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Need help understanding transformer impedance ratios and impedance matching

I am a bit confused about impedance ratios and actual impedances of the primary and secondary of a transformer when it comes to matching a source to a load.

An impedance ratio of 10:1 is required - for matching a 10k load to a 100k source.

Now there are two transformers both having an impedance ratio of 10:1 but one of them is spec'd as having a 600 ohm secondary and the other with a 15000 ohm secondary. My understanding is that if I put a 10k load on either of these transformer's secondary, the primary will simply reflect a 10x (100k) load to the source.

Then what does 600ohm and 15000ohm mean ? What impedance is this ?
 
Transformers may have the same ratios but with different number of turns in both primary and secondaries. The more turns in the primary - the more inductance. Higher inductance will allow higher impedance of the driving source within the same bandwidth - in very simplistic terms if you don't have enough primary inductance you can't get good bass from a high impedance source. If the source is low impedance high inductance is no longer essential and better results in the high frequencies may be obtained with a transformer using less wire in the primary.

Many other factors are at play when choosing the best impedance for a transformer but this can give you an idea.
 
Ok thanks, I will check that out...

analog_sa:
The piezo source is presumably high impedance, something like megaohm? And earphones are what, kiloohms?

I think thats the DC resistance you're referring to. Piezo's are typically megohm and magnetics are ~2Kohm.
Just to satisfy my curiosity I measured the impedance of a piezo earplug and and also a pair of magnetic headphones I had lying around...
The impedance of the piezo drops as the frequency rises. It goes from about 25Kohm at 200hz to settle down to about 1Kohm from 5Khz onwards - like a capacitor.

The impedance of the magnetic phone rises with frequency. From about 2Kohm at 200hz to about 12k-16kohm in the upper frequency range.- like an inductor.

Acoustic measurements reveal a horrible frequency response - barely usable from 200hz to 3Khz.

;)
 
An impedance ratio of 10:1 is required - for matching a 10k load to a 100k source.

Now there are two transformers both having an impedance ratio of 10:1 but one of them is spec'd as having a 600 ohm secondary and the other with a 15000 ohm secondary. My understanding is that if I put a 10k load on either of these transformer's secondary, the primary will simply reflect a 10x (100k) load to the source.

Then what does 600ohm and 15000ohm mean ? What impedance is this ?
The unwritten but implied spec you are not considering is inductance, as mentioned by analog_sa
Higher inductance will allow higher impedance of the driving source within the same bandwidth - in very simplistic terms if you don't have enough primary inductance you can't get good bass from a high impedance source.

You think:
if bass, bandwidth and fidelity are not really important - (the load is a vintage heaphone with a very limited bandwidth anyway, and the source a crystal detector) - then either of these transformers should do ?
But there is a BIG difference between "not really important" and being crappy unusable.

Let´s do some numbers.

When besides impedance ratio they also mention 600 ohm or 15k, what they are also implying is "transformer has enough turns/inductance to match a 600 ohm or a 15 k impedance" so those will be VERY different, specially in size and cost.
Of course you hope to use the cheaper one ;)

Ffact is, a reasonable mismatch is acceptable, but here we are talking almost 17:1 :eek: , a huge difference.

Suppose both transformers are rated flat down to 50 Hz into the proper impedance, using the 600 ohm one will mean now it will chop anything below 833 Hz !!! :eek:

Not only that, I guess your 100k source is either a tube plate or a diode detector, both will be very unhappy driving that short which is what the improper transformer become at lower frequencies.
Not only "lower" but Mid frequencies too. :cool:

Then choice might be acceptable only if you have to couple, say, 1 1kHz tone to a Piezo Tweeter with no lower frequencies present or similar "Alarm type" duty but not in an "Audio" situation.

Again: one thing is "not having Hi Fi specs" as in only interested in "voice/Telephone" bandwidth and the other as being practically unusable.

You would fare much better by adding some kind of buffer, such as a cathode follower; transformers become complicated (zillion turns of hair thin wire), demands of expensive core material such as Mu Metal, when low power at high impedance are needed.

EDIT:
Acoustic measurements reveal a horrible frequency response - barely usable from 200hz to 3Khz.

HOW did you measure that?

Did you drive earphone from an amplifier, sweeping then Audio band with an oscillator and measured frequency response with a calibrated microphone some distance away?

Earphones are NOT meant to be used in open air but into a closed or semiclosed cavity, our ear canals, so there are specially built "artificial ears" for that.

https://www.bksv.com/en/transducers/simulators/ear-mouth-simulators/4153

Not what you´d expect:

ArtificialEar_4153_600x600.ashx
 
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Suppose OPT turn ratio is 12 : 1 use for Headphone 32Ohms to get 250mW So the current need is 88mA. Hence the voltage will be 2.82 VAC.


However why when using 250 ohms headphone, Why the Turn ratio need to be lower to about 4:1?
You are talking about a COMPLETELY DIFFERENT situation, it is confusing and already derailing the thread, PLEASE post it on a separate thread.

This is Percy´s thread and he has not yet finished.