DIY transformers 600ohm:600ohm 1:1

[paulrichards7]

AFter coming across the latest Tape op, Ive managed to find a couple of Lundahl transofmers 1517s I think which im gonna make a box for
However here in the UK its kinda hard to get hold of vintage ones
I came across this article about winding your own
http://www.w6nbc.com/articles/EE0576transformers.pdf
Now the math seems ok if your gonna need step up or down, but what about 1:1 turns ratio?
Does anyone have any idea roughly how many turns and wire thickness to make a 600ohm 1:1?
Seems like the most expensive 1:1 transformers do their best to avoid distortion, as that seems like we're after coloration, Im gonna try and make some cheap ones
lol
Any help appreciated as I have absolutely no idea about electronics
Hope this will help others also
Paul

[Kevin S]

Your in the UK which gives you some good options.

Carnhill's from audio maintenance limited
Sowters
Lundahls
Hauff from Germany

I'd order up some of the ones from Audio Maintenance.

Kaz

[lassoharp]

AFter coming across the latest Tape op, Ive managed to find a couple of Lundahl transofmers 1517s I think which im gonna make a box for
However here in the UK its kinda hard to get hold of vintage ones
I came across this article about winding your own
http://www.w6nbc.com/articles/EE0576transformers.pdf
Now the math seems ok if your gonna need step up or down, but what about 1:1 turns ratio?
Does anyone have any idea roughly how many turns and wire thickness to make a 600ohm 1:1?
Seems like the most expensive 1:1 transformers do their best to avoid distortion, as that seems like we're after coloration, Im gonna try and make some cheap ones
lol
Any help appreciated as I have absolutely no idea about electronics
Hope this will help others also
Paul

Hi Paul

If you're looking to roll your own you might do well to pick up some 'blown' (open coil) transformers on the cheap and just use the cores/cases.

I assume you are looking for some tonal alterations - otherwise there's really no point unless you need electronic isolation between the circuits.

I have seen a number of Parmeko and Gardners iron come up at reasonable prices over at Prodigy fairly recently. An alternative would be to search up some interstage types. Steer clear of any UTC or Triad potted units as these will be just as pricey as the 600:600's have now unfortunately become aided in part by the aformentioned copy. What you want to look for are the non potted American units. These stay well below the radar most of the time and will give you some flavor and step up/down as well.

[paulrichards7]

Thanks for the info
Paul

[The Scum]

That's a sorta cool article.

As far as rewinding to make 600:600 transformers, there's nothing too tough about it. For every turn of primary you put on, put on a turn of secondary. It's easier if you buy two spools of winding wire, and wind both the primary and secondary interleaved at the same time.

The more turns you wind, the better the low end response will be.

If you want to be really geeky about it, wind as described above, assemble the transformer, and bench-test it. You'll find that the output is a tiny bit weaker than the input. You could add a few more turns of secondary to make up for the loss...making a 1:1.01 transformer, for instance.

Similarly, if you can find a power transformer with dual primaries (made for international-friendly 120 or 240 V reconfiguration), you can use one of the primaries as a primary, and the other as a secondary (and totally ignore the true secondaries). It'll work.

If you want cheap and colored, remove the little sugarcube transformers from old modems.

[paulrichards7]

Wow, cool thanks The scum
As of turns approx and wire diameter do you have any idea?
I understand that they would both have same amount of turns(although a few more turns on secondary for a bit of gain make up, is awesome)but is that something like 50 or 100?
As of winding them in general, Im not too sure there im getting the tapping points?(whether + - or ground for primary and secondary)
Do I tap the start of each wind and then the end of each wind?
And then say I want a ground, do I add a wire between primary-tape-ground wire-tape-secondary wire?
Also for winding both at same time, how does that work?
Thanks for any help in advance
Paul

[paulrichards7]

ps The Scum, as of those sugar cube modem types
I just got a load of them from the local car boot sale
Now for those I think I understand that they are 1:1 for isolation on telephone calls
The stats that Ive pulled up for them state the frequency response is roughly 300hz-5000hz
Now is that where they ideally operate,or will they operate between 20hz-20000hz, but not very linearly at all?
Thanks
Paul

[The Scum]

The stats that Ive pulled up for them state the frequency response is roughly 300hz-5000hz
Now is that where they ideally operate,or will they operate between 20hz-20000hz, but not very linearly at all?

The telephone system is spec'd for 300-5K, so that's what those little transformers are rated at. Actual performance may be somewhat better than that. I wouldn't be surprised by 100 Hz - 10KHz.

With their tiny cores, thay'll saturate easily, and get nice and fuzzy if you hit them very hard.

As of turns approx and wire diameter do you have any idea?

It depends on the specs of the core...if you just want to fool around with this, wind as much wire as you can afford, or will fit on the bobbin. 24 or 26 ga lacquered magnet wire might be a reasonable starting point - thick enough to not be too delicate, but thin enough to be easy to work with. Whatever's handy, really. 35 ga is a fragile angelhair nightmare...12 ga is very hard to wind.

If you want to do more than fool around, start by carefully reading the article you posted, and come to terms with the math there. Then do some research on core parameters and what A sub L means.

And then say I want a ground, do I add a wire between primary-tape-ground wire-tape-secondary wire?

What exactly would you be grounding?

Also for winding both at same time, how does that work?

Take two spools with winding wire on them, and the empty transformer bobbin. Run the strand from each spool to the bobbin, and tape it down, leaving maybe a 6" tail...enough to have some to work with once you've got the core reassembled. Then start rotating the bobbin. Each rotation will add one wrap from each of the spools. You can make a little jig with an axle to hold the spools next to each other, and a crank so you can turn the bobbin.

If you want to be scientific, count the number of turns you put on as you go. But I'm assuming it's pretty noncritical. If this transformer were critical, you'd simply call Jensen.

When the bobbin is full, snip the wires with another 6". Reassemble the core. If the bobbin has lugs for the connections, solder the tails to them. You can strip the lacquer off the magnet wire with sandpaper, or hold it over an open flame.

[paulrichards7]

Thanks so much The Scum, thats awesome

What exactly would you be grounding?

If I was using them in line with a positive, negative and groung wire(which would usually be connected to xlr or 1/4 balanced jack)would i just not connect the ground wire?

As stated Im going for color(saturation), so all of your advice seems perfect for that outcome

Thanks once again
Paul