audio-transformer's impedance: what does "ct" mean?

[myleftear]

Good morning allerseits 🙂

I'm on the lookout for audio-transformers (input), found some, but don't know how to interpret it.

The impedances are stated as (@ hammond)

106E = primary: 600 ct / secondary 600
106EE = primary: 600 ct / secondary 600 ct

So this seems to be of a certain significance. Does it mean Center-Tap?

Thank you!
david

 

[johnmath]

Yes, center tap.

 

[NetlistPCB]

I'm interested also. So, does this mean 600 ohm across the whole winding? Or just to the center tap?

 

[AllenB]

The whole winding.

 

[Hearinspace]

50-0-50 = 100 c.t.

 

[NareshBrd]

CT generally means Center Tapped, you have a single winding, you can use the entire coil for 220V, and half for 110V on the primary side, for example.
This was quite normal in Japanese sets, they could be set to work as per your area's mains supply.
I may have got that backwards, but you get the idea.

The center tap is used in some circuits for ground as well. One winding is used for (+) and the other for (-) rail.

 

[AllenB]

Well, yes keeping in mind this is a signal transformer 😉

 

[NetlistPCB]

Thank you all.

 

[Sangram]

the whole winding? Or just to the center tap?

The 600E is a 600CT:600 transformer, allowing 150:600 or 600 to 600 coupling. The 600EE is a 600CT:600CT, allowing 600:600, 150:600 or 600:150. Impedance ratio is square of turns ratio, so that's 2:1, 1:2 or 1:1. The CT is helpful for phase splitting, when on the output side.

All of this is reflected impedance, meaning that it gets converted to whatever your actual input and output impedance are. In most audio circuits that do not exhibit a 600 ohm input impedance, there will be a peaking HF response, needing a zobel on the output side. While high impedance coupling transformers are available, they're not particularly common and tend to be more expensive.

 

[JMFahey]

Agree and add:

* these are signal transformers (as noted above), even more, Input ones, so low level, absolutely unrelated to mains power transformers, so why mention 110-220V at all?

* yes, they can be used as 600 ohm input (full winding) or 150 ohm (half of it) but in general center tap was used to provide bias or ground reference in a balanced signal circuit or feed phantom power to remote equipment through the Audio line.

 

[steveu]

50-0-50 = 100 c.t.

Not exactly, unless you are talking about voltage. The impedance of half the windings is 1/4 the impedance, as in 600:150. But the "impedance" of a transformer is misleading. It has an inductance and wire resistance, capacitance and self-resonance. The impedance is just a recommendation based on these parameters. You may want to use a transformer at a lower impedance, both in and out, to extend the range of the bass, because the low frequency limit is where the primary inductance, inductive reactance begins to short out the source. This compromises the signal level where it saturates. It's all a big trade-off of parameters. Likewise you could use a transformer for higher impedances and higher power levels at high frequencies. Bigger is better because bigger is more inductance and more magnetic energy capability. For the same reasons, audio transformers perform best when driven by a low impedance and loaded secondary to control the self-resonance at the top of it's range.

 

[NareshBrd]

I think my reply was not up to mark set by the level of the more senior members.

I was trying to give the poster a general idea, and there have been very detailed responses later...

 

[NetlistPCB]

I think my reply was not up to mark set by the level of the more senior members.

I was trying to give the poster a general idea, and there have been very detailed responses later...

I think some got offended by the reference to power transformers, but it did help me to understand. Thanks for your help.