Author Topic: Do power amps sound the same? (Read 11418 times)

bumblebee · « **Reply #30 on:** Mar 16, 2007 at 11:17 AM »

This is regarding damping factor. How true?

High damping factor -> SS sound
Low damping factor -> tubey sound

ATJr. · « **Reply #31 on:** Mar 17, 2007 at 10:52 AM »

Quote from: bumblebee on Mar 16, 2007 at 11:17 AM

This is regarding damping factor. How true?

High damping factor -> SS sound
Low damping factor -> tubey sound

the reason why SS amps have high damping factor is that is uses global negative feedback, whereas tube amps does not nescessarily use it...tube amps can be designed to have high damping factor...

av_phile1 · « **Reply #32 on:** Mar 17, 2007 at 01:20 PM »

Quote from: bumblebee on Mar 16, 2007 at 11:17 AM

This is regarding damping factor. How true?

High damping factor -> SS sound
Low damping factor -> tubey sound

Quite true. Some tube amps can go as high as 100, but rarely beyond that, most hover in the 20 range. And this often explains why tubes are on the mellow side and SS power amps more biting. Typically at around 1000, well designed SS amps are generally more accurate in controlling driver movements primarily because of a higher damping factor. The Nu Froce Reference 8.5 has a damping factor of 4000. Now that's like having a vise grip on woofer movements. The amp literally tells the woofer where to go and when to stop with supreme precision.

MAtZTER · « **Reply #33 on:** Mar 17, 2007 at 02:05 PM »

Interesting. So if you want a tube hybrid setup, go for a low damping factor SS amp for a more "tubey" sound? instead of a high DF?

ATJr. · « **Reply #34 on:** Mar 19, 2007 at 04:25 AM »

no, what that post simply means is that an amp with a very high damping factor controls speaker movements better. the speaker cone assembly having a definite mass will have inertia, so that after the electriucal signal has subsided, the movemement still goes on due to inertia, so this adds another coloration of its own.

allan1836 · « **Reply #35 on:** Mar 19, 2007 at 03:56 PM »

Wowowie! Thanks to everyone for injecting there thoughts on the topic.

It's a highly educational trip reading this thread!! I thought I was in a Audiogon forum!

Seeing the remarks here it seems that it's probably a universal consencus, that the bottom line is "the beauty (of sound) is in the ears of the beholder".

I gathered that, technical or physical aspects in making an amp may differ, to a certain degree, but a lot of other attributes has to be considered. This includes associated equipments, listening room, choice of music, etc. I must say that another influence here is the stigma of "brand mentality". I say this because , in numerous occasions, I noticed a lot of audiophiles tend to "pre-judge" an equipment because of its brand.

Now, here is a follow-up question and more specific. Would a Sony T-AN55ES power amp, rated at 120watts/ch. rms be more or less similar to lets say a bryston or aragon power amp with similar watts, assuming all other associated equipments are constant and the system will not be driven to clipping (normal level only). When I say similar, will the final sound of the system be almost the same or radically different. Personnally,I'am assuming that the power amp would hardly be a factor in the overall sound.

Thanks again guys for a splendid support!

aHobbit · « **Reply #36 on:** Mar 19, 2007 at 04:06 PM »

Quote from: TonyT on Mar 19, 2007 at 04:25 AM

no, what that post simply means is that an amp with a very high damping factor controls speaker movements better. the speaker cone assembly having a definite mass will have inertia, so that after the electriucal signal has subsided, the movemement still goes on due to inertia, so this adds another coloration of its own.

Sir Tony,
In sonic terms (since I can not see which is extra inertia and which one is the sound itself

), how would you know that what you are listening to are an effect of bad damping effect?

aHobbit · « **Reply #37 on:** Mar 19, 2007 at 04:12 PM »

Quote from: allan1836 on Mar 19, 2007 at 03:56 PM

...
Now, here is a follow-up question and more specific. Would a Sony T-AN55ES power amp, rated at 120watts/ch. rms be more or less similar to lets say a bryston or aragon power amp with similar watts, assuming all other associated equipments are constant and the system will not be driven to clipping (normal level only). ...

