Nota Bene: Pops when switching, even with pulldown resistors

[petemoore]

As I previously stated "There are better ways to make connections than 1/4'' jacks. Especially for maintaining excellent amp to speaker continuity, I've seen amps killed by non continuousness of Speaker Connects.
 Phallic shape, and easy to insert, they have become the norm for guitar players though.
 What I'd like to know is how one could figure out that it's the resistance of the jack used as switch for PS that causes these unwanted pops !!!
 I've been cheating all along and dangling many of my circuits battery clip outside the box, I found out I like them there.
 However I'm beginning to tire of these battery's charging cycles [their batteries charging wave cycles have flattened somewhat, 0and I'm about to stray from buying more NiMh's 'they're getting old']  in lieu of regulated filtered power.

[Gilles C]

Last night, I added a PNP  power switching to the bi-color LED circuit I am experimenting these days.

I tried using only a PNP transistor and a 10K at the base to control it. I was always getting 4.4V-7.5V at the output instead of 0V...    

Then I added a 4.7M between the emittor and the base to help it switch off. Argg... Still getting some dc at he output.  :shock:

The LED was dim but always slighly ON. So I added a meter to check he curent used by the circuit. Hey, it's changing while I am manipulating the circuit...  :?

:idea:  I'm holding the board in one hand... and holding the wire connected to the 10K resistor going to the base of the PNP in the other hand.  :shock:

The PNP was using my body resistance to swith ON.   :oops:

:arrow:  Never  underestimate these little things when working with sensitive circuits...

The circuit is working correctly now, but I think I will keep the 4.7M anyway. Just to be sure.

Just for fun, I'll post the stripboard layout when it's all finished and installed in a box.

That was a good idea R.G., thanks.

Gilles

N.B. Sorry about the longer post, I had to let it out...  :shock:

[R.G.]

... But in the end aren't they (bypassing-power switching-LEDs and popping) intimately connected?

They are, but only because they're power supply issues - and in the end, everything is a power supply issue.

The culprit in LED-current popping is impedance in the ground path to the input jack. Do this thought experiment: remove the bypass circuit entirely, leaving only the LED-switching section. Now when you press the footswitch, the effect circuit does not change its sound at all, but the LED turns on and off.

That sudden change of current in the ground line causes a sudden voltage change in the ground line because the ground line is not a perfect conductor, and the effect sees what it thinks is a sudden signal change in signal, so it amplifies it into a pop. This effect is much, much worse if the effect is a giga-gain distortion pedal.

So no, a hypothetical perfect bypass won't help this particular problem. A slow-on LED circuit will, as RDV notes:

All my LED equipped boxes pop even with pulldowns, except for the ones I used the Millenium 1+ with. They pop not.

The Millenium 1 is (in)famous for slowly ramping the LED on. The "sudden change" in voltage on the input line is too slow to get past the coupling capacitors.

But minimizing the size of the transient by keeping the current in the grounding line down works too - the two ways are to put the ground current on the output wire (although note that this makes it worse for the **following** effect) and by cold switching with a transistor. The transistor cuts the sudden current transient by the gain of the transistor, usually 100 to 300, or 40-46db. If the cold switching transistor is saturated, the transient is effectively zero, since the transistor base current changes essentially nothing at all, massively less than even 40db down.

Re: switching the emitter of the NPN in the polarity protector:

I thought this would be the way... but, what are exceptional circumstances?

It's one thing to design a circuit that works when everything is normal - power supply voltages nominal, correct polarity, input signal the right size, no lightning in the neighborhood, phase of the moon correct, etc.

It's quite another to design a circuit that is not damaged, or even works almost correctly when things get weird. Things like reversed power supply voltages, sustained short circuits on the inputs and outputs, input or output connected to the 120VAC power line (don't laugh - I've seen this done), electrostatic shocks, playing in a wet environment like a stage in a drizzling rain ('course, the band's name in this case is Death Wish).

Those are exceptional circumstances. A guitar pedal should not need repair after those kinds of things happen. Those are the motivations for things like the parts in my article "What are all those parts for?".

As I previously stated "There are better ways to make connections than 1/4'' jacks. Especially for maintaining excellent amp to speaker continuity, I've seen amps killed by non continuousness of Speaker Connects.

Dead right. Tube amps particularly can die if (a) their speakers are disconnected and (b) the designer did not take this into account. If I design an amp, it carries internal protection agains speaker removal.

However, this is also why Speak-On connectors and others were designed. They are much less prone to intermittent continuity.

Here's a great April Fools gag for you all:
One of the worst things in the world you can do to your bass player is to coat the 1/4" plug ends of his cord with clear nail polish or lacquer. This is good for *hours* of fun.

[Paul Marossy]

Here's a great April Fools gag for you all:
One of the worst things in the world you can do to your bass player is to coat the 1/4" plug ends of his cord with clear nail polish or lacquer. This is good for *hours* of fun.

I remember reading that at GEO. Made me chuckle.
That is one case where Anderton's cable tester could come in handy!  :wink:

[brett]

Coated jack...hahahaha
Everyone loves a sadist

Pete.. regulated power supplies...
Electronics shops have fancy kits, or check out Figure 2 in this application note.http://www.national.com/an/AN/AN-178.pdf
or the High stability 10V regulator herehttp://www.national.com/ds/LM/LM117.pdf

cheers

[RDV]

You start with  a Wall Wart and ... []

Here's what I've done with all my unregulated wall-warts.


RDV