How could impedance damage a computer stereo output?

[venge86]

I've looked around the net for a while to find an answer, but no luck. I've connected my mobo sound output to a Marantz SR1000 (old masterpiece) amplifier and headphones simultaneously through a parallel connection (headphone output on marantz has very low volume). I presume a typical sound card/mobo sound output, is designed to safely drive a generic headset of 16/32Ω. Marantz has an input sensitivity of 160mV. While I'd really like to have a multi-meter, I don't, and I heard soundcards/outputs can drive up to 2V. Given the parallel connection fact, could this damage any of the equipment including of course the mobo sound output?

 

[americanaudiophile]

Probably would not damage anything.
When the receiver is off it might load down the output of the mobo to the headphones so I would connect one at a time.
You said the headphone out of the Marantz is low? Was the mobo line out connected to the Marantz and the volume PC set volume turned all the way up. The Marantz should drive the 16/32 ohm headphones fine.

 

[venge86]

Probably would not damage anything.
When the receiver is off it might load down the output of the mobo to the headphones so I would connect one at a time.
You said the headphone out of the Marantz is low? Was the mobo line out connected to the Marantz and the volume PC set volume turned all the way up. The Marantz should drive the 16/32 ohm headphones fine.

I thought with the Marantz closed, the input circuit opens, so it's like connecting the headset alone, so it's safe for the mobo. Am I wrong?
Also, yes, my first actions were to check the pc volume and close system 1 (the speaker output) cause speakers and headset were playing simultaneously. I had to crank the volume up to -18 to -14 (knob label is -infinite, -70, -60... to 0 and I think it's logarithmic) to make it just audible. With my 8Ω Philips speakers I get some crazy loud sound at -31 .

 

[asgard1123]

Impedance alone cannot damage anything, but current and voltage can. That is the reason that voltage and impedance or current and impedance are usually quoted together. It is possible that drawing too much current from the motherboard could damage it. Equally output equipment may be damaged if the input voltage is higher than specified. It is important to check the specifications to ensure a match.
Blind experimentation usually ends in tears.

 

[americanaudiophile]

If the input is powered down there are still passive components connected.
It is a log volume control so you get fine adjustment of volume with the remote. You do have to bring the vclume up quite a bit before you hear anything on most speakers. There are very high efficiency speakers used mostly in Asia that will play really loud with 1 watt so they make the control practical with those.

 

[gzuckier]

Probably would not damage anything.
When the receiver is off it might load down the output of the mobo to the headphones so I would connect one at a time.
You said the headphone out of the Marantz is low? Was the mobo line out connected to the Marantz and the volume PC set volume turned all the way up. The Marantz should drive the 16/32 ohm headphones fine.

I thought with the Marantz closed, the input circuit opens, so it's like connecting the headset alone, so it's safe for the mobo. Am I wrong?
Also, yes, my first actions were to check the pc volume and close system 1 (the speaker output) cause speakers and headset were playing simultaneously. I had to crank the volume up to -18 to -14 (knob label is -infinite, -70, -60... to 0 and I think it's logarithmic) to make it just audible. With my 8Ω Philips speakers I get some crazy loud sound at -31 .

Even if the computer output hits a whopping 2 volts, that's not going to fry anything on the input of the Marantz. It's not going to fry anything further down, either, because the output of that first stage is going to saturate; i.e. if the Marantz produces 100 watts at full blast, that's probably around 0.1 volts input, and if you crank the input up to 2 volts, it's still only going to deliver 100 watts, it's not going to produce 2000 watts. You would presumably hear it distort like crazy if the 2 volts were overdriving the input, and if you left it at that level for a while you might cook the output stages, or maybe the speakers, though.
Oddly enough, turning the Marantz off while connected to the computer output might have a bad effect on the sound through headphones connected in parallel to the computer output; the input of an amp often feeds through a resistor and/or capacitor into the base of a transistor; and when it's unbiased, i.e. when the power is off, that acts like a diode; so an unpowered input from an amp looks like a nonlinear load to whatever's feeding it, and the output of the computer sound card probably isn't robust enough to ignore that, and it might affect the headphones in parallel.

 

[venge86]

The truth is, when I close the amp (which still plays for about 10 seconds, probably because of the capacitor's load), the headphones' volume linearly increases. I think that's not really bad as the sound card and the amp don't have a sudden spike of voltage/current. Aamericanaudiophile, Asian speakers you mention could probably be 4Ω?