Does it have to be 1.43k res for oklt20?

[jock1092]

Hi Jock yes its the one between the pot and okl chip. i guessed that it may have an effect on the output due to its position and thought higher resistance would be lower max output but buy how much i dont know and maybe its not as simple as ohms law because its on a low power part of the circut so what fiqures do you work that out with? Does blow my mind really all that parallel circuit stuff im trying to learn some basic electronics also atm but i know nothing really LOL!

Thanks
Kev

Just went to hunt down the Info I read (it's been a while) but it says a 1.5k ohm will lower the minimum voltage for the okl t20 and give a max, 5.6v (which I think sits in its specs)

My guess would be the pot is increasing resistance to lower the voltage output of the chip, so the higher base resistance of the 1.5 would fit that as the minimum available would be 1.5 in place of 1.4 but that's a guess as to how it would work.

 

[Simon G]

ah, that's even more interesting ... pots are made to even less of a tolerance than resistors. If it's being used like that I definitely wouldn't worry, pots are typically only usually within 10% of what they are supposed to be ... so a 100K pot can be anywhere from 90K to 110K.

So using it as a variable resistor in this way isn't going to be that accurate anyway.

 

[HERBESTOS]

ah, that's even more interesting ... pots are made to even less of a tolerance than resistors. If it's being used like that I definitely wouldn't worry, pots are typically only usually within 10% of what they are supposed to be ... so a 100K pot can be anywhere from 90K to 110K.

So using it as a variable resistor in this way isn't going to be that accurate anyway.

Going on what you and jock said I'm thinking it should be fine and if anything it would lower the output max a bit.
I did phone Rick at mod makers and he wasn't sure as it was so long ago that it was worked out with help from others but he said he remembered some were able to get 6v max output as opposed to 5.5v but again couldn't remember what was changed to get that. He said to try the Facebook page but I don't really do Facebook.
Guess I could wire it up out the box and try a 1.4k and a1.5k and test the output with a meter.

On another note why is one of the pot legs joined to the wiper? From my basic understanding I thought the unused leg could just be left blank and the pot would function the same?

Thanks
Kev

 

[HERBESTOS]

well its all done now thanks very much for help my god it was a tight fit in the hammond 1590g and i think the MM510 used is just a bit longer than the source or the fat daddy is pressed quite hard against the okl and i think only the 510 and the okl did not have grinding and filing to make it all fit everything else was modified.

I got the 1.5k resistor but no 1.4k available so couldnt try both. it works great so far and voltage range is 3.4v with the pot all the way down and 5.3v all the way up so the resistor value had obviously been calculated to give max 5.5v when using a 1.43k resistor (i wonder the effect of a 1.4k i mean is it possible to get more than 5.5v out of the okl?)

thanks again for the help i must say again though it is a tight squeeze as i had to have a master on off switch also so no way could i fit a volt meter in there. ill get some photos uploaded if anyones interested

Kev

 

[the_atomic_fart]

Yes fella.
Would like to see some photos of the result of your efforts!!

 

[HERBESTOS]

Ok so here it is.
Okl t20 in a squared off Hammond 1590g enclosure with master on off switch it's a tight fit but the g is a nice size.
I have a nice trick with the magnets so the 4mm ones in the box insert into to lid as it closes making contact with the ones in the lid meaning there can be no movement of the lid once closed.

Thanks
Kev

 

[the_atomic_fart]

Very nice looking mod.
Cracking job.