Altec 604c crossovers? bi-amp?


Staff member
Very nice, welcome to the Duplex club!

I’ve got a pair of 604-8G’s myself that I don’t get to enjoy near as often as I’d like these days.
So after living with the speakers for a couple weeks in inappropriate cabinets with stock crossovers, I think I'm hearing the slight honkiness in the upper mids (in certain saxophone and harmonica parts)

So I think I'll go the bi-amping route. Any suggestions on initial crossover point? These used the n1600a network

also came across these

which won't work for me becaue they are 8 ohms netowrks, but might be of interest to others looking for duplex crossovers
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

Punker X

Junior Member
Jeff says about the E.

Bottom Line
The N-1500A filter is hard to equal, much less beat, when using competing parallel type designs with the 604E. An N-1500A filter with upgraded components and an MF EQ circuit added is probably the most cost effective crossover improvement one can make for this classic duplex.
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: Glow in the Dark Audio - Single Ended EL-84 (RH84 Circuit))

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?


pics of the new cabinet pair below


New Cabs.jpg
Thanks Nate.

actually worked out quite well in that the guy who had them was looking for a pair of EV cabinets for 15trx's so it was an ideal swap


Next Round Is On Me
Yes, great looking and period correct cabinets. Kinda shindo-esque?
I think @mhardy6647 has mastering labs crossovers.
I’ve not tried higher wattage amps but imagine they’d reproduce most notes with greater emphasis. Having a passive pre, it takes some gain out but crank the knob a little higher and wow! I don’t see the need for more than 3-8 watts.