screen?

Thanks all, I hope I can get the highs back, after all, they were used as studio monitors for many years.

---

I talked to Bill at GPA about the screens on my 604s, and he said that you would have to remove the horn to get at the screen, this would be very difficult for you do yourself. I would have a go at cleaning them with a long cotton swab and some soapy water or isopropyl alcohol, and then some gentle sucking with a bit of flexible tubing hose inserted into a vacuum hose, so that you only get a fraction of the sucking power of the vacuum and you can throttle it with your hand.

If that doesnt fix your highs, put a multimeter on your 604s and check the resistance. Good to do that anyway.

My bet is maybe one of the parts in the xo is the culprit. Move the wipers on the attenuators back and forth several times to "clean" them. Or better yet, if you can get some deoxit or something on them that would be good. And then put the MM on the various parts of the xo to see if they are all in spec.

- - - Updated - - -

from Altec Big Red Monitors - Page 2

I could say with the absolute confidence that bigger portion of that coil goes toward junction of 20 ohm resistor and 2.3 uF cap. Not vice versa as it was shown in this schematic posted above.

Attachment 4398

Quote:

---

Originally Posted by Phil-G

Les Nesman?

---

Quote:

---

I swear i thought turkeys could fly!

---

;) ...

I was looking at GPA's parts list today for another reason and saw the 604-16LN and 604-16HPLN listed there.

Parts – Great Plains Audio

the 604-LN has the same LF as the 604E

There is no HF listed for it, so maybe it is the same as the 604E - 34852?

Or maybe the HPLN - 35153?

They both have Note 11, "For superior HF reproduction, use original diaphragm. If high power handling is required, and excellent HF frequency response is also needed, use diaphragm #26421 (16 ohms). Call us if you need advice on the proper selection of a diaphragm for your particular application."

I dont understand what "Less Network" would mean in context of this driver? Weren't the crossovers a separate p/n anyway?