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UK to US step down Transformers and other things.

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Re: UK to US step down Transformers and other things.

Postby Moroccomoose » Thu Apr 16, 2020 8:18 pm

All great stuff, thanks chaps! If the rewiring of the internal transformer taps doesn't happen, I'll probably go for the one Trevor posted. It's the 100W version of the one I have. (The one I have is 45W) so, plenty of headroom.

All the screws are safety screws on the wart are like a slotted head but the slot doesn't run right across, so I'd need a notched screw driver. So bolt tightening is tricky.

Stu.
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Re: UK to US step down Transformers and other things.

Postby ef37a » Thu Apr 16, 2020 9:44 pm

Folderol wrote:Sometimes it can be as simple as tightening the bolts!

Indeed. There were inductors in the early colour TVs that used to drive a tiny few customers potty, mainly young women. The only material approved for dipping them was PVA glue so we had to de solder the culprit, soak it in glue then let it dry overnight.

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Re: UK to US step down Transformers and other things.

Postby Folderol » Thu Apr 16, 2020 10:22 pm

I don't remember that problem, but I do remember the frame output transformers that were held down with a tab one end of the clamp that went into a slot in the chassis and a single self tapping screw the other end. One of the engineers used to 'fix' the buzz by undoing the screw, slipping a large washer under the transformer then doing the screw up again :roll:
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Re: UK to US step down Transformers and other things.

Postby N i g e l » Fri Apr 17, 2020 1:10 am

ef37a wrote:
Folderol wrote:Sometimes it can be as simple as tightening the bolts!

used to drive a tiny few customers potty, mainly young women.
Dave.

Yes indeed, I was never potty but I could tell when the TV in the house was on. Somthing to do with ~16kHz scan rate coil.


Ahhhhhhh, 16 kHz, those were the days, endless summers,,,,,,,,,,,,
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Re: UK to US step down Transformers and other things.

Postby ef37a » Fri Apr 17, 2020 7:35 am

15,625 Hz 'EKtually Nigel!

Gave me considerable problems in the field because the distraught lady of the house would think I was being impudent when I told her that I could not hear it, even at age thirtyish my top end was going.

This was not much of a problem with the old 405 lines sets because there was only one line frequency inductor the line OP transformer (you did get 'singing scan coils' but very rarely) even though the frequency was a much more audible 10,125Hz because said traff' was usually in can and scanning power was much lower. Plus, cabinets were made of 3/8" ply!

The rot set in with 'all on PCB 'construction and <3mm plastic cabinets.

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Re: UK to US step down Transformers and other things.

Postby Moroccomoose » Sat Jun 13, 2020 12:45 am

OK Chaps,

I've been doing a service on my DS-8, Full strip down of the keyboard assembly and 30 years of dust removal. As part of the strip down, I have the power supply out and looking at the transformer. I think, if I only need to move the one wire, I'm gonna do this conversion. So I thought I'd just check before I heat up the soldering iron...

If I align the transformer to the schematic, the mains side appears exactly as it would suggest for being configured to 117V. ie Pin 6 and pin 3 and the orientation matches between schematic and the physical part. On the output side, the wires are inverted, the two blues at the bottom with the red-black-red above when compared to the schematic and the pins are labelled 7-13 o the physical part rather than another set of 1-6 per the schematic. (See page 19 in the link)

https://www.synthxl.com/wp-content/uploads/2018/04/korg-ds-8-service-manual.pdf

Is the only thing I need to do is move the tapping wire, currently on the 117 pin 3 to pin 1 for 240v?

This is a photo of the power card.

https://1drv.ms/u/s!ApHK3Zf8zN6Ej-Ru8JSqYj8liITXbQ

Cheers,

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Re: UK to US step down Transformers and other things.

Postby ef37a » Sat Jun 13, 2020 1:42 am

Yes Stu, it looks as though you do just need to move the live wire, meter it through to check, to the 240V tap. It is usual to fit a mains input fuse of about half the rating of that for 117V but for that relatively low power circuit probably not required.

I am rather surprised to see the earth tag on the IEC mains connector is not taken to chassis? I can only assume the transformer is rated as class 2? You say the device is 30 years old? I would suggest you have it PAT tested.

Thirty years ago imports from the states were not up to modern safety practice. Many here will recall the 'Death Cap' fitted to many a guitar amplifier!

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Re: UK to US step down Transformers and other things.

