1:2 out transformer questions!

Hi
Here is out transformer from one old very good sounding mixer.

Resistance on primary is 6 ohm and on secondary 12 ohm. Some dimensions are on pic.
Here is redrawn shematic of last stage. Out was 6db balanced (before transformer 0db)

Can I use this kind of transformers in circuit like API or similar?
Thank in advance
Duka

It will probably work fine.

Wow! Gapped C core! The only other person I know of is Bartolucci.
No need for a cap withthat gapped core. Should sound great. Wire it backwards perhaps so that the lower impedance winding is on the API opamp side.

[quote author="cjenrick"]Wow! Gapped C core! The only other person I know of is Bartolucci.
No need for a cap withthat gapped core. Should sound great. Wire it backwards perhaps so that the lower impedance winding is on the API opamp side.[/quote]

Yes gapped. You have hawks eyes!!!.
I work on that mixer 7-8 years and it really sounds very good. All transfrormers. Input mic (1:3) and line (1:1)was Beyerdynamic.
Duka

Forgive my ignorance - does a gapped core mean the core doesn't completely surround the bobbin? What are the differences?

Thanks

[quote author="dukasound"]Hi
Here is out transformer from one old very good sounding mixer.

Resistance on primary is 6 ohm and on secondary 12 ohm.
[/quote]

Looks like it's made by Zebra Industries. :grin:
Good job Stew! :thumb: :thumb: :thumb: :green: :green: :green:

Duka,

Did you measure it's actual ratio, or you base that it is 1:2 on pri/sec DC resistances?

Lets use this U-I lam as an example.



There are two ways to stack this core. One would be to alternate the lams form top to bottom, in other words, in a lap 1 core, you would lace one lam going one way, and then the next lam would come in from the opposite side. This would form an interleaving of the lams.

Or, you could have the U lams all facing on direction, and all the I bars stacked together in the other direction. This would allow you to slip a thin piece of insulation material, which is usually kraft paper or nomex or maybe some type of mylar. This would open circuit the magnetic path, which lowers the perm but allows dc to, be imposed on the core without it becoming magnetized or saturated, due to the increased perm which the gap creates.
Many times this gap is finely tuned, as in the building of pulse transformers, so that a slight rap on the core with a plastic hammer will change the inductance of the transformer. Once you find the right gap, the next difficulty is clamping down the core tight enough so that the gap does not shift at all. Some of the gaps used are very thin, like 0.001 inches or less.
In the case of that C core, banding strap is usually used to secure the core. On some of the big pulse transformers we built, we had to use three strips of 3/4 stainless steel banding strap to make sure nothing moved. We had to really torque on the strap tensioner to get a tight fit.
cj

Thanks, CJ. I have always wondered about that.

:thumb: :guinness: :sam: :guinness:

[quote="Marik"[
Duka,

Did you measure it's actual ratio, or you base that it is 1:2 on pri/sec DC resistances?[/quote]

Hi
I only measured DC resistance on pri/sec.
I know that is 1:2 ratio from documentation.
Duka

[quote author="dukasound"]Marik
Duka,
Did you measure it's actual ratio, or you base that it is 1:2 on pri/sec DC resistances?
Hi
I only measured DC resistance on pri/sec.
I know that is 1:2 ratio from documentation.
Duka[/quote]
There is relation between resistances of woundings
and ratio in noise - optimally designed transformers.
Noise-optimal design determines, that resistances of primary
and secondary (recomputed to the primary) may be the same.
(this "optimal" does not compute Barkhausen things into, he he...)
From this:
Rp/Rs=1/square
Problem is, that 1:1 transformer with two layers (primary and secondary)
wounded by the some wire
is not noise - optimal. Secondary layer have larger diameter and then resistancy.
Noise optimal 1:1 transformer may use thicker wire for secondary.
No transformers around us are not noise - optimal, but formula can
be as approximation.
xvlk

There are other reasons for wire size. For instance, a 600:600 input might have bigger wire for the primary. Why?

1: Mechanical. The primary is usually, but not always, wound first. The thicker wire tends to stregthen the cardboard former/coil structure, providing a solid base for the secondary windings.
2: If someone accidently gets 120 ac on the primary thru a ground loop or miswired mic cable, you won't melt the windings. For instance, a Black UTC A-10 has a primary inductance of about 10 Henries. So, it will have a resistance to 60 cycles ac of 2PI x 60cps x 10 H. This works out to 3768 ohms. 120/3768 is over 30 ma current in the pri. which could be too much for 0.002 wire. Also, if phantom power is used, a dead short of the 48 thru the tranny won't be as harmful with bigger wire. Overall, a general way to bullet proof whatever the poor input mic has to endure in the way of abuse durring it's lifetime.

[quote author="cjenrick"]There are other reasons for wire size. For instance, a 600:600 input might have bigger wire for the primary.
[/quote]
It is contraproductive to have bigger primary wire in the inner coil.
Inner coil have small diameter and then lower resistancy per turn.
...
There is some except. It is output transformers on the Si - Iron core
Here, losses of the core are fed from primary. The lower primary
(and output amp) resistance, the lower core distortion.
Core forms with primary resistance nonlinear divider and if primary
resistance is small then division coeff is small and distortion small.
xvlk

Yes you are right about the inner windings having a smaller circle.
But I am just going from what I have taken apart:

Like in my bedroom.
xvlk

Another reason for using bigger wire for the primary is it is just easier to work with, so if you only have say, 446 turns per coil, the bigger wire won't take up much space and is much easier to break out and solder.

[quote author="cjenrick"]Yes you are right about the inner windings having a smaller circle.
[/quote]
Cjenrick et al. s
this is shielded chamber.

Ït is solid sendust (Al+Fe) chamber with Cu inner one turn.
I use it very much in transformer - related noise ratio measurements.

xvlk