Sound Quality Vs. Measurements - Page 876 - 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 30th March 2013, 10:37 AM   #8751
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Hi Dvv . They say a little knowledge is a dangerous thing . DF 96 raised two very good criticisms of VAS degeneration . Douglas Self another . In a nutshell I am going to claim transistor sound has always been the VAS if talking about competent designs . Leak and Quad in my opinion never had obvious transistor sound ( the list will be large if I add to it , Armstrong ..... ) . What they probably had was some hint of TID on challenging material. Crossover distortion has no excuse , nor aggressive protection circuits . Designers who get that wrong should resign and run old folks homes ( no joke , that seems to happen , yikes , take me in my sleep , can you imagine the designer of the Amstrad IC 2000 as your care master ? Maybe the IC 2000 wasn't designed . Maybe it mutated from a liver fluke ? I tried to buy one on e-bay , no luck . The old Teleton GA 202 came up ) .

Standard thinking is that degenerating the VAS can only do harm . To quote D S it is not feedback in the sense it would be if a valve circuit . DF 96 says it reduces the grip of the amplifier at low frequencies and raises the VAS collector impedance . Thought about that a bit . The impedance of the CCS is preferably infinite . The output stage is a very nasty load . As D S says making it low impedance will help . That is analogous to an amplifier driving a speaker . So that must logically be right .

Here is my conjecture again stimulated by D S . He gave me to understand TID and IM distortion will always be manifested as harmonic distortion . My graphs seem to prove that . Even committing multiple sins I got my harmonic distortion down ( remember this is not instability creeping in ) .

So what is transistor sound ? Perhaps it is unquestionably seeking transconductance between input stage and the VAS base ? That horrible distortion like a bad triangle wave is not irrelevant . The cure ? Make sure the impedance's are vastly different . Whatever you do , do not match them . If you do then bandwidth limit to take the distortion away . The complementary feedback pair VAS seems ideal . It will give you almost a single transistor with no great requirement for current . One warning . It is not uncommon to have one transistor doing all the work in CfbP . I had absolutely no stability problems when I did it . Somehow I didn't quite get an improvement over the VAS resistor . A Russian guy ( ? ) made a special VAS that looks like a CfbP . I wish I had tried that .

D S makes another good point . The capacitance inside a transistor is not the best . Use a low Cob device and add externally . The upshot is a reduction in second harmonic distortion . On the other hand a bit of second is not so horrible .

That is what the debates we get into are about . Making us all good shots .

One thing someone said . If we trade away loop feedback and see no distortion difference then the distortion was covered by noise ( it has to be true ) . Well I hate to state the obvious . And how does something below noise intrude ? We assume a reasonable amp when saying this . That is sort of saying , dam the - 100 dB distortion isn't up to snuff .
  Reply With Quote
Old 30th March 2013, 11:55 AM   #8752
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
No matter who says what, if it sounds good to me, I'll use it. How many rules I break in the process is of no consequence.

Nige, I have heard I can't even remember how many amps using a single transistor for its VAS, with Miller capacitor, of course, which sometimes had rather low values (e.g. Sansui AU-7800, 22 pF) and sometimes unbelievably high values (a German amp from the 70ies, 220 pF).

The really odd thing for me at least is that amps which I would think of as overcompensated, as when you have 0.5 mA charging a 150 pF Miller capacitor, giving you a wild slew rate of 3.3V/uS, always managed to sound sort of warm and cuddly, even if imprecise.
__________________
Per Aspera Ad Astra.
  Reply With Quote
Old 30th March 2013, 01:33 PM   #8753
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
An open mind and some common sense is what it takes .

I always say for 4 things that prove a rule there is 1 that disproves it . When you repair things for a living you learn that . I did for 23 years and still do for friends now . Often I find people come to the right answers for the wrong reasons . I am certain even the most educated fall into that trap . It is only when repairing supposedly bad designs that work just fine that a pattern emerges . The Triumph twin motorcycle is a truly horrible design with one or two exceptions . The combustion chamber shape is OK and stroke and timings ( valve and sparks ) . The crank flexes badly . The barrels are seldom square to the crank ( 6 x <1/1000 inch within square was set to one side for racing machines ) . The strange thing is curing the design errors brought new problems . Stiffening the crank made already unbearable vibration even worse ( yikes ) . I said one or two exceptions . The exceptions made the Bonneville a piece of pure magic . I love the oil pump , so simple and excellent . Can be repaired at the road side with improvised tools . Never it's fault if it does , fit a filter and probably never will happen . The pump looks as if a child designed it . I works great .

