Adding a volume pot to the Easy Vibe question

[BDuguay]

Folks.
I've checked the archives and found the threads mentioning the .22mf/470ohm to ground and volume pot mod to the easy vibe to improve the fidelity of the circuit. I still don't get it. Would someone please explain to me how it all goes together. I'm very interested in trying this mod on the easy vibe I'm finishing up now.
As always, thanks to all responses.
B.

[Aharon]

Did you find it cuts highs a little,me too,but isn't that part of the charm of the EasyVibe?.
Anyways,I'd like a clarification of the mod too please.
Aharon

[jrc4558]

Imagine a non-inverting opamp gainstage.

Now imagine that the 470/.22µF is to ground and there's a 1k resistor int the NFB loop of the opamp.
That's all.

[BDuguay]

While I appreciate the response from a fellow Ontarian even, I can imagine all day and I still don't know how this is actually, physically wired up. It doesn't help that I'm not as educated with regards to electronics as you seem to be Constantin. For that I apologize. I need to know how the pot is actually wired in to the circuit. How is the 470ohm resistor and the .22mf cap tied in to the pot. How is the whole thing wired in to the circuit?
I'm using the geo layout.
Thanks again,
B.

[jrc4558]

Ok, GEO layout.
Replace the R4 with a 10k potentiometer.

Replace R3 with a 1k resistor in series with a 47µF capacitor. Observe polarity on a cap. Since the layout lacks extra holes to accomodate a resistor and a capacitor, just solder the positive lead of cap to thee 1k resistor. Then solder the 1k resistor to the soldering pad that connects to the pin 2 of the opamp. The negative side of the capacitor should be soldered to the other pad, where the R3 originally went to. That pad is connected to the bias voltage supply, the R2 (10M) also goes there.

On the personal note - I wish I could draw, had a scanner and could post things online.

Anything for a fellow Ontarian!
Good luck. Write back with the results.

[BDuguay]

Now I've got it!
The other threads I've read about this reffered to a .22mf , 470ohm resistor, and a 1k to 5k pot. What would be the difference between those, and the values you suggested?
Thanks again and I will definitely report my results when I'm finished.
B.

[jrc4558]

Hi.

The resistor-capacitor network is a highpass filter in this case. Corner frequency can be calculated here:

http://www.muzique.com/schem/filter.htm

Jack Orman is a nice guy and posts some nifty calculators for those of us who don't dig formulas(like me).

So, as you can see 470ohm/.22µF has a corner frequency of 1540Hz,
while 1K/47µF has a corner frequency of 3.4Hz. R(esistor)C(apacitor) network in this case will deduce 6Db per octave from anything below the corner frequency. Thus the 470/0.22µF will amplify the high mids and treble more than low mids and bass. Remember the Tube Screamer mid-hump issues that are discussed from time to time?
that's why you may want to use the values I suggest.
Mark Hammer said once that the lower the resistor values in the opamp NFB loop, the quieter it is. Hence the large capacitor value, just to keep the corner frequency low.
You also may want to go for a 0.01µF inout capacitor instead of a 0.001µF. Depending on your rig, it may sound deeper and fuller, as opposed to really trebly, like with some of my guitars. But if you play medium-scale humbucker equipped guitar - leave it stock.

Another idea for a modification:
1) instead of a 10k pot, use a 250k. this will give you HUGE boost in gain and will allow to overdrive the following phase shifting stages.
2) replace the output puilldown resistor with a volume pot.

Result? Phasing overdrive of a sort.  :twisted:

Good luck 2u.

It's nice to know that there's a fellow DIY'er in Burlington.

[BDuguay]

Thanks again Constantin!
This sounds exactly like it will achieve the changes I'm looking for. Not only that, I've learned a few more things too. I'm a little fuzzy about the volume pot instead of the pulldown resistor though. Time to get busy again.
B. from Burlington.

[jrc4558]

there's a pulldown resistor after the output capacitor, to keep the loud pops away when you switch the pedal in and out. take that out and feed the output capacitor dicectly to a typical volume control, like on Dist+.