Does this circuit look okay?

[earthtonesaudio]

Hi, I've just built my prototyping rig, and now it's time to de-bug, unfortunately. 

I used this circuit:



And I'm getting no voltage output (meter reads 2mV or so... same reading when it's unplugged), and the resistance value for my bias pot is 50k when set to the middle... it's a 200k pot so I expected 100k when set to the middle.  I know there's some other resistances in parallel with it, but I'm still a little puzzled.


So, any thoughts?  Does this circuit look like it should work?  I haven't really dove in to fix it yet, but I wanted to check if anyone has had a similar problem before.  One more thing: are all LM317 pinouts the same?  Or does it vary by manufacturer?  I used on from Radio Shack, and the documentation was not too great, to say the least.

Thanks,
Alex

[earthtonesaudio]

Anyone?

[Paul Perry (Frostwave)]

All LM317 pinouts are the same.
What voltage do you see on the other pins?

[frank_p]

Check out what tension is going out of your wall-wart (and in your chip).  Sometimes, it's just a tiny bit too low.  If so, you will (probably) get noting out of your LM.  It once happened to me.  In my case I tough it was wrong pinout but finally got a higher voltage transforemer and dit OK with more tension !

[earthtonesaudio]

Well I took it apart and did a closer inspection.  I do have the 317 put in the right way 'round, thankfully.  But there were some mistakes in there.  I have a polarity protection diode on the input (forgot to show in the schem), and it had a cold solder joint.  Also one of the cap-discharge protection diodes wasn't soldered at all  .  I still find it a little weird that my 200k pot shows a maximum resistance of 50k, at half rotation.  I'm assuming it's just the parallel resistance of the 317 and associated adjustment resistors...

Time to heat the iron up again...


Thanks for the help!

By the way, what do you mean by "tension," Frank?  Is that like Australian for current or something?   

[dschwartz]

tension=voltage

[frank_p]

By the way, what do you mean by "tension," Frank?  Is that like Australian for current or something?   

Quote from wiki:------
Voltage (word) does not reflect "the potetial difference" or "the current driving force" and hence is not a really good name. In non english speaking countries (france/germany/scandinavia) the word that translate to Tention denoted U is measured in Volts [V]. The frensh (who sould now SI) call it La tension électrique or just tension for short.  (Bla Bla...)
------
http://en.wikipedia.org/wiki/Talk:Voltage

So, it's the term used for Voltage in French.  Except that for us, Voltage is more viewed like the unit of the "tension".  Tension is the most common word for difference of potential (Voltage).  So you should view "tension" like the potential to force current (like in the mechanical way of seing it).

When we say: "C'est quoi le voltage?"  (What is the voltage?), it is viewed like an englicism, or if you're in school, a reason to have:  " -5pts. ... use correct vocatulary next time"   In industry it's OK we say voltage (with some culpability).

In school it's even better to say, electromotive force: "La force électromotrice".  That is probably from where the words "tension electrique" came from.

It's like the difference between Eddy's currents and "courants de Foucault".  It's the same thing... (I had a incomprehension with R.G. on that one too)  Foucault was the rench physicist that found what it was.  We call Eddy> Foucault in French.
http://en.wikipedia.org/wiki/Eddy_current

Sorry Again for my bad English, but that wiki talk is fun just for reminding us what Voltage is.
I was sure that you were also using the "tension" word in english too !

I understand now why I did not get responses for some questions here !!!! 

[Jered]

  It sounds like your pot is an audio taper. Check it with a meter.
  Jered

[gez]

Best to measure pots and resistors out-of-circuit whenever possible.  Also bear in mind errors due to the parallel resistance of cheap meters.

[earthtonesaudio]

Thanks guys, I fixed the solder joints last night and it works! 

I did measure the resistance of the pot out of circuit... and it was 200k linear.  There might be another small problem with my wiring that I have yet to discover, but for now my bias pot will give me a 1/2 main voltage reference, so that's the most important part.

So it's not a huge deal for the moment, as I'm getting the voltages out that I wanted, but I would still like to understand why it does what it does.  The resistance value decreases in both directions whenever the wiper is moved away from the center point.
Example: pot is turned to the center, R=50k.  Turn the wiper toward terminal 1, resistance decreases on BOTH sides (1 and 2 and also 2 and 3).  Same thing when turning the other direction.  I just don't get it.


Anyway, pictures to come.

[mensur]

Hre is the working PSU stabilization, i made several of them and they all worked.

http://img149.imageshack.us/my.php?image=psusm7.jpg

Bye

[gez]

Example: pot is turned to the center, R=50k.  Turn the wiper toward terminal 1, resistance decreases on BOTH sides (1 and 2 and also 2 and 3).  Same thing when turning the other direction.  I just don't get it.

Perhaps your meter is sinking current, which is buggering up results.  I very seldom take measurements in-circuit.  If I really have to, then I do so in situations where any parallel resistance can easily be calculated/accounted for.  Er, I also make sure the power is off (hint).  Even with power off, you have an alternative path to earth (in parallel) via the 10k trim, 220R and 5k trim resistance chain.

[earthtonesaudio]

Thanks for all the input, everyone.  I may or may not end up looking deeper into my circuit... if it works, I'll probably leave it alone!

Here's a pic of the finished thing:



The circuit mounted on the breadboard is a Runoffgroove New Clipper, with LEDs as clipping diodes, and pots instead of resistors pretty much everywhere!