[inzaman]

I was thinking of buying Godfathers Bryston but just before his ad i purchased another Rotel power for biamping duties, so will obviously give this a go first.

What i was amazed at, reading the review, was the amount of joules of energy the amp gave out, 270 for 5 channels compared to a Rotel 1075 at 159 joules. Yet the Rotel is rated at 125 wpc where as the Bryston is rated at 120 wpc, does anyone know how this is the case, i imagine that the greater the joules the easier it is to drive demanding speakers (B&W in my case), how come the joules dont also determine or have a correlation with the wattage power output?

Also if i was to use two Rotels for biamping assuming i had two 1075's would i then get 159x2 joules to drive my speakers, or is it not as simple as that? Cheers

[chedmaster]

as far as i know 1 watt is 1 joule per second, so thats very strange. maybe its something to do with the resistances etc

[severnsource]

That's the first time I've heard of Joules being used to specify an amplifier, and it seems completely irrelevant to me. The term is usually used when you are specifying something that gives an output for a very short period, e.g. electronic flash, ignition systems, electric fence energisers, all of which give short duration pulses separated by a long period of time, say a millisecond pulse every minute.

I suppose that they are using the term to give an indication of the short term output capacity of the amp, but audio transients tend to be significantly longer than a few milliseconds, so it doesn't seem to be a particularly meaningful measure to me.

To say that an amplifier is capable of delivering 270 Joules gives no information about how well it will drive difficult loads; in fact I would say it gives no information at all! On its own it is just a, more or less random, number.

Bill

[alexs2]

Being honest,joules is more often used as a measure of power supply capacity,and to see it used as a measure of amplifier power is unusual.

[inzaman]

Being honest,joules is more often used as a measure of power supply capacity,and to see it used as a measure of amplifier power is unusual.

Reading the review that appears to be what they are using this measurement for as follows;

All of these amplifiers are modular, with each module having its own complete power supply, including an 0.25 kVA (250 watts) toroidal transformer, dual 15,000 µF power supply capacitors, and ±60 Volts on the rail, providing 54 Joules per amplifier channel (that's 1,250 watts of toroid and 270 Joules of energy storage total, which is a LOT for a 120 watt/channel, five-channel power amplifier).

[alexs2]

Originally Posted by inzaman

Reading the review that appears to be what they are using this measurement for as follows;

All of these amplifiers are modular, with each module having its own complete power supply, including an 0.25 kVA (250 watts) toroidal transformer, dual 15,000 µF power supply capacitors, and ±60 Volts on the rail, providing 54 Joules per amplifier channel (that's 1,250 watts of toroid and 270 Joules of energy storage total, which is a LOT for a 120 watt/channel, five-channel power amplifier).

Not bad at all,but how about 300 J per channel( a conservative estimate of what's under the covers of my Krells)...thats for 100W per channel single channel amps!

Seriously though,the Bryston supplies are very well designed and provide ample storage for that design of amp,whereas the old Krells(KMA's and similar)were designed to provide sufficient current for up to 800W into 1 ohm loads.

[inzaman]

whereas the old Krells(KMA's and similar)were designed to provide sufficient current for up to 800W into 1 ohm loads.

I was very suprised at the amount of current the amp had though and it made for interesting reading and was curious for more info/knowledge.

[alexs2]

Thought that might amuse you!...one of the old ads they ran had a KMA running an electric jackhammer,and they were known to produce over 50A quite easily.

[davehk]

I guess the energy capacity of the PSU reservoir caps is related to the transient power output capability of the amp, since these caps have to maintain the supply voltage whilst the incoming AC supply cycles from+ve to -ve through zero.

[Steve.EX]

Originally Posted by davehk

I guess the energy capacity of the PSU reservoir caps is related to the transient power output capability of the amp, since these caps have to maintain the supply voltage whilst the incoming AC supply cycles from+ve to -ve through zero.

Quite so, although using large caps is only one way of "skinning a cat".

Steven