grammar help

There are various types of signals.

There is only one type of signal.

Btm, sorry and no offense but your sentences can subtly have probably a dozen other meanings. For instance, I can't decide whether 'current or voltage' is two types of signal or one

Probably two, in which case you need a comma after 'current'

But if one, (somewhat logical since the two measurements might be related within a single circuit in such a way that you need one or the other value but not both) then you could punctuate in any of several different ways depending on your exact meaning, where you'd have a number of further decisions to make; eg, as to the presence or distribution of 'ors' and 'ands'

But for what it's worth, for the latter case I might've writ:

There are various types of signals; such as audio or electromagnetic; or current or voltage

I would prefer 'signals'. Most sources assert that you must use a singular noun after 'types of', 'kinds of', unless the plural idea is overriding, e.g.: what kind of concerns are they? I would use the singular if the object is something specific like “beer”, “dog”, or “year”, and the plural if the object is less specific and can have many different definitions, like “shoe “, “car”, or “widget”.

Merriam-Webster supports the use of the plural:

[EDIT] Dale picks up well the point about 'signals'.

two
you can have a current signal or a voltage signal
but you cannot have one with out the other
V=IR
Voltage = current * R

Why thanks Cen, once more made my day, maybe two or three

Thanks Btb, after some of my recent foibles , I'm regaining a new sense of myself