High Bandwidth

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trekker

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High Bandwidth
« on: 17 Aug 2005, 03:03 am »
I was reading on the NuForce website regarding the bandwidth and it states "NuForce™ Analog Switching Amplifier provides a ruler-flat response from 5 to 50,000 Hz,...".  But when I looked at the measured Frequency Response for the Ref 8, it appears to be down about 3.5dB at 50KHz.   Is this considered ruler flat?   It doesn't make a difference to me, I was just curious.

Thanks,

Arnold

brj

High Bandwidth
« Reply #1 on: 17 Aug 2005, 03:10 am »
I've wondered the same thing, although I was looking more at the lower end rolloff, where it is 1dB down at 20 Hz and falling, and thinking about compatability with subwoofers...

rustydoglim

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« Reply #2 on: 17 Aug 2005, 05:58 am »
Oops that marketing statement need some adjustment.  Our FR were measured at different time throughout the development and with various versions.  We find that maintaining a ruler flat FR from 20 hz to 20Khz is more important.
Try comparing our FR with any other amps. You'll find NuForce has one of the best FR out there.  Trying to do well in all the following factors is more important: zero phase shift, low distortion (at various freq and power), high bandwidth, close-loop design (for error cancellation) and high damping factor.  I don't know of any amp that can do as well as nuforce in all of the above combined. Well, some amps do exceptionally well in a few areas and I guess nobody has tried to quantify and assign weight to these factors. At the end of the day, it is what you hear and love that count.

mmakshak

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I think that you mentioned this before
« Reply #3 on: 25 Aug 2005, 05:52 am »
The ability to play the other music when a bass note hits might be an underrated trait of your amps.

brj

Re: I think that you mentioned this before
« Reply #4 on: 25 Aug 2005, 12:42 pm »
Quote from: mmakshak
The ability to play the other music when a bass note hits might be an underrated trait of your amps.

Wouldn't this property really reflect current delivering ability?  In otherwords, you need enough current to keep the mids and/or tweeters supplied when your woofers are heavily engaged.

I was primarily looking at the high damping factor and thinking that it made the NuForce offerings well suited for use with sub-woofers, but if the amp is already rolling off at 20 Hz, then this might not be the case - no matter how much bass authority it has above 20 Hz.

Does the damping factor remain a constant 4000 even in the rolled-off region?

nuforce-casey

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Re: I think that you mentioned this before
« Reply #5 on: 25 Aug 2005, 10:49 pm »
Quote from: brj
Wouldn't this property really reflect current delivering ability?  In otherwords, you need enough current to keep the mids and/or tweeters supplied when your woofers are heavily engaged.

I was primarily looking at the high damping factor and thinking that it made the NuForce offerings well suited for use with sub-woofers, but if the amp is already rolling off at 20 Hz, then this might not be the case - no matter how much bass authority it has above 20 Hz.

Does the damping factor remain a constant 4000 even in the rolled-off region?


Ability to maintain composure in mid/treble despite heavy hitting bass is the result of switching amplifiers are immuned to 'Crowding Out' effect.  For more information you can refer to the FAQ on our site.   Switching device has 2 states (on and off), hence does not suffer from crowding out effect.

The 'roll-off' near 20Hz is due to our input cut-off filter to eliminate rumble and DC.  We can roll off at much lower frequency, but that will offer other compromise, such as bigger and slower capacitor, or having to increase the 47K input R to 100K or higher, resulting in higher THD.

The damping factor is a function of output, not a function of input.

ScottMayo

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Re: I think that you mentioned this before
« Reply #6 on: 26 Aug 2005, 02:05 am »
Quote from: Casey
The 'roll-off' near 20Hz is due to our input cut-off filter to eliminate rumble and DC.  We can roll off at much lower frequency, but that will offer other compromise, such as bigger and slower capacitor, or  ...


Any hope of pushing this down a little? I'd like to see an amp that puts out, say, 300W and is flat (+0/-0.1db) down to about 10Hz. I can understand blocking DC, but a good audio amp really ought to be razor flat 20-20k, and I like'm to hold up flat to 10Hz or so, in case I want to drive a sub.

