[SoundGame]

Alrighty... got some numbers here.

In the interest of getting as close to the theoretical max of the amp, I used a very conservative 1:200 ratio of signal to silence to test the 4BSST2.  Signal was 2KHz Sine Burst, single cycles.

At 8 Ohms the amp delivered 435 Watts, at 4 Ohms 845 Watts, and at 2 Ohms I measured 1580 Watts.  I would expect these numbers to drop as the ratio of signal to silence goes up, so I tried it.

At 2 Ohms, I measured the following results for these signal to silence ratios.

1:200 - 1580 Watts
1:100 - 1549 Watts
1:50 - 1509 Watts
1:25 - 1475 Watts
1:10 - 1350 Watts
1:5 - 1219 Watts
1:3 - 1074 Watts

Just for laughs, I tried it at 1 Ohm as well.  With the 1:200 signal to silence ratio I measured over 2650 Watts, which corresponds to just over 51 Amps of current.

Hope this helps...

Mike

Mike - just one more quick question - what is the time cycle to arrive at the 1:200 signal to silence ratio, if I'm understanding that correctly.  Is it 1ms signal to 200ms off-signal?

[Mike Pickett]

Hey Mike - I converted your figures into Headroom measures for both 8 and 4 ohms.  For the 4B-SST2 they stand as the following:
 
1.45 db @ 8 ohm
2.3 db @ 4 ohm
 
Thanks Mike!  What was very surprising is that this is virtually identical to the highest headroom measurement on amplifiers made by another respected Canadian audio product manufacturer i.e. Anthem - Sonic Frontiers / Paradigm.  On their amplifiers they share a headroom specification.  Their MCA20 has the exact same headroom measurement for 4 and 8 ohms.  An interesting coincidence.  I thought their measurement was very conservative - given some claims for amplfiers having 3 dB to 6 dB of headroom.
 
Have a great weekend!

As far as I know, the 'headroom' rating would be lower on an amp with a stiffer or better regulated power supply, as the continuous rating would be closer to the voltage limited maximum.  I've always wondered why a manufacturer would present a higher headroom rating as better.  I'm sure we can get a much higher rating if we use a transformer of the same voltage but half the VA rating, but I'm pretty sure the change would not be popular...

[Mike Pickett]

Mike - just one more quick question - what is the time cycle to arrive at the 1:200 signal to silence ratio, if I'm understanding that correctly.  Is it 1ms signal to 200ms off-signal?

It's actually 1 full cycle of audio, followed by 200 full cycles worth of time of silence.  So, the time between signals varies by frequency; if you choose a frequency where a cycle lasts 1 ms, your guess would be correct. 

[redbook]

  Thanks from me as well . I too have a 4b(ST) and appreciate your informative response to this post. Welcome to the forum............redbook, from Vancouver.

[Mike Pickett]

I guess I should look forward to running burst tests on the rest of the line-up next week, n'est pas?

[tim92gts]

I guess I should look forward to running burst tests on the rest of the line-up next week, n'est pas?

Hi Mike,
great to see the set of data even for the 4B. It would be interesting to see the same through the range.
Given that much of the time amps are running at a small percentage of continuous power rating we do have a vast amount of headroom.
Presumably there's not going to be much difference here when a stereo amp goes from one to two channels driven?
Tim

[SoundGame]

I guess I should look forward to running burst tests on the rest of the line-up next week, n'est pas?

Oui, oui - merci Mike.  It would be wonderful to understand both the rail voltages of the other amps in the line-up and how they translate into peak dynamic power.  Though the lower ohm examples were interesting, I believe your results around the 8, 4 and 2 ohms loads would be the most enlightening.
 
I know you talked about the maximum rail voltage and how that is a limiter on the peak power; however, could you explain how / if capacitance has any impact on this?  Thanks kindly!
 
 

[SoundGame]

Hi Mike,
great to see the set of data even for the 4B. It would be interesting to see the same through the range.
Given that much of the time amps are running at a small percentage of continuous power rating we do have a vast amount of headroom.
Presumably there's not going to be much difference here when a stereo amp goes from one to two channels driven?
Tim

Agree - with the BDP / BDA combo providing access to 24-bit music files - there is a theortical maximum on that file type of 144db of dynamic range.  Hence, in this new world of ours, dynamics are now an even greater part of the audiophile realm.

[Anonamemouse]

Alrighty... got some numbers here.

In the interest of getting as close to the theoretical max of the amp, I used a very conservative 1:200 ratio of signal to silence to test the 4BSST2.  Signal was 2KHz Sine Burst, single cycles.

At 8 Ohms the amp delivered 435 Watts, at 4 Ohms 845 Watts, and at 2 Ohms I measured 1580 Watts.  I would expect these numbers to drop as the ratio of signal to silence goes up, so I tried it.

At 2 Ohms, I measured the following results for these signal to silence ratios.

