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:
- posted
17 years ago
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:
================================= I though audio went down to 20Hz. This thing starts at 450Hz. What kind of audio is that? CB radio audio?
"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
All transformers in the signal path introduce various types of distortions.
For decent audio transformers check out Jensen, Sowter and Luhndahl for starters.
Graham
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.
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.
** Try Radio Shack.
Two channels for $17 is OK
........ Phil
load.
OEP ! Not quite so 'esoteric' but very adequate.
RS components and Farnell certainly used to stock them
Graham
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.
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.
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2.
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.
In message , dated Sat, 16 Sep
2006, Fred Bartoli writes
Two things:
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2.
Oh, OK I just read the 90R load and missed the notebook blahh...
-- Thanks, Fred.
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
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
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.
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2.
"Don Bowey"
** This dopey ham radio asshole must be completely pissed.LOL !!
...... Phil
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
In message , dated Sat, 16 Sep
2006, Fred Bartoli writesNo, there is confusion between two posts. The OP. Harry, has a 90 ohm load. It's 'miso' who wants a transformer for his notebook.
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2.
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.
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2.
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