Updated: 17-Dez-03

The DDDAC1543 Support Site
Trying to be of some on-line help......

Problems when using the "alternative" LT1085 in stead of the LM317 / Oscillations & Hard Noise !!

I had a few comments back about very loud and hard "digital" noise where you could hear the music in between.
Actually I had the same when the DAC was starting up from cold situation. I thought this was the DAC Tower warming up, as it disappeared after a few minutes. BUT, it might be, that in some other (critical) situations, the 1085 does NOT STOP making noise !!! It also appeared that this only occurred when a LT1085 was used !! These parts are extra sensible for oscillations, so I decided to check with the scope.... I wish I had done this earlier !! Just check below.

This is a time recorder of the output of the 1085.
After switch-on the oscillations start at approximately 0,6 Volt (!)
As time goes by, the oscillations start to decrease and suddenly disappears after approximately 235 Seconds.....
OK, 4 minutes warm up, never realized it is that much 

Below, the cold pictures show clear hard stuff !!!-15dB is not particularly a good noise floor level 
ANYWAY: try a larger C at the output of the 1085 or take a LM317..... I have now a 47uF Black Gate and everything works fine....

And now the warm situation,
Please do note the difference in scale !! When the warm up is done, the rest-noise is at an average of -90dB. This is ok enough, although I am sure some will disagree, 

just to make sure: These are FFT-spectrum images from the OUTPUT of the 1085.....

for easy to copy DIY-stuff I may be had better not mentioned the 1085 as an "alternative" for the LM317, which is clearly more stable! But with some small experimenting, the 1085 will be stable as well and I know some people (like me) like this one in particular...!

Happy Listening and Building !!!!

Doede Douma

IMPORTANT: The information provided on this page is intended as guide for DIY activities and therefore free to copy and or publish. If any one wishes to use any of the information from my WEB site, please make sure to refer and footnote to my URL Link as source! Doede Douma