Mpp - Page 172 - 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 17th August 2010, 03:35 AM   #1711
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Here is a picture of the buffer, with and without flash. I let it burn until tomorrow and then listen. I have two hours left so i will work on the +-17V Hypo. The picture shows the current state. 200 Ohm test resistors in the minus feed not installed yet. I have to go again through the sugestions.
Attached Images
File Type: jpg OL Buffer Flash.jpg (96.3 KB, 332 views)
File Type: jpg OL Buffer without flash.jpg (51.6 KB, 323 views)
File Type: jpg HYPO +-17V prepared.jpg (77.3 KB, 322 views)
  Reply With Quote
Old 17th August 2010, 03:42 AM   #1712
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
No, i use some of the Leds in the signal chain for current feedback and low impedance steering. Sorry that i can not tell more. One of my friends said : 99% for me (DIY) and 1% for god.
  Reply With Quote
Old 17th August 2010, 03:52 AM   #1713
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
That's another use then. But if the LEDS are from same intensity batch and Vf matched, then it must be different currents. One or another. You got to be sure by installing new LEDS from sure batch first. But I have also seen a 1.75Vf LED surely dimmer than a 1.82Vf LED from same bag for 5mA for instance.
  Reply With Quote
Old 17th August 2010, 04:03 AM   #1714
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Good sugestion, i will measure the batch before i install. Anyway, the buffer is working and the Leds that do the dirty job are similiar if not ideal still. Idealy i whould need a Led
( or a string of two ) that drops 3.2V at 3.5mA so you see my dilemma. A blue one ? A mini string of IR ? Who knows.
  Reply With Quote
Old 17th August 2010, 04:09 AM   #1715
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I tryed two red ones in series that should give 3.6V and that is close enough but they where starving in the circuit and gave only 1.8V in total. I ordered a batch of red and green in high efficieny and normal. Not a big issue, i have time for this experiment and will find a solution as usual.
  Reply With Quote
Old 17th August 2010, 04:11 AM   #1716
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
there are also low noise voltage references availlble that could do the job too.
  Reply With Quote
Old 17th August 2010, 05:40 AM   #1717
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
setting the Hypo to +-17V without load was not a big deal. I got 17,3 and 17,4 volt fast and easy. Connecting the ULN phonostage the voltage dropped to 9.7V positive and 15,5V negative so it draws more current from the positive side. Offset management was still not upset and i measured the same values as before. That is a good experience because that offset had caused me lots of trouble in the beginning. I will make the rest of the adjustments next day. By the way one shunt mosfet gets now warmer then the other but that is logical. Slowly i get into it. Its fun by the way.
  Reply With Quote
Old 17th August 2010, 11:30 AM   #1718
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Give it a good margin of CCS:Load. 2:1 if it can take the heat I would recommend. Measure load current with 317/337 handy PSU in each circuit before you set Hypno's CCS for different CCTs. It will save time in resetting.

*Blue LEDS are noisy compared to Red etc. Best for noise are IR. Given that you got good makes and batches for best noise from each color.
  Reply With Quote
Old 17th August 2010, 03:23 PM   #1719
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I found an Osram SFH409 that drops slightly over 1V at 3.5mA, so a string of 3 could work. I found another IR Led that only needs 0.4 mW/sr @ 1.2V.
  Reply With Quote
Old 17th August 2010, 06:13 PM   #1720
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I have now made more listening tests with the OL buffer 4 prototype and now i understand what PMA is saying. As long as you have not heard something better the OPA134-BUF634 is just fine. Switching to buffer 4 reveils a much bigger and more populated stage. Dynamic slamm is much enhanced and the Opamp buffer sounds clean but also lifeless and sterile in comparison. The question that now arises is if that is a function of using heavy voltage feedback or rather not as Allen Wright is fiersly advocating. I have just drawn a schematic that combines an Opamp with buffer 4 to make it a high feedback voltage follower and then i will do the listening all over again.
  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 06:28 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