Yamaha B-6 110V on ground

[Dr. Ear]

My two otherwise perfectly working Yamaha B-6 power amps have both 110 Volts on their housing. There is a small electrical sensation only when I touch the amp and another earthed device simultaneously. Current to ground is negligibly. This voltage gives me some hum in the preamp's phono input and killed the muting transistors of my C-80 when I connected it to the B-6 with power on (the B-6 was off, of course). The voltage is also there when the B-6 are not switched on (!) and independently from the position of the mains plug. I have installed a shielded mains cable and exchanged the spark suppressor caps which are directly soldered to the power switch in one of them, no change. Now I have earthed the amplifiers which solves the problem but I would like to know the reason for this voltage. Could it be a defective power switch?

 

[Vint Age]

My two otherwise perfectly working Yamaha B-6 power amps have both 110 Volts on their housing. There is a small electrical sensation only when I touch the amp and another earthed device simultaneously. Current to ground is negligibly. This voltage gives me some hum in the preamp's phono input and killed the muting transistors of my C-80 when I connected it to the B-6 with power on (the B-6 was off, of course). The voltage is also there when the B-6 are not switched on (!) and independently from the position of the mains plug. I have installed a shielded mains cable and exchanged the spark suppressor caps which are directly soldered to the power switch in one of them, no change. Now I have earthed the amplifiers which solves the problem but I would like to know the reason for this voltage. Could it be a defective power switch?

Sounds like you have some serious AC volts between gear. It doesn't sound very safe. Do you have a DVM? You could measure the AC volts and see what it is. :yes:

 

[Dr. Ear]

Thank you. AC is 112,3V but current to ground is not measurable, i.e. less than 10µA. So there is no danger at all. Please note that I have 230 V line in my house. Voltages are similar on both B-6, off or on, no change.

 

[Vint Age]

Thank you. AC is 112,3V but current to ground is not measurable, i.e. less than 10µA. So there is no danger at all. Please note that I have 230 V line in my house. Voltages are similar on both B-6, off or on, no change.

You're measuring 112V between preamp chassis and B-6 chassis? Sure sounds like somethings not wired right. You must be using a step down transformer?

 

[Dr. Ear]

No, between B-6 chassis and ground, e.g. a radiator or ground in the mains socket.

 

[Vint Age]

And what about the stepdown transformer?

 

[Dr. Ear]

Im from Austria, we have 230V and the B-6 are 220 V so I don't need a step down transformer. I think it is the power switch. Inductivity from the mains cable running quite a long way from the back to the front, a possible cause, I have excluded by mounting a shielded cable (shield connected to the ground of the mains plug only). In the European version the power switch switches both pos. and neg. whereas the US B-6 only switches pos.

 

[Vint Age]

My two otherwise perfectly working Yamaha B-6 power amps have both 110 Volts on their housing.

OK, I misunderstood. I thought you meant the 110 Volts was marked on their housing. It sounds like some kind of strange AC leakage ... but in both B-6's ... and why 110 V?

 

[Dr. Ear]

It's 112,3 V static voltage exactly, no current from chassis to ground measurable, just an uncomfortable sensation when you touch the chassis with one hand and another device or the radiator with the other hand. Sometimes a tiny spark is visible between RCA plug and socket when I connect the preamplifier to the B-6. Power chord is new and shielded. It does not matter if the B-6 are switched on or off, always the same. The amplifiers are working perfectly otherwise. I tested my other gear, tuner, CD, DAC etc., a value between 12 and 24 V seems to be normal. Any idea?

 

[Dr. Ear]

This is the schematic of the B-6 power supply (North European model).

 

[Dr. Ear]

It seems to be just logical to me that the power switch may be faulty. If it would be something after this switch there should be a difference when the unit is switched on or off, which is not the case in this special case.:scratch2:

 

[lixaudio]

Remember Yam A960 with bad suppressor condensers on switch? They were exploding (and still are). First I suggest you to take off, for now, those two.
You're using normal power, no transformer balanced dual 115V anywhere, right?
I once (no, wait more than once) had 117V on my PA system - everywhere. The broadcast truck had balanced power, they connected their signals to my splitters, with grounds on and did not connect their main ground anywhere. I could remain there, not only few miliamperes. So for now, do not connect anything on inputs. Still having problems? Have you used any contact sprays on switches recently?

LIX

 

[Dr. Ear]

Yes I use normal household power, no transformers. And yes, I have replaced those suppressor caps in the power supply, in one of my B-6 C404 was already detonated when I got the amp from a not so honest ebayer. I have replaced all caps and all power transistors, the triac, the optocoupler, and much more.
The electric installation is my house is ancient, my electrician calls it a mild nightmare. But if this was the reason, why does it appear only with the B-6?

 

[lixaudio]

I was checking the schematics - with european model there's no way to have anything on the chassis, because the switch disconnects everything, not so with other non european models, they are constantly connected to some point. Or yours B6 are modified for euro use, or the new suppressors are leaking too or some liquid is making fools of both of us. I don't see any other explanation. Or maybe there is a problem because of its pyramid shape, strange things happen under that shape )

 

[MOPAR3]

It seems to be just logical to me that the power switch may be faulty. If it would be something after this switch there should be a difference when the unit is switched on or off, which is not the case in this special case.:scratch2:

I think your on the right track the switch must be shorting to the chassis some how.

 

[Dr. Ear]

@lixaudio: ja, maybe your're right. The pyramid collects all the electrosmog in my environment and it gets more powerful with every day.
@MOPAR3: I was an the track but you confirmed me to remove the power switch form the chassis with wires connected and the voltage on chassis dropped to 55V. I don't think I can get a new switch for the old lady :tears:

 

[MOPAR3]

I think it should be closer to zero. Is there some wiring that is chaffed or pinched or something. I would be concerned about this If the chassis became hot with current potential and you touched it

 

[Dr. Ear]

No, nothing is pinched or damaged. The power chord is *new*, one is shielded and one is unshielded, make no difference. The power switch works perfectly, with my DMM I cannot measure any short when in position "off". The suppressor caps are new in one amplifier, makes no difference
My only remaining explanation is inductance due to the close proximity of the switch and other components (3-5 mm) on the main pcb. In fact, the power sw. sits in a small cut out of the main pcb and is surrounded by a number of components.