1:200 - 1580 Watts
1:100 - 1549 Watts
1:50 - 1509 Watts
1:25 - 1475 Watts
1:10 - 1350 Watts
1:5 - 1219 Watts
1:3 - 1074 Watts

Just for laughs, I tried it at 1 Ohm as well.  With the 1:200 signal to silence ratio I measured over 2650 Watts, which corresponds to just over 51 Amps of current.

Hope this helps...

Mike

(lowering myself to vegasdrivels standard of replying here)

WOW!

This amplifier does not only sound amazing, but it has the numbers to back it up as well... And yes, I would like to see the rest as well (if you can find the time of course...)

[SoundGame]

I guess I should look forward to running burst tests on the rest of the line-up next week, n'est pas?

Hey Mike - I appreciate that you're probably more than busy but do you think you might be able to get the tests run on the remaining amps in the SST/2 line next week or the week after?
 
Any chance that a dynamic headroom specification will be added to the published specs on SST2 amplifiers on the web / literature?

[Mike Pickett]

Hey Mike - I appreciate that you're probably more than busy but do you think you might be able to get the tests run on the remaining amps in the SST/2 line next week or the week after?
 
Any chance that a dynamic headroom specification will be added to the published specs on SST2 amplifiers on the web / literature?

I'm going to try to do at least the 7B this afternoon, once it clears out a bit in here.  As for a dynamic headroom spec; given the wide variety of measurement methods for non continuous RMS power rating, it's unlikely.  Let's just say "as close to 0db as we can make it" and leave it at that, unless James wants to open that crate of worms.

[SoundGame]

I'm going to try to do at least the 7B this afternoon, once it clears out a bit in here.  As for a dynamic headroom spec; given the wide variety of measurement methods for non continuous RMS power rating, it's unlikely.  Let's just say "as close to 0db as we can make it" and leave it at that, unless James wants to open that crate of worms.

Hey Mike - when you do, do the tests, would you be able to share the THD levels at those output levels. 

[Mike Pickett]

Hey Mike - when you do, do the tests, would you be able to share the THD levels at those output levels.

Not really.  The analyzer needs a steady state signal to trigger to and cancel the original waveform.  The best I can say is that I'm recording the level at a point below visible clipping on the 'scope, and well before the clipping indicator lights up on the amp (and it's quite sensitive at 2K).

[SoundGame]

Not really.  The analyzer needs a steady state signal to trigger to and cancel the original waveform.  The best I can say is that I'm recording the level at a point below visible clipping on the 'scope, and well before the clipping indicator lights up on the amp (and it's quite sensitive at 2K).

Before clipping should be more than good.

[Mike Pickett]

So, here's some 7BSST2 numbers:

Rail voltage on each channel is 135V with no signal, for a theoretical maximum RMS output of 47.7V RMS.  Since it's a bridged amp, that gives us 95.4 volts RMS as the limiting voltage, and an output power of just over 1137 Watts at 8 Ohms.  Also since it's a bridged amp, it behaves as if it's seeing a 4 Ohm load when connected to 8 Ohms, so we only get 640 Watts or so, and rail voltage on each channel sags to 112V.

Anyway, the transient readings I measured are:

8 Ohms - 1003 Watts
4 Ohms - 1861 Watts
2 Ohms - 3228 Watts

Same test procedure as the 4B tests, although I didn't bother with a 1 Ohm reading...

Have a great weekend all!

[SoundGame]

So, here's some 7BSST2 numbers:

Rail voltage on each channel is 135V with no signal, for a theoretical maximum RMS output of 47.7V RMS.  Since it's a bridged amp, that gives us 95.4 volts RMS as the limiting voltage, and an output power of just over 1137 Watts at 8 Ohms.  Also since it's a bridged amp, it behaves as if it's seeing a 4 Ohm load when connected to 8 Ohms, so we only get 640 Watts or so, and rail voltage on each channel sags to 112V.

Anyway, the transient readings I measured are:

8 Ohms - 1003 Watts
4 Ohms - 1861 Watts
2 Ohms - 3228 Watts

Same test procedure as the 4B tests, although I didn't bother with a 1 Ohm reading...

Have a great weekend all!

Yowser - that's one dang powerful and dynamic amp!  Thanks Mike.
 
Are you gonna swing in the 3B and 14B in the test cycle?  I need to go and calculate the headroom figures, using the rated RMS on the lucky 7s.  Have a great one Mike - appreciate you putting in the overtime..

[SoundGame]

So, here's some 7BSST2 numbers:

Rail voltage on each channel is 135V with no signal, for a theoretical maximum RMS output of 47.7V RMS.  Since it's a bridged amp, that gives us 95.4 volts RMS as the limiting voltage, and an output power of just over 1137 Watts at 8 Ohms.  Also since it's a bridged amp, it behaves as if it's seeing a 4 Ohm load when connected to 8 Ohms, so we only get 640 Watts or so, and rail voltage on each channel sags to 112V.

