ThermalTrak+TMC amp - Page 12 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 10th June 2012, 12:36 PM   #111
dadod is offline dadod  Croatia
diyAudio Member
 
dadod's Avatar
 
Join Date: Apr 2006
Location: Zagreb
Quote:
Originally Posted by Dave Zan View Post
No proposal yet! I have a few ideas but need to think more.
I believe a few people did have some trouble with Roender's amp when they built copies. I will check their solutions.
I am interested in better thermal stability but lower distortion is a nice bonus. Even if, as Andrew notes, it's only 1.5 dB.
But your decision to stay with a proven output circuit while you tested TMC and ThermalTrak is very reasonable and seems to have worked well.

Best wishes
David

Is Dado an informal form of Damir?
Yes
  Reply With Quote
Old 10th June 2012, 06:08 PM   #112
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
CFP compensation:

The best way is an RC across the B-E junction of the slave transistor. This has better performance then the Miller type (which doesn't necessarily work anyway) and it doesn't reduce PSRR. See attached schematic of my high-current K-multiplier.

Resistors:

I found in a double EF that 6.8k was the best value, reducing 3rd harmonic from -102db to -108db. This is at 18V into 6R with a single pair of outputs (try 15k resistors from output emitters to Q19 and Q21 emitters just to get close). I imagine it would be 15k or something like that for two pairs of outputs. Just lower or increase the value until you find the right value. If you don't like guessing you may inspect the phase of the third harmonic to determine whether you want to go up or down (overcomp vs. undercomp).

I don't know if it works the same for your heavily-buffered output stage. This technique has worked best for output stages where current gain nonlinearity was the largest concern for distortion. See attached schematic.

Furthermore, the Vbe transfer curve probably is not an exact fit to the high-current beta rolloff. So I think adjusting this compensation at max power level may eliminate the potential benefit from lower power levels where the fit is more accurate.

PS. Is this not a form of error correction?
Attached Images
File Type: png Kmultiplier_Poweramp_schem2.png (111.8 KB, 411 views)
File Type: png VbeResistors_Outputstage.png (103.0 KB, 400 views)
  Reply With Quote
Old 11th June 2012, 05:49 AM   #113
dadod is offline dadod  Croatia
diyAudio Member
 
dadod's Avatar
 
Join Date: Apr 2006
Location: Zagreb
Quote:
Originally Posted by keantoken View Post
CFP compensation:

The best way is an RC across the B-E junction of the slave transistor. This has better performance then the Miller type (which doesn't necessarily work anyway) and it doesn't reduce PSRR. See attached schematic of my high-current K-multiplier.
Here is what I get now with RC across the B-E of the predrivers. Now the stability is similar to the Triple EF.
dado
Attached Images
File Type: jpg keantoken-suggestion-2.jpg (181.4 KB, 317 views)
  Reply With Quote
Old 11th June 2012, 07:07 AM   #114
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
That looks good to me. I wonder if it will stay stable at high currents where the transconductance of Q19 and Q21 increases dramatically. This is one of the reasons I use degeneration in my Kmultipliers.
  Reply With Quote
Old 11th June 2012, 07:17 AM   #115
dadod is offline dadod  Croatia
diyAudio Member
 
dadod's Avatar
 
Join Date: Apr 2006
Location: Zagreb
Quote:
Originally Posted by keantoken View Post
That looks good to me. I wonder if it will stay stable at high currents where the transconductance of Q19 and Q21 increases dramatically. This is one of the reasons I use degeneration in my Kmultipliers.
With degeneration of 2.2ohm distortion increases a bit.
  Reply With Quote
Old 11th June 2012, 10:17 AM   #116
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Emitter degeneration on which transistors? The pre-drivers, the drivers, or the outputs? Or all of them?
__________________
regards Andrew T.
  Reply With Quote
Old 11th June 2012, 11:13 AM   #117
dadod is offline dadod  Croatia
diyAudio Member
 
dadod's Avatar
 
Join Date: Apr 2006
Location: Zagreb
Quote:
Originally Posted by keantoken View Post
CFP compensation:

Resistors:

I found in a double EF that 6.8k was the best value, reducing 3rd harmonic from -102db to -108db. This is at 18V into 6R with a single pair of outputs (try 15k resistors from output emitters to Q19 and Q21 emitters just to get close). I imagine it would be 15k or something like that for two pairs of outputs. Just lower or increase the value until you find the right value. If you don't like guessing you may inspect the phase of the third harmonic to determine whether you want to go up or down (overcomp vs. undercomp).

I don't know if it works the same for your heavily-buffered output stage. This technique has worked best for output stages where current gain nonlinearity was the largest concern for distortion. See attached schematic.

Furthermore, the Vbe transfer curve probably is not an exact fit to the high-current beta rolloff. So I think adjusting this compensation at max power level may eliminate the potential benefit from lower power levels where the fit is more accurate.

PS. Is this not a form of error correction?
I simulated with resistors from 15k down to 6.8k and here are the results.
My opinion is that this does not help enough to reduce odd harmoniks to be implemented in the triple ops.
First up left is with no resistors and then is written a resistors values.
dado
Attached Images
File Type: jpg keantoken-suggestion-3.jpg (249.4 KB, 292 views)
  Reply With Quote
Old 11th June 2012, 09:33 PM   #118
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
I guess it is not an issue due to the astronomical current gain of your output stage. It looks to me like voltage distortion appearing at the VAS output is much larger, along with distortion from compensation loading of the input stage. Have you tried TPC?

I was trying to find a schematic that I can simulate, but there are a lot of different schematics - which one should I use? Which one are you using?
  Reply With Quote
Old 11th June 2012, 10:00 PM   #119
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Also, try using the BC560C for the current mirror. Here you need a transistor with very good Vcesat parameters, the BC5xx and BC3x7 are better here than any transistor I've tried. The 2N5551 that are often used are just horrible. The KSA992 are also pretty bad. Look for the Hfe vs Vce curves.
  Reply With Quote
Old 12th June 2012, 05:27 AM   #120
dadod is offline dadod  Croatia
diyAudio Member
 
dadod's Avatar
 
Join Date: Apr 2006
Location: Zagreb
Quote:
Originally Posted by keantoken View Post
I guess it is not an issue due to the astronomical current gain of your output stage. It looks to me like voltage distortion appearing at the VAS output is much larger, along with distortion from compensation loading of the input stage. Have you tried TPC?

I was trying to find a schematic that I can simulate, but there are a lot of different schematics - which one should I use? Which one are you using?
Here is the zip file.
Attached Files
File Type: zip DADO-TT.zip (28.4 KB, 82 views)
  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
MEMDIST POWER AMP + JC + TMC - help to set up padamiecki Solid State 8 10th January 2014 09:38 AM
Compact Sized LME49810/11 +ThermalTrak Amp panson_hk Chip Amps 302 25th September 2013 10:23 AM
New 200 watt Kit amp features ultra low distortion and Thermaltrak devices snoopy Solid State 56 3rd May 2010 08:42 AM
Mini-Sized 49811 ThermalTrak Amp panson_hk Chip Amps 3 1st April 2010 08:06 AM
What to do with TMC tube radio gear? diamondsouled Tubes / Valves 4 31st March 2009 01:30 PM


New To Site? Need Help?

All times are GMT. The time now is 07:02 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