EA Tremolo pot - cant find a 250k; and other questions...

[glesconz]

Hi, am building a Modified EA tremolo, but cant source a 16mm 250k pot for the Depth....I can only get a 100 k or a 500k.  Can I place a resistor between two lugs of one of these to make it a 250k?? If so, which lugs on what pot?

Also, since the LED in the circuit shows the pulse, I take it a power LED is pretty much redundant?

Also #2...I see I must turn the trimpot till the voltage at Q1 drain is 4.5 - 5 v..do I measure the voltage on the leg when it is soldered into the circuit or measure it before I solder it onto the vero?

http://www.runoffgroove.com/eatremolo.html

Thanks for any help,
Cheers,
Glenn

[El Heisenberg]

U measure for 4.5 voltsa after everything is built. There needs to be juice running through the device to be able to measure anything.


Take a 500k resistor and solder it between lugs 1 and 2 or 3 and 2. Thatll cut the pots value in half. This only works on variable resistors and not always on voltage dividers

[glesconz]

Thanks, that solves my dillema!!!! you wouldnt believe the parts you cant get here in New Zealand!!

Cheers,
Glenn

[glesconz]

Hi, I found this this on the net that says to place the resistor between lugs 1 and 3....which makes more sense to me...who is correct?

Thanks,
Glenn

http://www.projectguitar.com/tut/potm.htm

[PRR]

In this particular circuit, the 120K 250K 68K string may be shifted to other overall impedances as long as you keep the *ratios* similar.

So 220K 500K 120K will work dandy. You may also reduce the 0.47u to 0.235u (use 0.27u).

470K 1Meg 220K 0.15u would also work.

Values far higher than 1Meg might annoy Q2, but you can't get higher pot values (easily) so we won't fret.

47K 100K 27K may work, but the total 170K is not "much-much" greater than the 10K collector load, and this type oscillator may not like the loading.

The 100K RA Rate pot is much more critical. Any real change here needs many other changes, and small rounding (or standard value) differences may stop the working. It might be best to plagiarize another oscillator designed around the pot value you can get. The RA is critical mostly to get smooth right-way action. A Linear will crowd most of the action into one end of the pot. A normal Audio taper will crowd much worse. You can use the Audio if you put the wiper to the other end, but then the action goes from fast to slow instead of slow to fast as we might expect.

[glesconz]

Hi, thanks alot, thats good stuff....just out of interest tho, if I was to use that resistor betweeen the lugs method, which way is correct?

Also, Reverse Audio pots are rarer than Hens teeth, no chance of getting one, Ill have to use a Log pot....

Thanks,
Glenn

[PRR]

> which way is correct?

Neither. Use the 500K. If you stick with the 120K and 68K then the ends don't do too much, 220K and 120K will spread the action over nearly the whole 0-10 scale.

For the RATE, use Audio, mark the dial Fast---Slow, and get used to it. Alternatively use Linear, it will go the right way but all the fast will be scrunched-up in the 8-10 end of the scale. (Look at your fretboard: the slow/low-pitch frets are far apart, the fast/high-pitch frets are close together.... for the limited range this type oscillator can do, it's not real-awkward, although the RA-modded plan may be nicer.)

[glesconz]

ok, thanks, Ill do that.....I found one place here in NZ that sold 100k rev log dual pots for $4...and $21 postage!!! In my own country!!!!

ill use audio instead, will try the swapped wiper as well.....

thanks
Glenn