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RE: The Monster Amp

This is more or less a copy of a reply I already gave to Paul: I am a grumpy, old, retired tech guy with arthritis. I don't know a whole lot but I do know a bit about electronics and I can tell you the following. This Sansui (along with millions of other items that have only 2-core mains cables) is double insulated. At no point does either of the two mains cables make any contact with earth/ground either inside or outside the amp. If this happened the person using it would be electrocuted. The 2-core mains cable enters the amp and goes via the On/Off switch straight to the primary of the mains transformer. Sometimes both wires go to the On/Off switch, sometimes only one wire is switched and the other is effectively direct to the transformer. Sometimes there are a few other components before the mains primary - but NEVER is it grounded. The mains voltage inside the amp is 'floating'. It does not care which way round it's connected. It goes into the primary winding of the mains transformer as mains AC volts. Then... out of the secondary winding is produced much lower AC volts, which is then rectified into a usable DC volts.

I do have a diagram for this, and many other vintage amps I've had the pleasure of knowing over the years. I can tell you specifically that the AC on the Sansui EXPORT model (Made for the US and other countries) has the On/Off with only one pole switched. Across the switch is a spark suppressor. The EXPORT model also has 3 non-polarized AC outlets on the rear panel (2 are permanently live, the other is switched). When the amp is switched-on the voltage from one pole is connected directly to one side of the transformer primary. The other pole goes via a fuse (7A for 100/120 volts or 3.5A for 220/240 volts) to the voltage selector switch. The position of the voltage selector switch determines which of the windings on the transformer primary that this other pole is connected to. The transformer secondary windings will then produce 35 volts AC on either side of a zero volts center tap. From there the AC volts is rectified to DC volts and then the nitty-gritty of amplification begins. I also checked out the other variants that Sansui made for Europe. I can tell you that the version supplied for the UK was essentially the same but without the 3 AC outlets on the rear, the voltage was switchable 220-240 volts, the fuse was 2.5A, both poles of the mains were switched and each side had its own separate spark suppressor.

Which way round the mains plug is connected will not make the slightest difference to the operation or safety of the amp or the user. These were made with a moulded 2-pin non-polarized mains plug. The manufacturer made no indication of which way round the plug should be inserted because is simply doesn't matter.

The Russian guy originally asked a very simple question: He basically asked which way round the 2-core mains cable should be connected to his mains outlet. The correct answer now - is the same as it was back in the 70's. "No, it doesn't matter which way round it's connected".

This Russian guy was most likely terrified with replies talking about "get it the wrong way and it could be dangerous", "need to understand a schematic to be safe", "smoke", "beer possibly spilled inside", "couldn't have been tested because no mains plug", "strange voltage from another part of the planet", "death capacitors", etc...etc. Well, maybe he's already visited his local Wal-Mart and bought some modern all-in-one crap in a plastic box with lots of flashing lights. If he has it's a real shame because the 517 is a beauty.


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  • RE: The Monster Amp - kendodsdadsdogsdead 13:08:15 11/03/14 (1)

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