Hi It's me again. Sorry for bothering you on this cold tuesday morning, i have a problem. I read a post about someone who purchased a china amp that kept breaking down. After some troubleshooting he figured this was because the secondary voltage was too high.
In china the ac mains voltage is 220v, and here in Britain it is 240v. He claims to have lowered the mains voltage the transformer sees to 220v by hooking up a 20v transformer with the stock amp transformer.
But I can’t shed any light of how exactly this was done. Do you have any idea, any suggestions
In china the ac mains voltage is 220v, and here in Britain it is 240v. He claims to have lowered the mains voltage the transformer sees to 220v by hooking up a 20v transformer with the stock amp transformer.
But I can’t shed any light of how exactly this was done. Do you have any idea, any suggestions
It's probably a bad and dangerous idea, but maybe the 20 V transformer primary was connected to the 240 V and the secondary 20 V were connected "out of phase" in series with the amp transformer primary, theoretically reducing the voltage of "amp primary" to 220 V.
But again: bad and dangerous idea.
But again: bad and dangerous idea.
240 to 220 is a very small difference, less than 10%, not enough to turn a good stable amp into a suicidal machine.
Either the design/build is marginal, to put it mildly, or there is some other problema we don't know: instability, oscillation, poor load, poor grounding of layout, poor heatsinking, etc.
In any case, what is happening to you?
You only mention something you read, happening to someone else.
If design is marginal, I would lower rails by 20% or so, to make any difference.
Anything less, not worth it.
Just don't.
Only cases where it's worth it is where you need to salvage some old or incompatible stuff: Japan Market stuff designed for 100V mains and used in 120 to 127V Countries where difference is gross and you can't replace a complex multi secondary transformer, and frail old 40s 50s Guitar Tube amps designed for 110/112 V mains, same thing.
But kludgy not worth it on modern amps.
As a side note: one Country where problem is widespread enough to merit a dedicated solution is Brazil.
Huge Japanese origin population (> 1 million), it's very common for Nisei (second generation) kids to travel to Japan for 1 year after High School.
They work at some modern Factory for good salaries, and being Rock lovers, many buy their dream amplifier.... "A Marshall !!!" 😱
All nice and good, except they get the local 100V version
Which to boot does NOT have multi voltage primaries.
Fuses start popping when back in Brazil ... so much so that you can buy in Mercado Livre (Brazilian E Bay) 110 or 127V primary to 100V secondary autotransformers, go figure.
It's called a bucking transformer.
Some cheap gear are... cheap, close to the limits, so better play it safe.
Some cheap gear are... cheap, close to the limits, so better play it safe.
If in the UK an area had a mains supply of 240ac, and another area had a supply of 220v ac, how much difference in secondary voltage would that give between the two areas