Amplifiers: Effects on sound if power does not double when impedance is halved? - Page 6 - AVS Forum | Home Theater Discussions And Reviews
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post #151 of 186 Old 02-11-2017, 09:38 AM
 
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Quote:
Originally Posted by PrimeTime View Post
A lot of this is semantic wrangling.

"Transconductance" simply means that the output conductance is controlled by the input voltage.

Conductance = 1/Resistance; the unit is, unsurprisingly, the mho ("ohm" spelled backwards). This is a basic property of MOSFET devices. When used in a conventional audio power amplifier circuit, however, the unit becomes a voltage source due to significant amounts of negative voltage feedback.

Speakers respond to current, as that is what activates the electromagnetic transduction. Current, however, doesn't exist in a vacuum. When produced by a power amplifier, which is a constant-voltage source, current becomes the dependent variable (y-axis) which, for a given output voltage, is a function of the complex transducer impedance (x-axis), itself a function of frequency and other complex variables.
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Speakers respond to current, as that is what activates the electromagnetic transduction.
BINGO! Tomas and myself have been saying this all along!

Quote:
When produced by a power amplifier, which is a constant-voltage source,
Amplifiers are not constant voltage sources. This is a misnomer. They're voltage output is proportional to the input, regardless of load in theory; however in real application, Voltage sages as / when impedances drop below nominal. As well evidenced by my previous posts.

Regardless of what type of design an audio amplifier is, it will always output current, and it is current that is the prime mover in powering the speakers motor system, if you will.

Bill has been incorrect, each time that he has directly stated or implied that a speaker ignores current, a speaker doesn't care about current, or anything to the same affect.

The math, measurements and schematic presented within this thread, objectively bear out these truths.

Peace
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post #152 of 186 Old 02-11-2017, 09:41 AM
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Quote:
Originally Posted by PrimeTime View Post
When used in a conventional audio power amplifier circuit, however, the unit becomes a voltage source due to significant amounts of negative voltage feedback.
Correct, this is a prime limitation of 'voltage drive' itself. The back history regarding current drive is an interesting read. The circuit topology inside the Hafler design is leveraging in solid state form the advantages of 'current drive' used in vacuum tube amps. This is why Jim Strickland' patented Trans.ana amplifier became the benchmark in the industry. IIRC this topology was later adopted by Dynaudio and Meyer sound powered monitors.

http://diy.ecpaudio.com/2010/08/the-...ode-based.html

“But, as I was about to disassemble it and put the parts away, I wondered what the circuit would sound like without any feedback. That is, just a pentode with a transformer load. I figured it was going to be awful, so I was not prepared for what I heard, which was near sonic bliss. From note one, this was something special.”

“Turns out, I had built a transconductance amp more or less by accident. Most amplifiers that people use are voltage sources, with a low output impedance. A transconductance amp on the other hand is a current source, with a high output impedance”
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post #153 of 186 Old 02-11-2017, 10:41 AM
 
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Originally Posted by Madmax67 View Post
I did for well over 20 years on a retail sales floor dealing with the general public 6 days a week 10 to 12 hours a day and the overwhelming majority didn't know ...
Right, thus that has been your observation. That's what it is.
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post #154 of 186 Old 02-11-2017, 10:43 AM
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OK, you caught me in a haggling mood, so I'll play.

Quote:
Originally Posted by Jady Jenkins View Post
BINGO! Tomas and myself have been saying this all along!

Amplifiers are not constant voltage sources. This is a misnomer. They're voltage output is proportional to the input, regardless of load in theory;
"Constant voltage source" and "voltage source" are terms of art used interchangeably. A more accurate term would be VCVS, or Voltage Controlled Voltage Source.

Quote:
... however in real application, Voltage sages as / when impedances drop below nominal. As well evidenced by my previous posts.
A true voltage source has zero source impedance, which means that it will supply, Krell-like, whatever amount of current that the load requires for a given voltage state. Audio amplifiers have near-zero source impedances; as such they will supply virtually any amount of power required that is available to them from their power supply. Reductions of power due to load are imposed by power supply limitations or specialized load-monitoring circuitry, not the amplifier itself.

