5 pin thumbwheel variable resistor pinout. - Page 1
Forum section: electronics / beginners

author: josephpate
author_rank: Contributor
timestamp: October 21, 2015, 03:19:24 am
content: I have this simple volume thumbwheel that I need to desolder and replace with a front panel mount pot.http://imgur.com/a/Ca4EgIt has two large solder joints that, as far as I can tell, are just for support. Then there's 5 other pins which presumably are in in/out pins for both audio channels.I found this image on google:http://cdn.instructables.com/F6K/QVPA/GAPUS878/F6KQVPAGAPUS878.LARGE.jpgWould my part have this same pin out? I tried figuring it out with my multimeter but none of the readings seemed to make sense (maybe when its out of the circuit it will.)Also, what's up with the ground pin? I should only need left and right input and output pins right?

author: Connoiseur
author_rank: Regular Contributor
timestamp: October 21, 2015, 04:06:45 am
content: Quote from: josephpate on October 21, 2015, 03:19:24 amGround pin is provided because it is a potentiometer and not merely a variable resistor. See the attached schematic.

author: josephpate
author_rank: Contributor
timestamp: October 21, 2015, 04:25:36 am
content: So what would the ground pin be used for in this scenario (audio)?

author: Connoiseur
author_rank: Regular Contributor
timestamp: October 21, 2015, 05:19:47 am
content: The potentiometer outputs are fed to the output power amplifier stage(s). Potentiometer is used to supply scaled (scaling varies from 0 to 1) version of the audio signal; which works by the principle of voltage division.You can't have voltage division unless you connect the potentiometer between input voltage and ground.https://en.wikipedia.org/wiki/Voltage_divider

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 21, 2015, 05:26:10 am
content: If you notice your first photo, you will see the larger copper track going to the left-most pin. That appears to correlate with the ground node.We are assuming that your unidentified gadget is stereo.

author: josephpate
author_rank: Contributor
timestamp: October 21, 2015, 09:33:10 pm
content: Its actually an el-cheapo USB audio interface, but same difference I guess.http://www.amazon.com/gp/product/B0023BYDHK/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687662&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B000KW2YEI&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0R3176QGNGRK4CY5MBRBSo Is there some reason that a voltage divider would work better than a variable resistance, considering that this is a crappy headphone volume knob?Either way it doesnt really matter for my project, since I'm just gonna wire in a new pot where that other one is.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 21, 2015, 09:52:38 pm
content: Quote from: josephpate on October 21, 2015, 09:33:10 pmIt comes down to a voltage divider either way. With a "variable resistance" you are dependent on the input impedance of the destination to form the "bottom half" of the voltage divider. By using a potentiometer (a variable voltage-divider) you have DIRECT control over the level. Otherwise a "variable resistor" may have no effect at all on the level if you have a high-impedance destination. Or the variable resistor could have almost no practical range if operating into a destination impedance that was very low.Using a potentiometer is the method that 99.999999999999999% of all audio gear uses for audio level control. It is completely impractical to use a simple variable series resistor.

author: Cliff Matthews
author_rank: Unknown
timestamp: October 21, 2015, 09:57:45 pm
content: Digikey has the EVU-TW series athttp://www.digikey.ca/product-search/en/potentiometers-variable-resistors/thumbwheel-potentiometers/262240

author: josephpate
author_rank: Contributor
timestamp: October 21, 2015, 10:53:30 pm
content: Quote from: Richard Crowley on October 21, 2015, 09:52:38 pmI see. Thanks for the info!