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Re: Bi-amp with 2 pair of M60 vs. single-amp with the MA1

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Posted by Al Sekela on September 17, 2004 at 09:56:14

In Reply to: Re: Bi-amp with 2 pair of M60 vs. single-amp with the MA1 posted by Michael Lin on September 16, 2004 at 15:30:12:

Yes, I meant what you stated, to create a high-pass filter within the M-60s that are to be
used for the treble range.

Another and simpler way to do this is to replace the coupling capacitors between the voltage
amplifier and driver tubes with small Teflon capacitors. This capacitor is large to prevent
phase shift in the deep bass, and the Teflon version is quite expensive. However, for treble
service, it can be replaced with a small Teflon capacitor at reasonable cost. The smaller the
capacitor, the better it works, so this tweak actually will improve the treble fidelity, in my
opinion. If you are careful, you can save the existing capacitors and put them back if you
ever want to restore the amps for full-range service.

This tweak will still require the voltage amplifier tubes to experience the deep bass, so an
input filter may still improve things. It adds another capacitor, though, so it is not clear to
me that the net result would be a gain or loss of clarity.

Be careful that the corner frequency for the amplifier high-pass is a couple of octaves away
from the speaker crossover's corner frequency, to avoid modifying the speaker's tonal
balance.

In my case, the external Magnepan MG-20 high-pass is a single capacitor, so I simply
calculated the capacitance and resistance for an input filter to mimic this, and bypassed the
Magnepan capacitor. I don't know if your speaker allows the same trick.

I don't have direct experience with M-60s on my speakers, so I can't say whether their
simplicity gives further improvements. My MA-1s are heavily modified in any case, so a
comparison would not be meaningful.

The best thing to do is consult the maker of your speakers about bi-amping. See if the
maker will provide a schematic diagram of the crossover.

This post is made possible by the generous support of people like you and our sponsors:

Atma-Sphere Music Systems, Inc.

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