tying lug 2 on a pot to which of the other lugs?

[mordechai]

I am trying to make a variable gain pot with a small value resistor (4.7K) wired to lug 3.  I would like it to work so that turning the shaft fully clockwise leaves only the 4.7K in the signal path (which would increase the gain), and where turning it fully COUNTER clockwise will bring the 25KB pot + the 4.7K pot into the signal path, reducing gain significantly.  I am not sure as to which lug I should tie the wiper.  Here's how I currently am plotting it out on the schematic:

http://s1130.photobucket.com/user/mordechaibenzev/media/gainpot_zpscbb54f18.png.html?filters[user]=124527051&filters[recent]=1&sort=1&o=0

Do I have this configured correctly so that with the wiper tied to lug 1, turning the shaft clockwise will reduce resistance down to 4.7K? 

[mth5044]

Think about it this way - the wiper is connected to lug two. The wiper being the thing that moves around. When all the way counter clockwise, there is basically no resistance between lugs 1 and 2 because the wiper is sitting nicely on top of the lug 1 terminal. Turn it all the other way and lug 2 is sitting on lug 3, minimal resistance between the two.

In your case, when you tie 1 and 2 together, you are saying 'no matter what happens, the only thing that is going to change is the resistance between 2 and 3. So, turn it all the way clockwise, you have basically no resistance between 2 and 3, leaving only the 4k7 in the signal path.

[mistahead]

Apply a little tinfoil and a multimeter... probably quicker than coming up with and typing the question... not trying to be abrasive just pointing out that experimentation at 9V won't (likely) kill you.

Most people learn more by "playing" than "asking" too - never know what revelations may follow!

And yes - I know it was answered before I even started typing - but for next time 

[GibsonGM]

Experimentation with an ohmmeter might be better ;o)     Even with a 9V battery, you can fry a small pot pretty easily!  Put 9V across ~ a couple hundred ohms, bye-bye pot. 

Then again - who hasn't fried a pot or resistor??  Transistors pop nicely, too.  It's a good experience, and 100% safe at 9V (as long as you don't have flammables nearby and don't get something in your eye, ha ha!)  )

[mth5044]

I've never burnt out a pot or resistor. Or anything that mad a substantial pop   I guess that's good as I usually solder with only socks on. And glasses.

..how do I get the title under my name changed to 'Nude Solderer'?

[bcalla]

I've never burnt out a pot or resistor. Or anything that mad a substantial pop  I guess that's good as I usually solder with only socks on. And glasses.

..how do I get the title under my name changed to 'Nude Solderer'?

You wear socks?  I'll have to try that.   

[Jdansti]

^On his hands. 

[mth5044]

Sorry... sock* 

[mistahead]

My multimeter can act as a volt or ohm meter... 

I've spent most of my life in IT - I've blown up some big caps, next to big caps, in cascading explosive failure, more than a couple of times back in the day. Damn those cheap power supplies.

If you've never incidentally/accidentally blown up some parts you're missing out on a certain anal tightening experience that is pretty unique - I call it the "-1 Iris Effect"

[GibsonGM]

My multimeter can act as a volt or ohm meter... 
If you've never incidentally/accidentally blown up some parts you're missing out on a certain anal tightening experience that is pretty unique - I call it the "-1 Iris Effect"

Yup, watch the smoke go, hear the sizzle, and see your $3 pot become useless, ha ha.  Get one wire in the wrong place on a breadboard, and you certainly can experience this.  Might take 500 builds to do it, but one day it will happen.  Sooner rather than later for someone new, I think.  Hook up any 1/2W pot to a 9V battery, turn it down, and you'll ruin it. Just pointing that out for the OP.  Sometimes we tend to 'make' stuff and watch the voltage output rather than take a sec. to figure out the power we're asking our stuff to dissipate...I know I did, anyway!

Reference to ohmmeter was to be clear what setting the $75 DMM should be on - rather than taking measurements in an energized circuit; does anyone actually try to measure resistance using an analog anymore??  I sometimes use one for watching trends (think time constant), and that's about all.

[Jdansti]

>Reference to ohmmeter was to be clear what setting the $75 DMM should be on - rather than taking measurements in an energized circuit; does anyone actually try to measure resistance using an analog anymore??  I sometimes use one for watching trends (think time constant), and that's about all.

Analog "ohmmeter" on live circuit: been there a few times!  Hopefully the fuse saves the meter!

[duck_arse]

what's the tinfoil for, mista?

anyone who has burnt a carbon, be it a resistor or a pot, knows they never want to smell that smell again.

[old_days]building the power supplies for the 8" floppy drives, with those wacking big clamp mount electros, we would turn on and measure the voltages. if that one was not -5V, I think it was, we would switch off, fast, and then step back, and wait. about 30 seconds before the capacitors' vent-plug flew straight into the ceiling, past where your face just was. and hide it from the boss, too.[/old_days]

[mistahead]

Jumpers - big flat wide jumpers.

Blue smoke, grey smoke, black smoke from electronics not only all smell terrible and are apparently quite bad for you, but if I recall the signature blocks from a while back here, also indicates escaping mojo.

Old days of IT were great, the PBx phone guys still have that shit going on, love them.