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Is there an electrical risk to headphones to run them off a LINE OUT port, directly off something like a DAC, that isn't intended for direct playback?

Quinton595

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Hello,

For years, I have been running a pair of HD6XX headphones directly off a Grace SDAC, as I've never actually owned an amp.

I've always known about the general concern that non-amplified input will be quieter, but frankly, Windows and the Grace SDAC put out enough volume in even the relatively high-impedance 6XXs that I can't listen to them above 60/100 windows volume, and typically listen between 20 - 40/100.

The thing is, I have now purchase a pair of HD800s, and don't yet have an amp for them either (working on it!).

I really want to make sure I don't damage the HD800s accidentally, by running them directly off the line-out of the Grace SDAC while I'm waiting on a real DAC and amp to arrive. I had a short discussion with people on head-fi about how the line-out has a different impedance and voltage than an actual headphone-out jack would have, but frankly, I don't understand the electrical theory enough to know if this somehow poses a threat to the HD800s.

Thank you!
 
I've seen a couple of burned out DACs and each time the seller said it just suddenly stopped working. Both included double RCA to 3.5mm female so they could run headphones direct off them. I've seen manufacturer warnings not to do it in a manual too. Someone here I'm sure knows the technical explanation. The parts/not working section of eBay has had several so I wouldn't risk it.
 
I've seen a couple of burned out DACs and each time the seller said it just suddenly stopped working. Both included double RCA to 3.5mm female so they could run headphones direct off them. I've seen manufacturer warnings not to do it in a manual too. Someone here I'm sure knows the technical explanation. The parts/not working section of eBay has had several so I wouldn't risk it.
Ah yes, I hadn't even considered the risk it poses to the DAC, rather than the headphones. I remember someone mentioned that on the head-fi thread, but didn't expand on it. Hopefully someone here knows what the possible risks are, both ways.
 
DACs are expecting at least 10000 ohms resistance on their outputs. Headphones are at best 600 ohms, the HD800S is 300 ohms. Thanks to Ohms Law, lower ohms means the DAC has to output higher current and most DAC output stages are just not equipped for that. Line level (the DAC output) is 2V peak to peak at 0db which most headphones can easily tolerate.
 
The headphone load is much lower than the DAC designer expected the DAC to drive. This may affect the frequency response. It will probably make the DAC output stage draw more current than expected and demand more current than the PSU was designed for. With luck the DAC will be fine but just run hotter than expected.
 
DACs are expecting at least 10000 ohms resistance on their outputs. Headphones are at best 600 ohms, the HD800S is 300 ohms. Thanks to Ohms Law, lower ohms means the DAC has to output higher current and most DAC output stages are just not equipped for that. Line level (the DAC output) is 2V peak to peak at 0db which most headphones can easily tolerate.
Thank you for your concise answer. My interpretation of your comment is that there's little risk to the headphones, but there is risk to the DAC, due to the resistance being too small, leading to too much current flow.

Would this current flow scale with volume output? Do you risk doing more damage at higher volume?

I've been using the SDAC in this way, to drive the 300 ohm 6XX's for a couple of years with no incident so far. Do you think I could get away with running the HD800s on it for a month, until I get dac/amp equipment?
 
An XLR out typical has an 100 ohm output impedance, so a >200 ohm headphone should be no issue at all.
Electrically , I see no issue, only the max SPL could be limited.
 
Would this current flow scale with volume output? Do you risk doing more damage at higher volume?
Yes. At zero volume there is zero current.

Ohm's Law says Current = Voltage/Resistance.

In reality you are unlikely to damage it, but you are "stressing" it and taking a risk. Often, these things can't put-out enough current to damage themselves, even if the output is shorted. (If it can't put-out the current, the voltage drops... Ohm's Law is a law of nature., with man-made units of measure, and it's always true.)

I've been using the SDAC in this way, to drive the 300 ohm 6XX's for a couple of years with no incident so far. Do you think I could get away with running the HD800s on it for a month, until I get dac/amp equipment?
300 Ohm's is probably "OK" but if it's not designed to drive a headphone there is SOME risk. And there is a possibility of the sound being "damaged" (frequency response variations or distortion).

