Sound Quality Vs. Measurements - Page 911 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st May 2013, 02:07 PM   #9101
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by nigel pearson
Yes all was religiously applied . My brother alas is no longer alive . I would have loved him to be here to answer .
Sorry to hear your brother is not able to tell us what he did.

Quote:
It was the worse feedback amp I ever heard and without feedback one of the best amps . I have never met it's like before or after .
Feedback amps need to be designed. That means feedback can't just be added or removed or changed in amount. Any decent feedback amp is likely to sound bad without feedback; at the very least it will have relatively poor frequency response. An amp designed for no feedback could develop problems when feedback is applied, such as response peaks (and consequent poor phase behaviour) just on the edge of the passband. This elementary point seems to be lost on many DIYers.

Quote:
Originally Posted by a.wayne
If so , shouldn't feedback be adjusted for different loads ....?
I'm not sure what you are asking. If an amp uses feedback to provide a low output impedance (among other virtues) then no change is needed when feeding different speakers of similar nominal impedance. If changing the OPT secondary to provide a different impedance then a change in feedback may be needed. This is standard engineering.
  Reply With Quote
Old 21st May 2013, 02:16 PM   #9102
diyAudio Member
 
vacuphile's Avatar
 
Join Date: Apr 2011
Location: Not where whatever I am looking for is at.
Quote:
Originally Posted by dvv View Post
@mr_push_pull

I read somehwre, can't remember where, that many people can hear a 4 degree phase shift at 20 kHz as a slightly out of focus sound, not clear enough. Working backwards, you need an actual bandwidth of about 200 kHz to avoid this problem.
DVV, there is very little basis for this. Phase sensitity of hearing runs out at around 2KHz. Blind AB switching between a flat signal and the same with a 180 degree phase shift at 2KHz (if I remember correctly) could be detected only by some as 'different', without any clear preference for one or the other.

For that reason, I don't see why bandwidth limiting (at the input, not the amplification stage itself) would be a problem, even with a low corner frequency of 50KHz or so.
__________________
Everything is somewhere. Where the @!#$ is it.
  Reply With Quote
Old 21st May 2013, 02:19 PM   #9103
a.wayne is offline a.wayne  United States
diyAudio Member
 
a.wayne's Avatar
 
Join Date: May 2008
Location: Front Row Center
Quote:
Originally Posted by dvv View Post
If we were to start with the harm already done to the sound, we might as well as give up right there and then, because no matter what we have, it will only add more degradation.

I prefer to think about adding as little degradation as possible to what has already been added on its way from the studio to my CD player.

Low frequency shift can be minimal with a little effort and thinking. While it is smearing, I believe it's far less damaging than high frequency shifts, which are much more easily heard. Few speakers reach down as low as 20 Hz, and besides, as far as I know, at 20 HZ one only has a few mammoth church organs and that's it. These days, I do beleieve frequency corners in the low region are at 3 Hz or lower, and if DC, then below 1 Hz. They are no longer relevant down there.

For those who still use decoupling caps, I note the are aware of group delay problems and tend to use really top quality caps, thus minimizing trouble.

To the best of my knowledge, no-one has established an iron clad connection between slew rate and quality sound, HOWEVER, only if one has gone above a certain point, 1 V/uS per every peak volt output, so SID, TID and TIM do not bedome a problem.

So, for a say 50 WRMS amp, minimum should be 28 V/uS, for a 100 WRMS amp 40 V/uS, and so forth. I mentioned it only because H/K likes it double, so the 680 integrated does 80 V/uS (yet needs 37 V/uS), the Citation needs 40 V/uS yet does 100 V/uS, etc. The point being that more can't hurt, while less can.

Also, in my experience, each and every superior sounding amp I have ever heard also satisfied this requirement without fail.

Does yours?
Most believe 40 v/uS to be sufficient ....

Quote:
Originally Posted by vacuphile View Post
DVV, there is very little basis for this. Phase sensitity of hearing runs out at around 2KHz. Blind AB switching between a flat signal and the same with a 180 degree phase shift at 2KHz (if I remember correctly) could be detected only by some as 'different', without any clear preference for one or the other.

