[G Georgopoulos]

Part of the beauty of some (primarily lower power and often single ended) class A amps is the simplicity of their circuitry. I think simpler circuitry often translates to better sound. Once you start getting into higher power amps, the circuitry gets more complex, and this is where I think the playing field evens out a bit to varying degrees (in terms of sound quality, distortion characteristics, etc. etc. of the different amp classes). It's all a system of trade-offs and figuring out what you enjoy listening to / what type of speaker suits your tastes, and finding a suitable amp for your sound / speaker choice.

You're absolutely right,very simple stuff,infact you could use a enhancement mosfet as common source
and a handful of other components and you have a class-a amp,2sk1058 is ideal in building simple
class-a amplifiers.

cheers

[Pneumonic]

Part of the beauty of some (primarily lower power and often single ended) class A amps is the simplicity of their circuitry. I think simpler circuitry often translates to better sound. Once you start getting into higher power amps, the circuitry gets more complex, and this is where I think the playing field evens out a bit to varying degrees (in terms of sound quality, distortion characteristics, etc. etc. of the different amp classes). It's all a system of trade-offs and figuring out what you enjoy listening to / what type of speaker suits your tastes, and finding a suitable amp for your sound / speaker choice.

No doubt we find instances where poorly designed and implemented complex ccts result in poor sound. But the same holds true of simple designs which can also be poorly designed and implemented.

But what of those ccts which are neither poorly designed nor poorly implemented?

For argument sake. We have 2 amps. One is a very powerful and complex class AB amp. The other is a very simple, class A amp. Let’s presume we hook up each of the amps to appropriate speakers, using appropriate speaker cable in appropriate rooms and play music such that neither enters, nor approaches, clipping levels. We properly measure the 2 amps to see how they are performing under such conditions.

Let’s say the powerful and complex amp is measured and is shown to perform with no audible errors in distortion, noise and frequency response. The same is true of the simpler amp. Effectively all both amps do to the inputted voltage signal is increase it by x amount of gain. Nothing more, nothing less.

If both amps are shown to add gain with no audible levels of distortion then does it really matter what cct topology they employed in order to arrive at that gain figure since both amps will sound like each other (ie like nothing)?

[Roger A. Modjeski]

No doubt we find instances where poorly designed and implemented complex ccts result in poor sound. But the same holds true of simple designs which can also be poorly designed and implemented.

But what of those ccts which are neither poorly designed nor poorly implemented?

For argument sake. We have 2 amps. One is a very powerful and complex class AB amp. The other is a very simple, class A amp. Let’s presume we hook up each of the amps to appropriate speakers, using appropriate speaker cable in appropriate rooms and play music such that neither enters, nor approaches, clipping levels. We properly measure the 2 amps to see how they are performing under such conditions.

Let’s say the powerful and complex amp is measured and is shown to perform with no audible errors in distortion, noise and frequency response. The same is true of the simpler amp. Effectively all both amps do to the inputted voltage signal is increase it by x amount of gain. Nothing more, nothing less.

If both amps are shown to add gain with no audible levels of distortion then does it really matter what cct topology they employed in order to arrive at that gain figure since both amps will sound like each other (ie like nothing)?

I would like to point out as I have previously that the things that have to be done in high power amps. Current limiters, reduced bias and high voltage swings can cause problems into various loads. Low power amps do not usually have limiters as they don't need them. I will go so far as to say the low voltage high current amplifiers have a far better chance of sounding better on a variety of loads than high power amps when used in their voltage range. When you exceed 25 volt rails on a bipolar transistor amp you start to need limiters for short circuit protection. Anyone care to say what power you get from 25 volt rails at 8 ohms? What happens at 50 volt rails?

I have experienced the problems of high power amps with many speakers. There are speakers where I had to put a 1 or 2 ohm resistor in series to get the limiters to stop cutting in. Of course that reduced the damping markedly so I am not saying that is a solution except in a pinch. At least the 250 watt amp stopped clipping at low power.

