Sound Quality Vs. Measurements - Page 349 - 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 15th March 2012, 06:08 PM   #3481
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by dvv View Post
Who or what is "Freescale"?
Former Motorola business I suppose?
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 15th March 2012, 06:09 PM   #3482
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
Thorsten, thank you for the pointer and schematics. I'll chalk up some more beer.

I'll have to mull over them a bit, this is terra incognita for me.
  Reply With Quote
Old 15th March 2012, 06:09 PM   #3483
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by dvv View Post
Who or what is "Freescale"?
Spinoff from Motorola some years ago. Moto stayed for a while in the cellphone business. The discrete semis went to On Semi. Freescale makes uC chips and does research.

See for example: About Freescale
  Reply With Quote
Old 15th March 2012, 06:34 PM   #3484
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by dvv View Post
I'll have to mull over them a bit, this is terra incognita for me.
It is strictly concept.

You need J-Fets with a high enough pinch-off voltage to bias the Bipolars, unless you explicitly bias them.

In this case you see two daisychained rush cascodes.

In this case it is a non-inverting gainstage with a Fet follower driving it.

A 2SK246BL/2SJ103BL will have around 4mA current with the BJT Bias and hence around 3mA/V transconductance which is passed on to the BJT's collector. Several common BJT and FET distortion problems are removed, no doubt we are adding some different distortions somewhere else, so that the eternal balance of the universe is preserved.

The concept also shows some freaky feedback approaches, for fun.

I probably would not even remotely attempt to build this, however it can serve to show some possible alternatives to the common way things are done.

BTW, adding one resistor and a choke to the output stage turns it into a quad style current dumper, which is way more effective for optimum bias or overbiased class AB than for pure class B...

Ciao T
  Reply With Quote
Old 16th March 2012, 12:38 AM   #3485
tvrgeek is offline tvrgeek  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Md
Quote:
Originally Posted by godfrey View Post
I've seen that in another circuit, with a footnote explaining that it's optional to use either the two diodes or the LED. Maybe that's the idea here too.
No note like that. Spice shows added capacitance which by my interpretation ( potentially flawed understanding), makes the CCS not as effective. This is a small Naim. Are LED's much slower than small switching diodes?

Staying with just the ccs. Baby steps.

I also notice on just about every schematic the IPS ccs is a single transistor where most of the VAS ccs are a feedback pair. Because of the higher gain in the VAS?

Comments say green led's are more stable than red, but red non-linearities track opposite and compensate for the ccs BJT. Both comments sound reasonable. What are the thoughts here?

Some authors suggest to isolate the IPS and VAS ccs references. Some use the same reverence. Cost savings, but would not they have negative influence on each other? Or is the influence an advantage?
  Reply With Quote
Old 16th March 2012, 01:22 AM   #3486
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by tvrgeek View Post
No note like that. Spice shows added capacitance which by my interpretation ( potentially flawed understanding), makes the CCS not as effective. This is a small Naim. Are LED's much slower than small switching diodes?

Staying with just the ccs. Baby steps.

I also notice on just about every schematic the IPS ccs is a single transistor where most of the VAS ccs are a feedback pair. Because of the higher gain in the VAS?

Comments say green led's are more stable than red, but red non-linearities track opposite and compensate for the ccs BJT. Both comments sound reasonable. What are the thoughts here?

Some authors suggest to isolate the IPS and VAS ccs references. Some use the same reverence. Cost savings, but would not they have negative influence on each other? Or is the influence an advantage?
Not an issue of LED or diode "speed". They are providing a reference voltage of a cetain temperature coefficient. The lower Z the better. It is not tracking of "nonlinearites" that is of importance, it's the temp coefficient ~match. If one has a stage that is intentionally modulating the LED current, that's another matter altogether --- but that would be peculiar, and rely on even more non-guaranteed parameters.

Paralleling an LED of any visible color with two standard junction diodes is of no imaginable advantage it would seem --- unless you anticipate the LED failing open-circuit, in which case it's like wearing suspenders anticipating that your belt is going to fail. They lost the footnote, which would have added that for the two diodes the emitter resistor would be correspondingly smaller than for the LED, for the same collector current.

I doubt that sharing the reference has any advantage. Again, it's a voltage reference of modest capability.
  Reply With Quote
Old 16th March 2012, 04:14 AM   #3487
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by tvrgeek View Post
No note like that. Spice shows added capacitance which by my interpretation ( potentially flawed understanding), makes the CCS not as effective. This is a small Naim. Are LED's much slower than small switching diodes?
For this type of CCS more capacitance on the base is actually a "good thing". As these are open loop the amount of local feedback and thus the collector impedance are largest if and when the emitter resistance is lowest and thus the base resistance is lowest.

A very worthwhile improvement is to keep one of the Diodes and add an LM329 instead of the other and a re-adjusted emitter resistor with a big elcap (maybe 10uF/10V?) across the whole shooting match on the base. The 329 gives around 10 times the emitter resistance of the single diode and thus 10 times the effective CCS Impedance.

In the input stage we have no issue with the extra voltage dropped out. It's not as usable for the VAS Load, lest we use boosted rails.

For a Killer CCS take an additional J-Fet with at least 1V GS voltage at the CCS and enough voltage/power handling and cascode this suckah (gate to BJT base, source to BJT Collector, drain is new CCS Output. This trick is really cool for modding existing stuff...

