[dvw]

Quote:

I'll I'm trying to say is that amps have different levels of amplification at different impedance. Headphones have different impedance at different frequencies. If you put those two facts together, your lows may be amplified x3 and your highs amplified x5. That is a "bright" amplifier. Now it has a sound signature. I suppose this doesn't qualify since now it's not "properly designed"?
Saying that even a majority of amps are "properly designed" is a pretty big leap.
All 0.5 watt amps have the same distortion? The same slew rate? The same damping rate? etc etc Even when using different technologies like j-fett, mosfett, or tubes? OTL, SET, etc topologies are the exact same? Even with Class A, Class A/B, or Class B power only?
Now we can add the skill level of the engineers. They all got it perfect eh?
I give it a 0% chance they all sound identical. I'm sure on some headphones you couldn't tell the difference, but they are all gonna be different.

If amp have a different gain depends on the load, I say the amp is not properly designed. The load should not be part of the gain loop. It is true that headphones do have different impedance at different frequency. And it could be that at certain impedance the amp is current limited, but that's because the amp does not have enough power margin. Again a design issue.
 
Now it is true that there are many design configuration and that could create a difference is sound. But I believed people are talking about amps with comparable specification. A tube amp with a warm sound typically has a hump in the mid range in the FR and they also have a different distortion characteristic. Obviously, they will sound different than a SS amp. This does not mean a SS amp can not be made to sound like a tube amp. Check out the Bob Carver challenge. He made a $700 SS amp to sound like a $12K tube amp in the 90s. The editors at Stereophile basically threw in the towel in trying to differentiate them. 
 
BTW, speakers have much more variation in impedance than headphone and are considerably more difficult to drive.

 

[bigshot]

I'll I'm trying to say is that amps have different levels of amplification at different impedance. Headphones have different impedance at different frequencies.

There are impedence mismatches and properly matched impedences. I'm talking about the latter.

 

[m2man]

Now it is true that there are many design configuration and that could create a difference is sound. But I believed people are talking about amps with comparable specification. A tube amp with a warm sound typically has a hump in the mid range in the FR and they also have a different distortion characteristic. Obviously, they will sound different than a SS amp. This does not mean a SS amp can not be made to sound like a tube amp. Check out the Bob Carver challenge. He made a $700 SS amp to sound like a $12K tube amp in the 90s. The editors at Stereophile basically threw in the towel in trying to differentiate them. 

Oh good, it's safe to buy using those friendly honest marketing specifications. I'm not sure any of us would visit head-fi if we could just use the published specs.

 

[bigshot]

If it doesn't meet the specifications, it's defective. Return it.

Honestly, I don't know why people churn through equipment. If you make the right choice, it should be a good decision for many years. I've never needed to replace an amp because of sound quality issues. Only when an amp dies.

An amp's an amp. If it has enough power, it just works.

 

[Siva108]

Wow, three pages. Didn't expect that.
 
So I'm assuming everything said here also applies to portable amps?

 

[bigshot]

Even more to portable amps. The lower the power, the easier it is to make it clean.

 

[eugenius]

Yes, amps have signatures, even solid state amps. I had three balanced amps so far: Headroom Balanced Desktop, CEC HD53N and Headroom Blockhead. They all sound different, but the differences are smaller than the differences between tube amps.

Think about it, when the specification is given as +/- 0.5dB over the audible frequency range, there will be amps that have +1dB compared to other amps over specific frequency ranges. They don't have to be a different model, just a different sample of the same amp.

And +/- 0.5db is not a bad number, the Burson HA160 which is a good amp with a lot of fans around here has +/- 1dB. A really great amp like my Headroom Blockhead has +/- 0.025 dB. Even a 0.1dB difference is audible, so says Bob Katz who wrote the book on mastering.

 

[wuwhere]

FR is usually measured at 8ohms. But we all know that impedance changes with frequency. So how does an amp reacts to different impedance at different frequencies, dynamically like music, nobody knows.

 

[dvw]

Quote:

FR is usually measured at 8ohms. But we all know that impedance changes with frequency. So how does an amp reacts to different impedance at different frequencies, dynamically like music, nobody knows.

I don't know who started this idea of amp acting differently with different impedance. The amp has two parts, a gain stage which is the pre amp and a driver stage which is the power amp. The load (speakers and headphone) are connected to the power stage So the amp pretty much acts like a power supply, it provides power to drive the load. This is very much like your power from your power company. The voltage does not change with different load unless it's under power.
 
