connecting headphones dirctly to power amp binding posts

[gaxxard]

I have 2 pairs of headphones (sennheiser HD25 70ohm and HD250II 300ohms) that I want to connect to my 8ohm Copland Valve Power Amp Can someone please give me advice on how to do this with the least risk of damaging any equipment?

 

[monkeytree]

just a couple of resistors i think

 

[David Bridgen]

Yes, a couple of resistors across each output.

From the output connector of each channel connect 1k and 10 ohms in series to the "ground" connectors, and the 'phones across the 10 ohms resistors.

If the sound intensity is too low at the volume setting you want to use, reduce the value of the 1k resistors until you find one which gives satisfactory results.

 

[Nigel Goodwin]

As it's a valve amplifer it would be a good idea to connect 8 ohm dummy loads across the output of the amplifier as well - valve amps don't like feeding into too high an impedance, and you might damage the amplifier!.

 

[Someone Electro]

you mean you can blow an valve amp by switching it on whith no load coneted to the outputs?

I didnt know that .i dont know much abot those vacum tubes stuf (i lerned that they use high voltage the hard way.Zapp!!!)

 

[Nigel Goodwin]

you mean you can blow an valve amp by switching it on whith no load coneted to the outputs?

Not just by switching it on, but by using it without the correct load - especially with no load at all!, unlike transistor amplifiers, which are safe into higher loads!.

Generally it's the output transformer which could be damaged in a valve amplifier, which is mostly one of the most expensive parts as well!.

 

[gaxxard]

won't the amp blow even a fairly high wattage 8 ohm resistor?

 

[David Bridgen]

won't the amp blow even a fairly high wattage 8 ohm resistor?

Probably not. It depends on how far you advance the volume control and to some exent on the type of music.

I once did a quick experiment to get an idea of the average power delivered to the 'speakers. The source was a particularly loud passage of a Beethoven symphony played at a volume which would be similar to that experienced in a seat half way back from the orchestra in a concert hall.

I used a commercial audio power meter. The average power in one channel was about 4 watts.

A "fairly high wattage resistor" will have an easy ride.

ps
Yes, of course Nigel. Silly of me to have overlooked that.

 

[Nigel Goodwin]

won't the amp blow even a fairly high wattage 8 ohm resistor?

You (obviously!) use an 8 ohm resistor of sufficient power rating!.