Just finished a Runoffgroove-improved EA trem. I initially built it as per the ROG schematic and perfboard from here:
http://www.runoffgroove.com/eatremolo.html , but got a fair bit of distortion, enough for me to contact the runoffgroove guys for some help. Brian very kindly replied with an image of an alternative MOSFET amplifier stage schematic designed by Gez :
http://putfile.com/pic.php?pic=5/14304484054.png&s=f5, and mentioned in this thread :
http://www.diystompboxes.com/smfforum/index.php?topic=27160.0In the alternative schematic Gez has a couple of different cap values, but I used the same values as in the ROG schem. I might do some tweaking but I’m very happy with the sound I have. To modify the circuit from what I’d already done I cut the connection where the 1M resistor+0.1uF input cap pair go to the MOSFET gate, and replaced that 1M resistor between the MOSFET gate and the 100k trimpot with the 1M pot (lug 1 to the 100k trim/47uF cap, lug 2 to the MOSFET gate, lug 3 to the 0.1uf input cap). I removed the 100k volume pot, with the output now going straight out with a 100k resistor to ground off it, using the ground connection that was there for lug 1 of the volume pot. It’s a bit tricky if you’ve already done the standard setup, but do-able. Brian at ROG has given his permission for me to post my roughly modified pic of the perfboard with this mod :
http://putfile.com/pic.php?pic=5/14304451832.gif&s=f5And I now have a distortion-free trem. I got bypass-level volume at about 11 o’clock on the input pot, and winding it on to about 3 o’clock I got a big boost but still didn’t get any distortion
Thanks to Gez, Brian and the ROG team for the improvements on the original EA trem, and for the help in setting up the the alternative amplifier stage.