I think people have to know more about the problems encountered in high power amps. That is the point of my entering this discussion.

I also think most people here find that amps sound like something.

[Pneumonic]

I would like to point out as I have previously that the things that have to be done in high power amps. Current limiters, reduced bias and high voltage swings can cause problems into various loads. Low power amps do not usually have limiters as they don't need them. I will go so far as to say the low voltage high current amplifiers have a far better chance of sounding better on a variety of loads than high power amps when used in their voltage range. When you exceed 25 volt rails on a bipolar transistor amp you start to need limiters for short circuit protection. Anyone care to say what power you get from 25 volt rails at 8 ohms? What happens at 50 volt rails?

I have experienced the problems of high power amps with many speakers. There are speakers where I had to put a 1 or 2 ohm resistor in series to get the limiters to stop cutting in. Of course that reduced the damping markedly so I am not saying that is a solution except in a pinch. At least the 250 watt amp stopped clipping at low power.

I think people have to know more about the problems encountered in high power amps. That is the point of my entering this discussion.

I also think most people here find that amps sound like something.

Roger, indeed, one may encounter issues if the amp isn't up to the job asked of it. But, with any of the many number of high powered amps out there that are well designed, have at er. 

Also, keep in mind that low power has as many potential issues as does high power designs should the user come anywhere close to placing the amp in non linear operation situation. There is nothing worse than the sound of a clipping amp! Also, let's not forget that load swings can also negatively impact fr with tube amps and must be acknowledged as well. 

As for sounding different. Too few audiophiles have actually properly measured their system under their own, specific, operating conditions to even know if they have properly functioning gear. As such, there opinion is purely subjective and, since none of us hears the same, or have the exact same preferences, or work off the exact same subjective definitions of what sound sounds like, is it any wonder why people hear differences?  In addition, many/most? fail to do properly administered comparisons, often times relying on results of non level matched and sighted comparisons. These testing conditions are fraught with inconsistences and errors and are a very large reason why no two people in this industry agree with each other. 

Answers, presuming RMS values, ~78w and 312w. 

[RDavidson]

No doubt we find instances where poorly designed and implemented complex ccts result in poor sound. But the same holds true of simple designs which can also be poorly designed and implemented.

But what of those ccts which are neither poorly designed nor poorly implemented?

For argument sake. We have 2 amps. One is a very powerful and complex class AB amp. The other is a very simple, class A amp. Let’s presume we hook up each of the amps to appropriate speakers, using appropriate speaker cable in appropriate rooms and play music such that neither enters, nor approaches, clipping levels. We properly measure the 2 amps to see how they are performing under such conditions.

Let’s say the powerful and complex amp is measured and is shown to perform with no audible errors in distortion, noise and frequency response. The same is true of the simpler amp. Effectively all both amps do to the inputted voltage signal is increase it by x amount of gain. Nothing more, nothing less.

If both amps are shown to add gain with no audible levels of distortion then does it really matter what cct topology they employed in order to arrive at that gain figure since both amps will sound like each other (ie like nothing)?

No. And that's the point I was trying to make.
However, we all know design and topology affect sound..........unless you believe all amps sound the same.
With that said, I think simple class A circuit (single ended particularly) may always have an advantage in terms of being more transparent to the source (due to less circuitry). I'm not talking about just distortion figures, I'm talking about signal preservation through the electronic chain. But, having said that, there's no way to currently design a practical single ended class A amp that is also higher powered. So that's where well designed class A/B has a major advantage. While one amp may be more transparent, it may not have enough power for a broad range of applications. The other approach may be less transparent, but has more power and is more practical (in general). It's more of an apples vs oranges discussion than an Fuji apples vs Gala apples discussion. Apples and oranges are both good. It just depends on what you're hungry for. One wouldn't eat an orange if he/she was wanting / expecting it to taste like an apple. Know what I mean?

[Roger A. Modjeski]

Roger, indeed, one may encounter issues if the amp isn't up to the job asked of it.

