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 11th May 2013, 08:16 PM   #131
astx is offline astx  Austria
diyAudio Member
 
Join Date: Jan 2011
Location: Tyrol / Austria
Quote:
Originally Posted by astx View Post
New driver bjt's (2SC4793/2SA1837 and MJE15032/MJE15033) arrived ...
The good news: 2SC5171 and 2SA1930 can be directly replaced by 2SC4793/2SA1837.

The bad news: the distortion figure of THD20kHz@200W@8R was about 0.0034% before and is now with this drivers 0.005%.
Maybe a compensation tuning helps to get closer to the predicted 0.003% THD from simulation. Let's see.

A complete THD/power test is now running. So we can compare the THD results also for lower level signals.

BR, Toni
  Reply With Quote
Old 11th May 2013, 08:45 PM   #132
astx is offline astx  Austria
diyAudio Member
 
Join Date: Jan 2011
Location: Tyrol / Austria
Quote:
Originally Posted by sajti View Post
The spice:

Sajti
asc file? Thank you.

BR, Toni
  Reply With Quote
Old 11th May 2013, 10:16 PM   #133
astx is offline astx  Austria
diyAudio Member
 
Join Date: Jan 2011
Location: Tyrol / Austria
Quote:
Originally Posted by astx View Post
The good news: 2SC5171 and 2SA1930 can be directly replaced by 2SC4793/2SA1837.

The bad news: the distortion figure of THD20kHz@200W@8R was about 0.0034% before and is now with this drivers 0.005%.
Maybe a compensation tuning helps to get closer to the predicted 0.003% THD from simulation. Let's see.

A complete THD/power test is now running. So we can compare the THD results also for lower level signals.

BR, Toni
The completed THD power test shows significant higher THD levels from low to high power!
Perhaps the new drivers needs a rebiasing? The new drivers have better SOA so after some simulations i decided to change R17 from 150R to 68R.
Bingo! 10ppm better THD in real life!
THD20kHz@200W@8R is now at 0.004% (measurement floor of VP7723D is at 0.00106%)
THD1K@200W@8R is now at 0.00130% (measurement floor of VP7723D is at 0.00045%)
  Reply With Quote
Old 11th May 2013, 10:36 PM   #134
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
A 25% difference in THD is pretty small, think in logarithmic terms. I used to worry about small differences but eventually I realized thinking logarithmically allowed me to make gains of more than 6db. Unless your design is nearly finalized, you should not be satisfied with fractional gains or you will spend time on only the minor sources of distortion. Look for the major sources of distortion and focus on eliminating those. To do this requires developing methodology but really it's just a process of asking a question and devising a test that will answer it. Doing this you can figure anything out.
  Reply With Quote
Old 11th May 2013, 11:15 PM   #135
astx is offline astx  Austria
diyAudio Member
 
Join Date: Jan 2011
Location: Tyrol / Austria
Quote:
Originally Posted by keantoken View Post
A 25% difference in THD is pretty small, think in logarithmic terms. I used to worry about small differences but eventually I realized thinking logarithmically allowed me to make gains of more than 6db. Unless your design is nearly finalized, you should not be satisfied with fractional gains or you will spend time on only the minor sources of distortion. Look for the major sources of distortion and focus on eliminating those. To do this requires developing methodology but really it's just a process of asking a question and devising a test that will answer it. Doing this you can figure anything out.
you are right regarding THD levels! I see them as a sign that something can be done better. So I found the underbiasing problem of the new drivers very quickly. Also the distortion residual waveform is important and a good sign of stability or instability ...

Btw: It seems to be no more necessary to keep the 22p bridge above TPC in place. Amplifier is stable without it. Will optimize TPC the next days. Square root overshoot is stable - shows no ringing.
All 2SC5171/2SA1930 have now been replaced by 2SC4793/2SA1837 drivers. Slewrate increased from 45V/s to about 80V/s. Square root overshoot is TPC typically and stable - shows no ringing.

BR, Toni
  Reply With Quote
Old 11th May 2013, 11:56 PM   #136
astx is offline astx  Austria
diyAudio Member
 
Join Date: Jan 2011
Location: Tyrol / Austria
Default Distortion analysis for R17=68R / 22p removed

All 2SC5171/2SA1930 have been replaced by 2SC4793/2SA1837 including VAS drivers!