Quote:
Regardless of what type of design an audio amplifier is, it will always output current...
Disconnect the speaker/load and there won't be any output current.

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Bill has been incorrect, each time that he has directly stated or implied that a speaker ignores current, a speaker doesn't care about current, or anything to the same affect.
That is a not an accurate characterization of Bill's post.
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post #155 of 186 Old 02-11-2017, 10:57 AM
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Greetings Prime Time,

I quoted Bill on the previous page...

Quote:
Originally Posted by PrimeTime View Post
That is a not an accurate characterization of Bill's post.
Quote:
Bill Fitzmaurice
Current does vary with frequency, and by dint of that so does power delivery, but speakers respond to voltage, not current.

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post #156 of 186 Old 02-11-2017, 11:15 AM
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Quote:
Originally Posted by Tomas2 View Post
Please take some time and parse the Hafler .pdf (schematic) I provided in post #133 . The speaker completes a series circuit.

Speakers excursion is without a doubt a product AC current.

It doesn't help your case that the amp schematic is that of a typical voltage amplifier just as the other 99.99999999% out in the wild.


Also note that conventional loudspeakers with a passive crossover have impedance swings at the crossover points and all loudspeakers have impedance swings at the lf corner frequencies .This will cause frequency response errors requiring dsp/eq.


In practice 99.999999% of all audio systems are voltage controlled.


In theory a current drive amplifier could be implemented in active systems with dsp for crossover and eq/roomcorrection.




http://www.current-drive.info/disto/65
http://www.current-drive.info/disto/68
http://www.parts-express.com/pedocs/...ions-46422.pdf


Note that the distortion examples only apply for 'the typical loudspeaker's without copper pole sleeves and long coil short gap and these at non linear to begin with.
A copper pole sleeve reduces intermodulation distortion. A short coil long gap speaker is more linear and together with the copper pole sleeve is perfectly happy with voltage drive.


However there could be a great advantage when using current drive amplifiers. Brownie points for figuring this one out.
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post #157 of 186 Old 02-11-2017, 11:30 AM
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Originally Posted by Frank Derks View Post
It doesn't help your case that the amp schematic is that of a typical voltage amplifier just as the other 99.99999999% out in the wild.
Greetings Frank,

The Hafler P1000 output stage topology is an example of 'current drive' in solid state form. The amp is fundamentally different than voltage drive systems. This design effectively models the behavior of earlier tube base systems. It also illustrates my conjecture...speaker excursion is simply a product of AC current regardless of the voltage present.

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post #158 of 186 Old 02-11-2017, 11:43 AM
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Quote:
Originally Posted by Jady Jenkins View Post
Amplifiers are not constant voltage sources. This is a misnomer. They're voltage output is proportional to the input, regardless of load in theory; however in real application, Voltage sages as / when impedances drop below nominal. As well evidenced by my previous posts...

Peace

A moot argument because the effect of voltage sagging is negligible for a voltage amplifier operating within it's design limits.
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post #159 of 186 Old 02-11-2017, 11:58 AM
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Quote:
Originally Posted by Tomas2 View Post
Please take some time and parse the Hafler .pdf (schematic) I provided in post #133 . The speaker completes a series circuit.

Speakers excursion is without a doubt a product AC current.


From it's spec's:
Damping Factor: 900 (to 1kHz); 400 (to 10kHz); 40 (to 100kHz)


I hope you know how to calculate it's output impedance. Hint the result is too low for this amp to be a current drive amplifier.


