transformer build thread

[nige2000]

im not sure if i changed the soekris output from the stated stock "Single ended 1.4V RMS, Zout 640R" when i used 3.3 v for the r2r instead of stock 4v

Is the Soekris internally balanced? If so then a trafo which converted from balanced to unbalanced and adjusted the output level to suit whatever amp you're using would be ideal. I'd expect reducing the Vref to 3.3V from 4V would reduce the output level by under 2dB, not particularly noticeable.

its not balanced

i suppose i should be looking at a 1.5v rms capable transformer for this app?

Would be right if the Soekris is internally just one DAC element per channel.

is most dac chips circa 2vrms? meaning they will require at least that capability?

Most of the modern ones are like that, from ES9023 and onward. Other older ones have balanced outs they'd be better off having a transformer which uses the balanced capability which might be more than 2V in total.

maybe if you did a an example solutions based on 2v rms

Good idea, I'll see if I can work up a worked example. Tell me what the narrowest wire you're comfortable using is and I can choose a big enough core to accommodate that.

hard to know i dont think i ever handled wire much less than 0.2mm
whats practical to start with?

loads of them ebay transformers on aliexpress too
and a couple different ones too

[jkeny]

primary is on the inside aint it?
if it is cant do anything with it

confused now..... on a step down is the secondary have more windings or less?

out of curiosity we could order them ebay ones

With a line level trafo, there's nothing to stop us turning the trafo around & using it's secondary windings as the primary input or is there? Wouldn't want to do this with a power transformer though :)

[abraxalito]

hard to know i dont think i ever handled wire much less than 0.2mm
whats practical to start with?

I'd suggest somewhere between 0.1 and 0.2mm, ideally stuff which is self-fluxing meaning you don't need to strip it, the insulation will melt when soldered. Stripping enamelled wire below 0.2mm is a PITA as its too easy to break it.

[nige2000]

primary is on the inside aint it?
if it is cant do anything with it

confused now..... on a step down is the secondary have more windings or less?

out of curiosity we could order them ebay ones

With a line level trafo, there's nothing to stop us turning the trafo around & using it's secondary windings as the primary input. Wouldn't want to do this with a power transformer though :)

found it secondary winding is less on step down

[nige2000]

hard to know i dont think i ever handled wire much less than 0.2mm
whats practical to start with?

I'd suggest somewhere between 0.1 and 0.2mm, ideally stuff which is self-fluxing meaning you don't need to strip it, the insulation will melt when soldered. Stripping enamelled wire below 0.2mm is a PITA as its too easy to break it.

i can imagine.,..

where can we get the materials over here?

[abraxalito]

I found a seller on Aliexpress though I don't have a clue whether they deliver to you guys at a reasonable rate : https://www.aliexpress.com/item/0-14mm- ... 101ea04b25

Polyurethane is I believe the solderable kind of insulation.

[nige2000]

http://ie.farnell.com/pro-power/rrp-g-1 ... /dp/146183
Delivery usually takes about a month from china
What about bobbins etc

[jkeny]

@Nige - I thought the Soekris was internally balanced - for each channel isn't there a bank of Rs for positive going signal & a bank of Rs for negative - maybe these signals are not the inverse of each other & so not balanced?

@Richard - Doesn't the wire diameter have a bearing on the transformer behaviour apart from core size but maybe not so important for these low signal handling function?

[jkeny]

Did a quick search on Taobao for trafos like your eBay ones, found these -

https://item.taobao.com/item.htm?spm=a2 ... =13#detail

Do you think they look similar enough? Same EI14 size and they say they're 600ohms. If so I'll order some up as they're stupid cheap here (like 0.15euro) and reverse engineer one.

My worry is that the laminations will be held together by varnish so almost impossible to disassemble.... but it'll be a cheap experiment nevertheless.

Yes, they look like them & have the same description as is used on ebay.
Much appreciate you buying some for experimentation - if they are dipped in varnish they will be impossible to disassemble even unwinding some turns will be impossible.

[nige2000]

@Nige - I thought the Soekris was internally balanced - for each channel isn't there a bank of Rs for positive going signal & a bank of Rs for negative - maybe these signals are not the inverse of each other & so not balanced?

not certain but at a glance and very primitive understanding there seems to be two banks of r's a pos and neg signal which are merged at the end of the ladder to provide the 1.4vrms
ive no idea what would happen if they were separated and used as pos and neg
maybe it dont work that way?

this is how they got the stock bal buffer out without a v- signal