HP (HeadPhone Impedance requirements

Mark C
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Joined: Wed Mar 22, 2023 6:32 pm

HP (HeadPhone Impedance requirements

Postby Mark C » Mon Sep 11, 2023 9:35 pm

HI Guys,
First of all forgive my ignorance, I am old.

I have been searching and searching and can't find an impedance rating for the Headphone jack on the rear of my G2 100 radio.
The only reference I can find says impedance for external speaker is 4 to 8 ohms.

Does anyone know the impedance range for Head Phone jack in rear of radio.

Thanks for reading.
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w-u-2-o
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Re: HP (HeadPhone Impedance requirements

Postby w-u-2-o » Tue Sep 12, 2023 12:25 am

See this topic: viewtopic.php?f=12&t=2612

If you look at the datasheet the answer is 16 or 32 Ohms.
Mark C
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Joined: Wed Mar 22, 2023 6:32 pm

Re: HP (HeadPhone Impedance requirements

Postby Mark C » Tue Sep 12, 2023 12:47 am

Thanks Jim for the information.

I looked at that diagram before I posted the question. Now after looking at it again, I am totally unable to figure out how you got 16 or 32 ohms.
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w-u-2-o
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Re: HP (HeadPhone Impedance requirements

Postby w-u-2-o » Tue Sep 12, 2023 1:30 am

Scott, not Jim ;)

Did you review the datasheet like I posted?
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w9ac
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Re: HP (HeadPhone Impedance requirements

Postby w9ac » Tue Sep 12, 2023 3:56 am

Mark C wrote:Thanks Jim for the information.

I looked at that diagram before I posted the question. Now after looking at it again, I am totally unable to figure out how you got 16 or 32 ohms.

According to the datasheet, the TLV320 output Z at the headphone output pins is close to 0 ohms -- like many active amp stages. The spec sheet shows "Headphone-amplifier output load resistance" of 0 as a minimum but that doesn't mean you operate it that way, nor does it represent the output Z at the headphone jack. The reference to 16 and 32 ohms on the datasheet is the maximum power delivered into those resistances.

As an example, the Orion MKII board (and I believe Angelia) has 10 uF caps in series with a tapped RF choke between the TVA320 and the audio jack. Those components form part of the output Z at the headphone jack and it varies with frequency but it's always more than zero. Not having the G2 schematic set, it's only a guess on my part, but I suspect Apache kept the same headphone output circuit.

As an example of the Orion board at 100 Hz, the reactance at the headphone jack is -160 ohms in series with the choke resistance, let's say 10 ohms. The Z is 10-j160 but since the reactive component is much more than the resistive component, the result is slightly more than 160 ohms at 100Hz. But at 4 kHz, it drops to 10-j4. Now, the resistive component exceeds the capacitive component for a total output Z of about 11 ohms.

Bottom line: any modern headphones have sufficient impedance. The output jack Z changes with frequency just as headphone impedance changes with frequency. My Sony MDR-7506 headphones have an impedance spec of 24 ohms but Sony correctly caveats the impedance at 1 kHz although it's much different at the audio spectrum extremes.

Paul, W9AC

P.S.

The RF choke has a small amount of inductive reactance that cancels the much larger cap reactance, but it's small enough to neglect at audio frequencies.
Mark C
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Joined: Wed Mar 22, 2023 6:32 pm

Re: HP (HeadPhone Impedance requirements

Postby Mark C » Tue Sep 12, 2023 4:08 pm

Sorry Scott....

Thanks Paul...yes I see on the diagram where it says Maximum output power, PO RL = 32 Ω and RL = 16 Ω.

Thanks for the help. Electronics theory and schematics were/are not my strong points. Morse code was far far easier than theory.
I do appreciate you all helping me understand how you ascertained the answers and hopefully someone else will benefit from this info.

73's
Mark

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