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[John Roberts {JR}]

Gian P. Portanova wrote on Fri, 15 December 2006 23:14

Hi Sara, Definitely a capable sub amp.  There is enough voltage swing to take peak clip-limiting out of the equation.  Sound is "tighter", which I think is characteristic of CLASS D amps compared to linear amps (my theory). >>>more to come...

Perhaps you can illuminate us regarding your theory. I recall reading a white paper in the mid '80s claiming class D amps had lower output impedance due to saturated switch output devices which almost sounds plausible until you realize the full PS voltage square wave needs to pass though an output LPF to extract the audio. Practical filters add some series impedance which can be reduced by overall negative feedback, but even how much of that can be applied is limited by the intrinsic delay of the filter.

Properly executed a class D amp can deliver adequate linearity and damping. I suspect bass performance will be more impacted by power supply headroom. If I was pressed to come up with a theory to explain good bass performance in this series I'd look to the switch mode PFC PS.

Merry Christmas,

JR

[Michael 'Bink' Knowles]

Quote:

...Sound is "tighter"...

Would this observation be measurable as a faster rise time? Just curious.

How much steady state power (24/7/365) can it deliver at 240v in bridge mode? Willing to guess?

-Bink

[Gian P. Portanova]

John Roberts  {JR} wrote on Sat, 16 December 2006 10:10

Perhaps you can illuminate us regarding your theory. I recall reading a white paper in the mid '80s claiming class D amps had lower output impedance due to saturated switch output devices which almost sounds plausible until you realize the full PS voltage square wave needs to pass though an output LPF to extract the audio. Practical filters add some series impedance which can be reduced by overall negative feedback, but even how much of that can be applied is limited by the intrinsic delay of the filter.

Properly executed a class D amp can deliver adequate linearity and damping. I suspect bass performance will be more impacted by power supply headroom. If I was pressed to come up with a theory to explain good bass performance in this series I'd look to the switch mode PFC PS.

Merry Christmas,

JR
[/quote]

Hi JR,

I guess I based my theory during an experiment by connecting a sub woofer directly to CLASS D amp with minimal LPF.  At this point your mention of the white paper (lower impedance) definitely applies.

While a general purpose amp will have a more complex LPF, I think the lower impedance stage benefits are still realized.  

The PSU I beleive contributes much to the sound qualities in amps (PWM or analog).  So that also applies to my thoery!

Happy "Holidays"!


GPP

[Gian P. Portanova]

Michael 'Bink' Knowles wrote on Sat, 16 December 2006 17:14

Quote: ...Sound is "tighter"... Would this observation be measurable as a faster rise time? Just curious. How much steady state power (24/7/365) can it deliver at 240v in bridge mode? Willing to guess? -Bink

Bink,

Observation is the proper term for that description.  Can it be measured by the rise time?  Not sure if that is the proper measurement for what I'm describing.  It may be measured by the fall time.  Or the "ripple" decay.  I think JR was more accurate in the post above regarding the "damping" characteristics of amplifiers.

The 32A input test was for under a minute.  So short term steady state.  I'll assume that at some point the amp may thermal (trying to reach 24/7/365).  I'll also assume that output power will go up at 240V/32A in.

I'll try out these tests if I get a chance and advise my results!

In response to all that are having "issues" with the LED voltage metering.  My application does not require 200V output swing, so I set it to 100V (2500W at 4 ohms).  Would you believe the LED bar re-calibrates to that setting?  Before I realized this, I was surprised to see any of the LED's flickering.  This amp also gives you enough output for some good power compression.

No drivers damaged yet though.


GPP

[Michael 'Bink' Knowles]

Quote:

...It may be measured by the fall time.  Or the "ripple" decay...

I like that: "fall time." Perfect.  

-Bink

[John Roberts {JR}]

Gian P. Portanova wrote on Mon, 18 December 2006 09:17

Hi JR, I guess I based my theory during an experiment by connecting a sub woofer directly to CLASS D amp with minimal LPF.  At this point your mention of the white paper (lower impedance) definitely applies. While a general purpose amp will have a more complex LPF, I think the lower impedance stage benefits are still realized.   The PSU I beleive contributes much to the sound qualities in amps (PWM or analog).  So that also applies to my thoery! Happy "Holidays"! GPP

Indeed a loudspeaker driver can integrate a PWM output to continuous audio. I even did this on the bench with a couple watt class D experiment back in '70s, I don't have a feel for how this would scale to higher power levels. Perhaps in a powered cabinet where you can specify a driver with this in mind, shield the box and maybe even the speaker cone.

