[vegasdave]

A guy I know wanted to know what the dynamic headroom is on the 4BSST? Also, what is the peak power? Thanks. 

[danman]

I have always wondered this as well!

[danman]

Now that I think of it, I thought I recalled reading somewhere that it was around 700 watts or so in 8 ohms however, don't quote me. Is that your question?

[Fernar]

According to the Hi-Fi New (June 09) - the 4BSST provided 480W into 8 OHMs; 900W into 4 OHMS; 1595W into 2 OHMS and 2160W into 1 OHM (at less than 1% THD) for 10msec.

Hope this helps..

[danman]

Great. I thought I might have been a tad high! However, goes to show how flexible this amp really is.

[James Tanner]

HI All,

As luck would have it I got this email this morning asking a question regarding amplifiers and output impedances vs power delivery. Thought you might find it informative as it relates to Dave's opening question.



From: Drew Daniels
Sent: Sunday, June 07, 2009 1:37 PM
To: jamestanner@bryston.com
Subject: Tech question
 
Greetings,

I am about to purchase a Bryston 4B SST2 for my mastering room. I have a question I hope is easy to answer.  Please correct me where I am in error.

In electrical engineering school, I was taught about voltage source and current source audio frequency amplifiers. In the 60s I worked for Gene Czerwinski who used to routinely sketch amp designs using trifilar output stage driver transformers, on one side of a sheet of notepad paper and hand them to me to go build in the shop (they all worked first time).  Gene had experience working for Bendix Corporation where he designed and built an all-germanium transistor 20 kilowatt amplifier for helicopter-deployed sonar use, as early as 1962.                   

Here is where I am hazy:  should a voltage source amplifier be regarded as essentially (metaphorically?) having zero output impedance, and therefore be expected to deliver twice the power output when the load impedance is halved?
Why do (most) power amps give power ratings that seem in conflict with impedance equations? Is it more due to power supply stability or to reactance magnitude differences between loudspeakers rated at a characteristic 8 or 4 ohms? Thanks for taking the time to answer.

Cordially,
Drew Daniels
Grammy nominee - best sound,
Winner, French Jazz Academy Record of the year, 2007.


Hi Drew;
 
Thanks for your question, it is an excellent one.
 
Amplifiers today are almost always designed to be Voltage sources. That is, their output impedance is very low, (on the order of a few milliOhms), so their output Voltage for the same input signal varies very little from open-circuit load to nominal full load impedance. (A theoretically perfect Voltage source would not vary at all).  In addition, if the power supply of the amplifier also had a zero ouptut impedance, the amp's power capability would vary exactly inversly with load impedance. That is, its power output capacity would double from 8 Ohms to 4 Ohms, and double again at 2 Ohms, etc.
 
In fact, of course, there is no such thing as 'perfect'. All amplifiers have finite output impedance, as do the power supplies in those amplifiers. Thus, no amplifier actually 'doubles' its output power capacity repeatedly with halving load impedance. If an amplifier has a large enough power supply it can come close enough for the manufacturer to quote the power at a low impedance like 2 or 4 Ohms, and then quote half those values with doubling the load impedance, (a bit of a 'fudge'). Bryston amplifiers are rated realistically but conservatively for specified load impedances.
 
In answer to your question about reactance, some amplifiers do in fact have problems with large reactances, and reduce their output Voltage and current drastically with large reactive phase angles. The manufacturer will not tell you that, of course, and the specs will never show it since power is measured on resistive loads.  Bryston's output Voltage and current specifications relating to power output are valid for any reactive phase angle from +90 to -90 degrees, or from completely capacitive to completely inductive and all in between, or in any combination.
 
I hope the above is helpful, but please let me know if you have any other questions.  Thanks for thinking of Bryston!
 
Sincerely,
Chris Russell
CEO, Bryston Ltd.

 

[b5pt9]

I googled "dynamic headroom" and found this article for reference.

http://forum.ecoustics.com/bbs/messages/34579/109459.html

I've always thought 3dB dynamic headroom meant the amp could double it's output power for a short period of time.  I'm not sure if "short period of time" is standardized to a specific number of mSec.  I suspect not and hence dynamic headroom specifications might be somewhat misleading.

[Dilbert]

More on Drew Daniels:

http://www.drewdaniels.com/

And here:

http://audioheritage.org/html/perspectives/drews-clues/drews-clues.htm

[werd]

Hello

I think it's pertinent to point out that dynamic power starts at the outlet or perhaps fusebox in the home.
A perfectly designed unregulated voltage source isnt going translate into respectable dynamic power unless the mains issues are addressed. Untreated 15 amp home circuits ime arent able to maintain transient power peaks. Ive only noticed the severity of this with the introduction my dedicated 240 volt rm-20. Although good cabling and responsive power cables help.