The test you are proposing is easier (SS to SS) compared to what has been done in the past, that of cheap SS and a high cost monoblock tube. If all of them are purely power amp, and any of the pre-amp to be used with them are adjusted such that the end signal (after amp) are of same loudness level - it is most likely, like other test in the past, will just sound the same, that is, highly indiscernible even with those claiming 'golden ears'.

Quote from: allan1836 on Mar 19, 2007 at 03:56 PM

...
I say this because , in numerous occasions, I noticed a lot of audiophiles tend to "pre-judge" an equipment because of its brand.
...

Maybe am an audiophile before because I prejudge equipment based before on its brand!

In truth, not only branding are used to pre-judge an equipment. Sometimes, one or combination of the following are used to pre-judge a system:
(1) price (if expensive, it must be audiophile)
(2) materials used (if it used exotic components and cables, then it is audiophile)
(3) construction (e.g. if it uses heavy torroid, and holco resistor, etc etc, it is audiophile)
(4) looks (it posseses hypnotic looks, pleases my eye, I want it as my audiophile

)
(5) my friend said it is audiophile, it must be audiophile
(6) 80% of the store said it is audiophile, then it is audiophile
(7) 60% of my community (pinoydvd?

) said it is audiophile, it must be audiophile
(

weight (it weighs 80kg, it must be audiophile

)
(9) I heard it audiophile, it should be audiophile

allan1836 · « **Reply #38 on:** Mar 19, 2007 at 07:15 PM »

aHobbit, You scored 9/9=100% !!

I guess the true criteria ,the sound!!!, can't really be made concrete. Nobody can really define the boundary between mid-fi and hi-fi when it comes to the sound. Its really a personnal opinion. Tnx

ATJr. · « **Reply #39 on:** Mar 20, 2007 at 09:40 AM »

Quote from: aHobbit on Mar 19, 2007 at 04:06 PM

Sir Tony,
In sonic terms (since I can not see which is extra inertia and which one is the sound itself ), how would you know that what you are listening to are an effect of bad damping effect?

it is hard to describe really, but there was this "motional feedback amp-speaker system" demonstrated by Philipps IIRC, wherein there was this band playing "live" in a corner inside of a cafe, when one by one, the band members took off until all them were gone, and yet the music still played on. to the delight of the audience, they were hoodwinked into believing that they were listening to a live performance when all the while it was just recorded music.....

to put it simply, the speaker movements were sensed as to direction and any error was immidiately corrected...

aHobbit · « **Reply #40 on:** Mar 20, 2007 at 12:19 PM »

Quote from: allan1836 on Mar 19, 2007 at 07:15 PM

...
Nobody can really define the boundary between mid-fi and hi-fi when it comes to the sound. Its really a personnal opinion. Tnx
...

Are you starting a debate?

What you stated above is basically the same argument I raised in one of the thread in this forum - that is to define mid-fi from hi-fi. And all I got is just noise, and no clean signal whatsoever. It seemed to me that majority of stereo listeners who claimed they have audiophilia blood can not categorically define the limit of when a mid-fi is mid-fi and when a hi-fi is hi-fi. The thread has RIP in it, so dont bother!

Er, how do you like your coffee sir?
(a) mid coffee (b) low coffee (c) high coffee (d) coffee less (e) coffee more
The cream sir?
(a) mid (b) low (c) high (d) less (e) more
The cup sir?
(a) plastic (b) aluminum (c) steel (d) wood (e) bronze (f) silver (g) gold

How about the coaster? the teaspoon? the sugar? the table? the temperature?
A bit further sir ..... do you have a tongue?

Just a warning sir ... you will have fatigue drinking mixture with less (real) coffee!!!
Because your brain will fill in the gaps of those taste missing in the coffee ... and your brain will eventually get tired doing that for you.

Sorry, was just carried away!!!

taste it! enjoy it!

I think my coffee is more (closer to the real) coffee than yours!!!

Or probably, the pasture is always greener at the other side!!!

aHobbit · « **Reply #41 on:** Mar 20, 2007 at 12:23 PM »

Quote from: TonyT on Mar 20, 2007 at 09:40 AM

...
the band members took off until all them were gone, and yet the music still played on. to the delight of the audience, they were hoodwinked into believing that they were listening to a live performance when all the while it was just recorded music.....

kakatakot pala effect ng mababang damping factor!!!

Quote from: TonyT on Mar 20, 2007 at 09:40 AM

...
to put it simply, the speaker movements were sensed as to direction and any error was immidiately corrected
...

