• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Do damping factor, slew rate and the like have possibly any influence on the "sound" of an amplifier?

pma

Major Contributor
Joined
Feb 23, 2019
Messages
3,313
Likes
6,908
Location
Prague
'damping factor' only matters at woofer frequencies and any number well above 10 is good enough.
This is oversimplified statement. Damping factor is a ratio between load impedance and output impedance. Both are complex functions and frequency response is modulated according to this complex impedance divider. This is physics, electrical engineering and electrical circuits rule. No subjective opinion matters. I have shown numerous measurements here that show influence of output impedance to various speakers frequency response. I will not make a search job, I expect that any qualified reader understands.
 

rwortman

Addicted to Fun and Learning
Joined
Jan 29, 2019
Messages
590
Likes
517
Please take into account that slew rate and bandwidth are not directly related. Bandwidth is often defined as a small signal parameter, especially in opamp datasheets. But slew rate is a large signal related parameter. You may have very wide bandwidth and low slew rate at the same moment with the same component.
But not power bandwidth which more of interest in a power amplifier.
 

Mnyb

Major Contributor
Forum Donor
Joined
Aug 14, 2019
Messages
1,594
Likes
2,116
Location
Sweden, Västerås
Thanks this modifies a bit on Tooles findings from the 70’s

 

Mnyb

Major Contributor
Forum Donor
Joined
Aug 14, 2019
Messages
1,594
Likes
2,116
Location
Sweden, Västerås
Are not >100 routinely achieved so this is still not a big issue ( but still an existing issue )

Avoid some tube amps and some simple class D amps and your probably never “hear” about this issue again ? Is that fair.
 

ebslo

Active Member
Forum Donor
Joined
Jan 27, 2021
Messages
267
Likes
351
Ok, but as far as I know, Amir never measures these, right? So it would be better he should or it is just too unlikey anythink noteworthy showing up?
Damping factor: He does usually provide a "Load Dependency" plot which shows frequency response for both 4 and 8 Ohm loads. Damping factor as a function of frequency can be inferred from the difference in responses for 4 and 8 Ohm loads.

Slew rate: He also provides a "Power vs. Distortion" plot at several frequencies. A slew-rate limited amplifier would show much higher high-power distortion in the highest frequency plot than in the lower frequency plots.
 

pma

Major Contributor
Joined
Feb 23, 2019
Messages
3,313
Likes
6,908
Location
Prague
Slew rate: He also provides a "Power vs. Distortion" plot at several frequencies. A slew-rate limited amplifier would show much higher high-power distortion in the highest frequency plot than in the lower frequency plots.
You think so? Like this one, right? No.

index.php


Regardless of opinion of armchair debaters, the only method to reveal slew limited issue is to measure full swing step response with a wideband oscilloscope. Low frequency instruments like AP limited to 1.5MHz cannot tell it, every real amplifier designer knows this.
What you see has a different reason.

High frequency distortion is a potential secondary effect of the slew rate limitation. It may have different roots.
 

KSTR

Major Contributor
Joined
Sep 6, 2018
Messages
2,231
Likes
4,911
Location
Berlin, Germany
Slew rate: He also provides a "Power vs. Distortion" plot at several frequencies. A slew-rate limited amplifier would show much higher high-power distortion in the highest frequency plot than in the lower frequency plots.
No. Sometimes there is an increased distortion at high frequencies and high levels, sometimes there isn't.
Slew-limiting is like clipping of any kind, the amp completely leaves stable operation region and any present feedback loop goes open. And just like some amps don't show any distortion increase right before clipping they may or may not show distortion rise before slewing.
 

restorer-john

Grand Contributor
Joined
Mar 1, 2018
Messages
10,019
Likes
28,652
Location
Gold Coast, Queensland, Australia
Not as such. They would effect other measurements, but you can't really separate out how much is the influence of slew rate or DF verses what comes from other mechanisms of distortion/frequency response error.

Both a loaded and unloaded frequency repsonse plot gives enough data to derive an accurate DF vs frequency plot.
 

