A little transformer question.

[hodad]

Here's a drawing of a transformer:
http://www.wee-scottie.com/tcr/15432A.pdf

My question concerns windings 1-2 & 1-3. They apparently have the same number of turns, but 1-3 has about 6 times the DCR, What gives? Does this mean there's also likely to be a similar impedance difference between the two?

I'm sure I'm not approaching this question correctly, but any thoughts are welcome.

Tom

 

[Svart]

hmm difference in DCR but same number of turns.. I'm guessing a different wire gauge?

 

[edanderson]

this is a very interesting transformer. if you look at the DCR numbers, you can see that the 1-2 primary winding and the 6-8 secondary winding have the same DCR. so those two windings were probably wound on first, as a pair of wires (whut chu cawl "bifilar"). this also means that there should be very good coupling between the 1-2 and 6-8 winding. the 1-3 winding has a much higher DCR first because it was wound on top of those other two windings, and so each turn is a bigger loop of wire. it also may have been wound using a smaller gage wire. finally, note that the 1-4 winding is a 10:1 turns ratio with the other windings.

i would guess that this was originally used in a circuit where the 1-2 winding and the 1-3 winding were driven by different parts of the circuit, and the 1-4 winding provided feedback through the transformer. for one example of this kind of circuit, see the class A 1176 output amp, or the nearly identical 1108 preamp. i'm not saying this transformer would work in those circuits, as it doesn't seem to be gapped (able to take DC current in the primary) and the feedback winding ratio is different. but it would be a good candidate to try to work up a simple opamp lineamp with feedback through the transformer. or you could ignore the 1-3 and 1-4 windings and use it as a 1:1.

ed

 

[CJ]

the 1-3 and 1-4 winding dcr is really impedance.
never try to figure out a factory print.
Mr. Alan Hadley was just using the tri-plicity of the xfmr to gain scribling space.
why the two figures xxx/xx, thats whats gots me.

i imagine thats tri-filar, with a few turns thrown in for 10 percent N.I.B.

 

[PRR]

1-3 is a Feedback Winding, the others can carry Power.

 

[edanderson]

cj could definitely be right; the 1-2, 1-3, and 6-8 windings could be all wound at the same time (trifilar) with a smaller wire gage for 1-3 since it almost certainly is (as PRR suggests) a feedback winding. since it is being used as feedback output, keeping the DCR low isn't as important as if it were being driven by the circuit. so the wire size can be smaller to leave more room for more windings.

for an example of how those three windings could be set up with an opamp output stage, see this jensen app note:

http://www.comtran.com/as/as025.pdf

1-2 would be red - brown, 1-3 would be yellow - orange, and 6-8 would be blue - green. this transformer doesn't have an extra winding that could be paralleled like gray - violet. the R1 - R2 resistive devider sets the amount of feedback through the transformer. looks to me like C2 and R3 gives the high end rolloff at 80k that they mention.

if 1-3 is used for feedback, i'm not sure what 1-4 is for. perhaps, a lesser amount of feedback to another stage? and/or i suppose it could be a DC current balance winding, but if that were the case, i would think the transformer drawing would have some mention of DC current.

in any case, an interesting and possibly useful transformer.

ed

 

[CJ]

The 1-4 winding was probably added as an after-thought, you can tell by the way the diagram is drawn, and sure enough, if you read the notes, "1-4 added".

So he took a 1:1:1 600 ohm tri-fi jobby, and wrapped 76 turns on the outside of the winding. Not a good way to link feedback.
Peerless S-217-D has tert winding in between pri and sec for max linkage.

 

[NewYorkDave]

Not a good way to link feedback.

How come?

 

[CJ]

spaced too far from the core and inner windings.

interesting, the customer for that transformer was gauss electrophysics, David Greg, head honcho, inventor of the CD!

 

[edanderson]

[quote author="cj"]spaced too far from the core and inner windings.[/quote]

mm, see that's why i wasn't sure that the 1-3 feedback winding was wound trifilar with the 1-2 primary and 6-8 secondary. because i've seen a few transformers with the primary and secondary wound bifilar, using equal gages, but split into two windings, with the equal turns feedback winding sandwiched in between, using a smaller gage. adding another high ratio feedback winding in there isn't a problem if you do it that way.

ed

 

[CJ]

i know someone who is doing it that wy and it works ok.
not a big hair to split, and it's only a feedback winding.

if you put the feedback winding inbetween the pri and sec, you can use it like a shield if the circuit does not need feedback.

split bi-fi, that sounds a lot like some Langevin stuff i have looked at.

 

[PRR]

> spaced too far from the core and inner windings.

Will work fine bass and midrange. All the windings get soaked in the same flux.

At the top of the band, it gets under-coupled. If the feedback forces the added winding to output "flat", then the main winding will rise at the top of the band. In real life, you have accumulated treble losses; this can be a handy/cheap way to semi-compensate them.