Audio Transformers are like Monster Cables

Ok, I need a 10mW audio transformer with a 1:1 turns ratio for my 90R load. So I look at many vendors and here is a typical spec:

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Let's forget cost, because we all know that PICO is like Monster Cables. The first unit I look at is the F-28003 with a pri:sec Z of 10R:10R. There are many other 1:1 transformers listed but from the data shown, this is the most efficient, best bandwidth and lowest distortion of all the 1:1 transformers listed. So why list any other 1:1 transformer? I must be missing something, so spank me with your keyboards. Harry

Reply to
Harry Dellamano
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================================= I though audio went down to 20Hz. This thing starts at 450Hz. What kind of audio is that? CB radio audio?

Reply to
BobG

"Harry Dellamano"

** How did YOU make that conclusion ?

The transformers on that page are speced with the same response - ie "

+/- 3db 400 Hz to 250 kHz at 1 mW"

So not an "audio transformer" in the world of pro audio.

** Funny how folk want to use other load impedances than 10 ohms.

Pico seem to be well aware of this.

** Bandwidth, efficiency and distortion characteristics all depend on using a transformer at or near its rated impedance values.

The title " 1:1" simply means transformer does not change the impedance levels in a circuit.

....... Phil

Reply to
Phil Allison

All transformers in the signal path introduce various types of distortions.

For decent audio transformers check out Jensen, Sowter and Luhndahl for starters.

Graham

Reply to
Eeyore

10 mW into 90 ohms is 948 mV RMS. 10 mW into 10 ohms is 316mV RMS

-- so a 10 mW 10 ohm xfmr is designed for voltage not exceeding 316 mV RMS -- which is about 1.11 mW at 90 ohms.

Reply to
Don Foreman

Those are good iron, but does anyone know of a source of audio transformers a notch lower than say a Jensen. I'd like to break the ground between communications gear and my notebook, which I use for recording. Connecting the notebook always effects the performance of the radio, even if you use ferrite chokes. A $70 Jensen transformer is overkill in such an application.

Reply to
miso

** Try Radio Shack.

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Two channels for $17 is OK

........ Phil

Reply to
Phil Allison

load.

OEP ! Not quite so 'esoteric' but very adequate.

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RS components and Farnell certainly used to stock them

Graham

Reply to
Eeyore

10mW in a 90R load is about 1Vrms Harry.

All these transformer do a maximum 20mW at 400Hz. For the 10R+10R that is only about 0.45Vrms.

To run with 1Vrms at 400Hz you need to choose one that does 20mW into between 50R and 90R. Say F-28030/28045.

If you are driving from a low source impedance, (say an opamp), you can get an improvement in the low frequency response by pushing the choice even further.

--
Tony Williams.
Reply to
Tony Williams

In message , dated Fri, 15 Sep 2006, snipped-for-privacy@sushi.com writes

The type of transformer used in modems will do that. In a phone circuit, the primary inductance limits the low-frequency range to some 300 Hz, but you notebook will drive it from a source much lower than 600 ohms, at a voltage much less than the maximum phone line voltage, so it will work OK.

No doubt a dozen people will give you reasons why it won't, so I suggest you just try it.

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Reply to
John Woodgate

Hmmm, the ones I've just tested have 65R primary and secondary resistance. Suitable for 600R impedance, but at 90R?

Either than that, no pb. So I'm half of those people. Still 11.5 other people to find.

--
Thanks,
Fred.
Reply to
Fred Bartoli

In message , dated Sat, 16 Sep

2006, Fred Bartoli writes

Two things:

  1. I've never seen a notebook or anything else in audio with a 90 ohm input impedance, so I'm doubtful about that. It certainly wouldn't suit an electret mic or any line-level source.

  1. There is plenty of spare gain in such a set-up, so the transformer losses are very likely quite negligible.

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Reply to
John Woodgate

Oh, OK I just read the 90R load and missed the notebook blahh...

--
Thanks,
Fred.
Reply to
Fred Bartoli

Right off the top, you want one rated for 10 mW and the absolutely greatest one you provided a link to, is rated at 1 mW.

Don

Reply to
Don Bowey

Hi Tony, Now that makes sense. So I should NOT try to match my load to their Z for best efficiency but choose the lowest Z that will support my voltage levels. So, I need 1.0V and they will transform to a max of 20mW so the lowest Z= E^2/P = 1/20m = 50R. They do have a 50R, the F-28030 so that is my selection. We had this discussion before and you had a good rule of thumb to determine primary inductance and better model these units, please refresh my mind. Why don't they list the max Vac, at maybe 5% distortion that each unit can operate? The data given is for users with little knowledge of electronics, maybe the "golden ears" crowd. Harry

Reply to
Harry Dellamano

In message , dated Sat, 16 Sep 2006, Harry Dellamano writes

I think you are very confused. First of all, where did you get '90 ohms' from? It's a very strange value, not associated with audio (or anything else that's analogue) at all.

Second, do you know the signal voltage that will be applied to your transformer? If it's feeding a normal notebook audio input, it is likely to be between 10 mV )from a microphone) and 0.5 V (from a line-level output).

You simply don't choose transformers by the methods you are using.

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Reply to
John Woodgate

"Don Bowey"

** This dopey ham radio asshole must be completely pissed.

LOL !!

...... Phil

Reply to
Phil Allison

John, I am doing circuit design, not hooking up audio boxes. Believe me, the load is 90R at 10mW so that is 0.95Vrms. To be most efficient I want the lowest loss in the transformer. Matching loads to sources is overrated. It will give you max power transferred at 50% efficiency but who can live with all those losses. It is much better to use the lowest Z transformer that can support your volt seconds. This is just between circuit designers but don't try to convince your audio crowd that. Harry

Reply to
Harry Dellamano

In message , dated Sat, 16 Sep

2006, Fred Bartoli writes

No, there is confusion between two posts. The OP. Harry, has a 90 ohm load. It's 'miso' who wants a transformer for his notebook.

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Reply to
John Woodgate

In message , dated Sat, 16 Sep 2006, Harry Dellamano writes

It would have been helpful, then, to give more details.

Indeed.

That just doesn't make sense. A transformer doesn't have an 'impedance'.

Matched loads haven't been used in audio for around 50 years.

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Reply to
John Woodgate

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