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Altec 604c crossovers?

zim bida

zim bida

AK Subscriber
Subscriber
Hi Everyone,

so it looks like I have stumbled into a pair of Altec 604c's with Altec N-1600A crossovers, and I'm over the moon about my luck. Since I got the first one I have been reading everywhere about how best to hear what these drivers have to deliver. My plan at the moment is to put them into EV Empire cabinets which are available locally until I get the ability to build a pair of "Billfort" cabinets or similar (and am able to fit such into my place).

So from what I am able to gather from reading, 604's are markedly improved by updating the crossover, a la Jeff Markwart designs. I've done a huge amount of reading (My eyes are a little "crossed over"), and maybe have missed something - but it seems all the designs I have found are for other variants of the 604, and not the C - I found one experience suggesting that using the published plans for the B with the MF EQ was successful with the 604C.

I exchanged a couple emails with Jeff Markwart, who was kind enough to take an out of the blue cry for help from a complete stranger, but he suggested that he didn't think the B crossover he suggested would work as laid out in his plans, he pointed out "While the acoustic centers of the B and C are in same locations, the differences of the horns and woofer responses of a B and C are enough that a B crossover would not be optimized for a C. Close, yes, but not optimized. You probably would be able to detect an audible difference between them. It really would take a bit more engineering and listening to know"

I do know that Werner Jagusch does offer Autoformer Crossovers for the 604c on ebay, but those are honestly somewhat out of my budget at the moment

this is all complicated by the fact that I am not that technical a guy - OK, all honesty, not technical at all, and would be relying on someone else to build me such a crossover, as long as I can find things like a schematic, parts suggestions etc.

Can anyone point me in the right direction?

Thanks!
 
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I don't know what you have access to, but if you have 2 stereo amps, an electronic crossover could help you determine crossover frequency and slope.
 
Thanks, don't have access to an electronic crossover, but am exploring that possibility
 
zim bida said:
Thanks, don't have access to an electronic crossover, but am exploring that possibility
Click to expand...

Even the cheap DBX are pretty good. The other thing you could do is upgrade components in the N-1600A. It isn't difficult and can be done incrementally so you can hear (or not hear, depending) the differences. I have done this exact thing with Altec N-501-8b's and have been very pleased with the results. Things like using oil-filled motor-run capacitors and upgrading the inductors.
 
Hello zim,

If those were mine I would first listen to them as they are.

I believe the initial limitation that you'll encounter is the somewhat under-sized cabinets you intend to use ( since just about everyone concurs that around 9 cu' is the minimum size for adequate bass reproduction from any 604 model ).

The stock crossovers are simplistic enough that you could easily rebuild them with new parts for an economical price.

N1600_caps_Cradeldorf_.jpg N1600_Cradedorf_.jpg N1600-guts_Cradeldorf_.jpg

It would be easy enough ( for those so inclined ) to simply replace the 3uF + 16uF caps with some modern MPP types ( say from Jantzen or Audyn ) for a change up in sound.
( MPP = "metallized polypropylene" )

I'm sure I've read that Werner Jagusch offers for sale, custom Autoformers. So you may want to eventually buy a pair of his coils ( say with 6, x 1db tap increments ) once you confirm ( from some other sources ) if the overall inductance of the coil is actually .92 mH.

:)

BTW; I'm confident that Cradeldorf was in error in his quoted inductance figure ( made between the -4db tap out and what he deemed the "postive" connection of the coil ).

I think he has one decimal place too many ( iow; .057mH should have been .57mH )

The following chart offers some guidance for deriving the correct mH figure );
- simply multiply .92mH by .398 and then subtract the answer from .92mH .

attachment.php
 
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Hi Earl , thanks for the quite sensible advice and the correction on the figures... I often, in these matters, have a tendency to get ahead of myself
 
Hi, in the interests of posterity - in case anyone comes across this thread looking for info on 604C crossovers - I spoke to Bill from Great Plains at AXPONA and he was of the opionion that for all but the earliest 604C's, Jeff Markwart's 604E crossover designs are appopriate
 
Hi there folks,

so quite some time back I asked about crossovers for my 604C's and received a lot of helpful information. I postponed the decision however, until I was able to source cabinets more fitting for their needs. It took me a while but I was able to find a pair of homemade cabinets that once housed a pair of 604B Hollywoods and I swapped out my EV Regency cabs for these (and noticed an immediate improvement without any further fiddling and with the stock crossovers).