In the schematic there is voltage feedback that sets the gain. The current through the loudspeaker is not measured and fed back as voltage to the input pair. (Only measured for soa protection)


Excerpt from manual:
"
The circuitry used in the Hafler Professional power amplifiers is our trans•ana (TRANSconductance Active Nodal
Amplifier) topology. The trans•ana technology operates the output stage with its full voltage gain, which allows
the input stage to operate from a low voltage regulated supply. The signal is then shifted up in level to the high
voltage section by the driver stage which forms an active node at ultrasonic frequencies. This results in very stable,
highly linear operation.
"


This is marketing speak that you misinterpreted.
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post #160 of 186 Old 02-11-2017, 12:00 PM
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Frank,

Earlier in this thread, you buttressed the position that speakers excursion is fundamentally a product of applied voltage. I think at this juncture you would agree i.e.
Quote:
Originally Posted by Jady Jenkins View Post
Bill has been incorrect, each time that he has directly stated or implied that a speaker ignores current, a speaker doesn't care about current, or anything to the same affect.
Jady's post being an empirical fact ?

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post #161 of 186 Old 02-11-2017, 12:20 PM
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Originally Posted by LFEer View Post
Right, thus that has been your observation. That's what it is.
More like a longitudinal study but define it however you want it's still correct😉. You asked earlier for long time retail experience from someone dealing with the general public and now that I'm giving you some( 22 years worth) it's just my observation but earlier it was his lack of having any retail experience that was the big disqualifier 😏. I'm going to take a few aspirins now. Good talk.👍
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Originally Posted by Madmax67 View Post
but earlier it was his lack of having any retail experience that was the big disqualifier 😏.
Oh, I think he does.
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post #163 of 186 Old 02-11-2017, 01:15 PM
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Voltage drive:


+/1 Volt in with gain 20dB +/-10 Volt out over 10 Ohm impedance = +/-1 Ampere current and loudspeaker moves to it's excursion points +/mm1 from mid position. (Cause and effect)
+/10 Volt in with gain 20dB +/100 Volt out over 10 Ohm impedance = +/-10 Ampere current and loudspeaker moves to it's excursion points.
If ls is linear the you would expect +/-10mm but alas voice coil moves out of linear range causing less force and compressing or expanding air in cabinet resist movement so excursion might get to +/- 8mm.
Back emf causes amplifier to compensate by applying more voltage. More power to drive the cone against the opposing forces!


Current drive:
0 volt input 0 Ampere output over loudspeaker impedance = no current, no movement, cone stays at mid excursion position. We all agree on this one.
+/-1 Volt input translate to +/-1 Ampere output current into the ls impedance. and excursion happens. Let's say +/-1mm.

+/-10 Volt translates to +/-10 Ampere output current.
This translates to +/-10 Amp output current into loudspeaker impedance and excursion happens. +/-8mm. No difference. Back emf due to the opposing forces subtracts from the measured output current and the amplifier compensates.


So far so good but what happens at the loudspeakers resonant frequency. Less power is required (higher impedance at fs 1) so with voltage drive excursion is still +/-8 mm but there is lower current draw.
Less power is required.


With current drive output is always the same amount of current so at fs the output voltage from the amplifier shoots up. (Oops clipping might become a problem.)
Now you get higher excursion at fs than at the nominal impedance 10Ohms.
This is why it is mentioned that eq is required to compensate for the non linear frequency response resulting from a non linear impedance curve.

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post #164 of 186 Old 02-11-2017, 01:36 PM
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Quote:
Originally Posted by Tomas2 View Post
Frank,

Earlier in this thread, you buttressed the position that speakers excursion is fundamentally a product of applied voltage. I think at this juncture you would agree i.e.


Jady's post being an empirical fact ?

Apply voltage over impedance resulting in current flow and cone moves.
Apply current into impedance, resulting in voltage over loudspeakers, and the same happens because current flows and cone moves.


