Switching capacitors in an LPB-1 clone (pics) help?

[BluffChill]

I've built a linear power booster - schematic here: http://pedalparts.co.uk/docs/LPB-V3.pdf

I did it on veroboard:



You'll note that it gives you the option of having different capacitor values to turn the pedal from a 'clean' boost to a treble booster. Ideally I would like to make one with a 3 way switch - ON-ON-ON (double pole) to be able to switch between capacitors.

Now I just tried this with a 3 way slide switch that looked like this:



Forgive the crude diagram, but it was a 2 pole  slideswitch so I used the other pole to do a similar thing with the other cap (C2, not actually electrolytic, just ceramic)

When I tried it, the first position with the high value (100n) cap sounded ok, but the others were choked and thin sounding. It's a guess, but are the other two (unused) capacitors acting like decoupling caps and filtering out loads of the frequencies? The sound is more trebley, but it's very quiet. Is there a better switching mechanism I could use so that I don't have to have 3 capacitors connected to the same place? Maybe a diode or six?

Thanks in advance!

[PRR]

Welcome!

Slide switches are often funny. Some have no "common" contact. Use your ohm meter to figure out what connects to what in each position.

[antonis]

Ideally I would like to make one with a 3 way switch - ON-ON-ON (double pole) to be able to switch between capacitors.

Easier (and cheaper) shoud be to use a SPDT toggle switch (ON-OFF-ON) with the middle lug permanently connected to the lower capacitor value..
This should put any ON connection capacitor in parallel with the middle one so you can easily calculate their individual values..

[Kipper4]

Similar to this Antonis?

http://www.aronnelson.com/gallery/main.php/v/mac/my+circuits/Tres+Hombres.GIF.html

[BluffChill]

Ideally I would like to make one with a 3 way switch - ON-ON-ON (double pole) to be able to switch between capacitors.

Easier (and cheaper) shoud be to use a SPDT toggle switch (ON-OFF-ON) with the middle lug permanently connected to the lower capacitor value..
This should put any ON connection capacitor in parallel with the middle one so you can easily calculate their individual values..

Thanks - would this mean an ON connection would use *only* the capacitor selected, and not both?

[Ben Lyman]

Another option is make two caps and a pot into a variable cap. I like it because if I am already drilling my box for a pot, it's just as easy to drill it for two pots.
You can play around with the cap values, I made a Tone Bender with a 4.7nF and a 10uF with a B500K pot that works well for me.
Take a look at this schematic for the Deluxe Bazz Fuss, it uses a 1nF, 2.2uF & B100K pot.

Note how the smaller value cap is connected straight through, while the larger value cap gets attenuated by the pot.

[BluffChill]

I did toy with this idea Ben, but the reason I chose a nice simple boost is to re-use an empty case I have lying around!
I was also never quite sure what value pot I should use to get a nice full sweep between the two.

[antonis]

would this mean an ON connection would use *only* the capacitor selected, and not both?

No, the exactly opposite..

On any ON connection there will be 2 caps used in parallel (Ctotal = C1+C2, that's why I've proposed to use the lowest value cap permanently connected..)

You may consider it as the same (or anti-phase..  ) as with switching between 3 pairs of clipping diodes via a SPDT switch with the pair of higher Vfd permanently connected..

Give me sometime to draw you a schematic..


You shouldn't experience "popping" isuues as long as you don't select caps during effect ON.. 

[antonis]

Similar to this Antonis?
http://www.aronnelson.com/gallery/main.php/v/mac/my+circuits/Tres+Hombres.GIF.html

Not exactly Rich..

Switch at Tres Hombres is a STDT (ON-ON) 1 cap selector (connected or bypassed) with no "indermediate" throw (OFF) which places (or not) the caps in series (leading to Ctotal = C1xC2/(C1+C2) when unconnected lug is selected)