Friday, May 20, 2011
sparkle motion schematic and updates
here is the schematic for the sparkle motion - a modified rangemaster - with which i will be doing a short of of 15 in the next 2 weeks.
the transistor is any NPN germanium you have available; i check what i have on hand for gain and used ones around 100 hfe. i don't check for leakage, i just pop it in and use my ears... i can hear if it's overly noisy or not.
the 33k/50k pot *should* allow for a bias range of around 3.5v-6.5v, though it will vary slightly depending on your transistor. personally, i like the rangemaster biased a little lower than usual, but this setup allows for a pretty wide sweep with lots of tonal variations.
the EQ control is a dual-gang potentiometer and allows for a wide range of sounds - from trebly boost to full-range boost to heavy driven boost. when the treble switch is (on) it disables the first section (eq, A) of the eq control and will allow for a "standard" rangemaster sound. in this mode the control will still work at adding some slight heft to the signal, though.
lots of possibilities here!
for those interested in one of the 15, the PCBs are on their way to me and should be here by monday or tuesday. it'll take me at least all week to get them finished, what with other orders and such, so i'll have a newsletter(!) sent out then as well as the requisite postings on the forum, etc.
2 quick edits:
*if you need a higher or lower travel on the pot, change the 33k to either a 22k or 47k. if you want less range, use a smaller value (25k) pot, though you'll probably need to tweak the emitter (33k) resistor to get the sweep you want.
*the input/volume pots are both audio/log taper while the EQ and bias are linear.