I may not see it myself ... but maybe somehow, if I have a good speaker, and somehow it sounds lifeless or dull ... chances are, the extra motion of the speaker affects the sonic quality of the outputted sound due to a low damping factor ... I bet, you need higher damping factor to system that permits more bass into the output ... I just thought that since mid and HF do not really require so much power as bass, the need for higher damping factor for a system that drives mid-hi is not as much as the one that will have the sound outputted as full range (which include the lower bass region of 20-100Hz) ... or am I talking sense here?

av_phile1 · « **Reply #42 on:** Mar 20, 2007 at 02:09 PM »

Damping factors have the most effect at low frequencies than at mids and highs. That's why some amps specify the DF into a load at a certain frequency, often at 60hz.

ditterdi · « **Reply #43 on:** Mar 20, 2007 at 02:30 PM »

Quote from: TonyT on Mar 20, 2007 at 09:40 AM

to put it simply, the speaker movements were sensed as to direction and any error was immidiately corrected...

I have one (snif snif only 1). They are small and have 2 build in amplies one for the midrange and tweeter and one for the bass. The bass speaker has a build in piezo christal that reports the movement of the speaker to the system, so errors can bee corrected.
They have no pre-amplier but can be connected to the speaker out of another amplie or to a pre-amplie.
They sound fantastic. There are still a lot floating around and they are worth good money.

Leo.

aHobbit · « **Reply #44 on:** Mar 20, 2007 at 06:10 PM »

Quote from: av_phile1 on Mar 20, 2007 at 02:09 PM

Damping factors have the most effect at low frequencies than at mids and highs. That's why some amps specify the DF into a load at a certain frequency, often at 60hz.

Yup, this is what I am saying that in the bass region, high damping factor is more required than in mid-hi.

If you have low damping factor, and your system is into lots of low end (bass region), then the life of your mid-hi can be sucked out by the unwanted return movement resulting to dull or lifeless sound.

Of course, it can also result in a confused bass sound!

ATJr. · « **Reply #45 on:** Mar 21, 2007 at 11:17 AM »

Quote from: av_phile1 on Mar 20, 2007 at 02:09 PM

Damping factors have the most effect at low frequencies than at mids and highs. That's why some amps specify the DF into a load at a certain frequency, often at 60hz.

yes, while SS amps can have high DF at any frequency within its passband, DF in the high frequencies are diminished because of the boucherot cells and or zobels connected at their outputs, these are needed in order to isolate the amp from capacitive loads...

aHobbit · « **Reply #46 on:** Mar 21, 2007 at 11:31 AM »

Quote from: TonyT on Mar 21, 2007 at 11:17 AM

yes, while SS amps can have high DF at any frequency within its passband, DF in the high frequencies are diminished because of the boucherot cells and or zobels connected at their outputs, these are needed in order to isolate the amp from capacitive loads...

But I understood those zobels are way beyond the audio band and its purpose is to avoid ringing (high frequency loop), so the DF should still be effective within the audio spectrum ... or is ringing a form of unwanted cone movement on the HF level?

ATJr. · « **Reply #47 on:** Mar 21, 2007 at 11:36 AM »

Quote from: aHobbit on Mar 21, 2007 at 11:31 AM

But I understood those zobels are way beyond the audio band and its purpose is to avoid ringing (high frequency loop), so the DF should still be effective within the audio spectrum ... or is ringing a form of unwanted cone movement on the HF level?

yes, but you'll be surprised how the output impedance of the amps increases with those once you do the math...any way speakers become both inductive and capacitive within the audio band...

MAtZTER · « **Reply #48 on:** Mar 26, 2007 at 04:30 PM »

Will a power amp that doubles its power rating at 4 ohms sound better or of better quality than an amp doesnt double at 4 ohms?

TIA

bumblebee · « **Reply #49 on:** Mar 26, 2007 at 05:10 PM »

SQ aside, I (just me ha?) believe that spec means little. You can always rate the amp lower for 8 Ohms to make it appear half of the rating for 4 Ohms.

