[Noske]

Hello! I'm hoping someone can help me with my question. I have a USB powered DAC with a built-in amplifier - model Signstek HIFI USB. This DAC has a PCM2704 chip (great sound BTW!) and according to its datasheet, the output power is 12mW with 32ohm load - also 1.8Vpp with 10k load. I'm assuming that this DAC board uses the chip's built in headphone amplifier - looks like it does from the absence of an extra op-amp chip. Unfortunately, this DAC does not have a volume potentiometer so it relies on the volume control from the PC side through PCM stream. As you know, this method is very prone to accidentally output at the maximum volume level.

So, here is my question: can SR80e play at 12mW without getting damaged? These headphones are extremely efficient - even more efficient than its predecessor SR80 (which I also own). And playing even at half way, they are way too loud. (They are rated at SPL 1mW: 99.8dB! So even couple of mW is already too loud). What is the maximum power that SR80e can handle? So far, the answers I found are: "if they are still playing without distortion, headphones are probably okay..." I'm hoping to get more definitive answers here - as I want to take other measures to attenuate the volume if potential damage exists. I am also aware of the bass "clipping" producing high frequency content commonly damaging speakers and such... not sure these headphones/DAC combo are immune from such clipping damage.

Thanks in advance.

 

[PurpleAngel]

I would say to get a solid state headphone amplifier to connect to the DAC's line-output,
The DACs with the MPCM2704 DAC chip, might have a headphone jack with a high output impedance
Modern solid state headphones amplifiers now come with very low output impedance, which helps bring out the audio detail, with low impedance (Ohm) headphones (SR80e).
I have bought several $15 DACs, from China, that use the PCM2704 DAC chip and they do sound nice, but they do not seem to last, usually tried to order several at a time, never knowing when one would stop working and it takes 3 weeks to ship from China to California U.S.A.
But the PCM2704 does sound nice.

 

[ProtegeManiac]

Hello! I'm hoping someone can help me with my question. I have a USB powered DAC with a built-in amplifier - model Signstek HIFI USB. This DAC has a PCM2704 chip (great sound BTW!) and according to its datasheet, the output power is 12mW with 32ohm load - also 1.8Vpp with 10k load. I'm assuming that this DAC board uses the chip's built in headphone amplifier - looks like it does from the absence of an extra op-amp chip. Unfortunately, this DAC does not have a volume potentiometer so it relies on the volume control from the PC side through PCM stream. As you know, this method is very prone to accidentally output at the maximum volume level.

So, here is my question: can SR80e play at 12mW without getting damaged?

Yes they'll survive that unless you do that too often and clip the signal often enough.

These headphones are extremely efficient - even more efficient than its predecessor SR80 (which I also own). And playing even at half way, they are way too loud. (They are rated at SPL 1mW: 99.8dB! So even couple of mW is already too loud). What is the maximum power that SR80e can handle? So far, the answers I found are: "if they are still playing without distortion, headphones are probably okay..." I'm hoping to get more definitive answers here - as I want to take other measures to attenuate the volume if potential damage exists. I am also aware of the bass "clipping" producing high frequency content commonly damaging speakers and such... not sure these headphones/DAC combo are immune from such clipping damage.

12mW wouldn't even get it to 120dB and that assumes the audio program doesn't have too high digital gain. If it does it runs out of steam by about 111dB.

In any case why not just unplug the headphone and then reduce the Windows volume before plugging it back in if you're so worried about that?

 

[Noske]

Thanks for the responses!

>>The DACs with the MPCM2704 DAC chip, might have a headphone jack with a high output impedance
This might be a true statement - appears that the same circuit is shared between the RCA and line-out... the DAC chip's reference design calls for multiple resisters in parallel* with the output load... if my calculation is right, output impedance of the headphone out is about 16ohms. (RCA should be round 10k) I doubt device this small will have other means of short protection. I haven't yet to open up the box to check. But this itself motivates me to hunt for a headphone amp. So thank you for pointing that out!

>>In any case why not just unplug the headphone and then reduce the Windows volume before plugging it back in if you're so worried about that?
This is exactly my concern. The system relies on the user to adequately avoid potential damage - causing damage is much easier to do with the headphone setup by accidentally walking away from the PC or due to surrounding noise, not realizing the blasting music until it's too late. For example, every time this DAC is reconnected with the windows 10, it defaults back to the max volume.

I haven't yet to see a hard number published by Grado regarding the power handling (hence my post here)... like often you see in specs on passive speakers. I feel this is still a gray area... But I'm sure they do bunch of testing at extreme limits - or even during production testing - for driver matching and such. It would be good to know this limit.

 

[ProtegeManiac]

>>In any case why not just unplug the headphone and then reduce the Windows volume before plugging it back in if you're so worried about that?
This is exactly my concern. The system relies on the user to adequately avoid potential damage - causing damage is much easier to do with the headphone setup by accidentally walking away from the PC or due to surrounding noise, not realizing the blasting music until it's too late. For example, every time this DAC is reconnected with the windows 10, it defaults back to the max volume.

If you walk off having been listening at safe listening volumes it would have to be an extremely badly encoded audio signal with very, very, very, very, very, very high nigh unusable gain to go through that to destroy it by the time you get back.

If it has to reconnect because the computer went to sleep, that's why I said just unplug it. It's like putting the car in neutral and if you know you're stepping out of the cabin you have to engage the handbrake and make sure the shifter is in neutral by gently swinging it left and right, then hit a button and check the door handle if it actually locked.

I haven't yet to see a hard number published by Grado regarding the power handling (hence my post here)... like often you see in specs on passive speakers. I feel this is still a gray area... But I'm sure they do bunch of testing at extreme limits - or even during production testing - for driver matching and such. It would be good to know this limit.

If the signal isn't clipping or badly distorting your ear drums are always more likely to get blown to bits before the drivers.

 

[Noske]

Since then, I measured the output impedance of the Signstek DAC - took multiple measurements at different output levels. It is: 3.74 - 4.43 ohms, ~4.2 average. Not too bad... Also, the headphones are working great!