Adcom gfa-585 dc servo opamp - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 24th September 2003, 07:03 PM   #11
diyAudio Member
EchoWars's Avatar
Join Date: Dec 2002
Location: Left of the Dial
Fred...the 555II has a single 20V zener setting up voltage for the positive supply, the neg side goes to ground. Inverting input connected to the power amp output via a 4.7M resistor, integrated with a .1µf cap. Non-inverting input goes to ground, also integrated with the same 4.7M/.1µf setup. Output feeds base of first diff-pair transistor via a 1.5M resistor, and is it's only source of bias.

As for using 'cheap' opamps, I popped in the only single opamp I have here, while I wait for the AD820 to show up. Stuck in a LM741C. DC offset is sitting at about 2V. Lol!

So yeah, I think something a little better is called for.
  Reply With Quote
Old 24th September 2003, 07:08 PM   #12
The one and only
Nelson Pass's Avatar
Join Date: Mar 2001
OK, OK. I always use the crappiest op amp so that nobody
will accuse me of putting it in the signal path....
  Reply With Quote
Old 24th September 2003, 08:16 PM   #13
Electrons are yellow and more is better!
diyAudio Member
peranders's Avatar
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Originally posted by djk
You cannot use an old FET opamp like a LF351 or TL071 that has phase-reversal when driven hard.
Yes, you can! But only if you design the servo slow enough. 20 Hz at full power (or 15, 25 or whatever) shall not make the servo opamp clip. This gives the maximum speed of the servo. Usually you must choose slower or much slower speed.
/Per-Anders (my first name) or P-A as my friends call me
PA03 LM4780 amplifier group buy, SIGN UP HERE for the group buy 0 boards left. 118 paid.
  Reply With Quote
Old 24th September 2003, 08:56 PM   #14
diyAudio Retiree
Join Date: Oct 2002
Location: Spain or the pueblo of Los Angeles
Red face The chump gets stumped

Looks like the AD820 will go about 0.2 below the negative rail for input common mode. I believe the dual version of this device is the AD823 for anyone curious. I was aware of any jfet input op amp that would do that. I learned something. It happens on this forum much more often than I let on......
  Reply With Quote
Old 24th September 2003, 09:10 PM   #15
diyAudio Member
georgehifi's Avatar
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
Yeh, Fred your right , put in the ne5534 and it pulsated the out put rapidly, i put a .0022uf comp cap across 1 and 8 and it slowed the pulse down to 1 pulse every 1 second, still not right.
Which one do i use guys that`s easily available at the corner shop is the lf351 the answer, the shop says the tlo71 is the same.
Cheers George
  Reply With Quote
Old 31st October 2003, 10:32 PM   #16
WaltJ is offline WaltJ  United States
diyAudio Member
WaltJ's Avatar
Join Date: Aug 2003
Location: USA
But, as you can see from the schematic, any good single opamp will do (LF411, AD711, OPA604, etc).
No it won't. It must be a low power part, since the op amp rails come from the lm329 zener supply. Use an OP97 or an AD820, which work OK.

  Reply With Quote
Old 1st November 2003, 12:50 AM   #17
djk is offline djk
diyAudio Member
djk's Avatar
Join Date: Feb 2001
Location: USA
I stand corrected.
  Reply With Quote


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
Help with DC Servo for Current Feedback Opamp klewis Chip Amps 31 4th June 2010 05:18 PM
opamp for DC servo lucpes Solid State 10 11th August 2004 09:33 AM
Opamp suggestion for DC-servo in an Alexander amp peranders Solid State 12 19th June 2004 06:18 PM
Schematic for Servo opamp. sonnya Solid State 17 26th July 2003 03:38 PM

New To Site? Need Help?

All times are GMT. The time now is 02:35 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2