API-312 output transformer 2503 style winding

Hi guys,

After my successful attempts at winding my own Neve style LO1066 output txf I thought I'd give a go some 2503 style ones for my API-312  pre amps.
I'm using  awg#32 as I have this spare onto a 25x25mm bobbin with 145 EI lams (66 of them)
I'm putting 400 turns per wind which should get me close to where I need to get.
Will update with results once done and put some audio samples up of everything.

Regards

Spence.

Not sure what 145EI lams are but the original uses 625EI lams, square stack. This is also a quadfilar wound, so you grab 4 wires and wind them at the same time, not one winding then the next, etc. 

35 AWG will give you way high DCR, you want 29, and about 300 turns or so. 

Hi Mitos,
I already spoke to CJ and he's given me some pointers and has said I should be good to hit the 1Mhz with 286 winds with awg26.
Im not wanting an exact original copy just something in the ball park for a couple of channels, this is just an experiment.
so im going to try 400 winds with awg32.
The 145 is a fair bit bigger, 25mm x 25mm bobbin. will see how they sound.

regards

Spence.

I have some awg29 so will try 300 turns and see how it comes out.

Regards

Spence.

Just thought I'd say about the AWG 32 (0.2mm) with 320 turns works out at 20ohms per winding, 40ohms in series 10ohms in parallel. Haven't tested it yet so don't know what I sounds like.

Sorry I corrected my previous posts as I'd put the wrong size!

Spence.

well, on such a large lam, you should also try larger wire. Your inductance per turn will be higher than the API so you need less turns, which means for the same inductance as the API, you'll have a half empty bobbin. Of course, you could wind more turns, which will get you more L and also more DCR, and most likely not the same performance.

As for the 320 turns giving 20 Ohm, that's due to the large lam = longer mean turn length, so more wire to make the same number of turns.  How full is the bobbin?

I'd say the bobbin is about 3/4 full, could probably get about another 200-300 winds on there before it would be a problem getting the lams on.
I was thinking about putting in a dpdt switch so I could switch between the line bal output and the txf output.

Regards

Spence.

This is getting interesting..

one of my API-312 4 channel preamps has gone down, think its the psu as all channels are faulty, gotta week off this week so will sort out some more transformers and sort it all out. once done i can then do some comparisons between the IC and the transformers.
have hopefully got some more EI m6 coming with smaller bobbins to make some accurate sized and wound versions as well.

regards

Spence.

Hi Spencer,
How is this experiment going?

I’ll be back on this very soon as I’m a bit disappointed with the line balancer output, going to try and wind a couple, already done one just need to solder on wires and wire up and test.

Have started to upgrade all my 8 x api now and remove the line balancers.
I’ve used a couple of OEP 1:2 but used them in 1:4 and sounds ok.
Will wind a few 1:3 txf and see how they compare.