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#385473 - 11/11/12 01:49 AM Re: Pre-Amps and Amps questions. [Re: wilwom]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7047
Loc: Canada
Originally Posted By: wilwom
This is sooooo much fun! Pass the popcorn please.

It would be more fun if I knew what they were talking about, but hey, pass the popcorn please. grin
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#385475 - 11/11/12 03:11 AM Re: Pre-Amps and Amps questions. [Re: dakkon]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10395
Alex, that's curious unless maybe it's just a matter of semantics, i.e., when Ohm's Law is used in its AC form some think it shouldn't be called Ohm's Law. However, it is of universal application and a quick googling turns up numerous examples illustrating application to AC, for example here and here . Of course, this is using the Z factor rather than R to take into account varying impedance with frequency.

Certainly the calculations for impedance are more complex than for pure resistance, but the point is that once done the result is a specific current: same speaker, same frequency, same input voltage results in a fixed current which can't be changed by changing the amplifier.
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#385477 - 11/11/12 08:39 AM Re: Pre-Amps and Amps questions. [Re: PaulCanada]
Boltron Offline
veteran

Registered: 11/18/11
Posts: 171
Loc: Toronto
Enjoy the music, not the math.
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#385479 - 11/11/12 10:21 AM Re: Pre-Amps and Amps questions. [Re: PaulCanada]
dakkon Offline
connoisseur

Registered: 02/08/04
Posts: 1846
John, it's not a matter semantics (well it may). If an EE degree was as simple as understanding Ohms law for AC theory, then there would be a LOT more people getting EE degrees... I have several friends with EE Degrees, and Cal 3 was easy for them in comparison to Differential eqn's...

John, as you know.. You have to be careful with your sources, your second source simplifies Z to much...

I found a power point of a lecture, this professor used Z=I/V. However, i think the true take away from the lecture is that Z is not anywhere near as simple to calculate as R (which the second source above implies).. It is the same base eqn, but that is about it... When you look through the power point, you still see what i mean. The powerpoint is a little long, at 252 slides... I did not "read" the entire thing, i skimmed it to see if it was portent to our conversation... Later today I will call a buddy of mine, to get is input and will share what he has to say..

Here is the power point
http://www.personal.rdg.ac.uk/~stsgrimb/teaching/ac_circuits.pdf

Boltron, what you fail to realize, is well.... we have been here before, and will probably be here again. The biggest take away, is this is a civil academic discussion not an argument, and we all will likely learn something from each other.


Edited by dakkon (11/11/12 10:22 AM)

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#385481 - 11/11/12 10:40 AM Re: Pre-Amps and Amps questions. [Re: JohnK]
dakkon Offline
connoisseur

Registered: 02/08/04
Posts: 1846
Originally Posted By: JohnK
same speaker, same frequency, same input voltage results in a fixed current which can't be changed by changing the amplifier.


John, i think this part of your statement is subjective... The subjective part of it is the design of the amp. Under ideal conditions the answer is yes. However, as we both know not all products are of the same quality. Under the statement you said above, this would be true for amps that are designed as a constant voltage source.. a good example of this not being the case is the Emotiva amps (not that i am saying emo's are bad). If you look at their ratings, as the resistance of the load is reduced by 1/2 the power does not double.. This means they do not maintain a constant voltage. With the amps i chose to buy, as the resistance reduces by 1/2 the power doubles each time; they are designed to be a constant voltage source. The large Emotiva monoblock is the only amp in their lineup that i am familiar with that doubles in power with a reduction of the load resistance.

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#385514 - 11/11/12 11:49 PM Re: Pre-Amps and Amps questions. [Re: dakkon]
pmbuko Offline
shareholder in the making

Registered: 04/02/03
Posts: 16280
Loc: Leesburg, Virginia
Does anybody here take issue with the results of double-blind tests, the data from which show, statistically, that listeners are unable to discern any audible difference between competently designed amps of differing designs (e.g. tube, solid state, class A, B, etc.) and price points?
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#385517 - 11/12/12 01:13 AM Re: Pre-Amps and Amps questions. [Re: PaulCanada]
dakkon Offline
connoisseur

Registered: 02/08/04
Posts: 1846
no, not really... the general concensus around here is thst most solid state amps "sound" the same. i personally have never heard a tube amp, so i can not speak to that... i have solid state amps at 3 different price points, ranging from the 1,000$ area to the many many thousands of $$ area. to me, they all "sound" the same.. the big difference is the amount of power.

one thing you may notice is, me and john are discussing more the power and calculation there of, with no mention to the "sound". This is primairly because me and him both agree, and know we both agree on this point smile.

That's my take anyhow....

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#385526 - 11/12/12 10:11 AM Re: Pre-Amps and Amps questions. [Re: dakkon]
Andrew Offline
Axiom Engineer
veteran

Registered: 12/18/01
Posts: 176
My personal bent on this, after having designed, modified, and lived with numerous amplifiers over the years with differing topologies and active components, is that the question is really too complex to answer. There are too many different parameters of an amplifier that can and do change the sound. Our biggest problem is the specifications that people typically look at when trying to compare amplifiers. They are mainly meaningless, other than to quantify a measurement that is performed on a test bench with a contrived load that does not in any way resemble a loudspeaker. The interaction between amplifier and load is extremely complex, and the math involved is even more daunting because with music you are dealing with a constantly moving target.
A good example that I can thrown out there is if we were to take a fictional Class A/B amplifier and Class D amplifier, both with identical power supply capability and both rated at 100 watts into an 8 ohm load, at 1kHz with 1% THD. They both have a frequency response at 1 watt of 10Hz-30kHz. These two competently designed amplifiers should sound similar if not identical if run within their rated power. Listening to them they sound totally different beyond a certain listening level. Why would that be? Well, we have not speicified the power bandwidth of the amplifiers. Turns out the Class A/B example can deliver full power at all frequencies, but the Class D example has limited output power in the low bass and high treble. There are numerous cases, such as the one described, that CAN account for two similar amplifiers sounding different. Throw a transformer-coupled tube amplifier into the mix and now you have added non-linear frequency response to the table! smile

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#385528 - 11/12/12 10:27 AM Re: Pre-Amps and Amps questions. [Re: PaulCanada]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17781
Loc: NoVA
OH BURN.
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#385529 - 11/12/12 10:52 AM Re: Pre-Amps and Amps questions. [Re: PaulCanada]
dakkon Offline
connoisseur

Registered: 02/08/04
Posts: 1846
I guess the point i was trying to make, was that the math gets ridiculously hard pretty quick when dealing with an AC circuit..

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