- Thread Starter
- #61
So if you were in the market for an amp, you'd find accurate damping factor specs a beneficial piece of information while doing research?
-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Can output impedance measurement/plot be added to the amplifier test repertoire?
- Thread starter mike7877
- Start date
So if you were in the market for an amp, you'd find accurate damping factor specs a beneficial piece of information while doing research?
- Thread Starter
- #62
I think if DF measurements are introduced, and along with the poorer results come explanations for why whenever possible (obviously sometimes no insight can be gleaned that hasn't already been from something else - situations vary) that people, myself included, could learn some things. I think that's why a good number of people come here - to learn things, share knowledge, and definitely to make better audio-related purchasing decisions. I'm extremely happy with my Topping G5 I got a few days ago. Thank you Amir and ASR, I will be forever grateful!
- Thread Starter
- #63
A really good point is it's done for headphones, which are less likely than speakers to be negatively affected by output impedance.
Maybe the bad apples in the headphone realm are worse offenders, but offenders are everywhere!
Think about this:
If you could snap your fingers and instantly, every amplifier review on here now had damping factor measurements... what would you find out? How many of them would you be like "definitely didn't expect that result!"
"How the heck does this piece of carp have a DF of 1100?!
etc.
It'd be entertaining and informative
Maybe the bad apples in the headphone realm are worse offenders, but offenders are everywhere!
Think about this:
If you could snap your fingers and instantly, every amplifier review on here now had damping factor measurements... what would you find out? How many of them would you be like "definitely didn't expect that result!"
"How the heck does this piece of carp have a DF of 1100?!
etc.
It'd be entertaining and informative
KSTR
Major Contributor
Actually, that is frequency response of output voltage is not the same as frequency response of output impedance, or (the derived) frequency response of damping factor.
--------:--------
Overall the problem starts with damping factor specification being a marketing dept. invention, making it easy to achieve impressively large numbers which suggest a "much better performance" from a lay-person's perspective.
But the effective damping is more adequately expressed by damping = speaker_impedance / (speaker_impedance + amp_impedance). The microscopic ratio change when bringing amp_impedance closer to zero much better reflects what's going on. It even reflects negative output impedance which gives a over-unity value which means the amp damps even better than a full short. Damping factor cannot reflect that because it has a pole (division by zero, values reaching infinity) when output impedance approaches and reaches zero. As said, a nice marketing trick.
It certainly wouldn't hurt to know that, even if only a minimum amount is specified. Again, most competent S.S. amps deliver way more than an adequate amount of D.F. I would certainly not use the 'more is better' approach regarding D.F. when looking for an amplifier. Other measurement parameters, such as SINAD, power output, etc., would be much more important to me. With tube amplifiers, I would pay attention to D.F. so that it meets some minimum amount, such as, say, 20, which works for my speakers. That could be too mushy for your speakers, I dunno. As it turns out, my circlotron-style tube amps are home brewed, transformers and all, and they show a D.F. of nearly 30. My speakers play well with that. Some very difficult to drive speakers would need the grunt afforded only by S.S. designs, and tube amps need not apply for a job in such a setting.
Last edited:
No parts were abused, but Bruno's class D amps have tremendous negative feedback to acheieve that, among other things.
The new designs are apparently capable of ~2 Ohms so how can anybody complain? The D.F. is a bonus result of the negative feedback loop? There was a urban legend of the damping factor circulating in the early 80s that a high rating would be better for large woofers. D.F. in general has been the sight of many a strange comment over the decades.
The internet is a honeypot for bizarre ideas. The less they know, the more creative they get.
mhardy6647
Grand Contributor
- Joined
- Dec 12, 2019
- Messages
- 11,375
- Likes
- 24,593
Some (actually, I suspect, most) most of the hearsay, myth, fantasy, and urban legend that swirls around damping factor predates the
EDIT: Note to non-Americans, youngsters, hipsters, tripsters, and real cool chicks, sir -- Al Gore was reputed to have circuitously claimed to have invented the internet. This, too, is in about the same bucket of urban legends as are most of the Tales of the Amplifier Output Impedance.
Yes, to some degree it's time-honored. But once it hit the internet it all ripened like a fine cheese.Some (actually, I suspect, most) most of the hearsay, myth, fantasy, and urban legend that swirls around damping factor predates theinternetwww -- even before Al Gore was fiddlin' around with ethernet in the White House basement with alligator clips and an INTEL chip programmer.
You mean 2 milliohms?
Output impedance of 1ET400A is 65 micro-ohm at 1 kHz (0.065 milliohm) per the spec. So if your cable has 20 milliohm resistance, amps output impedance won't mean a thing. Any effect in FR is easy to DSP away if it's bothering you. And output impedance is difficult to test because you need to know the exact impedance of cabling etc. That's probably why Amir hates testing it, but as I said before, if you want it, ask for it.
Obviously, lower performing amps deserve more scrutiny in that way.
Yes the series resistance in passive xover components speaker cables the voice coil itself , i think between 20--100 is good enough for the amp its not anything like that driving the actual speaker cone ? Off cours you don't want the output impedance of an older tube amplifier or class D without proper feedback but there no need to chase excessive values .
realy high df migth have more application in subwoofers and active speakers where the amp is directly connected to the driver .
realy high df migth have more application in subwoofers and active speakers where the amp is directly connected to the driver .
I saw an amp, I think it might have been by Phase Linear, that touted a DF of 1000. That kind of DF can be gotten by applying a ton of negative feedback to knock Zo down to preposterously low levels, in the few milli-ohms region. Negative feedback lowers output impedance in an amplifier. The problem was that stability of the amplifier when driving difficult loads was compromised, all in the name of an outrageous number for the spec-of-the-month club publications. Such a low D.F. is simply unneeded in any home stereo application. I'm not willing to pay for it, nor sacrifice anything else in the amplifier design to get it. The abuse comes in the excessive exaggeration of some amplifier spec in the service of advertising BS. I think this specsmanship was spurred by the spec of the month club, where reviewers would gush that some particular spec, when pushed to extreme levels, would usher in Audio Nirvana (nervosa?). First it was DC to light frequency response, then slew rate, then power in outrageous amounts, then distortion readings in the nano-percent range, and I don't know what else.
Last edited:
D.F. tells you about the ability of the amplifier to control the speaker's motions without the speaker having any say in how it moves. A low D.F. amp says, "Speaker, you are coming with me, do you understand?". Speaker says "Y-y-yessir!". With a low amplifier Zo, there is negligible voltage divider effect between the amplifier's Zo and the speaker's Z. As a result of this ratio, the speaker is unable to move the amplifier around by way of its back EMF, since a relatively high Z speaker is trying to push a near dead short around.Damping factor only tells you something about.......???? Yes educate me a bit
It's something of the past when tube amps did have high output impedances.
Similar threads
