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Mono amps...

are they all basiclly bridged stereo amps or are some designed with a clean sheet of paper as mono amps? I am asking because I have had monoblocks for more than a decade and like the idea of isolating each channel and having the amps as close to the speakers as possible (in fact I miss stereo consoles...just kidding). Being in the market for Bryston 7B-STs, I asked whether they are, in fact, bridged 4B-STs and was assured they are not. Looking at a review of them, however, I read that they are, indeed, bridged 4Bs. Why I should be concerned about this is not clear even in my own mind. I know there are pros and cons to bridging. The slew rate is dsoubled, if I remember correctly. What it all means is a little more blurred. Any thoughts?
pbb
sean
6,229 posts
 
I would contact Bryston and see what they say about the bridged 4B aspect of your question. They should know better than any salesman or reviewer.

Bridging creates problems with low impedance loads for most amps. While i can't remember exactly what the deal is, i know that the 7B has some strange numbers for an SS amp when looking into different impedances. You might want to ask Bryston what's up with that aspect while you've got them on the phone. Sean
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tacs
220 posts
 
also there's a newer Bryston that's 2 7Bs in one chassis (14B?), i.e., 500w per channel but one chassis. You might ask about that too.
TS
danielk141
488 posts
 
I agree with Sean, talk to Bryston & get your info straight
from the amp builder. I believe the appreciable change in
performance from a bridgeable amp running stereo vs. bridged mode is that the "damping factor" is halved when you bridge a stereo amp. Damping factor can be thought of as a measurement of bass control-how well the amp can control the woofer.
Also, bridging the amp halves the impedence presented by the speaker. If you have a 4 ohm speaker like a Magnepan, the bridged amp will see the load as 2 ohms-a lot of amps can't drive a load that low.

Good luck!
asterix
33 posts
 
just few words
bridged amp(from stereo) = more power - overall sound quality.
tom_munro
162 posts
 
I used to own the 7B STs. There are two modes that these amps can be run in, series (voltage), or parallel(current). I believe the series mode is for impedances > 4 ohms, and may in fact be a bridged 4B when run this way. Parallel mode is for lower impedances, < 4 ohms, or where high current is required. The output ratings for parallel mode are less, but still very powerful. The two modes sound slightly different as well. Series mode has an airier presentation, with a slightly more diffuse soundstage then parallel. Parallel mode is drier, but has a nicely focused soundstage, and controls the speakers more firmly. The 14B looks like it uses one large transformer per channel vs. the two per 7B monoblock.
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