There is a weak link in the power/ground setup in most effects using stereo jack switching. You can get pops when switching the relatively high LED current even if you have pulldown resistors on both input and output caps.
The culprit is ground noise. The ground noise happens when the sudden start and/or stop of current in the LED makes the signal ground voltage change suddenly. +9V decoupling may not help, and may make it worse.
The ground noise comes from our friend, the stereo jack ground switch. If your jack is new and the plug is new, things work great. When dirt, oil, crud, bar funk, and other nasties build up on the ground ring of the input jack and the second-channel contact that supplies ground through the plug into the input ground ring, and thence to the effect board, the resistance through that path can get high enough to make a noticeable pop when the LED current starts and stops.
This sudden transient is worse with mechanical switches because they really do go from fully off to milliohms of resistance in zero time when the metals contact. The sudden "ground bounce" can flow right into the input of your effect, and it doesn't take much to hear a pop from the input of a gain-of-a-zillion MegaBlaster.
What to do, what to do??
(1) Clean your plugs and jacks. Yep, and do it again. And again, every so often.
(2) Use the OUTPUT jack for power switching - it's less sensitive by the gain of the pedal.
(3) Use the GEO scheme for cold-switching +9V by using a PNP transistor with it's base tied through a resistor to the stereo lug on the input or output jack, and the battery minus tied directly to the board. The PNP transistor only lets +9 through when its base is pulled down by the plug in the jack, but this current does not change noticeably when the LED is started, and so any ground bounce is only through the hard-soldered milliohms of the battery lead, and is much, much smaller.
See the power supply switch in the Neutron filter at GEO or at GGG, or see the positive 9V switch in http://geofex.com/FX_images/oaspltr.gif for how to hook up the PNP.
good to know!
Peter - can u send that to FAQ?
Thanks, RG!
Jim
Thanks, RG. really very interesting and usefull info
Erio
Is there a way to incorporate this cold switching with your MOSFET polarity protection to kill two birds at once?
http://www.geofex.com/Article_Folders/mosswitch/mosswitch.htm
To continue the analogy, no, you'd have to toss two stones with one throw to kill both birds. A second MOSFET (or bipolar) switch is needed.
The MOSFET setup for protection is not oriented correctly for cold-switching power, as the intrinsic body diode is backwards for this purpose. If you tried to switch the thing with the gate-source voltage, you'd find that the body diode lets through the battery supply less one diode drop.
However, a MOSFET will do a dandy job of switching battery power - it's just more expensive and no more effective than a bipolar. A bipolar will NOT do the polarity protection job in this circuit.
Why was the stereo input jack power switching implemented as a standard instead of using the output jack?
Quote from: Fp-www.Tonepad.comWhy was the stereo input jack power switching implemented as a standard instead of using the output jack?
Just seems logical! :D I mean, plug guitar in, effect comes on. Attach effect to amp, effect comes on makes MUCH less sense to me. :D
if you`d pull out the output-plug while having the amp still turned on...
whereas pulling out the input-plug, a contact would switch the effect-input to ground;
also, in the beginning, you`d only use one pedal - and when you pack your guitar away, you usually pack the cord away with it (wether you`re using your own amp at rehearsal, or a rented amp at the venue);
when more than one band plays the same backline, the effect that`s not in use will be un-powered, when the player that used it has left the stage;
(there may be more reasons...)
Don Tillman (//www.till.com) suggests using a switched jack instead of our usual scheme to turn power on in his preamp-in-a-plug project. I'm not really sure what he means but then again he seems like the's got a subtle distain for our ilk.
Then again, heresey, but why can't we just use electronic switching and not worry about this? There's a circuit on J.Phillpott's site for a bypass switch based on a logic controller and a flip flop. Maybe this could be implemented to provide non-mechanical, quiet bypass.
Maybe the same True Bypass Mojo.
Most people prefer the mechanical contacts to the electronic one.
QuoteThen again, heresey, but why can't we just use electronic switching and not worry about this? There's a circuit on J.Phillpott's site for a bypass switch based on a logic controller and a flip flop. Maybe this could be implemented to provide non-mechanical, quiet bypass.