Postby Folderol » Sat Jun 13, 2020 8:07 am

The Good:
Surprisingly detailed manual.

The Bad:
That floating chassis. If the PSU is double insulated, it should say so somewhere on the synth (or have the square in square symbol). Without that it would fail a PAT test immediately for having a disconnected earth!
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Re: UK to US step down Transformers and other things.

Postby Moroccomoose » Sat Jun 13, 2020 8:46 am

The IEC connector is an earlier mod. The original connector was one of those (American I think) with the vertical slots. It was awful, the cable was far too easily pulled out. So the original was a 2 pin, no earth. If you think it is prudent, I could put an earth from chassis to the IEC earth.
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Re: UK to US step down Transformers and other things.

Postby Folderol » Sat Jun 13, 2020 10:23 am

Ah! I wondered if that had been done. Personally, I would wire that incoming earth to the chassis. The received wisdom is that you should wire to two different points if bolting - in case a bolt works loose - but that may be overkill.

The only possible issue might be earth loops if you are connecting through to other kit, but the standard isolation techniques would deal with that, and I'd rather have that than risk safety.
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Re: UK to US step down Transformers and other things.

Postby James Perrett » Sat Jun 13, 2020 2:09 pm

Moroccomoose wrote:The IEC connector is an earlier mod. The original connector was one of those (American I think) with the vertical slots. It was awful, the cable was far too easily pulled out. So the original was a 2 pin, no earth. If you think it is prudent, I could put an earth from chassis to the IEC earth.

That's interesting because I thought the soldering didn't look professionally done on that connector. I'd also suggest sleeving around the connections too (exposed mains pins always makes me worried).
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Re: UK to US step down Transformers and other things.

Postby ef37a » Sat Jun 13, 2020 10:20 pm

James Perrett wrote:
Moroccomoose wrote:The IEC connector is an earlier mod. The original connector was one of those (American I think) with the vertical slots. It was awful, the cable was far too easily pulled out. So the original was a 2 pin, no earth. If you think it is prudent, I could put an earth from chassis to the IEC earth.

That's interesting because I thought the soldering didn't look professionally done on that connector. I'd also suggest sleeving around the connections too (exposed mains pins always makes me worried).

Me too James. No matter the class of gear I always think it is very unprofessional not to sleeve and otherwise insulate all mains connection. There is no way you can make the internals of mains powered kit totally idiot proof, especially HV valve gear but a bit of thought can make it difficult to get a shock.

IIRC the mains earth must be taken to a dedicated bolt, nut, washer which must not be used to secure anything else.

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Re: UK to US step down Transformers and other things.

Postby Moroccomoose » Sun Jun 14, 2020 12:15 am

Hi folks, thanks for looking out for me and helping me to not get zapped. I definitely fall into the category of'Not a complete thicket, but do know enough to be dangerous '! So all your comments and observations are well received.

The whole synth is completely dismantled now and had a thorough dusting. The keys are clean and the felts re fluffed.

All the PCBs are all out, but still held together by their looms. Even still, I have a fair few connectors to reconnect, so I'm quite pleased to have the service manual.

I have done the transformer mod, but not tested.
I found the square in a square symbol so to that end I am happy to maintain the original design intent and not add the new earth.
I accept the point about sleaving, so that is now on the shopping list. I'll have a go at tidying the connector solder and sleaving it.

If I can get the sleaving, I should be able to have it up and running by mid week. All being well, I shall look forward to the next one synth challenge!
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Re: UK to US step down Transformers and other things.

Postby Hugh Robjohns » Sun Jun 14, 2020 1:26 pm

If you're going to have to desolder the chassis plug anyway to fit the sleeving, I'd replace the three-pin C14 plug with a C18 two-pin one. (A Shurtler C8 fig-8 type might have been better, but wouldn't fit the existing hole).

There's a screw in C18 type panel plug here: (ignore the picture, it really does only have two pins!)

https://uk.rs-online.com/web/p/iec-connectors/8702448/

the data sheet for it is here: https://docs.rs-online.com/a4c8/0900766b814421bc.pdf

And there's an insulating boot to slip over the whole plug here:

https://uk.rs-online.com/web/p/mains-connector-accessories/5260724/

I find these boots neater and easier than insulating the individual wires... although you can do that too, of course!
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Re: UK to US step down Transformers and other things.

Postby Moroccomoose » Sun Jun 14, 2020 2:12 pm

Thanks Hugh,

That looks ideal.

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