Voltage drive = no problems with frequency response.
Current drive = problems with frequency response.
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post #165 of 186 Old 02-11-2017, 01:56 PM
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Quote:
Originally Posted by LFEer View Post
Oh, I think he does.
Aaah ok. You were going for the old AVS classic, "I can't prove it but I think you've got something to sell" disqualifier. It's why I list my occupation in my sig. here but in other forums they either don't have a place for it or it's not relevant like my support account on XDA Developers. I've worked with some uninformed agenda driven salespeople in my time and I've worked with some really smart ones who studied and knew their product front to back ( mostly from when the .com bubble burst last time with fiber optics expansion.) Good thing about seeing them all face to face each day though was I actually knew their backgrounds and what type of person they were because I saw them every day so I'll leave that particular innuendo alone as I don't know for a fact one way or the other plus there's plenty of long time respected posters here with an "open for business" sign in their Sig. I'll return to reading this discussion and to all here who have contributed their own technical knowledge for us "eager to learn types" to pour through and learn from I say, "thank you" and that includes you @LFEer 👍.
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post #166 of 186 Old 02-11-2017, 04:33 PM
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Quote:
Originally Posted by Frank Derks View Post
It doesn't help your case that the amp schematic is that of a typical voltage amplifier just as the other 99.99999999% out in the wild.
Nothing could be further from the truth.

And I said above, there is nothing typical topology wise regarding this patent

"The driver stage of the Trans*nova (or Trans*ana) is thus a highly refined bilateral “current Source” –a transcondutance stage – driving the MOSFET gates directly. So now the 100% negative feedback is still present, because any voltage change coming back from the load side of things is NOT reduced. However, the important thing is that it now takes exactly the same gate voltage swing to drive the MOSFETS it would have, had the feedback RC network never been added."

"Lest it appear we have fooled Mother Nature here, let it be clarified that what we have done is only a better realization of her rules. In fact, there is a “payback” here we - must supply higher signal current to the gate “node” than we would have had to without the RC (shunt) feedback. Turns out this is actually an advantage."

http://www.hafler.com/pdf/the-transnova-topology.pdf

I'll let you read the rest here when time permits....

Cheers

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post #167 of 186 Old 02-11-2017, 04:59 PM
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Quote:
Originally Posted by Tomas2 View Post
Nothing could be further from the truth.

And I said above, there is nothing typical topology wise regarding this patent

"The driver stage of the Trans*nova (or Trans*ana) is thus a highly refined bilateral “current Source” –a transcondutance stage – driving the MOSFET gates directly. So now the 100% negative feedback is still present, because any voltage change coming back from the load side of things is NOT reduced. However, the important thing is that it now takes exactly the same gate voltage swing to drive the MOSFETS it would have, had the feedback RC network never been added."

"Lest it appear we have fooled Mother Nature here, let it be clarified that what we have done is only a better realization of her rules. In fact, there is a “payback” here we - must supply higher signal current to the gate “node” than we would have had to without the RC (shunt) feedback. Turns out this is actually an advantage."

http://www.hafler.com/pdf/the-transnova-topology.pdf

I'll let you read the rest here when time permits....

Cheers


Yes there is trans conductance going on in the amplifiers inner stages that enables the low voltage input stage to drive the output stage that uses significantly higher output voltage.
This doesn't make it a trans conductance amplifier as far as the load is concerned. The overall voltage feedback makes this amp a voltage amplifier. There is no current to voltage feedback from the outputs stage back to the differential input stage.


There is no current sense resistor connected in series with the loudspeaker speaker. The ls is directly connected between output and ground.
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post #168 of 186 Old 02-11-2017, 05:46 PM
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Quote:
Originally Posted by Frank Derks View Post
This is marketing speak that you misinterpreted.
FYI the words you just quoted were penned by the designer Jim Strickland himself..nothing to do with marketing speak.

Put another way...if this design (call it magic if you will) effectively does the exact same thing i.e. pentode tube "current source" amplifier ? Then just don't look under the hood With respect to speaker load interaction with the source...they are in the end effectively the same.