Answers, presuming RMS values, ~78w and 312w.

How does one determine if the amp is up to the job? What are the parameters you suggest to check?

Answers, RMS power 25 watts for 25 volt rails, 100 watts for 50 volt rails. These are the numbers found in practical amplifiers.

[Roger A. Modjeski]

No. And that's the point I was trying to make.
However, we all know design and topology affect sound..........unless you believe all amps sound the same.
With that said, I think simple class A circuit (single ended particularly) may always have an advantage in terms of being more transparent to the source (due to less circuitry). I'm not talking about just distortion figures, I'm talking about signal preservation through the electronic chain. But, having said that, there's no way to currently design a practical single ended class A amp that is also higher powered. So that's where well designed class A/B has a major advantage. While one amp may be more transparent, it may not have enough power for a broad range of applications. The other approach may be less transparent, but has more power and is more practical (in general). It's more of an apples vs oranges discussion than an Fuji apples vs Gala apples discussion. Apples and oranges are both good. It just depends on what you're hungry for. One wouldn't eat an orange if he/she was wanting / expecting it to taste like an apple. Know what I mean?

I would like to stick to Push Pull amps as that is what I believe the OP was asking.  Single ended amps are a thing to themselves in circuits and performance (they are all class A by necessity of that topology). In tube single ended the transformer is a big issue where it does not exist in SS designs. 

I do agree the topology is a big factor along with choices of operating points for the devices.

[Pneumonic]

How does one determine if the amp is up to the job? What are the parameters you suggest to check?

Answers, RMS power 25 watts for 25 volt rails, 100 watts for 50 volt rails. These are the numbers found in practical amplifiers.

The only surefire way to know is to measure it ... hooked up to your speakers, with your chosen speaker cables, in your room and playing the most dynamic music you'll play at the highest volume level you figure you'll listen at .... to see if it's performing with inaudible distortion errors. If it is then it sounds like ..... nothing. I realize this isn't a practical solution for most. But is for some.

I was listing the maximum power ratings attainable for a CVS amp based on P=E^2/R.   

[Roger A. Modjeski]

The only surefire way to know is to measure it ... hooked up to your speakers, with your chosen speaker cables, in your room and playing the most dynamic music you'll play at the highest volume level you figure you'll listen at. I realize this isn't practical for most. But is for some.

I was listing the maximum power ratings attainable for a CVS amp based on P=E^2/R.

.

What is a CVS amp?

Your equation is for peak power not RMS and does not include practical losses. 25 volt rails usually gives about 20 volts peak which is 14 RMS.
Typical 100 watt amps have 50 volt rails with about 10 volts of loss and draw down giving 40 volts peak, 28.5 volts RMS. You might get a bit more if the losses are less.

The surefire way I use is with an oscilloscope, hooked up to the speakers playing my max level.  With that  you can see how close you are getting to the rails and if any current limiting is happening.  What measurement technique are you using?

[Roger A. Modjeski]

Plenty of good discussion.

Here's my take on slew rates and TIM.

The argument is that large amounts of NFB results in slew rate limiting which ends up in increased amounts of TIM. So, if NFB is lowered we wouldn’t see slew limiting nor increased levels of TIM.

Those who argue against such a claim suggest that it is not the level of feedback that imparts slew rate limiting and the resultant TIM but, rather, it is improperly implemented circuits done with excessive compensation that is the real cause. 

AFAIK, there is no peer reviewed evidence that audible levels of TIM exists in properly conceived gear.

As for slew rate. Slew rate indicates the slope (steepness) of the wave the amp can produce and is just a handy way of combining amplifier power (voltage) and frequency response into a single, convenient, value. It’s specified as a change of voltage over a specific period of time. This single value is not really needed as you can get more meaningful info by looking at the amps power (voltage) and its high frequency response limit. But we like convenience it seems ….. even at the cost of inaccuracies. 

