Greetings all. First time posting. Trying to read archives for info and make this title accurately describe things.
I recently used a radio shack 273-1380 transformer to use a simple 16 ohm headset in a small plane.
Normally aviation headsets are around 300 ohms.
Dropping the part in line with some 3.5mm jacks worked fine for a few hours of test but later I could swear it was developing an ever so slight crackle or pop with certain sounds--made by me or someone else on the radio.
*Update*
I believe the source output impedance is 600ohms.
If the transformer lists 1000ohms - 8ohms, does that imply it will only accept 1000 as the source signal, or will it function 'up to' 1000 ohms? The destination is around 16ohms speakers.
Can this #273-1380 overheat with such a low ohm headset on the downstream side?
Any and all info appreciated.
I recently used a radio shack 273-1380 transformer to use a simple 16 ohm headset in a small plane.
Normally aviation headsets are around 300 ohms.
Dropping the part in line with some 3.5mm jacks worked fine for a few hours of test but later I could swear it was developing an ever so slight crackle or pop with certain sounds--made by me or someone else on the radio.
*Update*
I believe the source output impedance is 600ohms.
If the transformer lists 1000ohms - 8ohms, does that imply it will only accept 1000 as the source signal, or will it function 'up to' 1000 ohms? The destination is around 16ohms speakers.
Can this #273-1380 overheat with such a low ohm headset on the downstream side?
Any and all info appreciated.
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I doubt that the source output impedance is 600 ohms. It could be that the source 'expects' to be driving 600 ohms; that is a customary value.
The two are different things.
If you xformer is listed as '1000 to 8 ohms' it only means the turns ratio is the square root of 1000/8, which comes out to about 11.
If you load a 1000:8 xformer with 16 ohms instead of 8 ohms, that means that it 'looks' at the primary side as 2000 ohms. Your source thus has to drive 2000 ohms and that should be no problem at all.
I guess the transformer is not one of these very small miniature jobs that are used as line transformers, but a proper output transformer? How large is it? If it is miniature it could be overdriven, although xformers are about the most rugged parts available.
OTOH, a nice Dave Clark aviation headset is peanuts compared to the price of the plane ;-)
Jan
The two are different things.
If you xformer is listed as '1000 to 8 ohms' it only means the turns ratio is the square root of 1000/8, which comes out to about 11.
If you load a 1000:8 xformer with 16 ohms instead of 8 ohms, that means that it 'looks' at the primary side as 2000 ohms. Your source thus has to drive 2000 ohms and that should be no problem at all.
I guess the transformer is not one of these very small miniature jobs that are used as line transformers, but a proper output transformer? How large is it? If it is miniature it could be overdriven, although xformers are about the most rugged parts available.
OTOH, a nice Dave Clark aviation headset is peanuts compared to the price of the plane ;-)
Jan
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What I'm actually experiencing is a slight distortion when transmitting. The inbound actually isn't too bad.
What would you recommend for a transformer if trying to duplicate 300 speakers (2 of them) in parallel for 150?
It's a radio shack 273-1380 model.
Can you elaborate about the HP filter?
> not one of these very small miniature jobs
273-1380 is a transistor pocket radio transformer. About 15mm size. Intended for 100mW output into teeny speaker.
It will "fart" on strong bass; but aircraft radio is bass-cut.
It is not clear to me why it could distortion when transmitting.
Crackle after some use suggests bad joints.
273-1380 is a transistor pocket radio transformer. About 15mm size. Intended for 100mW output into teeny speaker.
It will "fart" on strong bass; but aircraft radio is bass-cut.
It is not clear to me why it could distortion when transmitting.
Crackle after some use suggests bad joints.
Bad joints? Ok, I thought I had them soldered well. What about crackle sound that sounds like very mild distortion with the strong (for lack of a better word) attacks in my speech? Subtle talking can get by but stronger pronunciations produces that. I'll check the joints when I get home.
These radios provide a little audio feedback when transmitting so you can hear yourself talk. That doesn't help you much, but that is what changes when transmitting.
A number of years ago, I created something similar (but opposite to what you want, I think), it was to be able to listen to a little portable radio while flying (through normal aviation headset). I first tried the transformer you have to match impedance, but ended up using a 1:1 transformer (if I remember correctly). I used it for thousands of hours on various aircraft without any problems.
That seems to indicate it is overload with higher level. Are you sure it is not the headphone itself that distorts, rather than the xformer?
The tiny xformer can also distort on overload but it would normally not be a 'crackle'.
Jan
Maybe. 16ohm stereo earbuds on the end of an 8 ohm mono signal? Not sure.
I did however find out the output impedance of the intercom is 600 ohms.
I need to go educate myself now: 600 ohms to 300 ohm headset (150 parallel). Why is that split ok but not 600 to 8.
And yeah, I think the transformer is working fine. I chose a poor earbud for the job. The audio sounds great. The side tone when speaking has the distortion.
I believe the terms may be incorrect. '16ohm stereo earbuds on the end of an 8 ohm mono signal' is not a sensible statement.
What is the exact wording of the output impedance of the intercom? It could be 600 ohms but more common is that it is expected to be loaded with 600 ohms, which is something else.
Not trying to be pedantic but it is important to know what the system consists of.
Jan
I received an email to the question of what the output impedance was--didn't specify load. 600ohms was the answer. It's expecting to be loaded with two people using 300ohm speakers (headset) that are 150 ohms wired parallel.
Could that be why it is 600? I read somewhere you'd want the headset impedance to be "higher" than output.
No worries on verbosity. I'm here for an education.
> I read somewhere you'd want the headset impedance to be "higher" than output.
That is customary in most audio, but not essential. Actually hi-Z drive to medium-Z phones used to be common in studios. I do not know aircraft custom.
Gross impedance differences will give weaker results.
Did you have to turn-up to get adequate level in your headphone? You could just be over-driving the amplifier. What changes if you turn-down a notch? (I know you have very little leeway on level when the mighty Jacobs is roaring.)
That is customary in most audio, but not essential. Actually hi-Z drive to medium-Z phones used to be common in studios. I do not know aircraft custom.
Gross impedance differences will give weaker results.
Did you have to turn-up to get adequate level in your headphone? You could just be over-driving the amplifier. What changes if you turn-down a notch? (I know you have very little leeway on level when the mighty Jacobs is roaring.)
Jan, in all the questions I've been dealing / learning about the output side of the transformer. Specifically, what is happening on the "in" side of the audio transformer when that 600ohms output suddenly runs into the 1000ohm end of my 1000:8 transformer? Is it reducing proportionally?
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