headphone as speakers

[Bill K Davis]

I know you shouldn't turn on an amp without speakers attatched. Can headphones be used as a substitute?

[E-Stat]

I know you shouldn't turn on an amp without speakers attatched. Can headphones be used as a substitute?

Yes, as it presents a load. As could using some appropriately rated resistors as is done frequently on the test bench.

rw

[markw]

If the headphones are driven from the padded down outputs of power amp stages, then you're good to go. If they are driven from a separate amplifier, generally an op amp of some type then no, the speakers will still not have a load.

[Kursun]

I know you shouldn't turn on an amp without speakers attatched. Can headphones be used as a substitute?

Contrary to the information you have, solid state amplifiers CAN be turned on without any speakers attached. As a matter of fact they'll much prefer this condition to having speakers attached! They just don't like to get short circuited at the speaker posts. Any higher impedance, especially infinite impedance (no speakers) is OK.

On the other hand, that information is true for tube amplifiers (or some very special solid state amplifiers with output transformers, such as some McIntosh designs). They don't like operating with no load, just as solid state amplifiers don't like short circuits.

[musicoverall]

Contrary to the information you have, solid state amplifiers CAN be turned on without any speakers attached. As a matter of fact they'll much prefer this condition to having speakers attached! They just don't like to get short circuited at the speaker posts. Any higher impedance, especially infinite impedance (no speakers) is OK.

On the other hand, that information is true for tube amplifiers (or some very special solid state amplifiers with output transformers, such as some McIntosh designs). They don't like operating with no load, just as solid state amplifiers don't like short circuits.

I wondered about this, too. Although this may be a totally different issue, the reason I wondered why it was not ok to run an amp with no speakers is because I've seen folks with multi channel amps that don't have anything hooked up to certain channels i.e a 7.1 channel amp with only four speakers hooked up.

[Kaboom]

Sorry for the ignorance, but i'm relatively new to this whole wonderful hi-fi world. why is it that amps dont like that? will they screw up? or burn? U cant TURN them ON or you cant PLAY music with no speakers attached? thanks!

[Kursun]

Sorry for the ignorance, but i'm relatively new to this whole wonderful hi-fi world. why is it that amps dont like that? will they screw up? or burn? U cant TURN them ON or you cant PLAY music with no speakers attached? thanks!

I did answer your question on my previous post. Here is a more detailed answer:

* %99.9 Of the Amplifiers on the market today are Direct Coupled Class AB solid state (transistorised) amplifiers. Here is the case for such amplifiers:
Output current = SquareRoot(W/R)
Let's say you are driving the amplifier to 20 Watts.
If your speakers are 8 Ohms then the putput stage of your amplifier is required to put out:
Output current=SquareRoot(20/8)=1.58 Amperes
If your speakers are 4 Ohms then the equation is:
Output current=SquareRoot(20/4)=2.24 Amperes
If you short speaker outputs, then you have Zero Ohms at the speaker outputs. Then the equation becomes:
Output current=SquareRoot(20/0)= INFINITE Amperes (in other words= INFINITE TROUBLE)

What happens if you have no speakers at the output?
Output current=SquareRoot(20/infinite impedance)= 0 Amperes (in other words=ZERO TROUBLE)
(In practice it won't ever drop down to zero because of small bias currents.)

With no speakers attached, the amplifier will idle at a cool temperature, its power consumption will drop, and it is safe.
In fact initially buying an amp plus a headphone was once a common practice. The speakers were bought afterwards when finances allowed. If you have speaker A/B switches at the front panel of your amplifier, these simply disengage the speakers from the output of the amplifier. If you have a multi-channel HT amp/receiver with no speakers on some of its channels, the channels that are used will benefit from this case as the power supply does not have to split its capacity to more channels.


* With tube amplifiers or solid state amplifiers with transformer coupled output stages (which are very, very rare) the stuation is completely different. Now there is an output transformer. If you do not connect a load (speaker) to its outputs (secondary windings of the output transformer) and you have turned up the volume control too high, the voltages across the primary windings of the output transformer may soar up to many times the normal operating voltage and the transformer (and other output devices) may get seriously damaged.