[jackman]

I spent a lot of time this weekend, fine tuning my system. I tested several cables, speaker positioning, and a couple different preamps. Not going to bore you guys with the details but there was one major discovery. My Legacy/Coda 4 channel amp sounds completely different in 2 channel bridged mode, compared to 4 channel mode.

Even though my speakers are efficient enough to work well in either mode, the sonic difference between both modes is staggering. Let me provide some background.  I was hoping to use the amp in four channel mode to power my monitors and the subwoofers of my Bamberg Series 5 speakers.  This would allow me to eliminate my Aragon 4004 amp from the system. The Aragon is very large and doesn't fit into my audio cabinet.

The amp has lots of power and drives the subs nicely in 4 channel mode but the mids and highs are thin and brittle, and the imaging is blurred and missing the magic. In bridged 2 channel mode, the sound is absolute magic. Speakers disappear and the presentation is wide, deep and very 3D.

I have always noticed differences between different amplifiers but have never experienced anything like this. The amp in four channel mode, even when I'm not running the subs, is just okay (okay maybe slightly less than okay) but the bridged 2 channel performance is magic, among the best I have heard in this price range. 

I've seen lots of these amps (Legacy 432 made by Coda), sell for very low prices and think I just figured out why!  The 4 channel sound is nothing special but 2 channel is awesome  The sonic difference between bridged mode and 4 channel is not small. I was going to sell the amp before I tried the bridged mode. Glad I did!  Does anyone have any ideas as to why it sounds so different in 2 versus 4 channel mode?

Cheers!

J

[neekomax]

Well, I don't know why your amp sounds better bridged, but those are some serious speakers you're working with right there. Damn!

Aren't the subs in the Bambergs powered by their own amps?

[jackman]

Thanks Neeko,

Mine are the older model with a DCX controlling the woofers. The new ones are powered and nicer but mine sound pretty good. The bass performance is excellent.  Phil Bamberg is a very talented designer and a good guy.

[Occam]

Jackman,

Your amplifier is implementing a balanced bridged topology.
An example of what is (probably) done in your amplifier is shown here -
http://sound.westhost.com/project20.htm
and an explanation of the topology at the bottom of -
http://sound.westhost.com/project14.htm

The theoretical advantages are -
1. Given the proper power supply a 4 fold increase in power output
2. Better utilization of the ps. While one amp side is drawing power from the negative rail, the other is drawing from the positive rail. I think? there may also be some level of power supply noise cancellation
3.Some level of even order harmonics cancellation. Those harmonics are out of phase on each side, and cancel each other out.

The extent to which those benefits apply is obviously dependent upon the specific implementation of that bridging.

AVA makes a bridging adapter for some of their amps, and Frank would be the person with both theoretical and hand-on expertise.

Regards,
Paul

[jackman]

Jackman,

Your amplifier is implementing a balanced bridged topology.
An example of what is (probably) done in your amplifier is shown here -
http://sound.westhost.com/project20.htm
and an explanation of the topology at the bottom of -
http://sound.westhost.com/project14.htm

The theoretical advantages are -
1. Given the proper power supply a 4 fold increase in power output
2. Better utilization of the ps. While one amp side is drawing power from the negative rail, the other is drawing from the positive rail. I think? there may also be some level of power supply noise cancellation
3.Some level of even order harmonics cancellation. Those harmonics are out of phase on each side, and cancel each other out.

The extent to which those benefits apply is obviously dependent upon the specific implementation of that bridging.

AVA makes a bridging adapter for some of their amps, and Frank would be the person with both theoretical and hand-on expertise.

Regards,
Paul

Thanks Paul, I appreciate your comments.  It's the strangest thing and probably explains why this amp was not a good seller for Coda/Legacy.  The bridged, two channel, sound is among the best I have ever heard in my system.  Very 3D and open sounding with excellent dynamics.  The 4 channel mode (even when it is just powering the same two monitors) is anemic, thin, and very flat.  Vocals are "small" sounding and uninvolving in 4 channel mode, but they suddenly become big and beautiful in bridged 2 channel mode. 

Coda probably had to make some design compromises when they created the 4 channel capability.  I'm going to check with Frank to hear what he has to say. 

It works well on my subs in 4 channel mode and has no lack of power, but the monitors are a different story.  I've had other amps with bridging capability (mainly 2 channel amps with a single channel bridged mode switch) but they didn't sound bad in multi channel (2 channel) mode.  The 432 is an amp with a split personality, one really good and one really bad!  After hearing the difference, I can't imagine using this amp in 4 channel mode. 

Thanks!

Jack