are all the amps set to the same gain and the same frequency response and the same input impedance and the same RF filtering response?
i.e. are the amplifiers comparable?
They are not the same since differences in the way they operate. Different gain, output impedance etc. Nonetheless what I wrote is about sound characteristic and bass quality not the filtering. Quantity doesn't equals with quality.
Different frequency response and different gain make an apparently enormous difference to relative levels of the different frequencies.
Frequency response is completely flat in the wide bandwith so what's the problem?
You simply don't get it as majority of us. We usually force the meaning into our understandig of physical phenomena. We think that there is direct linear relation between physical signal emited and what we hear. That's bad understanding. I mean we don't hear signal directly. Signal is heard by ears, then processed in brain (the whole brain not certain part of it like speach). Brain pulls out all the stops to make a sense out of signal and after that present it to the consciousness.
Have a look here - page 17:
http://www.firstwatt.com/pdf/art_f6_baf.pdf
So "Different frequency response and different gain " don't make an apparently enormous difference in a way we think.
The bottom line is that I don't know what makes difference but it's not you try to describe.
If two signals that are measurably different are heard as the same, then by definition, they are not audibly different -- the measured difference is not enough or is masked.
If two audibly different signals are heard as the same, then it is time to get a hearing test.
If two audibly different signals are heard as different, have another drink and listen some more....
If two signals that are identical ( ie cannot be audibly different) are heard differently, then the difference is not real -- it is imagined.
Consequently, for a difference to be real, it must be measurably real.
If, as NP says, we are sensitive to harmonic structure, then frequency response matters a lot.
If two audibly different signals are heard as the same, then it is time to get a hearing test.
If two audibly different signals are heard as different, have another drink and listen some more....
If two signals that are identical ( ie cannot be audibly different) are heard differently, then the difference is not real -- it is imagined.
Consequently, for a difference to be real, it must be measurably real.
If, as NP says, we are sensitive to harmonic structure, then frequency response matters a lot.
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So use baffle step correction and don't bother what I'm saing about.
I'll have another drink then enyoing music.
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Don't forget that an amplifier's ability to dampen a loudspeaker is limited by the DCR of the voice coil. Diminishing returns beyond a dampening factor of about a hundred or so. But I know many tube amps have dampening factors much worse than 100. Not sure about single ended transistor designs. They would probably be worse due to the lack of negative feedback in many of their designs. It's a trade-off. More negative feedback means better dampening but worse in other things like TIM distortion. But IMO, those amps that boast a dampening factor of like 1000 are just silly. They may sound very good, but it's not by virtue of their dampening. And that 1000 requires an insane amount of open-loop gain, meaning many stages that introduce more and more distortion or high gain stages that have poles in the range of 200Hz, and lots of negative feedback.
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One would think so, but you have to be careful with that - I have seen
examples where the DF is equal between to amplifiers and the subjective
bass response is different, even at low power levels.
Best example, Aleph 1.2 and X600 into Wilson Watt/Puppies.
😎
"What's dampening factor and why hundred instead of 75 or 125?"
Dampening factor is the ratio of the speaker's impedance to the amplifier's output impedance. The idea is that the lower the dampening factor, the better control the amp has over the loudspeaker, due to the ability of the loudspeaker motor to act like a generator. And when a load is put on this generator(the amplifier), it offers resistance to the motion of the cone, or dampening it. The amount of dampening is determined by the BL product(length of wire in the magnetic gap times the magnetic field strength), the moving mass of the speaker(cone + voice coil + spider etc) and the impedance of the circuit. Neglecting inductive and capacitive effects, this is the output impedance of the amp plus the resistance of the voice coil and interconnects. The resulting current flowing as a result of cone motion will be the voltage generated by the voice coil in the gap will be divided by this impedance. The greater this current, the greater the dampening.
A loudspeaker(assuming a dynamic driver here and not a ribbon or electrostat) relies on a certain amount of dampening to maintain flat frequency response and good transient response. Too much or too little dampening means the speaker can have bumps or dips in the response, or have ringing or slow transient response.
Of course the number 100 is not that precise. Just a reference point I threw out. I've read some articles claiming 30 or 40 is good enough. At 100, the amplifier's output impedance has the potential to change the alignment of a loudspeaker by 1%. To put this in perspective, day to day air pressure changes due to weather, which can also change the alignment of a loudspeaker, are about 5%.