Anyway, between

Amp A w/ 50W into 8 and 100W into 4
and
Amp B w/ 75W into 8 and 100W into 4,

I'd choose Amp B because I will get more power in 8 Ohms (SQ aside because the ears will decide hehehe)

ditterdi · « **Reply #50 on:** Mar 26, 2007 at 09:22 PM »

Quote from: bumblebee on Mar 26, 2007 at 05:10 PM

SQ aside, I (just me ha?) believe that spec means little. You can always rate the amp lower for 8 Ohms to make it appear half of the rating for 4 Ohms.

Anyway, between

Amp A w/ 50W into 8 and 100W into 4
and
Amp B w/ 75W into 8 and 100W into 4,

I'd choose Amp B because I will get more power in 8 Ohms (SQ aside because the ears will decide hehehe)

I would choose the A amp because it probably has a better power suply.

Leo

bumblebee · « **Reply #51 on:** Mar 27, 2007 at 08:41 AM »

Quote from: ditterdi on Mar 26, 2007 at 09:22 PM

I would choose the A amp because it probably has a better power suply.

Leo

You can always overkill the power supply for both Amps A and B and they'd still be rated the same way. Output power for a certain load will be limited by the current capability of the amp.

aHobbit · « **Reply #52 on:** Mar 27, 2007 at 12:33 PM »

Quote from: bumblebee on Mar 26, 2007 at 05:10 PM

SQ aside, I (just me ha?) believe that spec means little. You can always rate the amp lower for 8 Ohms to make it appear half of the rating for 4 Ohms.

Anyway, between

Amp A w/ 50W into 8 and 100W into 4
and
Amp B w/ 75W into 8 and 100W into 4,

I'd choose Amp B because I will get more power in 8 Ohms (SQ aside because the ears will decide hehehe)

By the specs, they are just the same into 4 ohms.

Amp B could have a higher bias into 8 ohms that's why it can attain 75watts [Power in watts = Vsquared/R, where R, the impedance of speaker, held constant will yield higher V than with the lower 50W of Power in 8 ohms].

Amp A could have been biased lower into 8 ohms so it can only attain less than 75watts.

Both Amps can deliver the current demands (because both can supply the current to attain 100watts at 4 ohms) .

In 8 ohms, the limiting factor of the power for both amps is not the ampacity of the power supply but the bias voltage!

In 4 ohms, they are just the same in RMS.

However, I will not be surprised if the headroom of amp B (being biased higher) will be better than amp A. (bigger headroom, technically, is more dynamics).

In 4 ohms, the limiting factor of the power for both amps is the ampacity of the power supply!

With the above choices, I will go for Amp B.

av_phile1 · « **Reply #53 on:** Mar 27, 2007 at 12:40 PM »

A power amplifier that doubles its power when the load is halved is said to behave more linearly across the audio spectra than one that doesn't. So I'd choose amp A with all else equal. It even has a higher headroom at 3db. But if you want more power into 8ohms, then amp B is better, just don't use material that will require 3db peaks at the rated power.

ditterdi · « **Reply #54 on:** Mar 27, 2007 at 03:37 PM »

Quote from: aHobbit on Mar 27, 2007 at 12:33 PM

Power in watts = Vsquared/R, where R, the impedance of speaker, held constant will yield higher V than with the lower 50W of Power in 8 ohms].

I will go for Amp B.

Power=Watts (W)
Current=ampere (I)
Impendance-resistance=Ohm(R)
Power=Voltage*Current W=V*I
Voltage=Resistance*Current V=I*R
So Power=Current square*R W=I^2*R

Leo.

aHobbit · « **Reply #55 on:** Mar 27, 2007 at 03:54 PM »

Quote from: av_phile1 on Mar 27, 2007 at 12:40 PM

A power amplifier that doubles its power when the load is halved is said to behave more linearly across the audio spectra than one that doesn't. So I'd choose amp A with all else equal. It even has a higher headroom at 3db. But if you want more power into 8ohms, then amp B is better, just don't use material that will require 3db peaks at the rated power.

avphile,

75watts is only a label ... had amp B used 50watts into 8 ohms (which it can, it may now alter your conclusion), the 2 amps has no difference (because both of them can now equally double its power, if 50watts is the reference point) ... and how did you compute 3db headroom (am refering to dynamic headroom) where in fact dynamic power was not given into 8 ohms?

at short burst, because of high bias in ampB, it can accomplish higher power both in 4/8 ohms ... that is granting, since it is not given, no 4/8 ohms switch is available

I can show it mathematically if you will let me

To further ditterdi,

I = V/R

from P = VI, then P = Vsquared/R

regards

aHobbit · « **Reply #56 on:** Mar 27, 2007 at 04:12 PM »

The math . . .

