Paying for stupid mistake.

[sangram]

Hi.

A sad story.

On my last trip out of town I picked up an HK PM665. It was fantastic.

I brought home and plugged it in. It blew fuses.

I figured out afterward that the amp was designed for 110 and not 220. No, I hadn't checked, I had assumed.

Fortunately the amp had two transformers and PSUs. Connected the trafos in series, and it was up and running.

Or so I thought.

The right channel is feeding about 15VDC into the speakers. The output devices seem fine, it's just blowing up my woofers. the left channel is delivering pristine audio.

I need to do a circuit trace, and I'm looking desperately for a schematic of the power amp section. The construction is similar to a truck, so pulling parts is not easy at all.

Anybody with any experience of this amp please do post.

Sang.

[yeti]

If the both transformers are supplying the both channels separatly,you cant wire the primaries in series.
The channel with higher output will cause his transformer to draw more current, resulting in a lower impedance in his primary winding.
This means that the other transformer has a higher voltage at his input causing overvoltage in the secondary.Almost sure the result will be smoking parts.
You can go two ways:
1.)Get a stepdown transformer 220 > 110 Volts, this can be a type that is not mains isolated (economy - type)
2.) You can wire the primaries in series and both secondaries in parallel,the easiest way will be connecting +Vb of the left channel with +Vb of the right channel and -Vb left with -Vb right, this automatically balances out the differences between the transformers.
The drawback will be that the channels are not separated any longer.

[Circlotron]

You could use a fairly smallauto transformer with a single 220v winding that has a centre tap. Put your two power trannies in series, (*HATE* that word "trafos") with the junction of the two primaries to the CT of of the auto tranny. The load on the autotranny is only the *difference* of the other two trannies at any given moment.

[sangram]

Originally posted by Circlotron
You could use a fairly smallauto transformer with a single 220v winding that has a centre tap. Put your two power trannies in series, (*HATE* that word "trafos") with the junction of the two primaries to the CT of of the auto tranny. The load on the autotranny is only the *difference* of the other two trannies at any given moment.

Circlotron

Did not understand.

Are the two ends of the auto*TRANNY* connected to the mains too? along with the two ends of the two 110 V trannies?

In which case it is one 220 V tranny connected in parallel with 2 110 V trannies (assume it is like two 220VCT primaries?) across the mains, with the two 'center taps' together?

Thanks

Sang

[Circlotron]

You got it!

[jean-paul]

What's wrong with the word "trafos" ? When I read trannies I think of grannies !

German/Dutch speakers will abbreviate the word transformer ( in German/Dutch: transformator ) to "trafo". Because of English/American influence people think this sounds to "hard" and today they soften it to the word "travo". This is wrong because a "travo" means a transvestite which is really something else I've been told.
Unfortunately a lot of words are changed because they have to be soft like in English. That is supposed to sound better so we adapt ( well, not all of us ). I don't understand why we have to change our language because of an other language !?!?! We even eat a "slice" of pizza nowadays instead of a "stuk". You can probably imagine what a monster our language is becoming through the years. Some kind of mixture that is very difficult to teach to children. All this because English is THE worldlanguage so we are taught. No wonder nationalistic parties are winning the elections the last years.

First I thought the French were very stubborn with their language. On the French national radio they practically only play French music ( I think it is even forbidden to play less than 70 % French music). Names of companies have to be French. I remember that they didn't even like the name Alcatel because it wasn't French enough. Now I've learned they are right. They will speak French after a hundred years from now, we will speak English for sure.

So let's accept both words: trafo and tranny.

Same goes for capacitor and condenser. Although a condenser is a part of a refrigerator the Japanese prefer to call capacitors condensers. I can live with that.

[Circlotron]

Originally posted by jean-paul
We even eat a "slice" of pizza nowadays instead of a "stuk".

Yeah, that's really strange, especially when you consider it isn't really a slice but a sector!

"Same goes for capacitor and condenser. Although a condenser is a part of a refrigerator the Japanese prefer to call capacitors condensers. I can live with that."

Condensor is an old "steam-age" word. Car engines are full of 19th century engineering words like manifold, flywheel, rich, lean, advance, retard, dynamo, radiator, battery, crank etc. A real time capsule of old words.

[jean-paul]

Yeah, that's really strange, especially when you consider it isn't really a slice but a sector!

Really ? So they even adapted the wrong word !?!? Ha ha !

Those companies are American and they offer : a slice of real American pizza ! I like that one too, it's like the Italians invented the hamburger.


BTW I learnt the word "generator" for "dynamo" as the latter wasn't supposed to be an English word !?! The German word "Lichtmaschine" ( lightmachine ) is fantastic and simply accurate at the same time.

Condensor is an old "steam-age" word. Car engines are full of 19th century engineering words like manifold, flywheel, rich, lean, advance, retard, dynamo, radiator, battery, crank etc. A real time capsule of old words.

The Japanese say "condenser", not "condensor". But I like the phrase about the time capsule. Those words remind one of the early age of technics and have a certain "mystique" ( might not be an English word ) around them.

Sorry for threadjacking, please back to the subject ( if necessary ).

[sangram]

Yes, yes, back on topic please.

I will now call it a transformer. I will have to get one made specially. Not a major issue.

Any clues to which parts of the circuit I should be looking at to solve the DC output problem? Any idea where I can get my hands on a schematic?

Thanks

[jean-paul]

Hi Sangram,

Did you check the transformators if they maybe have 230 V primaries too ? Most brands use only one type of transformer and rewire for the specific country. Don't know about HK.

I guess your one or both powertransistors broke down. You really need a schematic.