Paradise Builders - Page 97 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

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 9th January 2013, 11:37 AM   #961
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Some more experiments led to confirming my suspicions that it is the cascaded CCS which is to blame for the 7MHz oscillations. Replaced it with a basic 317/337 based CCS set to 125mA and all is now well.

Not really sure how to cure this. Base stoppers? Would prefer not to dismantle the heatsink but if nothing else works would probably replace the CCS with an Ixys cascode.


Any ideas?
Hesener?
  Reply With Quote
Old 9th January 2013, 11:41 AM   #962
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Can you post a part of the schematics, with values?
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 9th January 2013, 11:47 AM   #963
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Quote:
Originally Posted by PMA View Post
Can you post a part of the schematics, with values?
Pavel, please go to post 13 Paradise Builders
__________________
RC
  Reply With Quote
Old 9th January 2013, 11:53 AM   #964
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
For the convenience of discussion it's below
Attached Images
File Type: jpg CCS.JPG (48.6 KB, 335 views)
  Reply With Quote
Old 9th January 2013, 12:13 PM   #965
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Analog_sa, this is what I get. I will try to play with caps to compensate those local feedbacks.
Attached Images
File Type: png shunt_reg.PNG (51.1 KB, 327 views)
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 9th January 2013, 12:22 PM   #966
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
This is the 1st hint (1n cap in red circle). I am sorry if any of the guys has already suggested this, I was not able to read the whole thread.
Attached Images
File Type: png shunt_reg_comp.PNG (39.0 KB, 322 views)
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 9th January 2013, 12:28 PM   #967
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Wow. The simulated waveform is very similar to what i see on the scope. Seems like the simulation predicts something like 4MHz, right?
  Reply With Quote
Old 9th January 2013, 12:32 PM   #968
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Quote:
Originally Posted by analog_sa View Post
Wow. The simulated waveform is very similar to what i see on the scope. Seems like the simulation predicts something like 4MHz, right?
Yes it does, but I would rather call it indication only. That means, it could be 4MHz or 8MHz or something else depending on real transistor capacitances and PCB parasitic inductances/capacitance. It would be nice if you could try this simple modification and tell if it improves/worsens the situation.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 9th January 2013, 12:49 PM   #969
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Just tried it. A bit short of time atm, so didn't do the right thing and use an smd but rather a 750pF polystyrene. Waveform changed a lot and became a lot more complex, while the principal frequency came down substantially. Should have probably tried much larger value caps as well but really pressed for time right now.

Thanks for the help!
  Reply With Quote
Old 9th January 2013, 12:56 PM   #970
FdW is offline FdW  Netherlands
diyAudio Member
 
FdW's Avatar
 
Join Date: Feb 2009
Location: Both feet on the ground (near Gouda)
Quote:
Originally Posted by analog_sa View Post
Some more experiments led to confirming my suspicions that it is the cascaded CCS which is to blame for the 7MHz oscillations. Replaced it with a basic 317/337 based CCS set to 125mA and all is now well.

Not really sure how to cure this. Base stoppers? Would prefer not to dismantle the heatsink but if nothing else works would probably replace the CCS with an Ixys cascode.


Any ideas?
Hesener?
O.K. (as Hesener said) this is interesting, we/I replaced earlier 317/337 based CCS's with the current CCS due to the fact that (nearly all that where build) of these 317's and 337's oscillated.

There have been numerous builds of the new CVS/CCS combinations and none of them did oscillate, I am real happy that you found out that it oscillates (and not the shunt, the CVS/CCS is easier to compensate and not speed critical (as the shunt)). This will help solve the problem.

It still is not clear to me why some are oscillating, most are not, there must be a reason/different that makes that most do not oscillate.

The most obvious way to stop these oscillations are:
1) Lowering the 330ohm resistors to 50ohm, this makes high Hfe less significant (but this was tried and did not work).
2) Adding compensation capacitors, these should go in parallel to BC of Q104, 204 if the CVS oscillates or/and BC of Q102, 202 if the CCS oscillates (as mentioned by Pavel).
3) [edit] Remove C93 (or replace with an 'low quality'/'high esr' 1u electolitic) (as mentioned by Waly),

@Pavel, good call thanks for that.

I did/do prefere option 1 as it preserves the speed of the circuit.

Last edited by FdW; 9th January 2013 at 01:18 PM.
  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
Paradise phono stage hesener Group Buys 1316 Today 07:46 AM
DIY Paradise - Any good to buy from? gingerpimp0069 Vendor's Bazaar 7 21st June 2007 02:07 PM
DIY Paradise Charlize Jolojl Swap Meet 7 7th December 2006 06:42 AM
Diy Paradise! alexmoose Tubes / Valves 3 24th July 2006 04:37 AM
Another way to paradise ? Bernhard Pass Labs 3 8th August 2003 10:19 PM


New To Site? Need Help?

All times are GMT. The time now is 04:35 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