Ultra hi-speed small stone

[dave h.]

I searched through the "archives" looking for info about this and the answers were blurry at best.

All i want to do is add a switch to bring the rate knob on the small stone up a notch, so instead of ranging from uberslow to pretty fast, it would range from decently fast to "is this a phaser anymore?" speeds.

it seems like this should be an easy mod, by either adding or subtracting resistance before or after the rate potentiometer, or putting a capacitor in series or parallel, im not sure. There was a post asking for the opposite and i'm not sure how that experiment ended.

mod number two ive seen mentioned a few times but without a clear answer: id like to use a center-detenter pot to mix the wet and dry signals. i would imagine you would need to split the clean signal into two parts and buffer it using an opamp before sending one half to the phaser and the other half straight to the mix pot. would this work? has anyone completed one or the other or both these mods? they don't seem too complex. am i at least on the right track with my hypotheses? thats whats important to me, i might not be confident enough (or financially stable enough) to just try this stuff, but the more i ask questions the more i feel i can predict the answers. can anyone help me out?

[ExpAnonColin]

I'm looking at the schematic and assuming that the LFO frequency is controlled by the current going into pin 4 of one of the OTAs...  and that he 1meg pot helps set that, drawn from the voltage divider of the 27k resistor to V+ and to groudn.  If I'm right, then you could decrease the 27k resistor to create a larger voltage and to allow more current to flow through... keeping in mind that you wouldn't want to go much below 7.5k or so.  Someone pleeease correct me on this as I am curious.

As far as the mix goes, you have the idea.  I would use a basic op amp follower right after the .1uf input cap.  You should only need the buffer right there.  Then wire the output of the circuit ad the output of the buffer to either side lugs of the pot, the center to ground, and both outputs to the output jack.

-Colin

[puretube]

LFO rate: depends on the circuit (there are several schems...);
some have a 1µF (electrolytic or tantalum) cap in the LFO:
make that 100nF (switchable - series) and you`re in Ringmodulator heaven...

[dave h.]

LFO rate: depends on the circuit (there are several schems...);
some have a 1µF (electrolytic or tantalum) cap in the LFO:
make that 100nF (switchable - series) and you`re in Ringmodulator heaven...

how do you know which to replace? the schematic im seeing has several LFO sections?

[puretube]

in that case I`d love to see that schem...  (link?)

the ones I know circulating on the web, have 1 LFO

[dave h.]

in that case I`d love to see that schem...  (link?)

the ones I know circulating on the web, have 1 LFO

http://www.montagar.com/~patj/smlstone.gif

i could very easily just be misinterpreting it, having worked with LFO's before. i just saw several bubbles with "LFO" in them and assumed. is it the 10uf one?

[puretube]

"your" cap is the one @ pin 5 of the lowermost IC in the schem...
(sorry: can`t see here, if it`s 0.33µ or 33µ).
Anyway: smaller=faster; half value=dubble speed.

(from that IC, the LFO output current goes thru the 100ohm resistor
into the pins5 of the other 4 ICs, thus controlling their allpass
transfer behaviour (= "shift")).

[ExpAnonColin]

"your" cap is the one @ pin 5 of the lowermost IC in the schem...
(sorry: can`t see here, if it`s 0.33µ or 33µ).
Anyway: smaller=faster; half value=dubble speed.

(from that IC, the LFO output current goes thru the 100ohm resistor
into the pins5 of the other 4 ICs, thus controlling their allpass
transfer behaviour (= "shift")).

What about my idea-would that work at all?

-Colin

[puretube]

be careful with that pin - Colin!

(btw: you`re talking `bout a different schemo...  LM13700 vs. CA3094).

err, which idea:
a) increasing the current?
or
b) mixing?

conc. a): lowering the cap value is safer!

b): the input is already being buffered by the trannies - but be careful with the feedback (color): it can start squealing...