7B SST2 power question

[BlueFox]

Why doesn't the 7B double its power into a 4 ohm load? Would this be considered a deficiency compared to similar amps that do double the power output?

[Rod#S]

James will most likely chime in to answer but this is a trait of all Bryston amps, not just the 7B and is in contrast to almost every other amp from other manufacturers.

[RLL1]

I do not know why, but I always thought that doubling the power in to a 4 ohm load was normal. Moon, BAT, Bel Canto, Aesthetix, Jeff Rowland, ModWright are some examples.

[BlueFox]

Originally Posted by Rod#S

James will most likely chime in to answer but this is a trait of all Bryston amps, not just the 7B and is in contrast to almost every other amp from other manufacturers.

Yes, I hope he does. I need to get my 'retirement' amps soon, and while I love my BDA2 and BDP1, and hope the 7Bs perform at that level, the power issue is troubleling. Hopefully, they do double in power at 4 ohms, and they are just being conservative with the ratings.

[Rod#S]

I don't think you will like the answer if you expect a doubling.

What speakers do you have?

[BlueFox]

Aerial Acoustics 7T

[tdelahanty]

Doubling power output (@ 4ohms) is a very expensive venture. To do this the power supply and output stage must be extremely over built. At this juncture I won't delve into all the details. Suffice it to say if an amp has a good deal of headroom I doubt there would be any noticeable difference in sound quality under most conditions.

Look at Levinson's specs for their recent designs and the bread and butter of their line-up does not double output power, and the amps which do are far more expensive.

Is this a cost saving move? Yes !!! Do their amps and other reputable manufacturers still sound very good? Absolutely !!!

Bryston amps are very musical and are very rugged, as demonstrated by their 20yr warranty. You'll be fine, don't worry.

[Rayooo]

I've always wondered about this...not from a technical point of view, but from a purely specification basis.

i.e. I build a power amplifier, It can safely do 400 WPC into 8 ohms, and 700 watts into 4 ohms. Then a user questions, why doesn't this amp double into 4 ohms?

Then, imagine the very same identical amplifier, only it's specifications are now changed to: 350 WPC into 8 ohms and 700 WPC into 4 ohms, same amp, and everyone is happy.

Seems at least to me that at least to some degree, "specification headroom" may be a factor.

[tdelahanty]

Remember the heyday of HiFi ? All the big receiver manufactures were engaged in a more watts is better pissing contest. It's salesmanship (to a degree).

There are many things a designer can do to create doubled output @ 4ohms. All that I am aware of slide (change to class B) the bias to help in this regard. Very few if any build a fixed bias Class A amp that will double output. Way to costly to build and use on a daily basis. Short of this it's not of much concern to me.

[BlueSky]

Power is calculated by the formula P=I (squared) x R where I is the current and R is the resistance (impedance). For instance, 400 watts into 8 ohms would require about 7 amps of current. To deliver 800 watts into 4 ohms would require 14 amps of current. I suspect that most amplifier manufactures don't want, or need, to build power supplies that are double the actual capacity they need to deliver their amplifier's rated power.