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Old 4th July 2015, 02:27 PM   #1
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Default Question regard japanese voltage amp in us

This might not be the best place to put thus question (mods feel free to move), but I posted this question on head fi to the sound of crickets, and would like to know the safest way, if any, to use my new toy:

New to Stax, not new to headphones. After some research, I took the plunge and purchased a Stax SRM-1/MK-2 amp, as not only did the reviews seem good for solid state, but is also had outputs to both Pro and Normal Bias, if I wanted to collect vintage normal bias ear speakers in the future.

I purchased from a well rated seller in Japan. I have a couple of concerns regarding grounding this thing.
1. I read about how japan doesn't use three prong outlets, and there seller included a transformer for the voltage that goes goes from a japanese non polarized plug to a american non grounded polarized one, but there is a ground tap on the back of the amp. Is this an earth ground, like on a record player?

2. What the seller did not include is a power cable for the actual amp. It looks like a standard computer power supply input (I have one that fits), but it is a three prong plug... very confused now.

So, do I connect the ground from the back of the amp to the exposed ground that is on the plug going into my US three plug outlet, or, as I said before, to a different earth ground, leaving this third prong exposed?

I obviously want to avoid dangerous situations with this, as well as hum when I hook up my soon to be growing collection of STAX ear speakers.

I did do a search, but could not find anything.
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Old 4th July 2015, 02:51 PM   #2
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If it is a three pin IEC connector, the earth must be connected for safety. A two pin IEC should have the double insulated mark that doesn't need an earth.
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Old 5th July 2015, 12:06 AM   #3
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If the amplifier has a 3 pin receptacle, plugging a grounded IEC lead into it will not cause problems if there is no internal ground connection which, if it were intended for Japanese distribution only, should be the case. Otherwise, why would it be connected anywhere?

I'll assume the tap you refer to is a chassis connector, like a thumbscrew that was once fitted to amplifiers for phono inputs and is not connected elsewhere to the amplifier, such as signal ground on the input sockets.

The test is simple: Check for continuity between the receptacle ground (central pin) and the ground "tap" on the rear of the amp. Obviously, it can't be powered whilst you do this but if there is continuity, the "tap" and probably the chassis is clearly intended to be mains grounded. Either way, it should be fine, remembering that if the chassis is ungrounded, it does not comply with your local regulations for new products and neither for warranty conditions so it should not be considered legally safe.

Anyways, you should be able to see the requirements set out in the user manual - If you have one in English as you should. A service manual would confirm this but I guess the chances of access to one of those are about zero.
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Old 5th July 2015, 05:14 AM   #4
wwenze is offline wwenze  Singapore
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Doesn't Stax SRM-1/MK-2 have adjustable voltage?

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Old 5th July 2015, 07:48 AM   #5
AndrewT is offline AndrewT  Scotland
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the post4 unit is clearly intended to be "EARTHED".
This is a safe use issue.
If the unknown Stax unit is not similarly marked, then go back and ask the manufacturer.
regards Andrew T.
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Last edited by AndrewT; 5th July 2015 at 07:52 AM.
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Old 5th July 2015, 07:51 AM   #6
AndrewT is offline AndrewT  Scotland
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It concerned me when I read post1 that 100V (AC or DC?) for Japan use might be a problem in the USA where power is 110/120Vac.
Fortunately the post4 unit is switched to allow all supplies from 100V to 240Vac to be used.
regards Andrew T.
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Old 5th July 2015, 10:08 AM   #7
AJT is offline AJT  Philippines
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yes, Japan uses the 100 volt ac standard..
if your unit was meant for domestic use in japan, then isolation transformer is needed...
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
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