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Audio Output Impedance of the KX3

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Joseph Trombino, Jr

Audio Output Impedance of the KX3

Howdy Gang:

Checked the KX3 manual but was unable to find the audio output impedance of the KX3, i.e., what impedance headphones/speaker should I be using on the rig?

I’m looking to buy a lightweight headset for portable ops and want to know what impedance I should be looking for.

Many thanks for any info.

73, Joe W2KJ
KX3, KX2

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Jim Brown-10

Re: Audio Output Impedance of the KX3

On Mon,1/23/2017 9:22 AM, Walter Underwood wrote:
> For portable operation, I use Apple EarPods. Those are 45 Ohms.

Don't worry about impedance of headphones. There is no need to match
impedances in audio circuits.

73, Jim K9YC

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Eric Swartz - WA6HHQ

Re: Audio Output Impedance of the KX3

Administrator

In reply to this post by Joseph Trombino, Jr

For the speaker output, the K3 and K3S are optimized for 4 ohms. The SP3 is a 4
ohm speaker.

8 Ohm speakers work fine, but a a slightly lower audio output for the same
volume control position.

Eric
/elecraft.com/

On 1/23/2017 9:00 AM, Joe W2KJ wrote:

> Howdy Gang:
>
> Checked the KX3 manual but was unable to find the audio output impedance of the KX3, i.e., what impedance headphones/speaker should I be using on the rig?
>
> I’m looking to buy a lightweight headset for portable ops and want to know what impedance I should be looking for.
>
> Many thanks for any info.
>
> 73, Joe W2KJ
> KX3, KX2
>
>
>
> ______________________________________________________________
> Elecraft mailing list
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k6dgw

Re: Audio Output Impedance of the KX3

In reply to this post by Joseph Trombino, Jr

I think it is very low on practically all of today's radios and it
doesn't matter, the output stage will drive anything.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 1/23/2017 9:00 AM, Joe W2KJ wrote:

Mike Maloney

Re: Audio Output Impedance of the KX3

In reply to this post by Joseph Trombino, Jr

A good question?   See you got specific answer for K3/K3S but not KX3.   Any direct answers for KX3, rather than different headsets?   I would go for earbuds for lightest weight but would like high efficiency type with KX3.    Anyone found a good efficient set of earbuds with the KX3?
73, Mike AC5P

On Monday, January 23, 2017 11:01 AM, Joe W2KJ <[hidden email]> wrote:

Howdy Gang:

Checked the KX3 manual but was unable to find the audio output impedance of the KX3, i.e., what impedance headphones/speaker should I be using on the rig?

I’m looking to buy a lightweight headset for portable ops and want to know what impedance I should be looking for.

Many thanks for any info.

            73, Joe W2KJ
            KX3, KX2

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ANCLETUS ERNEST

Re: Audio Output Impedance of the KX3

I use from day one headset insten with mic works very will

From my DL750 Digicel

On Jan 23, 2017 2:35 PM, [hidden email] wrote:
A good question? See you got specific answer for K3/K3S but not KX3. Any direct answers for KX3, rather than different headsets? I would go for earbuds for lightest weight but would like high efficiency type with KX3. Anyone found a good efficient set of earbuds with the KX3?
73, Mike AC5P

On Monday, January 23, 2017 11:01 AM, Joe W2KJ <[hidden email]> wrote:

Howdy Gang:

Checked the KX3 manual but was unable to find the audio output impedance of the KX3, i.e., what impedance headphones/speaker should I be using on the rig?

I’m looking to buy a lightweight headset for portable ops and want to know what impedance I should be looking for.

Many thanks for any info.

73, Joe W2KJ
KX3, KX2

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w7aqk

Re: Audio Output Impedance of the KX3

In reply to this post by Joseph Trombino, Jr

Jim,

Maybe you could expand on that somewhat as I'm still confused a bit.
Perhaps I'm not understanding what I hear, or why, but it almost always
seems that when speakers (or headphones) are not closely matched to the
designed impedance I notice some deterioration in output. Some mismatch
doesn't seem too serious, but when the difference is high, it seems much
more noticeable.

On the other hand, I've also experienced that using headphones with higher
sensitivity ratings (like most Sony ear buds) tends to provide much higher
output. Most ear buds tend to be 32 ohm (16 at lest), but I find Sony ear
buds usually work best as many of them have sensitivity ratings up
around -108 dbm. I could very well be fooling myself!

