From: "Rheilly Phoull"
Subject: Re: How do you determine polarity of a phono amp?
Date: Fri, 10 Jan 2003 17:27:23 +0800
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Be careful, if the power input socket to the mixer is is marked AC then
polarity is not important.
I assumed you are talking of the Mains input plugs when mentioning "3 prong
and 2 prong" ??
If that is so and you have run it from the 12v adaptor then the remarks re
the power input to the mixer would be correct.
As regards 3 prong and 2 prong, which I assume are the mains plugs, it would
be that one adaptor is "double insulated" and the other has an earth
connection via the third prong and is not "double insulated". If you are
contemplating connecting the mains plug seek help.
Of course I may have misunderstood your descriptions which, to be honest, do
seem somewhat vague and scrambled to me, perhaps others will see it more
"Doc" wrote in message
> I have a phono mixer I bought at a pawn shop without a power supply.
> This particular model is a Gemini "Scratchmaster" PMX-18. On the
> outside the power input only says "15V ac", doesn't specify amps. I
> called the manufacturer and after asking several people who didn't
> seem to know the answer, someone finally advised me 500 ma as the
> rating for the power supply.
> I went to a local used electronics supply house and they advised me
> that a 12v, supply should be adequate, and they grabbed one rated 12v,
> 800ma and sure enough, it works. I also found another one that was
> rated at 14.5v ac and 1.16 amps, since I thought getting closer to the
> specified voltage might be a good idea, and it's my understanding that
> it's ok to have ampage that's over the rating, that the unit only
> draws what it needs. (yes? no?).
> The 14.v unit has no end plug so I have to solder one on, and is of
> the 3-prong variety, the 12v one is of the 2 prong variety.
> It ocurred to me that I've always heard that correct polarity is
> important, and to be honest, I don't know what the polarity
> requirements of the unit are, or what the polarity of the 12v 2-prong
> power supply is, though it does seem to work. I also find that by
> hooking up the Red and White leads from the 14.5v unit to the prongs
> of a plug end I bought, it seems to work either way they're hooked up,
> and I can't tell any difference in sound or noise floor.
> So, some questions
> 1) How would I determine what the polarity requirement is of this unit
> without going back to Gemini? For a couple of reasons - first it was a
> pain in the ass just trying to find someone who seemed to know
> anything, and also on principle, they seem to be trying to coerce you
> into buying THEIR power supply at what I'm sure is a lot more than
> simply picking up one locally.
> 2) Which way should I solder the red/white leads onto the plug end for
> which polarity? the longer connector goes to the outer sleeve of the
> connector, the shorter one goes to the inner portion. Which way for
> pos and which way for neg? I assume the black lead is to the ground on
> the 3 prong plug. Should anything be done with that or just leave it
> 3) Why does this unit seem to work no matter which polarity you use?
> I've always heard it's bad for a unit to use the wrong polarity.
> Thanks for all input.