Author Topic: Output wiring  (Read 351 times)

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Ansur

Output wiring
« on: September 10, 2017, 05:14:03 AM »
There's this pedal I have from an Italian builder, where he added 2 resistors and a capacitor (?) on the output jack.
From what I understand, the 1.5MOhm resistor serves as a pull-down resistor, but what's the use of the 91Ohm resistor across the output lugs?
Regarding this capacitor, I assume it's part of the pull-down resistor "design" to not cause a pop when switched?

As a bonus question :) Does it make sense to add these components to each output jack of a looper pedal?
Reading through this article, I would think not, as the looper doesn't have any capacitors that could leak to begin with.



tubegeek

Re: Output wiring
« Reply #1 on: September 10, 2017, 12:18:11 PM »
Some op-amps are (somewhat) likely to become unstable when their output has no series resistance. About 100 ohms is typically selected to prevent this. I suspect that's what your 91 Ohm R is doing here.

No op-amp=no need, for your looper. If the looper has an op-amp buffer, then it can't hurt to add it.
"The first four times, we figured it was an isolated incident." - Angry Pete

GGBB

Re: Output wiring
« Reply #2 on: September 10, 2017, 03:16:14 PM »
Have you measured any of this with a meter?

That 91R resistor looks to me like brown-black-black-silver-brown = 1R. Or possibly brown-grey-black-black-brown = 180R.

Either way it's not that simple looking to me as it appears to be connected between two lugs for the same jack connection (looks like tip) - at least based on my knowledge of those style of jacks - but I might be wrong. It might be there merely to prevent pop when the plug is inserted or removed - again depending on the internal mechanics of that actual jack - are the two tip lugs separate until connected by the tip of the plug? It's either that or there's some make or break switching inside that jack - otherwise that resistor is mojo nonsense. Probably. But I am happy to be educated.

These components appear to be post-switch, but without a schematic or at least full picture, hard to say exactly what is going on. The 1.5M looks like a pulldown, but I'm not certain it is. Being on the jack, if the jack is disconnected from the circuit, and the circuit contains the output cap, then the "pulldown" gets disconnected from the output cap when the circuit is bypassed, so it's not actually pulling down when it needs to. Of course I'm making assumptions about the switching which I can't see - once again would need a proper schematic or complete picture.

One thing interesting is that cap between the jack sleeve (ground) and the chassis. I'd guess that's to only allow the chassis to act as a ground for AC (RF, EMI), which is an interesting idea - new to me. Assuming of course that the jacks are isolated which appears to be the case.

Summary - can't really know for certain what exactly is going on without knowing the whole circuit which includes the switching and jack mechanics.

Ansur

Re: Output wiring
« Reply #3 on: September 11, 2017, 04:50:29 AM »
Hello, indeed I was incorrect in the values, I've uploaded a picture of the primary output, while giving the values of those resistors on the secondary output. This effect is a chorus pedal with a separate dry out.
I could show a full picture, but the circuit is fully covered in red, so wouldn't really serve? What might help is that it's buffered, and that the circuit is based on the Boss CE-2.

The jack is of this type: http://www.neutrik.com/en/audio/plugs-and-jacks/m-series/nmj6hc-s - so indeed the tip lugs are separated until a plug is inserted.

GGBB

Re: Output wiring
« Reply #4 on: September 11, 2017, 03:12:30 PM »
The jack is of this type: http://www.neutrik.com/en/audio/plugs-and-jacks/m-series/nmj6hc-s - so indeed the tip lugs are separated until a plug is inserted.

I may be mistaken, but that type of jack actually disconnects the two lugs when the plug is inserted, and the plug only makes contact with one of the lugs. So the resistor is shorted when no plug is inserted, and in series with the output when a plug is inserted.

I don't see the picture.

Ansur

Re: Output wiring
« Reply #5 on: September 13, 2017, 09:03:58 AM »
You are correct, the lugs disconnect when a jack is inserted.