This topic was covered somewhat similarly back when folks, including me,
were complaining about poor audio output from Heil headphones. The
headphone portion of my Yamaha CM500 works a lot better than my Heil, but
neither works as well as some ear buds. I don't really have another good
pair of headphones around here to try.

Also, it was interesting to see Eric's response to this question. He
indicates that the rigs are spec'd at 4 ohms, and that 8 ohm speakers would
diminish output somewhat.

Anyway, maybe you could make this all a bit clearer.

Thanks,

Dave W7AQK

From: Jim Brown <[hidden email]>

On Mon,1/23/2017 9:22 AM, Walter Underwood wrote:
> For portable operation, I use Apple EarPods. Those are 45 Ohms.

Don't worry about impedance of headphones. There is no need to match
impedances in audio circuits.

73, Jim K9YC

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Jim Brown-10

Re: Audio Output Impedance of the KX3

Hi Dave,

I've written about this many times, but here goes again. :) Your choice
of the words "designed impedance" is a good one.

Audio output stages have an internal impedance MUCH lower than the loads
they are designed to drive. For example, a typical speaker output stage
is designed to drive any load impedance greater than 4 ohms, but it's
own internal impedance (also called "source impedance") is a small
fraction of an ohm. The ratio between those two impedances is called the
"damping factor," and a value of 100 is typical. Line level outputs for
consumer gear are typically in the range of 200-400 ohms, and are
designed to drive 47K. Pro line outs are typically 100 ohms, designed to
drive 5-10K. The impedance of mics is defined as 5X their minimum load
impedance.

Output stages that feed plug-able jacks are usually built with resistors
in series to protect the output devices from damage by a short when a
jack is being inserted or is inserted improperly. Typical resistor
values are in the range of 10-500 ohms. Headphone outputs are designed
to feed headphone impedances between 8 and 500 ohms.

The impedance of headphones is simply a ratio between voltage and
current. Lower impedance headphones need less voltage but more current,
higher impedance headphones need more voltage but less current. That
series protection resistor tends to compensate for those differences.
Engineers who design headphones understand all of this and they want
their headphones to work with anything they are plugged into, so they
tend to design for high voltage sensitivity.

It's a pretty safe assumption that any "brand name" headphones are going
to work with any well-designed headphone amp. The KX3 is a bit of a
special case, because Wayne always designs for low battery drain, which
means that his audio output stages are somewhat "current starved," so
they don't provide a lot of output. As usual, I find his designs to be
very good compromises in that regard.

I find the KX3 plenty loud enough with any of the decent headphones I've
tried, and pretty good in a quiet location with the internal speaker. I
virtually always operate with cans, and use the speaker only for casual
monitoring. I find the KX3 quite useful for chasing RFI or checking out
temporary antennas.

73, Jim K9YC

On Mon,1/23/2017 12:06 PM, w7aqk wrote:
> Maybe you could expand on that somewhat as I'm still confused a bit.
> Perhaps I'm not understanding what I hear, or why, but it almost
> always seems that when speakers (or headphones) are not closely
> matched to the designed impedance I notice some deterioration in
> output. Some mismatch doesn't seem too serious, but when the
> difference is high, it seems much more noticeable.

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Jim Brown-10

Re: Audio Output Impedance of the KX3

On Mon,1/23/2017 12:54 PM, Jim Brown wrote:
> The impedance of mics is defined as 5X their minimum load impedance.

Correction -- one-fifth of their minimum load impedance. For example, a
250 ohm mic should drive an input impedance no lower than 1.25K. Most
pro mics are in the range of 150-250 ohms.

Another point I forgot to mention. ALL electro-acoustic transducers
(mics, loudspeakers, headphones) are very complex, and their equivalent
circuits are also very complex, containing multiple reactive components
and a few resonances. The impedance curve of a typical loudspeaker or
headphone has a low frequency peak of hundreds of ohms, a broad minimum
at the lower middle of its operating range, and rises rapidly with
frequency as it approaches the top of its operating range. The impedance
of a loudspeaker or headphones is defined as that minimum value of the
impedance. Multi-way loudspeakers have two such drivers, each with its
own equivalent circuit, fed respectively by low pass and high pass filters.

73, Jim K9YC

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Don Wilhelm

Re: Audio Output Impedance of the KX3

In reply to this post by w7aqk

David,

Let me try to respond and perhaps Jim will chime in a well.