By example. For an amp to produce 15v at 1 Hz, its output voltage would need to slew at a rate of 15v/second. So, a very shallow slope if viewed on a scope.  By contrast, if the voltage was increased tenfold to 150v, the slew rate would need to be 10 times faster or, in this case, 150v/second. And the slope would be 10 times steeper. If the frequency is raised from 1 Hz to, say, 10kHz, the slew rate would rise by a factor of 10k and we now get 1,500,000v/sec (or, since # is getting very large and unmanageable, expressed as v/uS instead). For an amp that outputs 150v and has a linear high frequency response of 100kHz (as is the case with most SS amps these days), the slew rate would be 150v/uS.
 
We know that output voltage determine power so lower powered amps will have smaller slew rates than higher powered amps … at the same frequency. Also, amps that have lower frequency response will have lower slew rates than amps that have higher frequency response. But, we also have seen that an amp that is spec’d out with a very high frequency response (ie 100kHz) will result in a large slew rate. But, us humans can’t hear above 20kHz so, in this case, the amp that goes to 100kHz won’t sound any different but, for a given power, it will have a slew rate that is 5x higher than that of the amp that is rated for 20kHz. And, you can almost bet that it’ll be deceitfully marketed as such. Thus the inaccuracy noted above.

It all can be confusing. Just note that, while slew rate must be high enough, a high slew rate, in and of itself alone, might not define the sound of an amp. Since all quality amps linearly produce 20kHz, it really is the voltage (power) that makes the difference when it comes to slew rates.

Hi, I was looking over some of your numbers today and wanted to see if you agree with some corrections. I kept you whole quote intact as I also don't agree with the first statement but do agree with the second. Excessive compensation is the issue not the amount of feedback.

I don't know why you started with a time period of 1 second but no matter. When you convert 1,500,000 volts per second to volts/microsecond the correct answer is 1.5 V/us. Raising the frequency from 10KHZ to 100 KHZ as in your example makes the slew rate 15 v/us, not 150.

The frequency response (usually stated at low levels of a watt) is independent of the slew rate. You can make an amp with very wide bandwidth that has a very poor slew rate. This is why slew rate became important.

It is also not true that low power amps have lower slew rates than high power amps. (granted this is true at the same frequency, but that is obvious)

[Pneumonic]

Sorry, constant voltage source for the acronym. I agree on the practicals. Yes, I scope test as well.

I am curious. Do you believe that current measurement techniques fully and adequately describe human hearing? Further, do you believe the general consensus on the distortion threshold of human hearing (as I described previously), is accurate? 

[Freo-1]

I would like to point out as I have previously that the things that have to be done in high power amps. Current limiters, reduced bias and high voltage swings can cause problems into various loads. Low power amps do not usually have limiters as they don't need them. I will go so far as to say the low voltage high current amplifiers have a far better chance of sounding better on a variety of loads than high power amps when used in their voltage range. When you exceed 25 volt rails on a bipolar transistor amp you start to need limiters for short circuit protection. Anyone care to say what power you get from 25 volt rails at 8 ohms? What happens at 50 volt rails?

I have experienced the problems of high power amps with many speakers. There are speakers where I had to put a 1 or 2 ohm resistor in series to get the limiters to stop cutting in. Of course that reduced the damping markedly so I am not saying that is a solution except in a pinch. At least the 250 watt amp stopped clipping at low power.

I think people have to know more about the problems encountered in high power amps. That is the point of my entering this discussion.

I also think most people here find that amps sound like something.

Excellent information.  Thanks for enlightening the readers here.  I've often noticed that the low to moderate power amps seemed to sound better (operated within their limits) than many of the higher powered amps of similar vintage.  Case in point:  My favorite sounding Threshold S series amps were the S-150 and S-200 after replacing the bias resistors with Mills types.  The larger amps did play louder, but some of that mid-range presence was missing with the larger amps. 

Having said that, the custom 1625 quad monoblocks I had made do sound quite a better than the 1625 monos with only a pair of valves.   The doubling of output power provides better performance across the board.

[Roger A. Modjeski]

Sorry, constant voltage source for the acronym. I agree on the practicals. Yes, I scope test as well.

