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jhendrix
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Headphone amp question

Hi there,

I hope this is not too stupid a question, but what causes the speakers to be muted while listening to headphones through a headphone amp?

My current integrated amp has a built-in headphone socket and I need to switch off A and B speakers, otherwise there will be a terrible racket in the house. If you are using a headphone amp and the speaker A/B switch-off facility is not available on the amp, does the headphone amp automatically mute your speakers? Or, do you always require a mute feature of some sort?

Thanks!

KBK
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Re: Headphone amp question

if you are using a true headphone amp, then it will not be able to drive speakers, or have the connectivity terminals for such.

If you are using an integrated, and there is no speaker switching, just a headphone jack, then there is high odds that the headphone jack is being driven by the 'preamp section' of the unit and not the power amp section.

In most integrateds, the power amp is also connected to the headphone jack but it is resistively loaded, to prevent damage to the headphones. They have speaker switching to shut the speakers off.

More modern units sometimes have relay switching with a automatic speaker muting circuit, that operates when the headphones are recognized as being hooked up...but this can be clumsy and expensive, so it is rare.

struts
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Re: Headphone amp question

Commodity headphone jack assemblies act like a two-way switch, plugging in the 'phones physically opens the switch and causes the speaker outputs to be disconnected. True headphone amps won't have these kind of jacks, a) because they degrade the sound and b) because they don't need them; 'true' headphone amps only drive 'phones and not speakers.

jhendrix
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Re: Headphone amp question

Thanks. With headphone amps, how do you mute the sound from the speakers while listening to headphones? Most high end amps don't have speaker off or muting buttons.

Jeff Wong
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Re: Headphone amp question

Quite often, a source will be fed directly to the headphone amp in its own separate setup, so speakers are not usually part of the equation. Incorporating a headphone amp into a speaker based system might be a bit tricky. I'm thinking you can feed the headphone amp a source via the tape monitor loop, but, I don't think that will necessarily solve the problem of the speakers still playing.

struts
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Re: Headphone amp question

jhendrix,

Feels like we're starting to go in circles here so we obviously haven't answered your question. Is it hypothetical or specific? I guess the actual answer differs from product to product and will depend on whether the amp in question is an integrated with a headphone socket, a 'pure' headphone amp or a headphone/pre combo.

I think you've had all the 'generic' answers. Maybe you have a specific product in mind in which case it might makes things easier if you tell us which one.

KBK
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Re: Headphone amp question

We may be talking about a preamp with a headphone jack.

For example, the Acoustat TNP preamp is an all FET, fully discrete 'op-amp' preamp. Pure transistor, no opamps. There are 'pre out' switches (2), and a headphone jack. The output section drives the headphones directly.

When fixed up (modded out), this is a very good headphone amp. Pure class A, all FET. Even capable of driving a very tiny set of 16-20+ ohm speakers (only after modification!). Very cool. Goes out to 1Mhz, too. For the headphone jack to work, both preamp outputs must be switched off. In this case, switching 'on' the headphones, kills the preamp outs. The best sounding preamps do it this way, some might argue. It is debatable, due to the use of a minimum of three switches to get it done. (two preamp outs {switched} and a headphone jack and associated switch)

The GFP-555 preamp from Adcom, for example, like most Rotel preamps, has a separate headphone driving op amp. It steals a line off the output that is going to the preamp outs, and drives the headphone op-amp seperately from the preamp outs. It cannot be defeated, but it would serve no need for such to be interrupted. The preamp outputs can or cannot be switched on or off, depending on the given model of preamp. This tends to be the most common design, when you see a headphone jack on a given preamp.

On the best preamps, that have discrete amplifier circuitry for driving the preamp outs, the headphone amp can also be discrete. Those preamps are rare. If if it sounds expensive to have two separate output amplifier sections, well, it is. Thus, not many were made. And figuring out which units were built this way is next to impossible, unless you have their promo literature in front of you.

If you don't use headphones at all, be aware that a headphone jack, enacted in the above fashion on your given preamp (or CD player!!) is done this way. The small bit of resistance within the given headphone amplifier's loading of it's inputs, where it steals a bit of energy off the outputs, actually degrades the sonics of the given CD or preamp output..ever so slightly. If this is your situation, you have suffered overall long-term sonic degradation, for something you rarely use. Just remember, I said slight degradation, not massive. Don't do the hippy/anal/audiophile freak-out dance. On the better systems, the effect of removing said headphone components and connectivity can be barely noticeable.

On some cheaper preamps, and integrateds...DANGER(!)..as they have the preamp outs lines 'cut' when you feed a headphone 1/4" plug into the headphone jack. This is not seen on real gear, as it can blow power amps and speakers.

The purist..has a wholly separate system for headphones, to avoid these issues.

jhendrix
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Re: Headphone amp question

I think you have all answered my question. Thanks!

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