For that reason, I don't see why bandwidth limiting (at the input, not the amplification stage itself) would be a problem, even with a low corner frequency of 50KHz or so.
Is that First law or second .....
__________________
World Cup Cat Hacky Sack given to Messi and with 30seconds to go D Germans and the rest of Europe save face ..
  Reply With Quote
Old 21st May 2013, 03:14 PM   #9104
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Quote:
Originally Posted by mr_push_pull View Post
yes, you're right, hi-fi is about as little deterioration as possible so if you can make an amp having low phase shift in the band of interest, why not.
but at the same time I can't help but think of the accumulated phase shift, starting from the air produced by say the singer's mouth and ending in our living rooms

and, again, how about the low frequency phase shift, caused by the decoupling caps? I did some calculations a while back and it looks like it can be a real problem, with objectionable group delay extending to the low-mid region.

do you have any explanation/speculation about why 80V/us would correlate to good sound?
When talking slewing it is seldom stated what the source and sink ability is . I suspect if symmetrical slower is fine . It also usually says enough current was available to drive the VAS if high ( and that is the big deal ) . My guess is if sensible bandwidth is used ( 70 kHz - 3 dB ) , sensible impedance ratios between input stage and VAS ( > 3 : 1 if you can ) and symmetry, then 6V / uS would be OK for 100 W . I very much doubt if SA CD nor MC pick up really justifies more ? Even though there is significant 50 to 100 kHz output from a MC pick up if has to get past 75 uS filter . If it is at a significant level then the tweeters better look out . Make it high because you can is no bad reason . As for SA CD , surely it is to a sensible standard ? It can not demand a > 80 V / us amp ? My feeling is the only question is this . If we avoid feeding an input from a high impedance then why would we do it with the VAS ? The analogy is the big V8 that is so nice to drive slow . The 140 MPH bit is not the guarantee . You wouldn't say to someone your granny must have a 140 MPH car as she is a slow driver would you ? The 100 watt amp I often use is 35 V / uS and symmetrical .

If slewing is connected with CCRR then I will accept it matters . Seems it would be . Some say that transistor amps are badly troubled by RFi , valves less so . CCRR would say the reverse . The high voltages of valves must help ?

From what I said earlier don't infer I dislike pentodes . I disliked them for that amp . I recently used them as the best choice . Friends thought I must be wrong ( mad ) until they were played them . The spectrum analyzer said pentodes and the spectrum analyzer was right . Triodes whilst OK were not the right solution . What I was trying to say previously was the amp with least measured high frequency was subjectively the one with most to offer in the HF . I doubt it was overshoot or HF resonance as no loop feedback was the preferred option .

Fascinating what you say about decoupling . Say more if you can .
  Reply With Quote
Old 21st May 2013, 03:50 PM   #9105
diyAudio Member
 
Join Date: Mar 2004
Location: At the output stage
Send a message via Yahoo to mr_push_pull
Quote:
Originally Posted by nigel pearson View Post
Fascinating what you say about decoupling . Say more if you can .
sorry for the confusion, I meant coupling cap.
__________________
we all love a good ol' stereotype until it's against us
  Reply With Quote
Old 21st May 2013, 06:55 PM   #9106
diyAudio Member
 
Join Date: Mar 2004
Location: At the output stage
Send a message via Yahoo to mr_push_pull
Quote:
Originally Posted by vacuphile View Post
there is very little basis for this. Phase sensitity of hearing runs out at around 2KHz. Blind AB switching between a flat signal and the same with a 180 degree phase shift at 2KHz (if I remember correctly) could be detected only by some as 'different', without any clear preference for one or the other.
somehow that doesn't surprise me.
I haven't done actual tests but, as I said, intuition tells me that evolution took care of this (and all the studies so far confirm it) our brain manages to do a lot with little and it doesn't have many resources to waste.
and I would speculate that evolution made it not spend too much effort dissecting a signal that doesn't contain much useful data to begin with.


on to slew-rate. being a computer science engineer and not an EE I tend to view everything from a system perspective. output vs input. I leave the VAS and input stage stuff to the EEs. all I care about is what the output adds to the input and so should everyone. so, from an user's (buyer's) perspective...
Douglas Self sais in his "Audio Power Amplifier Design Handbook":

The most meaningful definition of an amplifier’s speed is its maximal slewrate. The minimum slew-rate for a 100 W/8 amplifier to cleanly reproduce a 20 kHz sinewave is easily calculated as 5.0 V/μsec; so 10 V/μsec is adequate for 400 W/8, a power level that takes us somewhat out of the realms of domestic hi-fi. A safety-margin is desirable, and if we make this a bare factor of two then it could be logically argued that 20 V/μsec is enough for any hi-fi application; there is in fact a less obvious but substantial safety-margin already built in, as 20 kHz signals at maximum level are mercifully rare in music; the amplitude distribution falls off rapidly at higher frequencies.

Firm recommendations on slew-rate are not common; Peter Baxandall made measurements of the slew-rate produced by vinyl disc signals, and concluded that they could be reproduced by an amplifier with a slew limit corresponding to maximum output at 2.2 kHz. For the 100 W amplifier this corresponds to 0.55 V/μsec[18].

Nelson Pass made similar tests, with a moving-magnet (MM) cartridge, and quoted a not dissimilar maximum of 1 V/μsec at 100W. A moving-coil (MC) cartridge doubled this to 2 V/μsec, and Pass reported[19] that the absolute maximum possible with a combination of direct-cut discs and MC cartridges was 5 V/μsec at 100W. This is comfortably below the 20 V/μsec figure arrived at theoretically above; Pass concluded that even if a generous 10:1 factor of safety was adopted, 50 V/μsec would be the highest speed ever required from a 100 W amplifier.