I am curious. Do you believe that current measurement techniques fully and adequately describe human hearing? Further, do you believe the general consensus on the distortion threshold of human hearing (as I described previously), is accurate?

Thanks for the acronym, keep in mind that few people will know them. Its fine to use it once defined in each post.

I do not believe measurements fully describe amplifiers as we hear them. However if all the tests are done, and there are many that are not, we do get a lot closer to what makes a good amplifier.  One should pay attention to John Atkinson's measurements of frequency response alterations with a speaker load. It's the first graph he publishes in every amp measurement. Perhaps that is because he finds it most important also.

What I try to get listeners to understand is when amplifier A has some very measurable differences from amplifier B then we might want to consider how those differences influence what we hear. The very first big difference is damping, which is often ignored. Damping factors vary widely from amp to amp and their effect varies from speaker to speaker.

I would suggest a simple test. When two amplifiers are being compared, hopefully in an A/B test, make the amp with the higher damping factor equal that of the lower by adding a high quality resistor to make the damping factors equal. This resistor will usually be less than an ohm and not cause any significant loss of power. Now we have leveled the playing field to the point where other characteristics can be studied.

If it turns out that someone likes the sound of a low damping amplifier on his particular speaker and has a high damping amplifier, wouldn't it be nice to make that change with a resistor rather than a whole new amplifier?

[Pneumonic]

Hi, I was looking over some of your numbers today and wanted to see if you agree with some corrections. I kept you whole quote intact as I also don't agree with the first statement but do agree with the second. Excessive compensation is the issue not the amount of feedback.

Same here. The first sentence wasn't my opinion; just pointing out the contraction for some.

I don't know why you started with a time period of 1 second but no matter. When you convert 1,500,000 volts per second to volts/microsecond the correct answer is 1.5 V/us. Raising the frequency from 10KHZ to 100 KHZ as in your example makes the slew rate 15 v/us, not 150.

Ah, thanks for picking up my math error. Too many zeroes. My point was simply to explain how/why slew rates are posted as they are.

The frequency response (usually stated at low levels of a watt) is independent of the slew rate. You can make an amp with very wide bandwidth that has a very poor slew rate. This is why slew rate became important.

Indeed.  My point was that sneeky marketers can confuse potential buyers who want "high" slew rates simply by increasing the f (beyond the upper limit of human hearing) .... for the same given power.

In the end, all quality amps do 20k properly so don't get pulled into the trap of exceeding high slew rates sue to higher bandwidth calculations. Just worry about voltage (power) @ 20k #'s.

[Roger A. Modjeski]

Keep in mind that voltage alone has no power. You need current too. Power is voltage x current.

On another note for low power vs high power amps. I just thought of this analogy for the low power crowd.

When you want to get a lot of water through a hose and you are only a few feet from the spigot, doesn't a 15 ft hose provide a lot more water flow and power than a 100 ft hose? Does at my house.

Taking that analogy further, what is power in water? Isn't it flow x pressure?

[Pneumonic]

Thanks for the acronym, keep in mind that few people will know them. Its fine to use it once defined in each post.

Duly noted.

I do not believe measurements fully describe amplifiers as we hear them. However if all the tests are done, and there are many that are not, we do get a lot closer to what makes a good amplifier.  One should pay attention to John Atkinson's measurements of frequency response alterations with a speaker load. It's the first graph he publishes in every amp measurement. Perhaps that is because he finds it most important also.

In the absence of science, or even a single properly administered ABX test, that refutes the #'s, I do believe they do. As such, you'll find me clearly on the side of objectivity, favouring science and measurements over uncontrolled bouts of subjectivity. 

What I try to get listeners to understand is when amplifier A has some very measurable differences from amplifier B then we might want to consider how those differences influence what we hear. The very first big difference is damping, which is often ignored. Damping factors vary widely from amp to amp and their effect varies from speaker to speaker.

