100v MSP5A in UK with 240v

[valerianroot]

pulled the trigger on the transformers, they're working but gotta low level 50/60hz hum. Only audible when nothings playing..

[tpad]

If you're in the UK, I doubt you are hearing any 60 Hz hum! In any case, you might want to look and see if/how the secondary winding is grounded. You may have some sort of ground interaction that is causing the -50 Hz- hum.

[valerianroot]

yeah silly moment with the 60hz reference.

They have japanese (U.S looking) ac plugs without an earth (two prong). I'll have a look at the transformer inside again, and see if changing outlets changes anything. But I did assume there were going to be draw backs with speakers bought for 10% of retail.

Cheers for your help though

[LeeYoo]

Hi.
Do you also hear this low level hum when no leads are plugged into the inputs.
Hum in the sound (not a mechanical buzz from the transformer) could also come from the way you have connected them to your other gear.

Maybe the power transformer can be simply rewired/switched to 230volt.
Post pictures if you're not sure.
Leo..

[valerianroot]

Yeah hums with nothing plugged in, hum remains the same volume no matter what level you set them to. So once you get past a certain volume of music playing the hum is no longer audible. So they are usable.

I haven't got time to open them up right now but I'll try and take some pictures tomorrow. To me (this might be stupid so be warned) it sounds like the actual transformers are making the noise and the hum isn't in the audio path.


Thanks again

[valerianroot]

Here's those photo's you mentioned. Did some reading yesterday. I guess my options are, modify the existing transformers inside the monitors; buy a better step down; or replace the internal transformers. I could see if yamaha have anything. If it starts to get expensive I'd rather just buy something new tbh though.

[LeeYoo]

Hi valerianroot.
Looked at the pictures and I can see only two primary wires.
So not possible to rewire for 240volt.
Cheapest option without working out transformer voltages and soldering would be a stepdown transformer.
You can run TWO speakers from ONE stepdown transformer with a suitable US double plug or multibox. 250watt total would be OK.
The hum from the transformer could be voltage related, but I think it's more that that.
Mechanical transformer buzz is quite common.
You could try to fixing this by "floating" the transformer on rubber grommets.
Leo..

[valerianroot]

Ah cheers LeeYoo, sorry about the thread not making much sense. Might have a tidy later and throw some links in for some stuff I've read over the last couple of days.

After using the speakers a bit with the cheap step downs I bought, it's definitely mechanical buzz from the transformers and not a hum coming from the speakers. I'll give the grommets a go, and if that doesn't help; I may end up turning them into a project and buy some different speakers to use.

Thanks again for all your help.

[LeeYoo]

Hi.
Try unscrewing the transformer and resting it onto e.g. a piece of foam first.
My guess is that those transformers are +/- 18-0-18 volt, +/-2Amp.
Maybe you can find the diagram online.
Or measure the AC voltage on the two red wires.
Easy to find a replacements for 240AC.
Leo..

[CZ101]

Hey Valerianroot out of curiosity what op amp and/or chip amp(s) are in there? I can't quite make it out in the photos...

[White Falcon]

Originally Posted by CZ101

Hey Valerianroot out of curiosity what op amp and/or chip amp(s) are in there? I can't quite make it out in the photos...

+1

I love these speakers, but things can always be upgraded...

[valerianroot]

Alright bear with me. I'm not sure what the opamps/chipamps look like so I've taken some pretty pictures of what I reckon looks important. Am I right in thinking it's the pair of black rectangles next to the big blue box that's important?

Maybe I should do a course?

I'll try taking the transformer out and try it on foam tomorrow.

[LeeYoo]

The 4560 is the pre-amp and crossover filter.
The two black flat things are voltage regulators for the preamp. 79M15= -15volt/0.5Amp
The other one must be a 78M15 (+15volt).
The blue box is a relay that disconnects the speakers during startup/shutdown etc., to prevent pops.
The two power amps most be under or next to the board on a heatsink.
I can see two rows of pins on the side of the board.
Leo..

[valerianroot]

Haha, I was so sure. Right so I took the transformer out and put it on the foam. Wasn't expecting that to work quite so well. Why don't they put substations on foam?

The rows of pins go under where the transformer is ,and into a block about the size of a pack of rizla. (sort of) that's stuck down with that paste you use to glue hot things to heatsinks. I can't seem to remove the plate under the transformer with just the four screws holding it down.

[Richard Crowley]

Originally Posted by valerianroot

The rows of pins go under where the transformer is ,and into a block about the size of a pack of rizla. (sort of)

That is the amplifier module.

that's stuck down with that paste you use to glue hot things to heatsinks.

It is typically not "glue", it is just heat-transfer compound that remains paste to allow replacing the module if necessary.

[CZ101]

Thanks for posting those pics Valerianroot!

[White Falcon]

Yeah, thanks!