Finally - any plans to incorporate a digital input? If you're just going to flip an output device on and off, it seems a pity to have to sample an analog input first... 8)

brj

Re: I think that you mentioned this before
« Reply #7 on: 26 Aug 2005, 02:20 am »
Quote from: ScottMayo
Any hope of pushing this down a little? I'd like to see an amp that puts out, say, 300W and is flat (+0/-0.1db) down to about 10Hz.

I'll second that!


Quote from: ScottMayo
Finally - any plans to incorporate a digital input?

And add a second vote for that one too!

nuforce-casey

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High Bandwidth
« Reply #8 on: 26 Aug 2005, 02:25 am »
Hint:  it's as simple as replacing the input capacitor.  But the big caveat is that we chose a very special high quality MKP capaitor for its good sound, you can get a bigger value which will show ruler flat 10Hz response, but the midrange and transparency may suffer.

Even a big Teflon capacitor, perhaps you don't mind paying $90 for one, but the huge size, massive dielectric may change the presentation.

trekker

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« Reply #9 on: 26 Aug 2005, 12:58 pm »
I would rather give up 1dB @ 20Hz to have a more transparent mid.  Since the 1dB is a result of the input/coupling cap and not as a function of the amp itself, this can be corrected by using eq, parametric eq and/or room correction programs built-in newer pre/pros.

My .02

Arnold

brj

High Bandwidth
« Reply #10 on: 26 Aug 2005, 04:40 pm »
Quote from: trekker
Since the 1dB is a result of the input/coupling cap and not as a function of the amp itself, this can be corrected by using eq, parametric eq and/or room correction programs built-in newer pre/pros.

Interesting idea!

Jason/Casey, any potential harm to this, either to the cap or the switching power supply?  If not, how low could you safely have a parametric EQ capable crossover bump the demanded power before things become problematic?

2nd - any comment on Scott's request for a digitial input?

Thanks!

ScottMayo

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« Reply #11 on: 26 Aug 2005, 04:47 pm »
Quote from: Casey
Hint:  it's as simple as replacing the input capacitor.


Any harm in putting a bypass switch in, that takes the cap out of the circuit completely? I promise to use a quality preamp that won't dump DC on the line, and none of my sources need rumble filtering. That, presumably, wouldn't affect the transparency in any way, shape or form.

Course, I'd rather you, the manufacturer, made this an option. I have a "thing" about invalidating warranties.

brj

High Bandwidth
« Reply #12 on: 26 Aug 2005, 04:51 pm »
Ok, I confess that "rumble filtering" is a new one on me... what is it trying to filter, exactly?

ScottMayo

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« Reply #13 on: 26 Aug 2005, 04:57 pm »
Quote from: brj
Ok, I confess that "rumble filtering" is a new one on me... what is it trying to filter, exactly?


In the old days of phonographs, the needle picked up low frequency noises from the surroundings, and tried to blow your speakers with it. (Most speakers cook if you put a low enough frequency through them.) Filtering out this junk was a really good idea if you liked your speakers.

But these days, with digital sources immune to surrouonding noise, and movies having sound effects that drop as low as 8Hz, and subs designed to go lower than ever, filtering the low end is just plain annoying. If I want to shake the room at 15Hz and my speakers have the reach, I don't want my amp shoving its oar in. No amp should roll off at 20Hz.

nuforce-casey

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« Reply #14 on: 26 Aug 2005, 08:00 pm »
Please do not try to bypass the capacitor on the NuForce amplifier as we are using it to also couple noise into the chassis to maximize CMRR on RCA input.  

NuForce amp can amplify DC, so it's not a good idea to go without an input decoupling capacitor.   We recently investigated a 'high-end' preamp, and it puts out 7mV of DC.

It's about voiding the speakers' warranty more than voiding NuForce's. :mrgreen:

brj

High Bandwidth
« Reply #15 on: 26 Aug 2005, 08:58 pm »
...and the other pending question about the digital input?

Thanks!