bryston 4b with NHT 2.5's opinions

The non-linear byproducts ( distortion ) of a Bryston 4B take off like crazy above 2 KHz as documented in IAR 4. Moncrieff also documents that the 4B is load sensitive i.e. it changes tonal balance as the impedance varies. His findings are that the amp will sound brighter as the impedance rises. As such, i would avoid hooking this amp up to any speaker with metal domes, speakers that had a bright top end, speakers that were 8 ohms or higher or a system that made use of a mass produced digital front end ( cheap cd or dvd players ). As such, it might be a good match for a 4 - 6 ohm speaker with a medium sized woofer and a soft dome tweeter but anything else would tend to show the flaws in the design and possibly even highlight them. The newer Bryston's might be better sounding amps, but as far as i can tell, they still have problems driving very low impedance loads. Sean
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I have a pair of 2.5i's and at one point, i had a 4bst powering them...

it was definitely overkill

many ppl say that these speakers sound better the more you power them, but I feel that the 4Bst was over the top. I don't believe these speakers to be very difficult to drive, so long as there is quality power going to them. I have since sold it and will be buying an integrated. Eventually, the speakers will go too.

The 4bst and 4b are different sounding...the st version is more refined, not as grainy and has better bass control.

Still, you must make sure to get the proper preamplifier to tame what could be an otherwise glaringly bright sound.

I used the Bryston 3b-st with the NHT 2.5 and was very pleased. The amp provided just the right amount of power and finesse for the speakers.

I then had a NHT 2.9 powered with the 3b-st and the 4b-st (horizontally biamped). The 3b-st was not enough power for the 2.9 alone and my biamped config was overkill. A single 4b-st would have sufficed for the 2.9.

So I would say that your 4b is more than enough power for the 2.5. I wouldn't spend more money on a real fancy (expensive/refined) amp for those speakers. Instead buy some good speaker wire. I switched from some Monstor speaker cable to AudioQuest Caldera for my 2.9 and the improvements (especially the bass) was surprising.