[Ken B]

I recently purchased a used 717 and noticed an audible hum through the headphones. This occurs when the volume is advanced beyond the half way point. Under normal use, this would be quite a high volume level. But my modified SACD player puts out about .75 volts which is less than half of what a standard player outputs, so putting the volume control near maximum is not uncommon and not outrageously loud. My 006t hums slightly as well, but it is barely audible and insignificant. The hum is also audible without audio cables connected but to a lesser degree than with them.

I brought the amp to the Stax US distributor/service facility, with whom I purchased a 4040 system from last year, and I was told that the unit was not designed for the US market and even though it has a 117V sticker on the box and back of the unit, that it was probably set for the wrong voltage,
possibly causing the hum. I was also told that they will not touch this unit because they do not have any technical information on units they do not import. They implied that the audio circuitry, power supply and transformer may be different for Stax products designed for a specific country.

I mentioned that to my knowledge the only difference is the use of different transformer taps to set the proper voltage for a specific country and a fuse change. Is this correct?

The 717 I have is a later unit and does not have the external voltage selector. How can I check or determine for myself that the voltage is set properly? And I would be interested on any thoughts on the hum issue or if there are indeed any difference between Stax products that are officially imported for the US market and products sold by Audio Cubes or EIFL.

Thanks - Ken

 

[trbl]

Quote:

Originally Posted by Ken B I recently purchased a used 717 and noticed an audible hum through the headphones. (snip) The hum is also audible without audio cables connected but to a lesser degree than with them.

There are at least two possible reasons for the hum. One is a problem with the unit. The other is a grounding issue. You can test to see if the latter is part of the problem by using the grounding lug on the back of the 717 and running a wire from the lug to a good ground point. One place to try is the center screw of an AC wall socket. Usually the screw makes contact with part of the metal box that surrounds the wall socket assembly which should be connected to ground.

Normally you'd have grounding issues like this if the Stax amplifier was connected to one outlet, and the equipment feeding it was plugged into a different outlet, but it can happen in other circumstances too.

Quote:

I brought the amp to the Stax US distributor/service facility, with whom I purchased a 4040 system from last year, and I was told that the unit was not designed for the US market and even though it has a 117V sticker on the box and back of the unit, that it was probably set for the wrong voltage, possibly causing the hum.

I'd suggest contacting the original owner, to verify where the unit was purchased, and if in the US whether the owner sent in the warranty card to YEI (the US distributor and service provider). If you can prove the unit came from an authorized dealer, you may be able to get it serviced for a fee.

Quote:

I was also told that they will not touch this unit because they do not have any technical information on units they do not import. They implied that the audio circuitry, power supply and transformer may be different for Stax products designed for a specific country.

I doubt this. I think YEI just wants to discourage grey market sales by refusing to service such units, even for payment. As the sole US authorized importer and distributor, no doubt YEI earns money on each sale which helps to pay for their service center.

Quote:

How can I check or determine for myself that the voltage is set properly?

I've never seen a schematic for any current production Stax amplifiers, so I'm not sure what the supply voltages should be. Maybe someone else has this information, or can open up their 717 to see what the voltages are.

If this really is a 100 V unit running on 117 V, then obviously the supply voltages will be significantly higher than expected, and it's possible that the maximum voltage or power ratings of things are being exceeded, which could lead to premature failure.

 

[kevin gilmore]

If it really was a 100 volt unit running on 117 it would probably have
smoked by now. The high voltage rails should be about +/-360.
This unit has a completely unregulated power supply.

If the rails are more than +/-420 then the unit is definitely a 100 volt unit.

Its just taps on the transformer anyway and this should have nothing
to do with the hum. Some kind of grounding issue possibly within
the unit. Short the inputs and crank the volume control. Any hum
is a problem.

Recently i have seen units right out of the factory mis-wired such that
the left and right channel are actually tied together producing mono
and hum.