just a quickie from experts 500k log pot

[aTalwar]

Hi,

i am starting into tube screamer - ts-808 i have almost all the parts except the 500k log pot.
can that be substituted with a smaller value pot or a higher value.

ex: i can put a 1m resistor in parallel with 2 end pins of pot to make it 500k - would that work, and about the log thing
is that really necessary as all i have is 100k lin, 1 m Lin , 10k Lins but no logs/rev logs

i have gone through the articles o pot conversion but it seems a resistor between wiper and in hot pin would work only for rev log scenario for log all three pins should be used.

any help is appreciated. i am gonna use 100k pot for gain anyway for start but want to know how much tone it can affect . or shall i just use 1m ones but first gotta analyze to see how gain is working either ground choked or, the voltage follower.

also another quickie?
has any one used electronic workbench multisim to simulate some fx pedals.
i would love so have some files for that and go through them their response curves and approximate componenets rather than doing thevnin and Kirchoff equations.

[Mark Hammer]

I know a good Maharashtrian name when I see one!   Welcome. (I have a friend in Mumbai whose in-laws are Talwars)

The gain (and distortion) of the unit in this case will increase as the resistance of that pot increases.  When the pot is zero ohms, and there is only the 51k resistor in series, the gain will be (51k+4k7)/(4k7)= 11.85.  You will likely need to get at least a gain of 20 to hear any sort of distortion, which will imply a pot resistance of at least 38k.

What can we assume from this?  If you have a pot whose value can go as high as 100k, you will be able to achieve enough gain to get an easily audible, but not intense, distortion.  A 250k pot will get you more, and a 500k pot resistance will get you all the sounds the TS-808 is capable of.

Suppose you cannot find 500k, what then?  If you have some other way to get the same resistance, than all is fine.  So, if all you were interested in was the most intense distortion sounds form this unit, and were not at all interested in subtle sounds, then you could be satisfied with a 100k pot and perhaps a 390k, 430k or 470k resistor instead of the 51k resistor.  You would not have as much range of adjustment as with 51k plus a 500k pot, but you *would* have the required resistance.

Conversely, if you have a 1 meg pot, placing a 1meg resistor in parallel with it will turn it into a pot with a maximum value of 500k.

Being log or linear will depend on where you desire to have the greatest degree of control.  If you care little for one end or the other and wish to have finer control over one small portion of the range, then a log taper or anti-log taper is needed to spread a small proportion of resistance change over a large range of pot rotation.  If equal control over all parts of the range are needed, then a linear pot may be more desirable.  The taper of the pot will not change whether the circuit works or not, merely how easy it is for the user to attain the setting they want with some precision and repeatability.

[no one ever]

Check the calculators at muzique.com for resistor values.

[chunks717]

this is a case where the math is too simple to ignore.....
(r1*r2)/(r1+r2) r1 is one resistor, r2 is the other one(or pot, whatever)
the product of the two divided by the sum of the two.................
(for parallel resistance)
taper is a whole other matter.............................................

[aTalwar]

Thx Mark,
actually i am not maharastrian but a punjabi, but an indian nevertheless. i do have some frinds who are talwar and are maharastrians.

i do understand log and antilog, what my query was, do a 1 meg control give me more control over distortion (lin) or 1 meg parallem 1 meg pot but lin ( i am not too much concerned about frq being bunched up on one end and fine control over the other. i was planning to put a trimmer  in series  as well as parallel to attain a sweet generic spot. where the main 1 meg pot gives a a good control.

Another quickie - if i plug this pedal into another pedal (distortion wah or anyother for  chain) instead of a direct amp would they work fine as both have a low output Z(imped) and hign input Z(imped). i do think they should work but again many a times pracitcal components behave differently.