Now I'm returning to the idea of improved crossovers vs bi-amping these guys. While I was waiting on the right cabinet, amp possibilities have been piling up and I've got a number of them in various states of restoration. I also picked up a Mini-DSP unit as well as a Rane ACS-22 analog unit that has the ability to time delay. I can also acquire a set of mastering lab crossovers for a price at which I'm comfortable with. The amp possibilities (for either full range with mastering labs, or as part of a biamp solution) are:

Dynaco Mk III mono blocks (6550 tubes)
Ampex EL34 mono blocks
Heathkit AA-40 EL34 amp
Akai SEP el84 mono blocks from an M8 Reel to Reel
Pilot SA-232 EL84
Grundig NF2 el84
build an RH-el84 amp with parts from a Sony tc-500 Reel to Reel (as described here: http://glowinthedarkaudio.com/RH-EL84.html)

Preamp will be a re-capped/restored Scott 355

I know that the ideal process would be to listen to all the possibilities, however only the Dynaco's are currently up and running and the mastering labs crossover is only at the point a possibility and not in my possession

Do folks have any recommendation about if I am better off with the mastering labs crossover and one of these amps or using a pair in a bi-amp situation with active crossover and if so which amps would you choose use in such a setup?

also, as you can probably tell from that list of amps, I enjoy trying out various amplifiers, if I do go to a biamp situation, have folks made some sort of outboard solution so that I could switch between bi-amping and single amping the speakers so that I can play with the amps full range without resorting to opening up cabinets each time?

thanks

picturesof the new cabinet pair below

New Cabs.jpg

380004bb3fae3bab85587d3b3d24bd85281dea49-2.jpg
 
I have a similar story when I found my 604E on a yardsale very cheap I was looking for a long time and explored all possible variants on how to build an XO. I found a lot that was useful but it turned out that the xo that I wanted to build would cost as much as a pair of Jagusch. After a year of listening, I start to wonder if there is no more getting out of these elements but it is a feeling.

Good luck with your build, I'm curious about your new boxes to tell us a little about them.
 
K.A.B said:
I I'm curious about your new boxes to tell us a little about them.
Click to expand...

In asking around about these, it seems that these are built using jensen ultraflex designs, which I also just learned were the basis for onken cabinets.

I should stress that I am enjoying them as is (which I'm not sure from your comments, you were?) and maybe am stressing too much too get the last 1% improvement.
 
Having a cabinet sort of in a corner and one that is not is totally wrong, Can you rotate your system to get two identical corners? Your worry about your crossovers is a very minor issue compared to your speaker placements.
 
yeah, I'm aware. But....I live where I live

Not a lot of options on speaker placement, especially large speaker placement
 
You just need a false wall next to that left one, wouldn't have to be much bigger than the side of the speaker I should think. Something portable that stands on its own base. :idea:

Funny about the series crossover, I swear that came up in another thread just this morning...what is it, National Impossible But It Works, Series Crossover Week?
 
zim bida said:
In asking around about these, it seems that these are built using jensen ultraflex designs, which I also just learned were the basis for onken cabinets.

I should stress that I am enjoying them as is (which I'm not sure from your comments, you were?) and maybe am stressing too much too get the last 1% improvement.
Click to expand...

Yes i use mine 604E almost daily, but to get more out of them i have to build new boxes but i am not sure what i want build not stress to an deciding when it is as expensive to build something that you will not be satisfied with as succeed therefore I hasten slowly, but i love them probably I will never replace them and if I did it would be something very special.

Anders
 
My understanding is that the mastering labs XO is for a 604-8G. They may or may not work well with your 604c.

Nice cabinets BTW.
 
My understanding is that mastering labs crossovers were designed around the 604E (this is indicated here: https://www.technicalaudio.com/pdf/Duplex_Speakers_related_to_Altec_604/DUPLEX.html

Given that it seems that the Markwart style crossover would seem to work with all but the earliest 604c (at least according to my conversation with Bill from Great Plains), I would think the same would be true of the Mastering Labs crossover.

But obviously I am not an expert in the area and would love to hear from anyone who might have used the mastering labs
 
Zim,

Have you had a chance to play with the MiniDSP and the 604's yet? If so, how was the result?

I am looking at possibly going that direction with my 604's.

Thanks!
 
Haven't as yet. Only the Dynaco's are up and running at this point, though the aa-40 and the RtR amps should be soon, when those are good to go then I'll have fun trying it.
 
Those new cabinets are kinda cool Zim. And you look like you have them nicely up on some appropriate stands.
At this point I would probably go with a Markwart crossover.
 
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