MakeMineVinyl

Major Contributor
Joined
Jun 5, 2020
Messages
3,558
Likes
5,763
Location
Santa Fe, NM
Both a loaded and unloaded frequency repsonse plot gives enough data to derive an accurate DF vs frequency plot.
Yes true, but to do so requires some level of skill in intrepretation. Its far simpler to just have the relevant measurement there in the first place. I always strive to present data which I generate so that it can be plainly and simply used by the least skilled person that would likely be looking at the data.
 

Dlomb11

Active Member
Joined
Jul 6, 2020
Messages
214
Likes
72
Location
Milan, Italy
I'd like to ask a completely ignorant question.
Can't the concept of slew rate also apply to current and / or delivered power?
 

HarmonicTHD

Major Contributor
Forum Donor
Joined
Mar 18, 2022
Messages
1,206
Likes
1,463
I'd like to ask a completely ignorant question.
Can't the concept of slew rate also apply to current and / or delivered power?
Correct me if I am wrong, most simply put

U = R x I

And

P = U squared / R
 
Last edited:

restorer-john

Grand Contributor
Joined
Mar 1, 2018
Messages
10,019
Likes
28,652
Location
Gold Coast, Queensland, Australia
I'd like to ask a completely ignorant question.
Can't the concept of slew rate also apply to current and / or delivered power?

Slew rate is voltage vs time. It has no relationship to power delivered.

An amplifier with a rated 400V/uS slew rate does not actually swing 400V in 1us. It may only swing 40VRMS over an 8R load. It is usually referenced to microseconds (uS) or perhaps nanoseconds (nS) for ease of comparison.
 

conman

Member
Joined
Jan 11, 2022
Messages
20
Likes
38
If your damping factor is the minimum necessary of say 10, and then you use DSP to tailor the measured frequency response to whatever curve takes your fancy, does it even matter?
 
Last edited:

wwenze

Addicted to Fun and Learning
Joined
May 22, 2018
Messages
937
Likes
1,281
If your damping factor is the minimum necessary of say 10, and then you use DSP to tailor the measured frequency response to whatever curve takes your fancy, does it even matter?

That would be like using EQ to fix room reflections vs having a good room to begin with.
 

HarmonicTHD

Major Contributor
Forum Donor
Joined
Mar 18, 2022
Messages
1,206
Likes
1,463
Check out this test showing the different frequency response of an amp with a low du ping factor
It just confirms what was said previously: a SOTA amp with a damping factor larger than 10 to 20 will be fine. Keep in mind SOTA amps have damping factors in the order of 100 (200 to 400) across the frequency band. The Pass Amp is ages away from SOTA ( there is a review somewhere on this site - the Pass has many problems, not just damping factor).
 

restorer-john

Grand Contributor
Joined
Mar 1, 2018
Messages
10,019
Likes
28,652
Location
Gold Coast, Queensland, Australia
an amp with a low du ping factor

A low duping factor? Most audiophiles seem to go for the highest duping factor they can. ;)

Or that new Chinese brand- Du Ping who make amplifiers?
 

dominikz

Addicted to Fun and Learning
Forum Donor
Joined
Oct 10, 2020
Messages
563
Likes
1,932
If your damping factor is the minimum necessary of say 10, and then you use DSP to tailor the measured frequency response to whatever curve takes your fancy, does it even matter?
Given that the result of low damping factor / high output impedance is just a (small) change in frequency response, it is completely fixable by EQ.
However, to do a precise EQ correction you would first need to measure the amplifier output when driving a specific loudspeaker load - and I suspect this would not be trivial for most (non-technical) people. Also, the required EQ correction changes with any new set of loudspeakers you connect to the amp.

Of course, given that the change in FR due to low damping factor / high output impedance is normally small, and variability is mainly located in the LF range, it is usually swamped by room effects, and consequently implicitly taken care of by room EQ.

While I personally like to see amps that have very low output impedance, in my experience this is a relatively secondary issue in most cases - it is more important to have enough clean power. Thankfully these days you don't really have to choose one or the other, as most good amps also have low output impedance. :)
 
Top Bottom