Popping sound during switching true bypass

[rschultz]

Hi,

  I have a hybrid guitar that has both sets of pickups - magnetic and piezo. It uses a Fishman powerjack to control it and sends it out a stereo jack. I have had trouble in the past because the magnetic pickup is passive whereas the pieze runs on 9v, so when I would split this signal anytime I'd go into a true bypass circuit, the ring (piezo) would pop. This doesn't happen with buffered pedals.

  One solution Fishman told me was to put a .1mfd cap in line on the ring side. This works in a cable. But I wanted to build a switching box that takes the stereo signal and splits it to 2 true bypass switches and then out 2 mono jacks so I could turn each one on/off, the off side would go to a tuner. I've tried to put some caps in line, both on the signal lines and grounds, but this doesn't seem to be helping.

  One solution is to add a buffer circuit to both sides. Are there any passive solutions?

Thanks.

[Gurner]

If this is an onboard solution (ie all inside you guitar), then this might not be a classic bypass popping (pesky DC) problem....this might be EMI induced from abrupt changes in current on the fishman preamp (as it is switched on/off) permeating into your pickups 'over the ether'. One way to prove this would be to disconnect your mag pickup & see if you still get switching related popping noise...if you do then EMI is not the issue, but the pop is coming from the fishman.

I think we're going to need a diagram of your exact setup, as I'm having diffs visualizing your exact setup.

[R.G.]

I believe what's happening is the old pulldown issue.

It is likely that the active side has a DC level on the output. Hence the advice to put a cap in it.

However, with a cap in it and a true bypass switch after it, that cap now can give you the leaking/popping behavior that pulldown resistors help with.

I would put a 0.22uF cap in BOTH tip and ring sides (as long as that doesn't prevent the preamp from getting its DC) and then put a 2.2M resistor between tip and ring after the caps. Then do your bypass switching.

[EATyourGuitar]

but what do you do when its switched on with a stereo jack? would you just add a power switch to the preamp?

[R.G.]

but what do you do when its switched on with a stereo jack? would you just add a power switch to the preamp?

There exist phone jacks with switches that are mechanically operated by the plug insertion, but not electrically connected to the tip, ring, or sleeve. They are uncommon, but not unobtainable.

I would do that.

[rschultz]

I would put a 0.22uF cap in BOTH tip and ring sides (as long as that doesn't prevent the preamp from getting its DC) and then put a 2.2M resistor between tip and ring after the caps. Then do your bypass switching.

So put a .22mfd in series on the stereo input jack for both tip and ring and a 2.2M resistor across tip and ring. Does the sleeve need a cap? Then take those tip and ring wires each to a 3PDT, each 3PDT will either go to the output jack OR a tuner/mute jack.

Thanks.
Ryan

[R.G.]

I would put a 0.22uF cap in BOTH tip and ring sides (as long as that doesn't prevent the preamp from getting its DC) and then put a 2.2M resistor between tip and ring after the caps. Then do your bypass switching.

So put a .22mfd in series on the stereo input jack for both tip and ring and a 2.2M resistor across tip and ring. Does the sleeve need a cap? Then take those tip and ring wires each to a 3PDT, each 3PDT will either go to the output jack OR a tuner/mute jack.

Thanks.
Ryan

Actually, reading back over that, it occurs to me that I may need to see how the powered pickup gets its power and how its signal comes out.  Got a diagram?

[rschultz]

Actually, reading back over that, it occurs to me that I may need to see how the powered pickup gets its power and how its signal comes out.  Got a diagram?

Here is 1 diagram. But there's probably better information in a pdf off of the Fishman site: <http://www.fishman.com/products/view/powerchip>. Click on Powerchip Users guide.
http://home.fnal.gov/~rschultz/PowerBridge1.pdf

[rschultz]

One thing I'll mention about it that may or may not help is that I can't use the Magnetic pickups without a battery in it even though it's the piezo that generally needs the battery.
Thanks.
Ryan

[Gurner]

One thing I'll mention about it that may or may not help is that I can't use the Magnetic pickups without a battery in it even though it's the piezo that generally needs the battery.
Thanks.
Ryan

If that's the case, then certainly referencing that wiring you've linked....that ain't how your guitar is wired (the mag & piezo wiring circuits are independent on there....which means your mags should work regardless of a battery or not)

[rschultz]

Because of the selector switch, even the mag signal goes to the powerjack circuit which is powered.

[rschultz]

I don't know why I can't put in pictures. Selector switch:
<http://home.fnal.gov/~rschultz/selector.pdf>
http://home.fnal.gov/~rschultz/selector.pdf

[rschultz]

Obviously a passive solution is the simplest, but I'm not opposed to a simple powered buffer circuit like this one on GGG:
http://www.generalguitargadgets.com/projects/15/74-simple-ic-buffer

If I used one on both Tip and Ring, would that work to not only buffer the signal but remove the popping?

Thoughts?
Thanks.

[rschultz]

I would put a 0.22uF cap in BOTH tip and ring sides (as long as that doesn't prevent the preamp from getting its DC) and then put a 2.2M resistor between tip and ring after the caps. Then do your bypass switching.

I had a few misc. caps laying around, not exactly .22mfd, probably anywhere from .047 to .47mfd and a 1M resistor. So I wired it up and tried it out. It seemed to work. It gave an initial pop or two, but after that it was quiet. I wonder if the first 2 pops were where the caps were charging up... but once they were charged, they had enough of a "buffer" voltage to cover it when I switched.

Now that I know it works, I'll get the right ones and redo it. One question, how did you come up with .22mfd and 2.2M resistor?

Thanks.
Ryan

[R.G.]

One question, how did you come up with .22mfd and 2.2M resistor?

WAG formula.

That's a TLA for Wild A$$ed Guess. 

Well, OK, there was some reasoning. Fishman said 0.1uF. I was proposing putting another cap in series, effectively, so two 0.22uf in series gets to about 0.1uF. And I didn't want the stock answer (1M) to load things down, so I doubled it.

But the calculations were... highly simplified.