I am so pleased people who design headlight of cars get it right . My old Rover Montego ( 5 litres / 100 kM , 100 % reliable over 300 000 kM , rust bucket ) I think only ever had 3 bulbs ? I installed a proper transformer in my girlfriends kitchen to try to get the 20 W lights reliable ( and did all the other things one should , good flow of air ). this was to replace the standard switch mode devices . Even at 10 V rms they only last a month or so ( 80 VA 230 V to 9 V run at 40 W and 242 V = 10 V rms ) . That's no 2000 hours and that's no 12 V , come on guys stop lying . I think she needs headlights next ? I might take the light switch out as I don't think it ever gets used ? Now who can explain that ? The waveform shape is OK ( 4 % THD ) and there are no bad surges .
  Reply With Quote
Old 31st March 2013, 06:06 PM   #8754
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
I thought the BBC approach to engineering might be enjoyable . I do get the impression BBC were sponsors of the belief in TID ! Thinking about it they would be .

What I love is the unthinkable . Scientists who happily accept listening tests . More on the bases of testing the reality of it I feel ? Make it bad enough to hear , give it some numbers . The rigorous testing of BBC digital transmission links made one forget it was digital . Stone-age BBC digital better than whizkid/fast-buck CD .

http://www.keith-snook.info/Wireless...easurement.pdf
  Reply With Quote
Old 31st March 2013, 06:26 PM   #8755
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
What BBC has taught me, on purpose or by chance I know not, is that one can design for the specs, or for the sound.

The trick is to design it for the sound, but still with reasonable specs. As if you didn't know that.
__________________
Per Aspera Ad Astra.
  Reply With Quote
Old 31st March 2013, 10:26 PM   #8756
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 10
The simple truth is that conventional specs tell you little about how it subjectively sounds, because they're not measuring what the ear is sensitive to, finds objectionable - merely what is easy and obvious to measure. Until someone finally takes this seriously, and nails the distortion factors that irritate, add greyness to the sound, the enthusiasts will keep going round and round and round in circles, discussing such things ad nauseum ..
__________________
Frank . . . the truth is, I just like a bit of ASMR ...
  Reply With Quote
Old 1st April 2013, 12:16 AM   #8757
benb is offline benb  United States
diyAudio Member
 
Join Date: Apr 2010
There's also this attempt at correlating objectionable sound with a number:
Perception

I propose that, rather than replacing THD with a single weighted-harmonic measurement. it should be replaced with TWO numbers - one that's heavily weighted toward the low-order harmonics (second, third), and the other weighted toward the high-order harmonics (with the ear's rising sensitivity with harmonic number, this one might need little weighting). The first would be "amount of tube sound" and the second would be "amount of transistor sound."
  Reply With Quote
Old 1st April 2013, 07:32 PM   #8758
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
I would defend the BBC and say they often got things right . My feeling is transmitting is plagued with problems . Multipath , hiss , clipping , transmitting over distance ( landlines and via the aerial ) . Whilst multipath is mostly a user problem working with FM must make people aware of how to get the perfect window of performance . That thinking will get ground in . How an amplifier works is much the same . The difference is if a broadcast engineer maybe more searching questions get asked ? For example if it was a transmitter would it be ideal ( it's envelope of performance ) . I know the analogy brakes down because the FM transmitter is a very different animal . The thinking may not be so different . As I say it is no surprise to me that the BBC would understand TID , I am sure it's equivalent is easily found in mildly wrong FM , not least the Nicam 13 bit system .

After all terrible things that have to be done to FM to transmit it is remarkable how good it sounds . That's dedication ( and a miracle ) .
  Reply With Quote
Old 2nd April 2013, 03:16 AM   #8759
mjona is offline mjona  New Zealand
diyAudio Member
 
Join Date: Jul 2007
Location: Upper Hutt
Quote:
Originally Posted by fas42 View Post
The simple truth is that conventional specs tell you little about how it subjectively sounds, because they're not measuring what the ear is sensitive to, finds objectionable - merely what is easy and obvious to measure. Until someone finally takes this seriously, and nails the distortion factors that irritate, add greyness to the sound, the enthusiasts will keep going round and round and round in circles, discussing such things ad nauseum ..
The late John Linsley-Hood is one who has defined the problems you refer to - most recently in his book "Valve&Transistor Audio Amplifiers". This covers a host of other areas of audio design in addition to that of immediate interest.

It is an interesting read and I would not be without it.

Michael J.
  Reply With Quote
Old 2nd April 2013, 04:45 AM   #8760
diyAudio Member
 
PlasticIsGood's Avatar
 
Join Date: Mar 2012
Location: Bradford
Quote:
Originally Posted by mjona View Post
The late John Linsley-Hood is one who has defined the problems you refer to - most recently in his book "Valve&Transistor Audio Amplifiers". This covers a host of other areas of audio design in addition to that of immediate interest.

It is an interesting read and I would not be without it.

Michael J.
Best thing about the book is that it's a story. Especially for a novice, seeing how a circuit works isn't the same as knowing why it's used, which is generally a matter of history.

It's probably a very English history, and partisan in several respects, but illuminating all the same. Not up to date though, obviously.

If I remember his story, life was a struggle for transistor power output stages until reasonably matched NPN, PNP pairs became available. Can't much remember why...problem of symmetrical drive for PP I guess.
  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 10:16 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