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LM317 current sink
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=5&t=6722
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Author:  M. Gregg [ 14 Feb 2020, 10:48 ]
Post subject:  LM317 current sink

I was looking at the LM317 chip circuit diagram,

This is a LM317 used in current sink mode cathode load.
Looking at the Adjust pin that connects to the 1.25V reference.
I was thinking what effect would a Ferrite bead have if fitted over the regulator leg so its on the diode leg in the diagram.
So just for interest I tried it. (Pic) I was thinking about RFI etc.
I could have fitted some PTFE sleeve to distance the bead from the chip I'm not a fan of contact across connections with anything,
so just as a quick try I melted some solder at the top of the leg to thicken it so the bead is fixed away from the chip.

It had an immediate effect of making the sound "seem" clearer.
Now this was just a suck it and see trial but I thought it worth a mention.

Regards
M. Gregg

Author:  gofar99 [ 15 Feb 2020, 20:39 ]
Post subject:  Re: LM317 current sink

Hi, Have you done any measurements since then?

Good listening
Bruce

Author:  M. Gregg [ 16 Feb 2020, 06:40 ]
Post subject:  Re: LM317 current sink

gofar99 wrote:
Hi, Have you done any measurements since then?

Good listening
Bruce


Hi Bruce,

No I haven't had time, there is something strange with the LM317 in current mode.
I just had a quick scribble and tried a couple of discreet modules to see/hear if there was any difference.

I had a quick look on the net and built up a couple of modules to "directly replace" the LM317 in the cathode position. Just three 1n4148 and BD139.
So they are pin compatible.

For any interest the build is just pad board with a hole drilled for the heatsink pin, then a nut on the other side then washer to give area on the back of the BD139 then heatsink compound, mica insulator and then nut and washer/spring washer to give compression to the heatsink. So there is a nut and washer between the pad board and BD139.
I'm just curious at the moment to have a listen. I took the B+ supply off the Ultra linear tap because it was close to the module.

Regards
M. Gregg

Author:  M. Gregg [ 16 Feb 2020, 07:03 ]
Post subject:  Re: LM317 current sink

Short research done,

However nothing gave any clues to the Adjust pin an the LM317 but some very interesting ideas.

https://www.tubecad.com/2018/01/blog0409.htm

http://valvewizard.co.uk/ccs.html

Regards
M. Gregg

Author:  gofar99 [ 16 Feb 2020, 16:16 ]
Post subject:  Re: LM317 current sink

Hi, how linear is it over say a 30volt input range.

Good listening
Bruce

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