Bryston 7BST or bridged 4BSTs

I have the feeling/impression that a bridged 4BST is same as, or at least similar to, a 7BST, since advertised power outputs are the same.

Can anyone confirm or refute this?

If there is a difference, what are the advantages/disadvantages of using one or the other?

BTW---I'm powering SoundLab A3s, which I realize can be problematical impedance-wise.
The 7B ST has a voltage versus current switch on the back. The switch should be set to current if the impedance of your speakers dips meaningfully below 3 ohms over part of the frequency range. Higher impedance loads are driven with the switch set to voltage. The current setting might be appropriate for your SoundLabs. I don't think the 4B STs have this option.
Hi, 914nut (from 911nut):

I'm sure you'll get good info from the A-gon regulars who own Bryston amps, but you might also direct your question(s) to James Tanner at Bryston. Go to the Bryston home page using the following link, and at the bottom you will see another link reading "Technical questions, please click here" that allows you to send an E-mail with technical questions (they go to James Tanner):
Hi 914nut. I've been going back and forth between these two amps myself, albeit for a subwoofer application.

Jameswei is correct, there's a switch on the back of the 7B that allows you to use the amp in parallel or series mode with just one speaker being driven. Some 7Bs have two speaker terminals and some have four, but from what I've seen they all have the parallel/series toggle switch.

My quandary was whether to get the 4B for it's ability to power one or two mono or stereo subs, and also have the ability to be bridged. It'd be nice to have a stereo Bryston around for fun as well. But, my main reason for looking at these two amps was for subwoofer use, and after corresponding with Bryston I've decided to get the 7B.

Basically, the reasoning is that while the 4B is rated at 800 watts into 8 ohms bridged, it may not be meant to run lower impedances in that mode. Where as the 7B can handle just about any load down to 1 ohm, and can be tailored by the switch on the back for that. Since you're running speakers that are problematic impedance-wise, that would be something to consider.

The person/dealer I bought the 7B from notified me that it had started smoking when he checked it. He sent it in to Bryston for repair and a full check up, and lent me a 4B during the interim. To reduce any risk since this is a loaner amp I'm not running it bridged, but let me tell you it's a potent amp even in stereo.

I hope this helps. Good luck!
We are a Bryston dealer in Hamilton, Ontario, Canada. Simply using the amplifiers stand-alone, I would have to say that the Bryston 7-B ST (in series mode) is a much better sounding amplifier than the 4-B ST. Personally, this is striking since it appears that the circuit topology is very similar. I have not confirmed the variations/similarities between the two from Bryston, but these are my consistent listening observations.

peter jasz (managing director --AUDIO)
A while ago, a dealer told me that the bridged 4's would not produce the same quality level as the 7 since the 7's are not merely two 4's put together. I've owned the 3st, 4st and 7st and they do sound differently. The dealer had nothing to gain by telling me that and did provide me an explanation -- I just don't remember the details. Sdcampbell made a good suggestion to contact Bryston directly. There must be something there or Bryston would simply allow for the bridging and not bother with the 7's (I don't think Bryston is a marketing hype company). This is not the case with all manufacturers since the Sierra amps sound better (and are predominately designed for) running in the bridged mode.