j-curve
100+ Head-Fier
- Joined
- Apr 15, 2002
- Posts
- 489
- Likes
- 11
...because output resistors are evil!!
It's tempting to think that driving a set of headphones should be a walk in the park for an integrated amplifier. If the thing can pump 80 watts into 4 ohms then 10mW into 300 ohms shouldn't be much of a challenge.
Well, that's true, but unfortunately there's usually a nasty little component between the speaker terminals on the back panel and the headphone socket on the front panel, known as the output resistor. Kind of necessary in a way, since the effect of plugging a mono phono plug into the headphone socket or incompletely inserting a regular stereo plug can be a short circuit, which could have disastrous consequences if the volume was turned up and the amplifier's full power was available to the headphone socket. Melting the lugs to the plug would be quite likely. Fried output transistors could also be on the menu. Hence most manufacturers employ the cheapest method known to man - the output resistor - to limit the current.
Now if you're driving Ety 4P's and the output resistor happens to be around 80 ohms I guess you couldn't be much happier. If on the other hand you're pushing HD600's then you can expect to suffer loose lower-mids and a bass hump.
Having seen how a car battery can melt the end of a chrome vanadium spanner, I wouldn't advise wiring your own headphone socket direct to the speaker terminals. A better approach would be to use the existing front-panel headphone output with an external resistor divider, say 47 ohms and 4.7 ohms in series. The total 52 ohms goes across the headphone output, while the headphones are connected across the 4.7 ohm resistor. You need to turn the volume up a bit higher but you get a low impedance output to drive your phones.
It's tempting to think that driving a set of headphones should be a walk in the park for an integrated amplifier. If the thing can pump 80 watts into 4 ohms then 10mW into 300 ohms shouldn't be much of a challenge.
Well, that's true, but unfortunately there's usually a nasty little component between the speaker terminals on the back panel and the headphone socket on the front panel, known as the output resistor. Kind of necessary in a way, since the effect of plugging a mono phono plug into the headphone socket or incompletely inserting a regular stereo plug can be a short circuit, which could have disastrous consequences if the volume was turned up and the amplifier's full power was available to the headphone socket. Melting the lugs to the plug would be quite likely. Fried output transistors could also be on the menu. Hence most manufacturers employ the cheapest method known to man - the output resistor - to limit the current.
Now if you're driving Ety 4P's and the output resistor happens to be around 80 ohms I guess you couldn't be much happier. If on the other hand you're pushing HD600's then you can expect to suffer loose lower-mids and a bass hump.
Having seen how a car battery can melt the end of a chrome vanadium spanner, I wouldn't advise wiring your own headphone socket direct to the speaker terminals. A better approach would be to use the existing front-panel headphone output with an external resistor divider, say 47 ohms and 4.7 ohms in series. The total 52 ohms goes across the headphone output, while the headphones are connected across the 4.7 ohm resistor. You need to turn the volume up a bit higher but you get a low impedance output to drive your phones.