Neptune switch pop - better when nothing's plugged in

[lincolnic]

Well, I've finally run into the dreaded popping switch. In over 20 builds, I've never had this problem, but my Neptune seems to be set on breaking the streak. I tried putting a 1M resistor between input and ground on the switch (with alligator clips, to see if it'd work) - no help. I reflowed my connections at the switch and the in/out jacks in case there was a cold joint somewhere, and still no luck.

Oddly enough, the pop seems to be significantly lessened (if not eliminated altogether) when nothing's plugged into the input, much like the problem Jon was having with his Joshua Tree build.

I've read the Jack Deville article, as well as the AMZ one about LEDs. I don't think it's the LED, as the Neptune isn't exactly a high gain pedal. Any other advice?

[midwayfair]

Try putting a 1M-2.2M to ground on the effect output. (I had a switch pop on my Neptune when I built it, too.) http://jonpattonmusic.files.wordpress.com/2012/05/fomorii-guts.jpg

[wgc]

Sometimes I wonder if it isn't just one of the blue Taiwanese stomp switches that's on one side of the mechanical tolerance for the switch, so that ground somehow breaks much earlier than signal.

[lincolnic]

Thanks, Jon, I didn't think to try it on the output. I'll give that a shot on Monday and report back (tomorrow I've got a session).

Sometimes I wonder if it isn't just one of the blue Taiwanese stomp switches that's on one side of the mechanical tolerance for the switch, so that ground somehow breaks much earlier than signal.

I did use a blue Taiwan switch, actually, but I've never had a problem with them before. Is there a known issue with some of them breaking ground before the input signal?

[wgc]

It's just a hunch on my part.  There's a lot of mechanical action in a very tiny space, so if it's a little off somehow, things won't work exactly as intended.  Usually it probably is close enough but odds are that you might have an issue once in a while?

I've also noticed if you have a hot iron or sit too long on a pin, they can shift a little.  Not sure what it does to the insides but doubt it's good.

[midwayfair]

If you're revisiting this tonight, just a little tip I picked up while trying to debug the pop in mine:

If the pop is electronic, somewhere in the audio line (this includes the delay's "audio line" -- stuff around the repeats and mix knobs), there is a DC offset created when switching. It might take a while to find it, but get your multimeter and see if you get a DC change anywhere in the audio line when switching on, then off again. Wait a bit if you're anywhere at a junction with a capacitor, because they can hold charge -- I didn't see the jump at first because I wasn't waiting.

if you do find a DC offset, the question of what to do about it might be a bit more complicated, but at least you'll have found it.

[LaceSensor]

Well, I've finally run into the dreaded popping switch. In over 20 builds, I've never had this problem, but my Neptune seems to be set on breaking the streak. I tried putting a 1M resistor between input and ground on the switch (with alligator clips, to see if it'd work) - no help. I reflowed my connections at the switch and the in/out jacks in case there was a cold joint somewhere, and still no luck.

Oddly enough, the pop seems to be significantly lessened (if not eliminated altogether) when nothing's plugged into the input, much like the problem Jon was having with his Joshua Tree build.

I've read the Jack Deville article, as well as the AMZ one about LEDs. I don't think it's the LED, as the Neptune isn't exactly a high gain pedal. Any other advice?

Hi

This is expected with any DBD deep blue delay type design in my experince. 100k on the output to ground will fix it. You can solder it directly to the footswitch.

Search the forum it's been discussed a few times already. I had it on my Neptune and this worked.

[lincolnic]

Thanks for the advice, both of you - I didn't get to look at the pedal today, but I'll report back when I do.

[pickdropper]

If you're revisiting this tonight, just a little tip I picked up while trying to debug the pop in mine:

If the pop is electronic, somewhere in the audio line (this includes the delay's "audio line" -- stuff around the repeats and mix knobs), there is a DC offset created when switching. It might take a while to find it, but get your multimeter and see if you get a DC change anywhere in the audio line when switching on, then off again. Wait a bit if you're anywhere at a junction with a capacitor, because they can hold charge -- I didn't see the jump at first because I wasn't waiting.

if you do find a DC offset, the question of what to do about it might be a bit more complicated, but at least you'll have found it.

Once in a while, you'll find an opamp has a higher DC offset as well.  I ran into that when building a headphone amp a while back.  I ended up measuring opamps in circuit and screening them for lower DC offset.

[culturejam]

This is expected with any DBD deep blue delay type design in my experince.

It must also be true of any Rebote-based design, since the DBD is damn near the same thing with a few value swaps.    Actually, most of the PT2399 delays out there right now are remarkably similar to the Rebote, which is itself not terribly different from the application note (apart from input and output amps).

[lincolnic]

A 1M resistor between output and ground took care of my popping issue. Thanks to all of you for the help, I'll post a build report later tonight or tomorrow.

So why is this a common issue in DBD/Rebote-based designs? What is it about these circuits that causes these pops?

[culturejam]

My guess is that there is no ground reference on the output after the coupling cap. Most circuits will have a volume pot (at least) that is connected to ground, but the Rebote / DBD / Neptune / etc does not, so adding a resistor may indeed solve the problem (by giving the stored charge in the output cap a place to "go" other than the next device in the audio chain).

[lincolnic]

Makes perfect sense to me.