2SC4793/2SA1837 are biased with R17=68R
22p bridge capacitor (above TPC) removed.

Note: 20 and 200Hz measurements above 100W are inaccurate as lab powersupply current limiter has actived.

The second plot is the loop measurement of the analyzer itself for comparison.
Attached Images
File Type: png thd_20_to_20k.png (85.5 KB, 385 views)
File Type: png reference_thd_20_to_20k.png (74.3 KB, 316 views)
  Reply With Quote
Old 12th May 2013, 12:11 AM   #137
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
I've seen too many C5171/A1930 counterfeits than I'd like to have. It would not surprise me at all if yours were fakes and were causing stability issues.

At the same time, the C5171/A1930 are actually a bit faster than the C4793/A1830.

Hopefully removing the 22p TPC bridge lowers THD20. Eventually it may become evident that the only distortion left is that from the output stage base currents, in which case it will be time to improve the frontend or change OPS topology. Or let well enough be.

It is possible to correct the overshoot with an RC across the feedback resistor. The idea is to optimize TPC for 6db overshoot and then correct it by lowering gain above the TPC corner by 6db (other figures than 6db could work). This may seem superfluous, but it is important to limit overshoot so that you can test step response close to full output swing where 6db overshoot would clip badly. TPC is often oversized to prevent this overshoot but when it is allowed and corrected for, significant gains can be made (that is, if TPC was the dominant distortion mechanism).

Last edited by keantoken; 12th May 2013 at 12:13 AM.
  Reply With Quote
Old 12th May 2013, 10:47 AM   #138
sajti is offline sajti  Hungary
diyAudio Member
 
Join Date: Apr 2003
Location: Vác, Hungary
Quote:
Originally Posted by astx View Post
asc file? Thank you.

BR, Toni
I will give it tomorrow, as it is in my home PC.

Sajti
  Reply With Quote
Old 12th May 2013, 10:50 AM   #139
sajti is offline sajti  Hungary
diyAudio Member
 
Join Date: Apr 2003
Location: Vác, Hungary
Quote:
Originally Posted by keantoken View Post
I've seen too many C5171/A1930 counterfeits than I'd like to have. It would not surprise me at all if yours were fakes and were causing stability issues.

At the same time, the C5171/A1930 are actually a bit faster than the C4793/A1830.
Try Mouser. They have stock, and I'm sure that they sell real Toshiba.

5171/1930 is faster, and have lower internal capacitances.

Sajti
  Reply With Quote
Old 12th May 2013, 11:21 AM   #140
diyAudio Member
 
Join Date: May 2005
Location: Bristol, UK
Quote:
Originally Posted by keantoken View Post
I've seen too many C5171/A1930 counterfeits than I'd like to have. It would not surprise me at all if yours were fakes and were causing stability issues.
Don't forget the C5171/A1930 are very fast (for their power rating) - as such they may be more susceptible to parasitic oscillations. astx may have been seeing this rather than global loop instability.

Quote:
Originally Posted by astx View Post
The good news: 2SC5171 and 2SA1930 can be directly replaced by 2SC4793/2SA1837.

The bad news: the distortion figure of THD20kHz@200W@8R was about 0.0034% before and is now with this drivers 0.005%.
Maybe a compensation tuning helps to get closer to the predicted 0.003% THD from simulation.
You say predicted THD with the new drivers is 0.003%, but what models are you using for the C4793/A1837?
  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
f5 based high power class ab amplifier 400kg Solid State 6 18th February 2013 04:42 PM
Contest: Linear Power Amp in a mint tin (class Aa, class AB, or class B) danielwritesbac Chip Amps 206 19th January 2013 08:52 PM
High End AB Class Amp - Need recomendation velicko Solid State 19 12th November 2007 05:42 AM
Ultra-High performance OpAmp-based MOSFET Power Amp tlf9999 Solid State 20 7th September 2005 09:41 PM


New To Site? Need Help?

All times are GMT. The time now is 10:40 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