I would suggest a simple test. When two amplifiers are being compared, hopefully in an A/B test, make the amp with the higher damping factor equal that of the lower by adding a high quality resistor to make the damping factors equal. This resistor will usually be less than an ohm and not cause any significant loss of power. Now we have leveled the playing field to the point where other characteristics can be studied.

If it turns out that someone likes the sound of a low damping amplifier on his particular speaker and has a high damping amplifier, wouldn't it be nice to make that change with a resistor rather than a whole new amplifier?

You see, this is why I actively biamp my setup 

[Freo-1]

I do not believe measurements fully describe amplifiers as we hear them. However if all the tests are done, and there are many that are not, we do get a lot closer to what makes a good amplifier.  One should pay attention to John Atkinson's measurements of frequency response alterations with a speaker load. It's the first graph he publishes in every amp measurement. Perhaps that is because he finds it most important also.

What I try to get listeners to understand is when amplifier A has some very measurable differences from amplifier B then we might want to consider how those differences influence what we hear. The very first big difference is damping, which is often ignored. Damping factors vary widely from amp to amp and their effect varies from speaker to speaker.

I would suggest a simple test. When two amplifiers are being compared, hopefully in an A/B test, make the amp with the higher damping factor equal that of the lower by adding a high quality resistor to make the damping factors equal. This resistor will usually be less than an ohm and not cause any significant loss of power. Now we have leveled the playing field to the point where other characteristics can be studied.

If it turns out that someone likes the sound of a low damping amplifier on his particular speaker and has a high damping amplifier, wouldn't it be nice to make that change with a resistor rather than a whole new amplifier?

Bob Carver kind of did just that with some of his Sunfine amps.  He had a "voltage connection" and a "current connection".  The current connection would attempt to mimic the tube sound by a resistor in line to vary the load seen by the amp, and thus change the load impedance.

I do think there are measurements that could capture performance better.  A spectrum analyzer could provide much more information about the amp interaction with a given speaker load.  The current measurements of a a set of various single frequencies into a load resistor may help tell ho stable it is, but not much about the sound. 

[Pneumonic]

Keep in mind that voltage alone has no power. You need current too. Power is voltage x current.

On another note for low power vs high power amps. I just thought of this analogy for the low power crowd.

When you want to get a lot of water through a hose and you are only a few feet from the spigot, doesn't a 15 ft hose provide a lot more water flow and power than a 100 ft hose? Does at my house.

Taking that analogy further, what is power in water? Isn't it flow x pressure?

My prof explained it to me this way many moons ago. Voltage is the "pressure" that pushes electrons through a conductor while current is the "flow" of electrons. Power is the product of them.

[Pneumonic]

Bob Carver kind of did just that with some of his Sunfine amps.  He had a "voltage connection" and a "current connection".  The current connection would attempt to mimic the tube sound by a resistor in line to vary the load seen by the amp, and thus change the load impedance.

I do think there are measurements that could capture performance better.  A spectrum analyzer could provide much more information about the amp interaction with a given speaker load.  The current measurements of a a set of various single frequencies into a load resistor may help tell ho stable it is, but not much about the sound.

There is no substitute for measuring the amp in question in ones system. I have used a scope and spectrum analyzer to do so and the clarity both bring to the sonic equation is immense. 

Carver's T function modified idea was neat project. He did this to mimic the output characteristics of one of his tube amps. Basically he raised the Zout (ie lowered the damping factor). When the Zout is high enough (relative to the speaker's impedance), the amplifier's fr will tug toward the shape of the speaker's Z vs f curve. It's this error curve in transformer-coupled tube amps which give it the "warmth" that many people desire.

[Roger A. Modjeski]

My prof explained it to me this way many moons ago. Voltage is the "pressure" that pushes electrons through a conductor while current is the "flow" of electrons. Power is the product of them.

That is true, I often use that analogy. Now what happens when an amplifier has the capability of a lot of voltage but runs out of current, which can happen when the load impedance drops? What happens to the devices (tubes or transistors) in this situation?