Simplistic NJFET RIAA - Page 752 - 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 April 2012, 03:43 AM   #7511
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Having more Ib with lower hfe is interacting with the cascode bias ref to an extent though.
  Reply With Quote
Old 15th April 2012, 09:10 PM   #7512
diyAudio Member
 
Join Date: Jan 2006
Location: North west England
I have finally started to build the RIAA circuit with shunt supply.

I am getting a strange phenomenon at the moment with the shunt. It's fed 38.7V from via a LM317 pre regulator. The first time I switched on the supply I could only get 38.33V out however I adjust the 5k pot. The LEDs light up OK. So I disconnected and double checked the shunt circuit with the schematic. There seemed to be no error so I wondered whether the I had connected the sense wires properly to the dummy load (it's all lashed up temporarily). So I powered up again and bingo I was able to adjust the voltage across the dummy load to 28V. It seemed steady for a few minutes so I checked the temperatures of the IRFP9140s - cool, no problem there. The LM317 was hot though - it's getting 50V in and dropping to 38.7V (30V ac secondary on the trafo). I then blew gently on the components and suddenly the voltage shot up to 38.3v across the load again. It was as if someone had flicked a switch.

I'm wondering whether it's the LM317 that's struggling or possibly a dry solder joint.
  Reply With Quote
Old 15th April 2012, 10:58 PM   #7513
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Try using a CRC with a high wattage resistor for pre-filtering and voltage drop. Not sure in your case but I think I remember another member with next of kin Reflektor shunt reg having a 317 pre-reg kicking when feeding it.
  Reply With Quote
Old 16th April 2012, 08:21 AM   #7514
diyAudio Member
 
Bksabath's Avatar
 
Join Date: Dec 2007
I had trubles with the LM317 oscillating aparentley they do not like large capacitance at the output (this is what I think so it may be wrong)
I got things much quiter using a common mode coke which I was tring out for sometink else.
  Reply With Quote
Old 16th April 2012, 09:48 AM   #7515
diyAudio Member
 
Join Date: Aug 2009
Quote:
Originally Posted by Bksabath View Post
I had trubles with the LM317 oscillating aparentley they do not like large capacitance at the output (this is what I think so it may be wrong)
I got things much quiter using a common mode coke which I was tring out for sometink else.
Have you used small caps (0.1F)? Try soldering them directly at the pins of the LM317. This should avoud oscillating.
  Reply With Quote
Old 16th April 2012, 10:43 AM   #7516
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
The 317 is a series regulator. The power dissipated in the series regulator is Vdrop times average output current.

If you hang a shunt regulator on the output of the series regulator then the total and substantially constant current of the shunt regulator becomes the average current being supplied by the series regulator.

Equals very hot series regulator. Possibly hotter than either of the CCS or the Shunt mosFETs. Compare the sinking and size of those three semiconductors to see your problem.
__________________
regards Andrew T.
  Reply With Quote
Old 16th April 2012, 12:31 PM   #7517
diyAudio Member
 
Join Date: Jan 2006
Location: North west England
Thanks for your help on this guys. It looks like I should ditch the 317.

Is it OK to feed this shunt unregulated DC?
  Reply With Quote
Old 16th April 2012, 12:35 PM   #7518
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Its OK with raw DC just from a bridge and filter capacitor.
  Reply With Quote
Old 16th April 2012, 12:40 PM   #7519
diyAudio Member
 
Join Date: Jan 2006
Location: North west England
Great. I have a 25V secondary trafo. The PSU already has CRC.

thank you
  Reply With Quote
Old 16th April 2012, 12:44 PM   #7520
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Fine, remember to adjust for >=7V raw dc input than reg's output to have a safe voltage drop margin.
  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



New To Site? Need Help?

All times are GMT. The time now is 04:27 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