[vegasdave]

James, that was informative. So, what's on paper is less than what is going on when the amplifier is running in a system?

[werd]

Hello

I think it's pertinent to point out that dynamic power starts at the outlet or perhaps fusebox in the home.
A perfectly designed unregulated voltage source isnt going translate into respectable dynamic power unless the mains issues are addressed. Untreated 15 amp home circuits ime arent able to maintain transient power peaks. Ive only noticed the severity of this with the introduction my dedicated 240 volt rm-20. Although good cabling and responsive power cables help.

By my own admission... this post reads too harsh. I didnt mean it to sound like that. I am sure 15 amp circuits can be made more power responsive. I was just trying to draw attention to the mains issues.

[James Tanner]

HI All,

As luck would have it I got this email this morning asking a question regarding amplifiers and output impedances vs power delivery. Thought you might find it informative as it relates to Dave's opening question.



From: Drew Daniels
Sent: Sunday, June 07, 2009 1:37 PM
To: jamestanner@bryston.com
Subject: Tech question
 
Greetings,

I am about to purchase a Bryston 4B SST2 for my mastering room. I have a question I hope is easy to answer.  Please correct me where I am in error.

In electrical engineering school, I was taught about voltage source and current source audio frequency amplifiers. In the 60s I worked for Gene Czerwinski who used to routinely sketch amp designs using trifilar output stage driver transformers, on one side of a sheet of notepad paper and hand them to me to go build in the shop (they all worked first time).  Gene had experience working for Bendix Corporation where he designed and built an all-germanium transistor 20 kilowatt amplifier for helicopter-deployed sonar use, as early as 1962.                   

Here is where I am hazy:  should a voltage source amplifier be regarded as essentially (metaphorically?) having zero output impedance, and therefore be expected to deliver twice the power output when the load impedance is halved?
Why do (most) power amps give power ratings that seem in conflict with impedance equations? Is it more due to power supply stability or to reactance magnitude differences between loudspeakers rated at a characteristic 8 or 4 ohms? Thanks for taking the time to answer.

Cordially,
Drew Daniels
Grammy nominee - best sound,
Winner, French Jazz Academy Record of the year, 2007.


Hi Drew;
 
Thanks for your question, it is an excellent one.
 
Amplifiers today are almost always designed to be Voltage sources. That is, their output impedance is very low, (on the order of a few milliOhms), so their output Voltage for the same input signal varies very little from open-circuit load to nominal full load impedance. (A theoretically perfect Voltage source would not vary at all).  In addition, if the power supply of the amplifier also had a zero ouptut impedance, the amp's power capability would vary exactly inversly with load impedance. That is, its power output capacity would double from 8 Ohms to 4 Ohms, and double again at 2 Ohms, etc.
 
In fact, of course, there is no such thing as 'perfect'. All amplifiers have finite output impedance, as do the power supplies in those amplifiers. Thus, no amplifier actually 'doubles' its output power capacity repeatedly with halving load impedance. If an amplifier has a large enough power supply it can come close enough for the manufacturer to quote the power at a low impedance like 2 or 4 Ohms, and then quote half those values with doubling the load impedance, (a bit of a 'fudge'). Bryston amplifiers are rated realistically but conservatively for specified load impedances.
 
In answer to your question about reactance, some amplifiers do in fact have problems with large reactances, and reduce their output Voltage and current drastically with large reactive phase angles. The manufacturer will not tell you that, of course, and the specs will never show it since power is measured on resistive loads.  Bryston's output Voltage and current specifications relating to power output are valid for any reactive phase angle from +90 to -90 degrees, or from completely capacitive to completely inductive and all in between, or in any combination.
 
I hope the above is helpful, but please let me know if you have any other questions.  Thanks for thinking of Bryston!
 
Sincerely,
Chris Russell
CEO, Bryston Ltd.

 

Follow Up Email from Drew:

From: Drew Daniels
Sent: June 10, 2009 2:15 AM
To: Bryston
Subject: Re: 4B SQ


The 4B SQ amp is being driven from the balanced outputs of a high-quality digital crossover (Rane RPM26z) and is silent--it can't be measured by loudspeaker noise, above the 25 dBC of the control room's background noise. 

Very pleased so far. 

Horns and reverbs have a new subtlety, and I have a new confidence.

Drew Daniels

[vegasdave]

Ok, cool.