Perhaps this will help: Look up the specs on a good home audio amplifier — say, QSC or Crown. You’ll find something called “damping factor”, and it’s often 50 or more. Roughly speaking, it’s the ratio of the (loudspeaker) load impedance to the internal (source) impedance of the audio amplifier. So modern semi-pro and stereophile audio amplifiers are “grossly out of specs”, as you put it.
I have a legacy, hernia-inducing McIntosh power amplifier, circa-1960s, with output transformers and three taps — for 4-, 8-, and 16-ohm loudspeaker loads. Nothing I’ve owned since then uses output transformers or matched loads. Most audio amplifier designs these days are voltage followers. Most manufacturers don’t attempt to match source impedance to load impedance. Highly damped output stages are “good” things to have. Yes, it’s true that voltage-follower amplifiers deliver more power to low-impedance loads than to high-impedance loads. But if I were to follow your line of reasoning to its logical conclusion in the home audio arena, I would conclude that 4-ohm speaker systems are sonically superior to 16-ohm speaker systems simply because they require more output power from the audio amplifier to play my music collection. Does that seem like a reasonable way to choose your stereo system loudspeakers? Or headphones for your K3? If your 100-ohm (or higher) headphones can’t provide reasonable levels of undistorted sound pressure at your ears when your K3 or K3S audio gain control is at, say, 9 or 10 o’clock, perhaps it’s time to buy a new pair of “cans”. That’s certainly gotta be cheaper than reverting to a 75A-4 with its audio output transformer and 500-ohm tap. Bud, W2RU > On Dec 28, 2015, at 2:57 22PM, Steve Ellington <steven...@gmail.com> wrote: > > No problem...Just grossly out of specs. > Whatever happens....happens > 73 > > Steve N4LQ > > On Mon, Dec 28, 2015 at 2:53 PM, W2RU - Bud Hippisley <w...@frontiernet.net > <mailto:w...@frontiernet.net>> wrote: > What am I missing? > > I use 600-ohm stereo headphones plugged directly into the front panel jack of > my K3S. > > I run the Audio Gain control at 9 o’clock — roughly a 25% rotation toward > full volume. > > I have more than enough audio for my elderly ears, and when I pull the > headphone plug out of the jack, my speaker audio is at a comparable level. > > What is the non-problem with high-impedance phones that you guys are trying > to solve? > > Bud, W2RU > > > On Dec 28, 2015, at 1:59 09PM, Steve Ellington <steven...@gmail.com > > <mailto:steven...@gmail.com>> wrote: > > > > K3 uses the. > > > > LM4811 Headphone Amplifier > > > > Texas Instruments Specs for output Z > > > > RL = 16Ω 105 mW > > RL = 32Ω 70 mW > > > > At 60 ohms the output power drops to 20 mw. Per their graphs. > > > > 300 ohms is not even considered. > > > > Amplifier gain control is done digitally within the chip. With such a high > > Z load, gain would likely need increasing. > > The results of doing so are unknown. Consider pop, click, white noise etc. > > > > Also consider what happens when switching from headphones to speaker when > > the AF Gain control is turned up high. Blasting? > > > > I suggest sticking within the 16 to 32 ohm range. > > > > Steve N4LQ > > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
