Accomidating for a different size pot

[Joker94]

Hi Everyone

I am building the effects box as built on Hack a week.

http://hackaweek.com/hacks/?p=423

As i was not able to pickup any 5k pots from Jaycar is it possible to add a voltage divider to the output of a 10k to half the output to effectively half the output to behave like a 5k pot?(it is the pot above the signal input)

I did not that in the video explanation the original schematic showed a 10k pot, I assume the 5k was used as it provided better results in controlling the 'depth' of the signal. Based on this using a 10k pot will not prove a problem.

Cheers

Joker94

[IanB]

You can use a 10k pot where the 5k pot is shown; it will just give reduced sensitivity on the control. If you like you could put a fixed 10k resistor between the wiper and the top of the pot in parallel with the variable resistance. That will change the range back to 5k at the cost of some linearity, but if the pot is originally a log pot it might not be too bad. You'd have to experiment and see what you find more acceptable.

[jimmc]

Oops wrong pot, my bad.   Thanks Ian

The output of the 555 is high for 0.693(RA +RB).C and low for 0.693RB.C where RA is the pot, RB the 100 ohm and C the 100uF.
Thus if you want identical results with your 10k pot (to the 5k shown) reduce the cap to 50uF (47u is close enough) and increase the 100 ohm to 200 ohm (220 will do).

For more information see fig 5 of the data sheet http://www.ti.com/lit/ds/symlink/lm555.pdf

Jim

[IanB]

The output of the 555 is high for 0.693(RA +RB).C and low for 0.693RB.C where RA is the pot, RB the 100 ohm and C the 100uF.
Thus if you want identical results with your 10k pot (to the 5k shown) reduce the cap to 50uF (47u is close enough) and increase the 100 ohm to 200 ohm (220 will do).

The existing 10k pot above the 555 timer is not the pot in question. It is the 5k pot above the input.

[Joker94]

Thanks Ian

If there is some loss of linearity this will not prove a big issue as it is just a depth control of the tone. If however this proves to be an issue or i dont like it i can always swap it out for a 5k pot when i have one.

cheers

Joker94