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How I made my SMU

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Bansci:

--- Quote from: jaromir on December 25, 2021, 09:31:15 pm ---Please find...

--- End quote ---
Thank you for such a comprehensive and well illustrated reply!

A winding machine does indeed seem like a nesscessity, six hours of winding sounds very frustrating. I'm trying to find a local (UK) transformer EI lamination supplier but I've already ordered the NK-1 you speak of. I'm really inspired to try winding myself and to learn it so thank you again. The split bobbin seems like a nice way to separate the shields!

Roehrenonkel:
Hi Bansci and all,

when winding a transformer yourself keep in mind not to build a short-circuit with the shield-foil.
Start and end of the foil can be lead to the outside (for test purposes), but never connected together.
Also i would highly recomend vacuum-impregnation/potting.
 
And for the very best noise-reduction run it over an UPS (sine-wave of course),
like the hardcore-hifi-freaks. ;-)))

Will post my ideas regarding the output-connectors in Daves SMU-thread.

cnt:
wow this is fantastic.  I know its never the point but what do you think the BOM cost was?

Bansci:
The original design this is based off has a BOM goal of $350.
https://www.djerickson.com/diy_smu/

Bansci:
Jaromir, I've found a UK supplier of split bobbins, EI inserts, and I'm just putting together my order. It was http://www.ascocomponents.co.uk/, who have very reasonable prices and small order quantities, you just have to email to get them. My winding machine has also arrived!

I had a few questions I was hoping you'd help me with.

(1) How did you avoid forming a shorted turn with your shielding? Did you insert paper to prevent a short while overlapping your copper tape, or did you leave a gap?

(2) I plan to use kapton as insulation. Did you do this between windings and shields? Paranoid I can see isolation being needed everywhere, but actually I think we're nowhere near the enamel breakdown voltages...

(2) I've seen this video on YouTube where the guy pots the transformer using bees wax
https://youtu.be/K4VcmJIoNBA?t=1174
I think he's winding a audio output/input transformer though.
Did you pot your mains transformer? I'm tempted not to do this as I'm worried about it melting, but perhaps my transformer shouldn't get that hot anyway.

Thanks again for all the detail you gave, I'm much more confident about buying/designing this transformer now and I'm really looking forward to developing this new skill.

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