frankengraphics
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Joined: Wed Dec 20, 2017 2:17 pm

3.5mm output and impedance?

Wed Dec 20, 2017 2:20 pm

Hello, i have a quick question.

Will a headphone with 100 ohm impedance work nicely enough with the raspberry pi:s 3.5mm audio output?
What range of impedances are suitable?

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Burngate
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Re: 3.5mm output and impedance?

Wed Dec 20, 2017 5:30 pm

If you hunt round you'll find the Raspberry-Pi-3B-V1_2.pdf

100 Ohm headphones should not be a problem.
The output impedance is 69 Ohms, so somewhere around that value would be optimal for best power transfer. The output is both short-circuit and open-circuit tolerant.

However the output level is rather low at 3.3v p-p, 1.1v rms, so you may find them rather quiet.
An amplifier is recommended.

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Imperf3kt
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Location: Australia

Re: 3.5mm output and impedance?

Wed Dec 20, 2017 8:47 pm

100Ohms?
Throw them in the recycling skip and buy something better. Even the cheapest of cheap Chinese headphones are only 32Ohms
55:55:44:44:4C
52:4C:52:42:41

drgeoff
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Re: 3.5mm output and impedance?

Thu Dec 21, 2017 10:24 am

Imperf3kt wrote:
Wed Dec 20, 2017 8:47 pm
100Ohms?
Throw them in the recycling skip and buy something better. Even the cheapest of cheap Chinese headphones are only 32Ohms
That his headphones are 100 Ohms does not necessarily make them quieter or worse sounding than 32 Ohm ones.

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Burngate
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Re: 3.5mm output and impedance?

Thu Dec 21, 2017 10:26 am

Actually, the power into 32Ω from 69Ω is remarkably similar to the power into 100Ω from the same source - 3.1mW as against 3.5mW
So spending good money on Chinese cheapos won't gain you anything.

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Imperf3kt
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Re: 3.5mm output and impedance?

Thu Dec 21, 2017 8:30 pm

From the Pi, sure, but headphones plug into more than just a Pi.
55:55:44:44:4C
52:4C:52:42:41

drgeoff
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Re: 3.5mm output and impedance?

Thu Dec 21, 2017 10:08 pm

Imperf3kt wrote:
Thu Dec 21, 2017 8:30 pm
From the Pi, sure, but headphones plug into more than just a Pi.
There is much more to it than just the electrical power into the earpiece. Just like loudspeakers, all earphones do not have the same sensitivity ie dB/mW.

ait
Posts: 127
Joined: Sun Oct 30, 2011 6:51 pm

Re: 3.5mm output and impedance?

Fri Dec 22, 2017 10:02 am

Even the cheapest of cheap Chinese headphones are only 32Ohms
sennheiser HD 660 S 499 EUR 150Ohms

https://www.head-fi.org/threads/meet-th ... -s.862720/

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