Need opamp recommendation - Page 2 - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, 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 15th December 2008, 08:35 AM   #11
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
I would also be careful here... the ad744 might indeed not be stable on a pcb designed for the (way) slower lf351.

You might have a quite safe improvement by simply replacing R21,22,23 by 5ma CRD's (1N5314 ?).
__________________
Ben.
  Reply With Quote
Old 15th December 2008, 08:49 AM   #12
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Yes, those 100uF lyts across R30/31/32 looks too way much.
I usually try with 1nF, 2.2, 4.7 or 10nF here.

Also there are no 100nF supply film caps from V+ and V- (pins 7, 4) to GND.
__________________
lineup
  Reply With Quote
Old 15th December 2008, 10:13 AM   #13
00940 is offline 00940  Belgium
diyAudio Member
 
Join Date: Sep 2003
Location: Paris
Quote:
Originally posted by lineup
Yes, those 100uF lyts across R30/31/32 looks too way much.
I usually try with 1nF, 2.2, 4.7 or 10nF here.

Also there are no 100nF supply film caps from V+ and V- (pins 7, 4) to GND.
And what do you expect a 1nf cap to do there ?

Read again the articles by Walt Jung (freely available on his website) and you will understand why a 100uF cap isn't a bad idea at all in those positions.
__________________
Ben.
  Reply With Quote
Old 15th December 2008, 02:34 PM   #14
diyAudio Member
 
Juergen Knoop's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
this design violates the common mode restrictions of most opamps. Even the chosen LF351 may only work by accident.
Wild opamp swap is risky!
regards
  Reply With Quote
Old 15th December 2008, 02:45 PM   #15
phrarod is offline phrarod  United States
diyAudio Member
 
Join Date: Aug 2005
This is a great discussion. The board is a commercial product. Its the Audio Note kit dac board. I'm building a new one because of issues. I put three ps in my ps box from twisted pair so each section would have its own separate supply.

When I turned it on one section blew either the LED or diode. A friend fixed it so I'm not sure which. When its working its fine although at times when I do mods to other things it can get fussy. I blew one just by trying to diagnose it. I noticed I'm getting voltages (5v and -5v) that aren't in spec. When I use some spare but different opamps it settle back so I though I would just get all new ones.

I have a spare pcb and plan to build a new one from scratch as this one is a little beat up. Since its the heart of the unit I would love to make any improvements I can.
  Reply With Quote
Old 15th December 2008, 03:26 PM   #16
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
Originally posted by 00940
And what do you expect a 1nf cap to do there?
Read .. Nnnnnnn Nnnnnn.. and you will understand why a 100uF cap isn't a bad idea at all in those positions.
00940
If you know, which I doubt until you can tell us with your own words
.. then why not tell me and others.
Why keep your secrets, if you are a sharing DIY Member.
What dicussion would be, if we always reply with a link to somebody who knows better



Actually, I have several great working Regulator circuits using 1nF - 10nF for feedback resistor.
This is why I think you may not be 100% correct.

Regards, Lineup
__________________
lineup
  Reply With Quote
Old 15th December 2008, 03:35 PM   #17
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
You could probably do a lot worse than to use the lm337/317 regulators or something on those lines.
Juergens comments are spot on.
It's a flawed design I'm afraid.
But don't let that put you off, things can only get better
  Reply With Quote
Old 15th December 2008, 03:50 PM   #18
phrarod is offline phrarod  United States
diyAudio Member
 
Join Date: Aug 2005
I've wrestled with this board for many years now wanting to just replace the whole thing unless I could improve it. Kind of frustrated. The 744s sounded less grainy and smoother than the original opamps.

Since I'm building a new one with one of their pcb's I'm open to improvements. I had thought of just replacing it with a buffalo dac board/iv from Twisted but I can't find reviews on it apart from "sounds good".

Little frustrated. This grew from a lowly dac kit to a two box monster with dual mono for the analog, separate fils trans for the ps and the analog tubes, now 3 separate supplies for the dac board. Switchable to run off battery. Its pretty elaborate. The flaw has always been this board.
  Reply With Quote
Old 15th December 2008, 04:09 PM   #19
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
The aim of the power supply is to provide a stable output voltage independant of load variations, temperature, mains fluctuations etc.
Why not try the IC regulators ? Look up the datasheets and have a go.
Discrete regulators can perform very well, but you can't just throw a few bits together and hope it will outperform a device that's had 100's of thousands or more spent developing it.
Even easier, the 7805 and 7905 regs.
  Reply With Quote
Old 15th December 2008, 04:13 PM   #20
phrarod is offline phrarod  United States
diyAudio Member
 
Join Date: Aug 2005
Since I'm now using regulated supplies where as the original was unregulated isn't it stable now?

Yes, redesigning it is above my skill set.
  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
DIY DAC recommendation Rightbrained Digital Line Level 9 23rd June 2009 09:20 PM
Need opamp recommendation phrarod Digital Line Level 0 14th December 2008 07:13 PM
Single supply opamp - unequal rail voltage and opamp selection Hans L Parts 8 19th February 2006 02:15 PM
Recommendation for inexpensive fet inout opamp zerodigit Parts 2 30th May 2005 05:14 AM
Regulate the psu of a power opamp with a similar power opamp? Franz G Chip Amps 34 19th October 2004 10:49 AM


New To Site? Need Help?

All times are GMT. The time now is 01:28 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