Tomas
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post #169 of 186 Old 02-11-2017, 06:13 PM
 
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Quote:
Originally Posted by Frank Derks View Post
A moot argument because the effect of voltage sagging is negligible for a voltage amplifier operating within it's design limits.
Quote:
Originally Posted by Bill Fitzmaurice View Post
I think I might understand what you're trying to say, that since the impedance of a speaker varies with frequency that the power delivery would have to be constant into any impedance load for linear response. That's not the case. The voltage output of an amp is constant into any load impedance.
If that's not what you're trying to say then you'll have to further clarify it.
QUOTE]

In that you're late to this thread, I will point you to where this myth was busted when Bill first presented it.

https://www.avsforum.com/forum/91-aud...l#post50287697

https://www.avsforum.com/forum/91-aud...l#post50290817

https://www.avsforum.com/forum/91-aud...l#post50322081

https://www.avsforum.com/forum/91-aud...l#post50325369

https://www.avsforum.com/forum/91-aud...l#post50337617

https://www.avsforum.com/forum/91-aud...l#post50339297

https://www.avsforum.com/forum/91-aud...l#post50353521

https://www.avsforum.com/forum/91-aud...l#post50365865

https://www.avsforum.com/forum/91-aud...l#post50372593

https://www.avsforum.com/forum/91-aud...l#post50372785

https://www.avsforum.com/forum/91-aud...l#post50372977

https://www.avsforum.com/forum/91-aud...l#post50404473
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post #170 of 186 Old 02-11-2017, 06:17 PM
 
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Quote:
Originally Posted by Frank Derks View Post
Apply voltage over impedance resulting in current flow and cone moves.
Apply current into impedance, resulting in voltage over loudspeakers, and the same happens because current flows and cone moves.


Voltage drive = no problems with frequency response.
Current drive = problems with frequency response.
I agree will all of these statements. However, frequency aberrations relating to current drive approaches are based on early iterations of the design topology. It's plausible to overcome the frequency response issues, which are primarily rooted in very high series resistances.
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post #171 of 186 Old 02-11-2017, 08:14 PM
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After reviewing all the information inside this very thread, clearly the premise that all well designed power amps sound the same IMO has no merit...

Tomas
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post #172 of 186 Old 02-11-2017, 10:26 PM
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Quote:
Originally Posted by Tomas2 View Post
After reviewing all the information inside this very thread, clearly the premise that all well designed power amps sound the same IMO has no merit...
Nobody I know says that.
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I would say to test an amplifier power, it would be better to use a large floorstander to determine the bass quality. I have a large B&W 801 nautilus and the pair of emotiva XPA1 controls the 15inch woofer tighter compared to my rotel RB1090. At all types of volume, low to loud, the mono block XPA1 controls the woofer better. But if you were to use a small floorstander or bookshelf, amplifier power may not be so obvious i guess.
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post #174 of 186 Old 02-12-2017, 05:48 AM
 
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Quote:
Originally Posted by Jady Jenkins View Post
QUOTE]
In that you're late to this thread, I will point you to where this myth was busted when Bill first presented it.
The only myth I see is the one where you claim to have credentials that are in the same game, let alone the same league, as Bill where speakers are concerned. As for my credentials, you can call me Doctor, PhD.EE.
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post #175 of 186 Old 02-12-2017, 07:42 AM
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Quote:
Originally Posted by RickJames View Post
The only myth I see is the one where you claim to have credentials that are in the same game, let alone the same league, as Bill where speakers are concerned. As for my credentials, you can call me Doctor, PhD.EE.
With all due respect, referencing the evidence embedded within this very thread alone, several myths have indeed been "busted".

Quote:
Bill Fitzmaurice
I think I might understand what you're trying to say, that since the impedance of a speaker varies with frequency that the power delivery would have to be constant into any impedance load for linear response. That's not the case. The voltage output of an amp is constant into any load impedance.
#1

Quote:
Prime Time
..When produced by a power amplifier, which is a constant-voltage source
#2

Quote:
Bill Fitzmaurice
Current does vary with frequency, and by dint of that so does power delivery, but speakers respond to voltage, not current.
#3

These quoted post are linked in such a manner a false premise permeates each.

