Help with switching circuit from GEO

[Electron Tornado]

I am using a switching circuit from the GEO web site:

http://www.geofex.com/Article_Folders/cd4053/cd4053.htm

I am using this is for switching in an overdrive circuit. It switches the effect in and out as advertised, however, it also pops very loudly when switching both in and out. It is noted twice in the article that the analog inputs and outputs need to be held somewhere near the middle of the power supply voltage to minimize clicks.

I am powering this with a battery which is reading 8 volts. The voltage divider is showing 3.5 volts. Here are the voltages on the pins of the 4053 chip:

Pin                Effect Out (V)          Effect In (V)

1                        0                             0.7
2                        2                              2
3                        0                              0
4                        0                              0
5                        0                              0
6                        0                              0
7                        0                              0
8                        0                              0
9                        0                              0
10                      0                              8
11                      0                              8
12                      2                              2
13                      1                              1
14                      2                              2
15                      2                              2
16                      8                              8


Pins 3-5 are not connected, and pins 6-9 are connected to ground.
According the the article at GEO, the voltages on pins 1,2,12,13,14,15 need to be roughly half the supply voltage, which certainly is not the case right now. So it looks like I need to raise the voltage on those pins, which I could do by eliminating the 1M resistors shown in the second figure in the article. (Come to think of it, it looks like I can save a few components and some board space by using a single 1M resistor and connecting its output to the applicable pins.) I'm also a bit puzzled why pins 2 and 12 show a full volt difference when the effect is engaged.

Does anyone have any ideas how I can eliminate the pops when the effect is switched in and out?


Thank you.

[Pushtone]

Sorry I can't be much help but....

I remember this coming up before.
I think the answer then was to compare The Tone God's "wicked switches" to the GEO.

Article:
http://www.geocities.com/thetonegod/switches/switches.html

Schem:
http://www.geocities.com/thetonegod/downloads/downloads.html

From what I can remember there are some extra "belt and suspenders" components in the Tone God's version that can prevent the popping behavior.

You might want to do an advanced search for "4066" and "The Tone God" to find that thread.

Good luck.

[R.G.]

You MUST use those capacitors at each switch pin of the CD4053 to break any DC from outside the circuit. The capacitors allow the 510K to 1M resistors to pull the pins of the CD4053 to the middle of the power supply. Your voltages show the pins not to be at your bias voltage, so it can't be not popping.

[Electron Tornado]

R.G.,

I used figures 2 and 3 for the circuit - the 4053 controlled by the 4013. If I understand your reply, are you saying that I need to add the capacitors shown on pins 2 and 12 in figure 1? They are not shown in figure 2. I do have the 2.2uF caps on pins 14 and 15, while using the effect's own in and out caps on pins 1 and 13.

[R.G.]

What I'm saying is:
(1) EVERY switch pin on the CD4053 needs a capacitor between it and the rest of the world to block the world's DC from messing with it.
(2) EVERY switch pin on the CD4053 needs to be connected to a resistor to a bias voltage in a way that the bias voltage is constant on that pin when it's switched.

So in figure 2, there is to be a resistor to Vbias on each of pins 1, 13, 14, and 15. There is to be a resistor to bias shared by pins 2 and 12, which are connected.

Also: there is to be a capacitor in series from pins 1, 13, 14, and 15 to the rest of the world, wherever they are connected. Pins 2 and 12 are connected only to themselves and do not need a "rest of the world" cap, as they do not connect to the rest of the world. Make these caps non polarized, NP electros or ensure that they never become reversed if you use polarized electros which can be gotten wrong.

From your voltages, yes, you're getting huge pops. Pin 1 on the cd4053 is moving 0.7V. It should be the bias voltage before and after the control changes. Why isn't that reference more like 4V instead of 2V like you're showing?

[Electron Tornado]

R.G.,

I have the caps and resistors in the circuit just as you've said.  The caps on pins 14 and 15 are non-polarized electrolyics, the effect's in and out caps are ceramic disc.

I figured the popping was due to those pins not being biased correctly. Time to re-check my wiring (again), and work back from the 1M resistors to find why I'm not getting the correct voltage at pins 1,2,12,13,14,15.

[Electron Tornado]

OK, rechecked my connections and wiring. Double checked the pinouts for the ICs as well. Checked that all pins on both the 4013 and 4053 that should be grounded are grounded. All pins on the 4053 that need a 1M resistor have one. All the 1M resistors that connect to Vr connect to Vr at the same point. Continuity from the voltage divider to the 1M resistors is good along with continuity from those resistors to their respective pins.

Effect works, switching works, but still getting pops when switching.

On the 4053 chip, I looked at voltages across the 1M resistors connected to Vr. Battery = 8V, Vr=4V.

Pin         Effect On (V)      Effect Off (V)
1                  4                     4
2                  0                     0
12                0                     0
13                0                     0
14                0                     0
15                4                     0


Looked at the voltages at the pins themselves on the 4053 (pin vs ground)

Pin         Effect On (V)      Effect Off (V)
1                  0.1                   0
2                  1                      2
3                  0                      0
4                  0                      0
5                  0                      0
6                  0                      0
7                  0                      0
8                  0                      0
9                  0                      0
10                8                      0
11                8                      0
12                1                      2
13                1.5                   1
14                1.5                   1.9
15                0                      2
16                8                      8


I have two 4053 chips so swapped them out with no change.


I don't know what else to do or test at this point. Anyone have any ideas? Am I missing something fundamental?