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#375641 - 05/09/12 12:16 PM Re: Axiom Amplifiers: The Next Generation [Re: Ian]
MarkSJohnson Offline
shareholder in the making

Registered: 09/27/04
Posts: 10831
Loc: Central NH
I guess there are several terms, such as slew rate and damping and rise time which are sometimes, and sometimes not, published.

I just don't know how important they are. Seems like Damping Factor used to be touted everywhere, and now, not so much.

I don't know if their importance has been found to be less than initially thought, or if it's just a matter of marketing, or what.

OK, I hear the groans from bringing up an amp discussion. But I've got a chance to ask someone who designs them.

Here's the real meat of it: JohnK always states that all amps are the same, assuming a flat frequency response. But are there other factors that can make an amp better than another other than FR?

I know the discussion has been beaten to death over the years, but I'm still trying to determine if that perceived difference 15 years ago was false (it certainly COULD have been, it was nowhere near an instantaneous switch!!) or if there are factors that come into play beyond a "flat frequency response".


Edited by MarkSJohnson (05/09/12 12:20 PM)
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#375686 - 05/09/12 04:16 PM Re: Axiom Amplifiers: The Next Generation [Re: Ian]
Bayne Offline
local

Registered: 10/19/06
Posts: 266
Loc: Calgary, Alberta, Canada
My Denon AVR-3808CI has a built-in 130 watt internal amplifier for each speaker. I know not all AVR's are like the older Japan-built Denon's. Would adding one of these amp's make any difference in my case? Based on room size, the 1000 series would be what I need, but at 8 Ohms, the 125 watts this amp delivers is already below what the 3808 claims to supply.
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#375687 - 05/09/12 04:22 PM Re: Axiom Amplifiers: The Next Generation [Re: Bayne]
CatBrat Offline
axiomite

Registered: 08/05/09
Posts: 5798
Loc: Some random location
I was wondering how many Watts the 1000 was in 8 ohms. It's 125. I think for my setup a 1000 series with 6 amps would be perfect. Maybe someday I can make that happen. My next upgrade would be 2, preferably 3 QS8's to complete a 6.1 system.

Not sure what color to go with though. All the other speakers are black, except the subwoofer, which is Cinnamon Beech. Perhaps Cinnamon Beech would be good for the QS8's also. No reason they have to be black.

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#375694 - 05/09/12 06:20 PM Re: Axiom Amplifiers: The Next Generation [Re: MarkSJohnson]
Ian Offline
President
aficionado

Registered: 03/13/01
Posts: 796
Mark,

I doubt that the difference you heard from your NAD amp to other amps would be related to the speed, or slew rate. The slew rate difference in amplifiers is measured in micro seconds and is not likely to contain any audible difference. The power reserves you mentioned are very likely the reason though. NAD amps tended to be low continuous power with good head room and a nifty soft clipping circuit. This soft clipping circuit would keep the usual harshness associated with clipping to a minimum but you would still lose some of that “attack” we all like that comes from being able to actually cleanly reproduce the dynamic peak requested in the original source.



Edited by Ian (05/09/12 06:21 PM)
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#375696 - 05/09/12 06:42 PM Re: Axiom Amplifiers: The Next Generation [Re: Bayne]
Ian Offline
President
aficionado

Registered: 03/13/01
Posts: 796
Bayne,

The difference you are wondering about really comes down to the power supply. Coincidently I wrote a little piece about this in our newsletter today. I suspected it would be a question many people would have. Receiver power is almost always rated at the RMS power per channel with one channel driven or with the remaining six channels running at 1/8 power. This means that 130 watts per channel is either 17 watts or 32 watts per channel with all channels driven. Beyond the weak all channels driven power receiver amplifiers are generally also hard limited at the max power rating, 130 watts in your case. This lack of dynamic head room means any required short burst of power above 130 watts will not be reproduced. In some ways quite similar to the type of problem Mark was commenting on.
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#375719 - 05/09/12 10:24 PM Re: Axiom Amplifiers: The Next Generation [Re: Ian]
Bayne Offline
local

Registered: 10/19/06
Posts: 266
Loc: Calgary, Alberta, Canada
Ian, thanks for the info. For some time I've been wondering if an amp would be beneficial for my system or just overkill. I'm going to be closely watching the developments here over the next few months. I still need to figure out how the 1000 would be incorporated into my set-up and what sort of cables would be best to connect it to my AVR. You may have just introduced me to my Christmas present to myself this year.
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#375720 - 05/09/12 10:27 PM Re: Axiom Amplifiers: The Next Generation [Re: MarkSJohnson]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10360
Mark, as Ian and Chris point out, what you were referring to is termed "slew rate". This is the rate at which the amplifier changes voltage level over time. The usual parameter is given in volts per micro second. When a frequency during music appears which is higher(faster)than the previous frequency or is louder, the amplifier has to supply more voltage because of the higher level and do it more quickly because of the higher frequency. This is needed to produce that note at the required level and with low distortion. Note that this has nothing to do with sharper transient response or a perceived "tighter, quicker" sound; it's just doing the frequency accurately with low distortion.

The required slew rate at any instant in time is given by 2 x pi x freq. x voltage(peak). For example, to reproduce 20,000Hz at 100 watts(i.e. 40V peak, 28V RMS for 100 watts into 8 ohms, since power equals voltage(RMS)squared/impedance)the slew rate would be about 6.28 x 20,000 x 40 = 5,240,000(in micro-volts)or a slew rate of 5.24 volts per second.

This number contrasts with numbers on the order of 50, 100 or even more which some amplifiers proclaim, and is unrealistically high as is, because no music recordings require full power at 20,000Hz. Many years ago Baxandall
tested LPs for maximum slew rate required and found that 0.5 volt per second was all that was needed. British amplifier designer Michael Renardson updated this work for CDs, as shown here and found a maximum requirement for 100 watts into 8 ohms of 2.5 volts per second(would be 5 volts per second for 400 watts). All receivers/amplifiers of a high fidelity standard handle a band width to 20KHz or more at full rated power, and slew rate isn't a problem with any of these units. Making it 10 or more times higher than required is of no audible benefit and may increase costs.

On the amp "sound" point, you've left out some requirements given beyond flat frequency response, e.g., inaudibly low noise and distortion, and should note holding other factors equal, particularly matching sound levels to within 0.1dB when running blind tests. The same point always has to be repeated: all an amplifier does is add more voltage, and all more voltage does is make the sound louder. If this would ever change it wouldn't be in audio forum discussions, but might be published in my AES journal and possibly lead to a Nobel Prize in Physics.
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#375723 - 05/09/12 10:46 PM Re: Axiom Amplifiers: The Next Generation [Re: Ian]
Bayne Offline
local

Registered: 10/19/06
Posts: 266
Loc: Calgary, Alberta, Canada
Just thought of a quick question: With a powered sub such as my EP500, you would not need to connect it to an external amp, is that correct?
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#375725 - 05/09/12 10:54 PM Re: Axiom Amplifiers: The Next Generation [Re: Bayne]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10360
Correct.
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#375726 - 05/09/12 10:54 PM Re: Axiom Amplifiers: The Next Generation [Re: Bayne]
avjunkee Offline
veteran

Registered: 07/28/10
Posts: 110
Originally Posted By: Bayne
Just thought of a quick question: With a powered sub such as my EP500, you would not need to connect it to an external amp, is that correct?


That is correct; the amp for that sub is already built in.
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