This is a fairly deeply plowed field. There is a lot of discussion of bypassing as a technology at GEO, as well as relay, FET, and CMOS switching bypassing, information and some designs with CMOS logic and microcontrollers to do the heavy lifting.
Besides, bypassing wasn't the question - power switching was. Electronic switching requires some constant power, and that will eat batteries. The whole reason for power disconnect is to avoid draining batteries, which is what the stereo switching jack does, as well as the variants at GEO with cold switching to avoid ground current problems.
All my LED equipped boxes pop even with pulldowns, except for the ones I used the Millenium 1+ with. They pop not.
RDV
Hey R.G. - I saw your "Cheap and Intelligent" polarity protector - and I've two questions:
1. Does the 4M7 resistor introduce much thermal noise to the circuit?
2. Can amy implamentation of a cold swithing arrangement be used with this design?
(I know- two dirds... a couple of stone...oh well... if I won't ask I won't learn...)
Thanks R.G.!
QuoteHey R.G. - I saw your "Cheap and Intelligent" polarity protector - and I've two questions:
1. Does the 4M7 resistor introduce much thermal noise to the circuit?
2. Can amy implamentation of a cold swithing arrangement be used with this design?
1. any thermal noise from the 4M7 resistor does not matter. I realize that you may be confused by the way I labeled the drawing. "Vin" is the battery, not an audio signal. As it is set up, the 4M7 resistor is used to pull the PNP fully off when there is no pull down from the NPN. When the PNP base is pulled down, the PNP is saturated, and the 4M7 resistor cannot cause noise; when the PNP base is NOT pulled down, the PNP is off, so any thermal noise stays there, because the PNP cannot conduct it into the circuit, which is not working anyway because the PNP is not giving it power.
2. I want to say that you could simply connect the emitter of the NPN to the stereo second channel lug, grounding it that way. That will work except in exceptional circumstances, but I still need to think through what happens when the battery is reversed, no signal, etc.
Quote from: R.G.Besides, bypassing wasn't the question - power switching was. Electronic switching requires some constant power, and that will eat batteries. The whole reason for power disconnect is to avoid draining batteries, which is what the stereo switching jack does, as well as the variants at GEO with cold switching to avoid ground current problems.
No absolutely, of course, R.G. But in the end aren't they (bypassing-power switching-LEDs and popping) intimately connected?
Gross over simplification on my part methinks...:mrgreen:
Thanks for another excellent post RG.
Why I use a regulated supply;
- grounding is usually better (reduces switch "popping")
- they don't need power switching
- gives more space inside the box
- they don't go dead or weak, except for exceptional circumstances
- they cost almost nothing to maintain and feed
- they are cheap (an LM317, a couple of caps, etc in a box)
- lots of power lets you use cheap/multiple/coloured/flashing LEDs
--> they save the environment from waste batteries
There's probably more reasons.
cheers
Brett R
Quote. I want to say that you could simply connect the emitter of the NPN to the stereo second channel lug, grounding it that way. That will work except in exceptional circumstances, but I still need to think through what happens when the battery is reversed, no signal, etc.
I thought this would be the way... but, what are exceptional circumstances?
Quote from: brettThanks for another excellent post RG.
Why I use a regulated supply;
- grounding is usually better (reduces switch "popping")
- they don't need power switching
- gives more space inside the box
- they don't go dead or weak, except for exceptional circumstances
- they cost almost nothing to maintain and feed
- they are cheap (an LM317, a couple of caps, etc in a box)
- lots of power lets you use cheap/multiple/coloured/flashing LEDs
--> they save the environment from waste batteries
There's probably more reasons.
cheers
Brett R
You start with a Wall Wart and ... [???]
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.
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 :P
N.B. Sorry about the longer post, I had to let it out... :shock:
Quote... 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:
QuoteAll 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:
QuoteI 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?".
QuoteAs 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.
QuoteHere'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:
Coated jack...hahahaha
Everyone loves a sadist :D
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
Quote from: petemooreYou start with a Wall Wart and ... [???]
Here's what I've done with all my unregulated wall-warts.
(http://img.photobucket.com/albums/v165/rickydon/Wall-WartRegulation.gif)
RDV