I'm not sure where those 5V/usec come from (my calculations give less) but at any rate it's way less than 80V/us.
__________________
we all love a good ol' stereotype until it's against us

Last edited by mr_push_pull; 21st May 2013 at 07:05 PM.
  Reply With Quote
Old 21st May 2013, 06:56 PM   #9107
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
Quote:
Originally Posted by vacuphile View Post
DVV, there is very little basis for this. Phase sensitity of hearing runs out at around 2KHz. Blind AB switching between a flat signal and the same with a 180 degree phase shift at 2KHz (if I remember correctly) could be detected only by some as 'different', without any clear preference for one or the other.

For that reason, I don't see why bandwidth limiting (at the input, not the amplification stage itself) would be a problem, even with a low corner frequency of 50KHz or so.
Perhaps so, but over the years I havecome to realize that to me, an amp with a smaller phase error will most likely be more pleasing to me than another with a greater phase error.

While this is certainly hardly scientific, I am not in the business of advancing science, and am well aware it's all about my taste (for me). For example, I dislike the sound of tubes in general, though I have heard a few impressive devices in my time, or, oh blasphemy!, the older Mark Levinson electronics sounded a little too dry for my taste, etc. Krell was more brash, perhaps even more brutal, but gave me a warmer sound than ML.

As for bandwidth limiting, you are free to do as you please, but in my view, 20 kHz is WAY too low. I don't see how it can fail to impact the sound. Initially, many will say it's a nice, warm sound, cuddly, but givem a few days and something good to compare with and they will realize what a price they are paying for the curtailed sound.

Personally, I took a hint from reVox and Sony and first get them to 350 kHz or so at full nominal blast, then cut the input signal at around 200 kHz. It never failed me, I never had oscillations or some such problem. Of course, there's always a first time.
__________________
Per Aspera Ad Astra.
  Reply With Quote
Old 21st May 2013, 07:01 PM   #9108
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
Quote:
Originally Posted by a.wayne View Post
Most believe 40 v/uS to be sufficient ....
As do I, so long as it slews at a rate of 1 V/uS per every peak volt of output. Since 100W/8 Ohms is 40V p-p, a slew rate of 40 V/uS is all I need.

I've never done a more powerful amp than that, so I can't comment, perhaps it would also be just fine for say 200W/8 Ohms. National Semi's famed and now reprinted book on audio states 0.5V/uS is quite enough per every peak volt of output, which is half of what I think, and they are probably right. I just like to be double sure.
__________________
Per Aspera Ad Astra.
  Reply With Quote
Old 21st May 2013, 07:29 PM   #9109
diyAudio Member
 
Join Date: Mar 2004
Location: At the output stage
Send a message via Yahoo to mr_push_pull
Quote:
Originally Posted by dvv View Post
IMO Initially, many will say it's a nice, warm sound, cuddly, but givem a few days and something good to compare with and they will realize what a price they are paying for the curtailed sound.
fixed that for ya
__________________
we all love a good ol' stereotype until it's against us
  Reply With Quote
Old 21st May 2013, 10:50 PM   #9110
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 10
Quote:
Originally Posted by dvv View Post
Perhaps so, but over the years I havecome to realize that to me, an amp with a smaller phase error will most likely be more pleasing to me than another with a greater phase error.

While this is certainly hardly scientific, I am not in the business of advancing science, and am well aware it's all about my taste (for me). For example, I dislike the sound of tubes in general, though I have heard a few impressive devices in my time, or, oh blasphemy!, the older Mark Levinson electronics sounded a little too dry for my taste, etc. Krell was more brash, perhaps even more brutal, but gave me a warmer sound than ML.
I reckon it's as simple as that the amp with a high bandwidth will automatically have better distortion numbers, where it counts, in the treble end of the spectrum. Better behaviour, better sound.

dvv, your preferences for the 'sounds' of various types of electronics matches my own - I think we would be in agreement when assessing some new piece of kit, in situ ...
__________________
Frank . . . the truth is, I just like a bit of ASMR ...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Quality Control differences = variations in sound quality? KT Class D 3 4th June 2014 12:02 AM
Sound Card for Measurements Marik Solid State 2 2nd January 2012 08:59 PM
Sound Card Recommendations (For Audio Measurements) dchisholm Equipment & Tools 5 16th July 2011 09:40 AM
How to protect sound card during amp measurements? okapi Everything Else 13 2nd September 2008 03:06 PM
Sound cards - test and measurements jackinnj Everything Else 2 5th July 2003 03:02 PM


New To Site? Need Help?

All times are GMT. The time now is 12:02 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2