Modern audio amplifier output stages are very low output impedance devices.
As such, they can produce as much power as the device connected will
allow. In a practical design of course there is a limit to how much
current the attached device (speaker or headphones) can draw from the
amplifier.

With that being said, the lower the impedance, the more current that
will be drawn. Speakers are generally in the 4 ohm to 8 ohm region and
a 4 ohm speaker will draw more current and develop more power than an 8
ohm speaker. The efficiency of a speaker makes a big difference in the
amount of sound it produces.

Headphones are a slightly different matter (but only slightly) in that
they are typically higher impedance and the current will be lower, and
the voltage across it can be higher, but they are more efficient than
speakers so it usually does not matter. The efficiency of headphones is
usually expressed in SPL - the higher the number, the greater the
sensitivity. Impedance does not matter much except in some low
efficiency Hi-Fi audiophile headphones.

In an analogy, consider the AC power line - that is a very low impedance
source of a fixed voltage. How much power is taken from the line
depends on the impedance of the device plugged into it. Within limits,
an audio amplifier shares some of the same characteristics even though
its voltage and power are much more limited.

73,
Don W3FPR

On 1/23/2017 3:06 PM, w7aqk wrote:

> Jim,
>
> Maybe you could expand on that somewhat as I'm still confused a bit.
> Perhaps I'm not understanding what I hear, or why, but it almost always
> seems that when speakers (or headphones) are not closely matched to the
> designed impedance I notice some deterioration in output. Some mismatch
> doesn't seem too serious, but when the difference is high, it seems much
> more noticeable.
>
> On the other hand, I've also experienced that using headphones with
> higher sensitivity ratings (like most Sony ear buds) tends to provide
> much higher output. Most ear buds tend to be 32 ohm (16 at lest), but I
> find Sony ear buds usually work best as many of them have sensitivity
> ratings up around -108 dbm. I could very well be fooling myself!
>
> This topic was covered somewhat similarly back when folks, including me,
> were complaining about poor audio output from Heil headphones. The
> headphone portion of my Yamaha CM500 works a lot better than my Heil,
> but neither works as well as some ear buds. I don't really have another
> good pair of headphones around here to try.
>

Elecraft mailing list

Re: Audio Output Impedance of the KX3

OK, here goes my two cents on my KX3 operation. I use the internal speaker for CW only. I use a miniX self powered speaker for quiet portable work and I use a FM modulator from the phone jack while in the mobile to the car FM receiver. All seems to work fine. This way I don't worry about impedance issues.

Mel, K6KBE

From: Don Wilhelm <[hidden email]>
To: w7aqk <[hidden email]>; Elecraft Reflector <[hidden email]>
Sent: Monday, January 23, 2017 1:35 PM
Subject: Re: [Elecraft] Audio Output Impedance of the KX3

David,

Let me try to respond and perhaps Jim will chime in a well.

Modern audio amplifier output stages are very low output impedance devices.
As such, they can produce as much power as the device connected will
allow. In a practical design of course there is a limit to how much
current the attached device (speaker or headphones) can draw from the
amplifier.

With that being said, the lower the impedance, the more current that
will be drawn. Speakers are generally in the 4 ohm to 8 ohm region and
a 4 ohm speaker will draw more current and develop more power than an 8
ohm speaker. The efficiency of a speaker makes a big difference in the
amount of sound it produces.

Headphones are a slightly different matter (but only slightly) in that
they are typically higher impedance and the current will be lower, and
the voltage across it can be higher, but they are more efficient than
speakers so it usually does not matter. The efficiency of headphones is
usually expressed in SPL - the higher the number, the greater the
sensitivity. Impedance does not matter much except in some low
efficiency Hi-Fi audiophile headphones.

In an analogy, consider the AC power line - that is a very low impedance
source of a fixed voltage. How much power is taken from the line
depends on the impedance of the device plugged into it. Within limits,
an audio amplifier shares some of the same characteristics even though
its voltage and power are much more limited.

73,
Don W3FPR

On 1/23/2017 3:06 PM, w7aqk wrote:

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w7aqk

Re: Audio Output Impedance of the KX3

In reply to this post by Joseph Trombino, Jr

Jim and All,

Thanks much for the explanation. Makes a lot more sense now. Not sure how
I missed your past comments that covered that.

I also got several other responses which were most helpful, and I appreciate
them as well. It sure is nice to ask a question and get good answers!! Hi.

Cheers!

Dave W7AQK

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