I did my LM3886 power amp and it is a good exercise of these simple formula ...

Let's design a 50-watt amp into 8 ohms. So I need to know the bias voltage.

P = Vsquared/R : P = 50 = Vsquared/8

Vsquare = 400 Vsquare : Thus, V = =/- 20Vdc
(I will not deal with factor of 1.4 for simplicity of presentation)

What bias do I need to come up with 100W into 4 ohms

100 = V^2/4 : this is simply V = +/- 20Vdc (as well)

Thus, a Vdc of +/-20 will yield me 50W/8ohms and 100W/4ohms.

From the equation P=VI, we can solve the current into 4/8 ohms respectively.
4ohms: I = 100W/20V = 5A 8ohms: I = 100W/20V = 2.5A

Checking it out:
I=5A to 4ohms load will deliver I^2*R = 100W power!
I=2.5A to 8ohms load will deliver I^2*R = 50W power!

I have to ensure I will not go over 100W/4ohms to protect the amp. Thus, I have to limit my fuse rating to 5A. I need a power supply able to deliver 5A with a tap voltage equivlent to +/-20Vdc.

Then, I will get all my parts now and contruct my amp. I have one designed at 60W/4ohms and 30W/8ohms (LM3886).

aHobbit · « **Reply #57 on:** Mar 27, 2007 at 04:29 PM »

To those who want to exercise ... I may be wrong here ... feel free to point it out ...

Lets design a 75W/8ohms

The bias voltage I need should be: P=V^2/R = 75W = V^2/8ohms : V^2 = 600Vsquare

This will give me about +/-24.5Vdc.

However, based on previous computation, I only need +/-20Vdc to accomplish 100W/4ohms.

Let's see the current:

I = P/V = 75W/24.5V = 3.06A to accomplish a 75W/8ohms

Again, to accomplish 100W/4ohms, I only need 5A.

The difference of this amp to the previous amp is only the bias voltage I have to implement! Here I need same power supply that can handle 5A but with tap voltage equivlent to +/-24.5V. The PSU of previous amp can only handle P=VI=20V*5A=100W max (simple computation for presentation only), while this amp transformer can handle P=VI=24.5V*5A=122.5W

And with this bias voltage, my amp can kick at 4 ohms about :

P = V^2/R = (24.5V)^2/4ohms = 600/4 = 150W (dynamic power burst) giving me 150w (dynamic power)/100w (rated power) of about less than 3db into 4 ohms.

(This is with the assumption that both amplifier were limited with those computed bias voltage, which in real life is more than that because of ac/dc conversion factors).

bumblebee · « **Reply #58 on:** Mar 27, 2007 at 04:40 PM »

If you run 24.5V into 4 Ohms, you get 6.125A. E, 5A lang fuse mo.

Btw, isn't it that supply voltage is held constant?

aHobbit · « **Reply #59 on:** Mar 27, 2007 at 04:48 PM »

Quote from: bumblebee on Mar 27, 2007 at 04:40 PM

If you run 24.5V into 4 Ohms, you get 6.125A. E, 5A lang fuse mo.

Btw, isn't it that supply voltage is constant?

omaygawd!!!

... But my fuse is slow blow

You are correct, if my fuse is fast blow, this will trigger the protection mode of the amplifier.

Also, as I said in my post, values are higher than what has been presented (for simplicity of computation). Short burst as in music reproduction do not blow fuse. The RMS (average) value of power usually will trigger protection mode.

Typically, manufacturers allow a 10% overload to have the amp deliver power at 10%THD. So to do this, I can have ampA fitted with 5.5A. If this amp go beyond 5A (burst mode) at 4ohms, clipping will occur (so thus distortion) because the max V is already attained at 5A. WIth ampB, will implement same fuse. If this amp go beyond 5A (burst mode) at 4 ohms, no clipping until it reaches 24.5V. In fact it can reach 5.5A (121W) at 4 ohms and not clipped!

The supply voltage, after you install the transformer, will now be constant: +/-20Vdc for ampA and +/-24.5Vdc for ampB.