4-ohm to 8-ohm question

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4-ohm to 8-ohm question

k6sdw
My K2 audio output is 4-ohms which I drive into an 8-ohm ICOM speaker with filters. Yes, it works OK, but I would like to match them better.
In the "olden" days I would simply use a 4-ohm to 8-ohm audio transformer, but I can't find them anymore! Really, I've looked at all the suspect places, including eBay and Amazon.
Any suggestions, I just want and easy, simple way to matching the two impedance's without losing power which would happen if I used a resister across the ICOM speaker. I know I can just drive a small audio amp between them, but that means more wires to power up the amp......
Thanks to all
73
ed    
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Re: 4-ohm to 8-ohm question

Don Wilhelm
Ed,

There is no need to match speaker impedances.  That may have been the
case when audio output stages had output transformers, but it is no
longer desired or needed.

The audio output stage is a low impedance source - which means that the
available output is determined by the load.  You can get more power into
a 4 ohm load than you can into an 8 ohm load.
The power is determined by the load.

A parallel example - consider the AC receptacle in your wall - it is a
veery low impedance source.
If you plug in a 40 watt light bulb, enough current will be drawn to
light that lamp to its full brilliance - drawing about 40 watts of power.
Now plug in a 25 watt bulb.  It will draw less current, but will still
light to its full briliance -drawing only 25 watts.  The point here is
that with a low impedance source, the output power is mainly determined
by the impedance of the load, and no amount of Impedance matching is
going to make a big difference.

73,
Don W3FPR



On 5/2/2016 4:15 PM, Eddy Avila wrote:

> My K2 audio output is 4-ohms which I drive into an 8-ohm ICOM speaker with filters. Yes, it works OK, but I would like to match them better.
> In the "olden" days I would simply use a 4-ohm to 8-ohm audio transformer, but I can't find them anymore! Really, I've looked at all the suspect places, including eBay and Amazon.
> Any suggestions, I just want and easy, simple way to matching the two impedance's without losing power which would happen if I used a resister across the ICOM speaker. I know I can just drive a small audio amp between them, but that means more wires to power up the amp......
> Thanks to all
> 73
> ed  
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Re: 4-ohm to 8-ohm question

Phil Kane-2
In reply to this post by k6sdw
On 5/2/2016 1:15 PM, Eddy Avila wrote:

> In the "olden" days I would simply use a 4-ohm to 8-ohm audio transformer, but I can't find them anymore!

Not necessary because today's audio amplifier designs do not require
matched impedances.  You are "good to go" with no further matching.
--
73 de K2ASP - Phil Kane
Elecraft K2/100   s/n 5402

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
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Re: 4-ohm to 8-ohm question

Joe Subich, W4TV-4
In reply to this post by k6sdw

 > Yes, it works OK, but I would like to match them better.

Don't bother.  There is no benefit in doing so.

Modern audio amplifiers are essentially zero impedance sources
(current drivers).  The K2's 4 Ohm specification is based on the
audio power output for a given power supply voltage and distortion
level.

The LM-380 data sheet shows 2W at 12V with 3% distortion for a 4
Ohm load.  Move to 8 Ohms and you will get about 1.2W at 12V with
3% distortion.  If you want more power output into an 8 Ohms speaker,
increase the voltage to the LM-380 to 20V (yes, it's rated all the
way to 22V max).

If you don't want to modify the radio to supply 20V to the audio
amplifier (not a good idea <G>), you rally need to find a high
efficiency 4 Ohm speaker or use an external amplifier to get more
sound.

73,

    ... Joe, W4TV

On 5/2/2016 4:15 PM, Eddy Avila wrote:
> My K2 audio output is 4-ohms which I drive into an 8-ohm ICOM speaker with filters. Yes, it works OK, but I would like to match them better.
> In the "olden" days I would simply use a 4-ohm to 8-ohm audio transformer, but I can't find them anymore! Really, I've looked at all the suspect places, including eBay and Amazon.
> Any suggestions, I just want and easy, simple way to matching the two impedance's without losing power which would happen if I used a resister across the ICOM speaker. I know I can just drive a small audio amp between them, but that means more wires to power up the amp......
> Thanks to all
> 73
> ed  
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Re: 4-ohm to 8-ohm question

Elecraft mailing list
In reply to this post by Phil Kane-2
Eddy, the transformers were made tor tube type amplifiers where the output was several thousand ohms and transforming was needed.  Some audiophiles still use tube amplifiers for mellow sounds from music, but the transistor output stages match either 4 or 8 ohm speakers directly and are fine for communications audio or ordinary tone deaf  listeners for music. Willis 'Cookie' Cooke,

      From: Phil Kane <[hidden email]>
 To: [hidden email]
 Sent: Monday, May 2, 2016 4:04 PM
 Subject: Re: [Elecraft] 4-ohm to 8-ohm question
   
On 5/2/2016 1:15 PM, Eddy Avila wrote:

> In the "olden" days I would simply use a 4-ohm to 8-ohm audio transformer, but I can't find them anymore!

Not necessary because today's audio amplifier designs do not require
matched impedances.  You are "good to go" with no further matching.
--
73 de K2ASP - Phil Kane
Elecraft K2/100  s/n 5402

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
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Re: 4-ohm to 8-ohm question

Jim Brown-10
In reply to this post by k6sdw
On Mon,5/2/2016 1:15 PM, Eddy Avila wrote:
> My K2 audio output is 4-ohms which I drive into an 8-ohm ICOM speaker with filters. Yes, it works OK, but I would like to match them better.

There is no need to do that. Audio output stages are constant voltage
sources -- that means they have a VERY low output impedance, typically a
fraction of an Ohm. The impedance rating of a loudspeaker output stage
is the MINIMUM impedance that the stage can drive safely. Any higher Z
will work fine. A transformer would do three things 1) increase the
headroom (max loudness) by about 2.5 dB (there's loss in the xfmr); 2)
increase distortion at low audio frequencies (because most audio xfmrs
aren't very good; and 3) deplete your bank account.

73, Jim K9YC
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Re: 4-ohm to 8-ohm question

N5GE
In reply to this post by k6sdw
Y'All,

Please put the name of the device you need help with or wish to
discuss.

That helps those of us who don't have the device and therefore can't
be of help to you.

Thanks

On Mon, 2 May 2016 13:15:00 -0700, you wrote:

>My K2 audio output is 4-ohms which I drive into an 8-ohm ICOM speaker with filters. Yes, it works OK, but I would like to match them better.
>In the "olden" days I would simply use a 4-ohm to 8-ohm audio transformer, but I can't find them anymore! Really, I've looked at all the suspect places, including eBay and Amazon.
>Any suggestions, I just want and easy, simple way to matching the two impedance's without losing power which would happen if I used a resister across the ICOM speaker. I know I can just drive a small audio amp between them, but that means more wires to power up the amp......
>Thanks to all
>73
>ed    
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html
>Message delivered to [hidden email]
ARS N5GE

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Amateur Radio Operator N5GE