[Elecraft] External speakers for K3?

[Joe Subich, W4TV]

I would not use any speaker less than 8 Ohms with the K3. 

The audio amplifier draws more current and distortion increases 
as the load impedance decreases.  Best case THD+N vs. frequency 
for the audio amplifier is three times WORSE with 4 Ohm loads 
compared with 8 Ohm loads.

2 Ohm loads are not even spec'd. 

73, 

   ... Joe, W4TV 
  





> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Tom Hammond
> Sent: Tuesday, May 12, 2009 7:23 AM
> To: Brendan Minish; elecraft at mailman.qth.net
> Subject: Re: [Elecraft] External speakers for K3?
> 
> 
> Brendan:
> 
> >For general communications use I am very fond indeed of the speakers 
> >Motorola made for their various mobile rigs over the years, They are 
> >very cheap, efficient and sound great for good quality 
> communications 
> >audio. These are not Hifi speakers but for speech / CW they 
> do a superb 
> >job.
> >
> >Mostly they seem to be a pretty close match in size and 
> colour for the 
> >K3 too.
> 
> I agree completely.
> 
> >Some of them are 2 Ohm though, The ones I use with My K3 at 
> the moment 
> >are 2 Ohm ones, Since I do not know for sure if the AF amp 
> in the K3 is 
> >happy driving an impedance this low I stuck a 2Ohm 2W resistor in 
> >series with each speaker and still have more than enough audio in my 
> >shack.
> >
> >I have seen these available in 4-Ohm and amplified variants 
> too. Pretty 
> >much every radio in the shack is connected to a Moto speaker and I 
> >still buy them at rallies, collecting stuff I might need 
> someday must 
> >be habit
> >
> >Anyone know if the can K3 drive a 2Ohm speaker without bad stuff 
> >happening ?
> 
> In a recent e-mail from Lyle Johnson, KK7P, he stated that, 
> while not 'designed' to drive 2-Ohm loads, the K3s AF amp 
> should "probably" work OK BUT that if one attempted to drive 
> the speakers too hard, and the AF amp attempted to draw 
> excessive current (and starts to overheat), the amp would go 
> into a protective shut-down mode, rather than risk damaging itself.
> 
> For what it's worth, MOST (possibly all nowadays) of the 
> newer, plastic-cased, Motorola NON-amplified speakers are now 
> 8-Ohms... there may be some 4-Ohm speakers in the newer-style 
> plastic ('fitted back') cases, but I suspect that almost all 
> have now been switched to 8-Ohm speakers.
> 
> I'm using a pair of 8-Ohm Motorola speakers on my K3 and it 
> sounds just fine.
> 
> Cheers,
> 
> Tom Hammond   N0SS
> 
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