MPSA18 and grounding

[Lbzg]

Hi,


Two quick separate questions.

1. How to know that MPSA18 does not work? I'm using it in Vox percussion pedal. What are voltages or how to find and read data for that so that I don't need to ask any more? :-)

2. Does pedal that uses plastic input/output jacks needs to be grounded so that ground lug from jack is wired to pedal box? What are possible effects of not doing so?


If more info is needed I will provide all the data you need.

[nocentelli]

http://www.diystompboxes.com/smfforum/index.php?topic=103700.0

This thread has guidance on the sort of voltages you should be getting with MPSA18s - First chech the pinout, they're like 2N3904/5088/9.

[R.G.]

1. How to know that MPSA18 does not work? I'm using it in Vox percussion pedal. What are voltages or how to find and read data for that so that I don't need to ask any more? :-)

If you mean when it's used for the transistor that attenuates the input, with its collector grounded, you can't. The only good test in that situation is to feed the circuit a test signal, put a varying voltage on the base drive resistors, and watch what happens when the base is driven.

One of the most common questions we used to get from beginners is "which part is damaged/bad?"; however, the VAST majority of problems are incorrect hookup, including wiring and pinout problems, and poor soldering. Sometimes a new part will be bad - but it's rarer than finding money lying on a sidewalk.

2. Does pedal that uses plastic input/output jacks needs to be grounded so that ground lug from jack is wired to pedal box?

Let me state it a different way. A metal box must be connected to signal ground in some way. If you use plastic jacks and it's not grounded that way, you must arrange for it to be attached to ground some other way.

What are possible effects of not doing so?

Hum and noise. Possibly RF/radio station pickup. If your power switching setup depends on the box being grounded, no power and no operation.