Anyway, the transient readings I measured are:

8 Ohms - 1003 Watts
4 Ohms - 1861 Watts
2 Ohms - 3228 Watts

Same test procedure as the 4B tests, although I didn't bother with a 1 Ohm reading...

Have a great weekend all!

So, I quickly calculated the Headroom figures on the lucky 7's based on your numbers and using their rated RMS, as follows:
 
2.2 dB @ 8 ohms; 3.2 dB @ 4 ohms
 
This is considerably higher than the 4B headroom, which were calculated as follows:
 
For the 4B-SST2 they stand as the following:
 
1.6 db @ 8 ohm; 2.3 db @ 4 ohm
 
The 4B was stong, but it's clear the the 7B is a monster of an amp in terms of it's dynamic capabilities.  Any chance of getting any others to the test bench this week?
 

 

[SoundGame]

So, here's some 7BSST2 numbers:

Rail voltage on each channel is 135V with no signal, for a theoretical maximum RMS output of 47.7V RMS.  Since it's a bridged amp, that gives us 95.4 volts RMS as the limiting voltage, and an output power of just over 1137 Watts at 8 Ohms.  Also since it's a bridged amp, it behaves as if it's seeing a 4 Ohm load when connected to 8 Ohms, so we only get 640 Watts or so, and rail voltage on each channel sags to 112V.

Anyway, the transient readings I measured are:

8 Ohms - 1003 Watts
4 Ohms - 1861 Watts
2 Ohms - 3228 Watts

Same test procedure as the 4B tests, although I didn't bother with a 1 Ohm reading...

Have a great weekend all!

Hi Mike,
 
I just got some details on how McIntosh establishes their headroom specifications.  Take a look at this (would be interested in how you feel your method compares):
 
McIntosh Dynamic Headroom Method conforms to EIA RS-490 test method http://www.ce.org/standards/cea-490-a_r-2008_preview.pdf:

·         Test signal: sine wave, 1kHz.
·         On time: 20mS
·         Off time: signal is never turned off just reduced by 20dB for 480mS.
·         Load: Amplifier rated load (8/4/2 ohms).  For McIntosh amplifiers with Output Autoformer, the rating is nearly identical for any rated load connected to the correct output terminals.
·         Distortion:  standards specify visible distortion on an oscilloscope pattern; however, the Power Guard indicator is used as the distortion analyzer, which is far more accurate than a visual opinion 
·         

[SoundGame]

Hi Mike,
 
I just got some details on how McIntosh establishes their headroom specifications.  Take a look at this (would be interested in how you feel your method compares):
 
McIntosh Dynamic Headroom Method conforms to EIA RS-490 test method http://www.ce.org/standards/cea-490-a_r-2008_preview.pdf:

·         Test signal: sine wave, 1kHz.
·         On time: 20mS
·         Off time: signal is never turned off just reduced by 20dB for 480mS.
·         Load: Amplifier rated load (8/4/2 ohms).  For McIntosh amplifiers with Output Autoformer, the rating is nearly identical for any rated load connected to the correct output terminals.
·         Distortion:  standards specify visible distortion on an oscilloscope pattern; however, the Power Guard indicator is used as the distortion analyzer, which is far more accurate than a visual opinion 
·         

Just looked at their on/off cycle with is 20mS (on) to 480mS (off) which would be 4%, which I would think would best correlate to your 1:25 on/off cycle measurements.

[SoundGame]

I looked back at the test results, which were based on a 1:200 on/off signal cycle and calculated that going up to a 1.25 on/off cycle would result in approximately 93% of the measured 1:200 outputs.  Adjusting for this on both the 4B and 7B results, and comparing the adjusted peak power ratings into both 8 and 4 ohms to the corresponding published rated RMS power ratings, I get the following:
 
4B-SST2:
8 ohms (1:25) = 405 watts = headroom 1.3 db
4 ohms (1:25) = 786 watts = headroom 2 db
 
7B-SST2:
8 ohms (1:25) = 933 watts = headroom 1.9 db
4 ohms (1:25) = 1731 watts = headroom 2.8 db
 
So the ratings are still very respectable on the 4B, especially into 4 ohms but the 7B considerably more balsy in terms of dynamic headroom.  Though these are only estimates, given I didn't have complete test figures on the amp for a 1:25 on/off signal, I believe they shed some light.
 
The conclusion is that if you want to get closer to real-life dynamic capabilities - the more powerful Bryston amps rule.  Oh, yes, another conclusion is that using a 4 ohm nominal speaker, it seems that one of the clear benefits would be higher dynamics and therefore, greater dynamic realism potential.
 
Not sure if Mike will get to testing the other amps or comment on these results but I appreciate him sharing the info.  Very enlightening.