It remains debatable how much of impact an improved CCS has though.

LM329 and cascoding can easily get you 50o times the impedance of the original though and a flat impedance to a much higher frequency.

Quote:
Originally Posted by tvrgeek View Post
I also notice on just about every schematic the IPS ccs is a single transistor where most of the VAS ccs are a feedback pair. Because of the higher gain in the VAS?
Hard to say. Maybe because of dropout voltage or greater collector current?

Quote:
Originally Posted by tvrgeek View Post
Comments say green led's are more stable than red, but red non-linearities track opposite and compensate for the ccs BJT. Both comments sound reasonable. What are the thoughts here?
I would avoid LED's, they are fashionable, but I find them too inconsistent. The days when you could just buy HP Red Ultrabright and have a really good and consistent Voltage source are over...

Quote:
Originally Posted by tvrgeek View Post
Some authors suggest to isolate the IPS and VAS ccs references. Some use the same reverence. Cost savings, but would not they have negative influence on each other? Or is the influence an advantage?
I think DS showed that especially the VAS CCS can influence the IPS one adding distortion. If anyone would spend a few cent on a small 1,000uF/10V (< 2 Ohm @ 100Hz) cap most of that would go away. So in a new design I would seek to optimise the CCS's individually while for an existing one with shared reference I'd probably just put the "magic cap" across the diodes and be done...

BTW, in Samuel Groner's commentry on Selfs APADH he proposes a small modification that turns the VAS current source into a Push-Pull VAS at high frequencies (only really usable with a buffered VAS though), which will help the slew rate quite a bit. I first saw this clever bit of trickery in an all Fet design by Jim Strickland (Hafler 915/100SE Preamp linestage), very clever.

If one was interested in polishing a t... ähhhhmmm standard "Lin" type amplifier rather than designing a better topology there are many of the "a resistor here and a cap there and a J-Fet buffer elsewhere" tricks that can dramatically change the circuits performance.

If you like, open a thread strictly on that subject invite me and elect a subject Amp and we can have fun...

Ciao T
  Reply With Quote
Old 16th March 2012, 04:16 AM   #3488
godfrey is offline godfrey  South Africa
diyAudio Member
 
Join Date: Nov 2009
Location: Cape Town
Quote:
Originally Posted by tvrgeek View Post
Some authors suggest to isolate the IPS and VAS ccs references. Some use the same reverence. Cost savings, but would not they have negative influence on each other? Or is the influence an advantage?
IMHO, the main trick is not to let the IPS current be affected by the VAS output voltage.

The pic below shows how to completely screw it up. If the output ever clips to the negative rail, Q3 saturates, the voltage across the diodes drops, the IPS is starved of current, and the output remains stuck to the negative rail indefinitely.
Attached Images
File Type: gif bad.GIF (3.9 KB, 86 views)
  Reply With Quote
Old 16th March 2012, 04:19 AM   #3489
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by godfrey View Post
IMHO, the main trick is not to let the IPS current be affected by the VAS output voltage.

The pic below shows how to completely screw it up. If the output ever clips to the negative rail, Q3 saturates, the voltage across the diodes drops, the IPS is starved of current, and the output remains stuck to the negative rail indefinitely.
Correct. How do we fix it?

1K in line with the based of Q3.

And then maybe 1nF from the base of Q3 to that of Q5...

Ciao T
  Reply With Quote
Old 16th March 2012, 07:42 AM   #3490
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
Quote:
Originally Posted by ThorstenL View Post
Hi,



It is strictly concept.

You need J-Fets with a high enough pinch-off voltage to bias the Bipolars, unless you explicitly bias them.

In this case you see two daisychained rush cascodes.

In this case it is a non-inverting gainstage with a Fet follower driving it.

A 2SK246BL/2SJ103BL will have around 4mA current with the BJT Bias and hence around 3mA/V transconductance which is passed on to the BJT's collector. Several common BJT and FET distortion problems are removed, no doubt we are adding some different distortions somewhere else, so that the eternal balance of the universe is preserved.

The concept also shows some freaky feedback approaches, for fun.

I probably would not even remotely attempt to build this, however it can serve to show some possible alternatives to the common way things are done.

BTW, adding one resistor and a choke to the output stage turns it into a quad style current dumper, which is way more effective for optimum bias or overbiased class AB than for pure class B...

Ciao T
I probably won't be trying it myself, but it will teach me some.

As you have probably guessed, I am not too comfortable with FETs, I have done very little work with them. Perhaps this is an opportunity to catch up a little. Lord be praised, my good friend Oliver, who does my PCB artwork (I'm pretty good at it, but he's way better), loves FETs, MOSFETs and tubes, so I do have someone to check up on me.

One thing I think I see as definitely coming is use of FETs in the input stage as shown on my previous schematic, and in version "B", the one which has cascodes for their second stage of voltage amplification.

FETs make a lot of sense, and there's nothing to be gained by shying away from them, especially now that I have been told that those which are available to me will do quite nicely.

This also serves to remind me of my own view that after having the initial idea, the most important link in the development chain of anything is the feedback one receives if one asks for it. It's so easy to get locked up in one's own little world and miss out a lot that's going on and that is quite possible.
  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 12:04 PM.


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