1M Reverse Audio Pot

[brewdude]

Thanks for the link. It is quite informative.
My plan is to get a 5M linear pot with my next Mouser order, and experiment with strapping different resistor values from 750k to 1.5M and see what works best for this application.

Steve's (Apex Jr.) pot would probably be a better way to go. If you create a "RA" pot with a shunt, the resistance across the element will change with the setting, so you are likely to get some other changes to the circuit that you don't want. In your example using 5M with a 750k shunt, it'll go from 650k to 5M from 0 to 100% rotation.

I am under the impression that using it as a variable resistor it would go from 0R to 650k, with the 750k. I expect that a 1.25M across the 5M would be just about right. However, I think your right about the Apex Jr. pot being the best way to go.

[brewdude]

double post.

[tubeswell]

Use a straight 3MRA pot or you can taper it. Increasing the antilog taper will not make the pot perform much worse

FWIW I did a spreadsheet a few years back to calculate pot tapers. You plug in the pot and resistor values (in ohms) up the top (in the boldened cells) and the chart does the rest. then you can graph it and look.

PS the spreadsheet is not a '.pdf'. that is jst a trick to get it to upload here. you need to change the '.pdf' to '.xls' and it will work.

To increase/do a log taper, put the resistor between the pot's input and the pot's ground. To do an antilog taper, between the pots wiper and the pot's wiper. Doing both will make a log/antilog taper.

[brewdude]

Thanks tubeswell, but I can't get anything from the spread sheet link above.

[martin manning]

I am under the impression that using it as a variable resistor it would go from 0R to 650k, with the 750k. I expect that a 1.25M across the 5M would be just about right. However, I think your right about the Apex Jr. pot being the best way to go.

You're right, I should have looked at the schematic. In that use, using the shunt to create a RA taper is fine.

[tubeswell]

Thanks tubeswell, but I can't get anything from the spread sheet link above.

I just amended it. try it now. (and remember to change the .pdf declension to .xls)

[martin manning]

Thanks tubeswell, but I can't get anything from the spread sheet link above.

I just amended it. try it now. (and remember to change the .pdf declension to .xls)

No need for the ruse, Excel files upload fine.

[xenrelic]

Here's one: http://www.ebay.com/itm/Vintage-CTS-USA ... 2c7dfff1f1