In design, the load impedance, frequency etc can all be simulated by computer. This is how we achieve a robust design today. Engineers do not use trial and error. It is just too expensive not to use proper computer tool.

 

[wuwhere]

Quote:

I don't know who started this idea of amp acting differently with different impedance. The amp has two parts, a gain stage which is the pre amp and a driver stage which is the power amp. The load (speakers and headphone) are connected to the power stage So the amp pretty much acts like a power supply, it provides power to drive the load. This is very much like your power from your power company. The voltage does not change with different load unless it's under power.
 
In design, the load impedance, frequency etc can all be simulated by computer. This is how we achieve a robust design today. Engineers do not use trial and error. It is just too expensive not to use proper computer tool.

 
Unless its a perfect voltage source. Simulation is not the real thing either.
Anyway, since you have such ability (simulation) then you can say whether a certain speaker will or will not sound good with your amplifier?

 

[dvw]

Quote:

 
Unless its a perfect voltage source. Simulation is not the real thing either.
Anyway, since you have such ability (simulation) then you can say whether a certain speaker will or will not sound good with your amplifier?

Simulation is only as good as the model you put in.  A proper design will not have a perfect voltage source. A proper design verification and field trial is needed for most design to catch variable that's not included in the simulation. We have field failure sometimes. But once the fault is identified. It can pretty much be verified in the simulation.
 
In my experience, if I have sufficient data, I can pretty much tell speaker will sound good with a certain amp. However, sounding good is a matter of preference as well. I have gone through a period that I prefered the warm tube sound vs the SS sound. One thing I do know for sure. If you don't the speakers, no matter how much burn in, changing amp and cable will change the sound. Maybe if you put some magic quartz disk on top of the amp will change the sound. BTW, one of the six moon review set up I read actually does that.

 

[wuwhere]

Would you fly on a jet plane that was only tested on simulation to take off? Did they simulate the landing? Would you buy an amp for your > $20k speakers simulated tested? You said the keyword, "preference". That's why there are so many amp makers out there, both tubes and SS.

 

[dvw]

Quote:

Would you fly on a jet plane that was only tested on simulation to take off? Did they simulate the landing? Would you buy an amp for your > $20k speakers simulated tested? You said the keyword, "preference". That's why there are so many amp makers out there, both tubes and SS.

Jet plane design also used simulation and of course the design will have to be verified. But with the same analogy, would you fly on a plane that's designed by trial and error without any simulation. And when I bought my amp, I got a loaner first. But I selected my amp by spec. It does not make sense to get a wimpy receiver to drive a Maggie. And I would not be buying any quartz disk or cable lifter any time soon. Would you buy any cable, CD or LP (vinyl) de-magnetizer? 

 

[wuwhere]

Quote:

Jet plane design also used simulation and of course the design will have to be verified. But with the same analogy, would you fly on a plane that's designed by trial and error without any simulation. And when I bought my amp, I got a loaner first. But I selected my amp by spec. It does not make sense to get a wimpy receiver to drive a Maggie. And I would not be buying any quartz disk or cable lifter any time soon. Would you buy any cable, CD or LP (vinyl) de-magnetizer? 

 
I flew on an old 747, I don't think these jet planes were simulation tested, there were no hardware and software that could do that back then. I used to own a pair of Apogee Scintilla, I bought a pair of Eagle mono amps from John Iverson (before he disappeared), he swore that his amps can drive them. Well, he lied.

 

[dvw]

Quote:

 
I flew on an old 747, I don't think these jet planes were simulation tested, there were no hardware and software that could do that back then. I used to own a pair of Apogee Scintilla, I bought a pair of Eagle mono amps from John Iverson (before he disappeared), he swore that his amps can drive them. Well, he lied.

I see. You are a man of faith. I come from a design/manufacturing background. We like predictability. If things don't go as expected it could cost us a lot of  money. With audio, there is just so much misinformation. I just want to clear up some of the misinformation. For me amp is just a simple thing with no real magic. I do not mean to degrade amp designer. I think in the 70s, 80s and 90s. There were some real big progress. Today's amps are so good, I can't tell any difference. I haven't bought a new amp in 15 years because I think my amps are good enough.