Earlier I made this conjecture:

"2) Speaker excursion is a product of 'current' regardless of the voltage presented"

When asked (Bill or Frank) if this statement seems empirically valid ? A simple yes or no query. Franks reply reads as follows..

Quote:
Frank Derks
If two would be the case then you would getting different voltages for different speaker designs. This is obvious not the case.

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Last edited by Tomas2; 02-12-2017 at 08:31 AM.
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post #176 of 186 Old 02-12-2017, 09:05 AM
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Nothing could be further from the truth.

And I said above, there is nothing typical topology wise regarding this patent

"The driver stage of the Trans*nova (or Trans*ana) is thus a highly refined bilateral “current Source” –a transcondutance stage – driving the MOSFET gates directly. So now the 100% negative feedback is still present, because any voltage change coming back from the load side of things is NOT reduced. However, the important thing is that it now takes exactly the same gate voltage swing to drive the MOSFETS it would have, had the feedback RC network never been added."

"Lest it appear we have fooled Mother Nature here, let it be clarified that what we have done is only a better realization of her rules. In fact, there is a “payback” here we - must supply higher signal current to the gate “node” than we would have had to without the RC (shunt) feedback. Turns out this is actually an advantage."

http://www.hafler.com/pdf/the-transnova-topology.pdf

I'll let you read the rest here when time permits....

Cheers



I quoted from the hafler P1000 manual:
>>>
The circuitry used in the Hafler Professional power amplifiers is our trans•ana (TRANSconductance Active Nodal
Amplifier) topology. The trans•ana technology operates the output stage with its full voltage gain, which allows
the input stage to operate from a low voltage regulated supply. The signal is then shifted up in level to the high
voltage section by the driver stage which forms an active node at ultrasonic frequencies. This results in very stable,
highly linear operation.<<<


This trans*ana technology used in the P1000 is not the same topology as the transnova mentioned in the the-transnova-topology.pdf you link to.


The Hafler P1000 is a voltage source amplifier.
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post #177 of 186 Old 02-12-2017, 09:10 AM
 
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Originally Posted by Tomas2 View Post
After reviewing all the information inside this very thread, clearly the premise that all well designed power amps sound the same IMO has no merit...

Tomas
To come up with opinion on amp sound, one would need to listen with ears. Something tells me that you've never done a level matched double blind listening test. I doubt you've even been near one.
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post #178 of 186 Old 02-12-2017, 09:24 AM
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Originally Posted by Tomas2 View Post
...
Earlier I made this conjecture:

"2) Speaker excursion is a product of 'current' regardless of the voltage presented"

When asked (Bill or Frank) if this statement seems empirically valid ? A simple yes or no query. Franks reply reads as follows..


That conjecture (2) you made was preceded by another conjecture "1) The power amp output being a relatively high current (AC) source" (#135)
From this post and your other posts I get the impression that your position is that all amplifiers are current sources.
And then you posted a schematic from an amplifier that you claim acts as a current source but in reality is voltage source....


In electronics a current source delivers a constant current and a voltage source delivers a constant voltage.
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post #179 of 186 Old 02-12-2017, 09:30 AM
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After reviewing all the information inside this very thread, clearly the premise that all well designed power amps sound the same IMO has no merit...
Quote:
Originally Posted by m. zillch View Post
Nobody I know says that.
+1 Zillch, myself included

If you took a quick poll of this forum (collective) opinion on the subject, most citing past ABX trials, they seem to conclude subjectively "zero difference"

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post #180 of 186 Old 02-12-2017, 09:32 AM
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FYI the words you just quoted were penned by the designer Jim Strickland himself..nothing to do with marketing speak.

Put another way...if this design (call it magic if you will) effectively does the exact same thing i.e. pentode tube "current source" amplifier ? Then just don't look under the hood With respect to speaker load interaction with the source...they are in the end effectively the same.

Tomas
Why do you want a solid state amplifier that mimics a mediocre pentode tube "current source" amplifier?
(It is wrongly characterized as "current source". Tubes have higher output impedances and that makes it a poor voltage source)
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