Toroidal I/P & O/P Transformer Design Questions

[gyraf]

..so did the original Focus-Rite ISA's..

 

[abbey road d enfer]

My experience with toroids (at least the ones used by Focusrite, Klark Teknik and Neve) is that they don't overload nicely. When the iron reaches saturation, they behave almost like a short-circuit to the drive stage, clipping off transients. That's why they ended up using larger than needed cores, which counteracted the expected size and weight saving. In the end, they are more expensive than EI or C-core, and the only real benefit is better magnetic field rejection. Add to that the fact that sandwiched construction is more difficult thus costly on toroids.
I have made some experiments on using power trannies for audio and found them very disappointing. If you measure them with a very low source impedance, they seem to be ok, but once you start using real world source impedance, like 200 ohm microphones, you'll find distortion climbing to heights and HF dropping like crazy.

 

[rodabod]

Sorry for going off-topic again, but I just thought I'd add that the STC 4038 ribbon mic transformer is toroidal. So I suppose that's STC/Coles, Beyer and Oktava.

 

[Marik]

[quote author="rodabod"]Sorry for going off-topic again, but I just thought I'd add that the STC 4038 ribbon mic transformer is toroidal. So I suppose that's STC/Coles, Beyer and Oktava.[/quote]

Roddy,

Are you sure with Beyer? The 260 and 160 have small EIs.
The Royer is toroid.

Best, M

 

[rodabod]

[quote author="Marik"]
Are you sure with Beyer? The 260 and 160 have small EIs.
The Royer is toroid.[/quote]

Hi Mark,

Sorry - I assumed when Jakob said that the miniature Beyer transformers were toroidal that they all were. Have you opened up the M160 transformer? Was it much different from the M260 model? I have a few of the M260 ones. I didn't know that Royer were toroids.

 

[Marik]

[quote author="rodabod"][quote author="Marik"]
Are you sure with Beyer? The 260 and 160 have small EIs.
The Royer is toroid.[/quote]

Hi Mark,

Sorry - I assumed when Jakob said that the miniature Beyer transformers were toroidal that they all were. Have you opened up the M160 transformer? Was it much different from the M260 model? I have a few of the M260 ones. I didn't know that Royer were toroids.[/quote]

I did not measure them, but from outside they look identical. Ideally, since the 160 is a double ribbon it should have different ratio for the same output impedance.
It is in fact not even EI, but some kind of similar to rather V72 choke type of lams (albeit much smaller and I am sure no air gap), with sides of 11 and 16mm and 3mm stack.

Royer tour shows his transformers as toroids.

Best, Mark

 

[analag]

I did two hand wound toroidal output transformers for a tube power amp a couple years back, with five interleaves on the primary and two on the secondary. Very balanced DCR, with very extended top and bottom frequency. If I were to do it again, I would try some new ideas I came up with after my first experience with it.

analag

 

[CJ]

Just an idea, wind another primary that is equal to the turns of the real primary.
Then put a reverse DC bias current that is equal to the SE tube current.
You would have to build a seperate regulated DC B+ supply.

 

[gyraf]

Good idea indeed!

Is it necessary to have the same number of turns - couldn't it possibly be done with a low-voltage winding and higher current (as low voltage/med-to-high current is much easier to control with standard regulator chipsets)?

kinda' of veryalternative DC-Servo :razz:

Jakob E.

 

[analag]

Hey, what was the question again?
It can be done, but it's gonna take some experimentation to get it right. After that you can have your boy reproduce it. If you do interleaving you will need an inductance meter to connect them up right, because one wrong connection and your inductance goes to hell.

Hey CJ, where you been hiding, boy?

analag