Dampening factor is the ratio of the speaker's impedance to the amplifier's output impedance. The idea is that the lower the dampening factor, the better control the amp has over the loudspeaker, due to the ability of the loudspeaker motor to act like a generator. And when a load is put on this generator(the amplifier), it offers resistance to the motion of the cone, or dampening it. The amount of dampening is determined by the BL product(length of wire in the magnetic gap times the magnetic field strength), the moving mass of the speaker(cone + voice coil + spider etc) and the impedance of the circuit. Neglecting inductive and capacitive effects, this is the output impedance of the amp plus the resistance of the voice coil and interconnects. The resulting current flowing as a result of cone motion will be the voltage generated by the voice coil in the gap will be divided by this impedance. The greater this current, the greater the dampening.
A loudspeaker(assuming a dynamic driver here and not a ribbon or electrostat) relies on a certain amount of dampening to maintain flat frequency response and good transient response. Too much or too little dampening means the speaker can have bumps or dips in the response, or have ringing or slow transient response.
Of course the number 100 is not that precise. Just a reference point I threw out. I've read some articles claiming 30 or 40 is good enough. At 100, the amplifier's output impedance has the potential to change the alignment of a loudspeaker by 1%. To put this in perspective, day to day air pressure changes due to weather, which can also change the alignment of a loudspeaker, are about 5%.
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One other thought I had. A high dampening factor does probably mean that high amounts of open loop gain and negative feedback are used to achieve this. The result being the amplifier's ability to correct distortions in it's devices and, perhaps more importantly for the bass frequencies, overcome distortions introduced by modulation of the power supply rails, is really good. These things(high open loop gain and large amounts of negative feedback) can be detrimental at high frequencies depending on the design of the amp. But it's great at low frequencies. And I've read that we can be more sensitive to distortion in the bass range due to our ears rolling off at low frequencies. The fundamental is heard at a reduced level relative to the harmonics, which is the opposite of what happens at frequencies close to the upper range of our hearing.
So choosing an amp, at least for bass performance, based on dampening factor may not be all that bad. But I would add, as Nelson Pass said, that a low dampening factor doesn't necessarily mean bad bass performance.
So choosing an amp, at least for bass performance, based on dampening factor may not be all that bad. But I would add, as Nelson Pass said, that a low dampening factor doesn't necessarily mean bad bass performance.
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The way you explain it, it sounds almost the same as what is commonly known asl damping factor 😎
I was trying to see if he catches it. But... 
well , one need to declare about what we are contemplating .... speakers , or welding apparatus testing gear
So we need special speakers for welders then ....
My point is that in the end we are not listening to the signal as spectrum analysing gear but what is transformed by the brain and then given to our consciousness or mind. There are many examples showing that substantial change in physical parameters like impedance don't have any or very little influence on what we hear.
My point is that in the end we are not listening to the signal as spectrum analysing gear but what is transformed by the brain and then given to our consciousness or mind. There are many examples showing that substantial change in physical parameters like impedance don't have any or very little influence on what we hear.
It's a very insightful comment from Mr. Pass himself. I was thinking about it in the bed this morning...
If I do blind test between 3 amps with damping factor 10, 100 and 1000, I think I can easily tell which amp is which due to the base response, BUT if all amps have the same damping factor, I probably still hear the difference between them regarding the bass response. I'm not sure if I can tell which is CLASS A and which is AB, if the comparison is about A vs AB.
I love to hear the comparison Aleph 1.2 and X600 on Wilson Watt/Puppies, must be very interesting.
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I'v mostly built and heard Class AB amplifiers and my experience was that the bass was all over the place. There was one amplifier, my TGM8, which to my ears produced the punchiest, cleanest and most powerful bass of all of them. I'm not sure why. Some of the design features that may be important:
1) the pcbs have on-board rail caps very close to the output power devices, in a CRC configuration with 4,700uF per C
2) there is a high feedback factor so a relatively high damping factor
3) the output is a CFP, so lots of local feedback around the output devices (40dB or so) which ensures they are very linear
4) the outputs are a combination of BJT and IRF MOSFETs operating in parallel. The BJT operates in Class AB up to around 1A to 2A. At this point the MOSFET kicks-in, operating in Class C with power limited by rail voltage (+/- 50V). The result is a high transconductance output without any 'beta droop'
I've not hear an amp like it for bass performance, even my Bryston amp is outshined.
1) the pcbs have on-board rail caps very close to the output power devices, in a CRC configuration with 4,700uF per C
2) there is a high feedback factor so a relatively high damping factor
3) the output is a CFP, so lots of local feedback around the output devices (40dB or so) which ensures they are very linear
4) the outputs are a combination of BJT and IRF MOSFETs operating in parallel. The BJT operates in Class AB up to around 1A to 2A. At this point the MOSFET kicks-in, operating in Class C with power limited by rail voltage (+/- 50V). The result is a high transconductance output without any 'beta droop'
I've not hear an amp like it for bass performance, even my Bryston amp is outshined.
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