Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Having trouble with LM1972 circuit
Having trouble with LM1972 circuit
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 30th March 2002, 10:58 PM   #1
John Miles is offline John Miles
diyAudio Member
Join Date: Mar 2002
Location: Kirkland, WA USA
Question Having trouble with LM1972 circuit

Greetings from a short-time lurker, first-time poster.

I'm wondering if anyone has experience with the LM1972 volume-control chip from NSC. I am trying to use this device with a single 12V supply rail, and have been running into oscillation problems in the unity-gain JFET op-amp buffer that follows it.

The LM1972 data sheet is not very good about providing circuit specifics. They recommend using a JFET-input unity-gain buffer at the LM1972's output to keep from loading the LM1972 and producing clicks when the attenuation level changes. However, the 1972's output impedance changes over a pretty wide range depending on the level it's set to, and it seems that there are always a few spots in the adjustment range where the unity-gain follower will break into oscillation.

I have tried the LF356 as well as NSC's recommended LF412 as the buffer with the same results. I have tried hardwiring the inverting input directly to the output, as well as using a 1K resistor. I believe that supply bypassing and the like are adequate. The oscillation occurs regardless of the load (or lack thereof) at the op-amp's output.

Has anyone here successfully used the LM197x chips? There seem to be no app notes or example circuits anywhere on the web for this chip. What, exactly, does its unity-gain buffer need to look like?
  Reply With Quote
Old 30th March 2002, 11:13 PM   #2
Jocko Homo is offline Jocko Homo  United States
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Does your buffer oscillate with its input isolated from the other chip?

  Reply With Quote
Old 30th March 2002, 11:47 PM   #3
John Miles is offline John Miles
diyAudio Member
Join Date: Mar 2002
Location: Kirkland, WA USA
No, both the LF412 and LF356 are unity-gain stable. The buffer and the PA that comes after it don't exhibit any stability problems until the LM1972 is connected.

Actually, I think I answered my own question a few minutes ago... neither of these opamps are designed for rail-to-rail service, and the LM1972's output DC offset falls below 0.7V right where the oscillation happens. I'm going to have to run these guys off a split supply, it looks like.
  Reply With Quote


Having trouble with LM1972 circuitHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Trouble with speaker protection circuit (Randy Slone's circuit) whalefat Solid State 3 13th April 2005 11:13 AM
XL-280 circuit card trouble-shooting Dick West Solid State 5 10th April 2005 04:58 AM
loudspeaker protection and muting circuit trouble :( Mattyo5 Solid State 1 21st March 2004 03:18 AM
LM1972 Freddie Solid State 7 27th January 2002 08:55 PM

New To Site? Need Help?

All times are GMT. The time now is 02:07 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio