bi-amping 604s with passive line-level xovers?

[billfort]

I intend to bi-amp my Altec 604-8Gs with a pair of 300B SET amps. Long term, I will probably go with a Marchand tube cross-over with 12db slopes, 1500hz cross and possibly frequency compensation on the horn. In the short term, I have been thinking of trying passive line-level crossovers with a level pot to pad the horn.

Has anyone tried this? Considering the low power involved, is it safe to try 6db slopes? Am I just wasting my time here and should I just wait till I can pony up for the Marchand?

Thanks, Billfort

[Jim D]

Pony Up. It is very hard to make a good passive line level crossover. First 604s need minimum 12dB/octave slopes. The G has a 12dB LF slope, an 18dB HF slope. To make a passive crossover you must have a known load. This not only includes the loading resistors but also the input inpedance of the amp. This load must be actual, not what is published. An amplifier may drive to full power with a zero dB 600 ohm signal, but often has a much higher input impedance load. Years ago ALTEC made some passive transformer style line level crossovers contained in a can. If you missloaded their inputs or outputs to anything other than 600 ohms, they were less than accurate. I am a firm positive beliver in Multi-amping. Just get the right device fo the job and you will be pleased. Jim

[RonSSS]

I like the thought of line level passive crosovers, but agree with Jim that implementing them would be quite difficult. The inductors being the most difficult part. The statement about needing controlled drive and output impedances is right on.
I built op-amp based 24db/oct crosovers for my 904's, and was disappointed with the results. The sound just never came together, and I played for a long time with different slopes and crosover points.
In the end I went back to the 12db/18db crossovers that Altec built. I did upgrade some of the caps, and removed the switchable feature. I prefer the adjustable slope setup on the HF section.
I would love to fool around with a Marchand sometime, or maybe just build my own. The circuit isn't that difficult.
Ron