Again I don't know if this is practical. I've kicked the idea around for years in the context of making a cheap portable amp/pa with very good battery life. Never made much headway on the cost effectiveness aspect due to RFI considerations.

Even with the low output impedance of a saturated switch I suspect the characteristics of the power supply, that that switch is clamping the speaker to hard matters more. In a class D amp any power supply artifacts are injected directly into open loop audio (reduced by overall negative feedback). Of course without the output smoothing filter, any negative feedback signal will need to be conditioned somehow or the amp must run open loop.  

IMO damping factor is mis identified and over rated as audibly significant beyond some nominal amount.

JR    

[Jens Droessler]

The K10 is a fullrange amp, not limited to bass. So the integrated lowpass filter that will make an audio signal out of the PWM output of the actual amp will have to be a very complex one. The requirements are high: It mustn't affect the higher frequency range, it has to be of low impedance AND it has to work with ALL specified loads, as in 16 ohms, 8 ohms, 4 ohms, 2 ohms AND also with highly reactive loads. That is not a simple thing. Some of the requirements can't be met that easily.

Just to clarify if there are any doubts: JR wasn't talking about an applied lowpass filter to keep highs from the subwoofers (at least I think .

Another thing about this amplifier: I already said the same thing about the LAB Gruppen fP+ 13000. If you use the high output power capabilities just for the comfort of having that much headroom you'll be fine. BUT: If you use the amp to drive a lot of speakers that can actually take the power without problems for a longer period, the PSU will limit the amplifier. That means you can't use the full output capability on 'low crest signals'. I'm not bashing the amp, I'm just informing you on something that somehow is a missconception nowadays: The amp can't create additional power. If the PSU is limited to 30A current draw at 115V, it can't give more power than that (RMS!). Don't be scared or pissed. The higher peaks possible are what makes these amps better than smaller amps...

[Langston Holland]

Jens wrote on Tue, 19 December 2006:

...it has to work with ALL specified loads, as in 16 ohms, 8 ohms, 4 ohms, 2 ohms AND also with highly reactive loads.

Looks to me like it just might do that. I'm not allowed to remember where I got these measurements (I didn't do them), but they were sent to me a while ago after I posted my I-Tech measurements. They are effectively identical to my I-T8000 results and add a couple of other amps in comparison. Only resistive loads were used. I believe I'm going to be able to demo the K10 in this thread before long and I'll measure it using the same resistive and reactive loads I placed on the I-Tech.

[Gareth James]

Wow, bearing in mind that's just resistives loads those are some pretty revealing graphs Rev L  

The Lab fP isn't so bad being 2dB down at 20khz/2ohm load but >5dB on the Itech...

Looking forward to seeing how reactive loads alter the playing field. Any chance you might be able to get your hands on the new FP+ Lab amps? Would be interesting to see if there is much difference with the new model.

[Jens Droessler]

@ Langston: Let's say it is supposed to..... It won't and it can't, but if it was a very simple filter the differences would be worse by far.

The LAB fP is not a good comparison, as it (depending on the way you look at the design) has an active, dynamical filter circuit.

The K10 obviously has a lp filter of pretty high order, making me think about phase issues up there. Do you have some phase measurements too?

@ Bink:

Michael 'Bink' Knowles wrote on Sat, 16 December 2006 22:14

Quote: ...Sound is "tighter"... Would this observation be measurable as a faster rise time? Just curious.

I'm not the original poster of your quote, but I dare to answer anyways.
I don't think so. You can calculate, how fast of a rise time is needed for that power in bass range. I don't think that there is ANY current design that would be limited by the rise time/slew rate in bass range. There WOULD be limitations with SOME designs in HF range, but OTOH no one needs 2x5kW at HF from one amp, so the demands up there aren't that high.

Quote:

How much steady state power (24/7/365) can it deliver at 240v in bridge mode? Willing to guess?

I did not measure the K10 for that, but I can tell from the old DigAm7000 (which couldn't be bridged) that it would do 2x500W continous at any load (not below 2 ohms!) 24/7. That's enough to keep up the rated power for typical rock music, but not with 'electronic music' (I know that from experience). The K-series will have a similar design, allowing maybe 800-1000W per channel at any load. That means they'd have to step down the output power if the RMS would be too high for a too long time.