An XLR out typical has an 100 ohm output impedance, so a >200 ohm headphone should be no issue at all.
Electrically , I see no issue, only the max SPL could be limited.
That doesn't mean it's designed to drive a 100 Ohm load. Power amplifiers typically have an output impedance of a fraction of an Ohm but they are designed to drive 4 or 8-Ohm speakers and "bad things" can happen if you go lower.
 
Yes. At zero volume there is zero current.

Ohm's Law says Current = Voltage/Resistance.

In reality you are unlikely to damage it, but you are "stressing" it and taking a risk. Often, these things can't put-out enough current to damage themselves, even if the output is shorted. (If it can't put-out the current, the voltage drops... Ohm's Law is a law of nature., with man-made units of measure, and it's always true.)


300 Ohm's is probably "OK" but if it's not designed to drive a headphone there is SOME risk. And there is a possibility of the sound being "damaged" (frequency response variations or distortion).


That doesn't mean it's designed to drive a 100 Ohm load. Power amplifiers typically have an output impedance of a fraction of an Ohm but they are designed to drive 4 or 8-Ohm speakers and "bad things" can happen if you go lower.
Output impedance of xlr and rca outputs are most of the time made series resistors. You can even short circuit them without any issue
 
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Output impedance of xlr and rca outputs are most of the time made series resistors. You can even short circuit them without any issue
Except for reduced output. Any output impedance that isn't an order of magnitude or less than the load isn't desirable. A good DAC should not be damaged by a shorted or low load output but the frequency response and volume levels may suffer.
 
Interesting that there's a bit of a split between people saying it will damage the DAC due to it pushing too much current, and then others saying it's not an issue.

It seeks everyone is in agreement, though, that the HEADPHONES are at no risk, it's only a risk to the DAC, depending on how its designed and if its able to limit its own current draw.

I take it everyone here thinks it'll be okay to run my HD800s for a while until I get the gear, with the only risk being to the DAC itself?
 
Amir's review of the Grace shows that it is a well engineered DAC. The output limit is just over 2V which should be no issue for the SD800s. I don't think it is ideal to run off of the line out but nothing should break either.
 
Hello,

For years, I have been running a pair of HD6XX headphones directly off a Grace SDAC, as I've never actually owned an amp.

I've always known about the general concern that non-amplified input will be quieter, but frankly, Windows and the Grace SDAC put out enough volume in even the relatively high-impedance 6XXs that I can't listen to them above 60/100 windows volume, and typically listen between 20 - 40/100.

The thing is, I have now purchase a pair of HD800s, and don't yet have an amp for them either (working on it!).

I really want to make sure I don't damage the HD800s accidentally, by running them directly off the line-out of the Grace SDAC while I'm waiting on a real DAC and amp to arrive. I had a short discussion with people on head-fi about how the line-out has a different impedance and voltage than an actual headphone-out jack would have, but frankly, I don't understand the electrical theory enough to know if this somehow poses a threat to the HD800s.

Thank you!
from their website:

Following is a list of some of the technical features of the SDAC:
  • XMOS X200 USB streaming controller operating in asynchronous transfer mode.
  • IDT XLH series oscillators provide and exceptionally stable and low noise sample clock for DAC. 12kHz to 20MHz phase jitter is 750fs. Note that the jitter below 12kHz is generally more important in audio applications but the 12kHz-20MHz specification is commonly used for specifying oscillators so it is useful in comparing to other clocks. In the SDAC the clock jitter artifacts are well below the DAC noise floor so they are essentially irrelevant.
  • AK4452 DAC provides 32 bit internal processing , 115dB dynamic range, and the same architecture as the AK4490.
  • Output amplifiers are Burr Brown OPA1652. These are extremely low noise low distortion FET input amplifiers with excellent output cable drive capability. Note that the output impedance is set at 150 Ohms so the SDAC is not intended to drive headphones. While it will not harm anything to do so, the fidelity will not approach what is possible with a good headphone amplifier.
 
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