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New Audiolab DAC - Page 48

post #706 of 857
Quote:
Originally Posted by zigy626 View Post


Interesting I never considered that. Thanks for your input. Personally I find that with M-DAC the HD800 sound too forward. It's like being in the middle of the musicians. On the other hand my Meier Jazz puts me maybe like in the second row which is more enjoyable. I think the M-DAC has a nice headphone amplifier in terms of instrument separation and detail but it really lack in soundstage. I also have found it to be sometimes a bit flat in the upper frequencies.

 

I've not had the pleasure of the HD800 yet, but I agree with your soundstaging observations.

post #707 of 857

The HD800 will sound forward in the midrange and tops with any headamp that doesn't have the energy to drive the massive 55mm drivers. So high current output is required from the headamp section. Going by the info provided by those who have tried the HD800 with the MDAC I would say that the headphone amp is underpowered as far as the HD800 is concerned.

But I wouldn't condemn the MDAC based on that observation. I own both the HD800 and D7000. What I found out over the last couple of years of trying out both headphones on the same headamps is that if the HD800 is driven properly, the D7000 is too bassy. ANd when the D7000 is driven properly the HD800 is too weak in the bass, and too forward in the mids. 
 

post #708 of 857

The headphone amp is even underpowered for the HD600. With most source material (via PC and USB) you have to use it at the extreme of its capabilities and put is almost at the loudest and sometimes really at its loudest. I would think the performance of the headphone amp really has deteriorated at that point.

post #709 of 857

The volume control is a digital attenuator  so it doesn't matter if you are listening closed to 0dB. In fact,  it should sound better. 

post #710 of 857
Quote:
Originally Posted by daniel_hokkaido View Post

anyone use lcd2 with mdac? 

I have, but I think that even the SR71B improves upon the sound as compared to what I get from the MDAC direct.
post #711 of 857
Quote:
Originally Posted by zenpunk View Post

The volume control is a digital attenuator  so it doesn't matter if you are listening closed to 0dB. In fact,  it should sound better. 

 

Wouldn't that be the case if you use it as a preamp and not as a "normal" amp driving your headphones directly.

post #712 of 857

John Westlake said the line out and the headphone out share the same circuitry. As far as I know there is no separate or independent headphone amplifier within the MDAC.

post #713 of 857
Quote:
Originally Posted by zenpunk View Post

John Westlake said the line out and the headphone out share the same circuitry. As far as I know there is no separate or independent headphone amplifier within the MDAC.


I am surprised about that if it is indeed true. The headphone out has to handle between 32 to 300 Ohms in most cases, whilst the line out would have to handle around 47K. A different level of gain and feedback would be required to cope with the two different requirements.

post #714 of 857
post #715 of 857

I am speechless.
 

post #716 of 857
Quote:
Originally Posted by Baxide View Post


I am surprised about that if it is indeed true. The headphone out has to handle between 32 to 300 Ohms in most cases, whilst the line out would have to handle around 47K. A different level of gain and feedback would be required to cope with the two different requirements.

 

Please explain.

I don't see why you need different gain and feedback.

If the line stage has enough output current and low enough output impedance, then it should be fine for driving headphones.


Edited by Chris J - 7/8/13 at 6:10pm
post #717 of 857

Assuming that the basic DAC chip output is the more common 2Vrms and the CD line input of your amplifier is 2Vrms then the line output op-amp only needs to be of unity gain and be an impedance match for between 22K to 100K amplifier inputs.

 

A headphone output amplification stage needs to be able to drive a far lower than 22K impedance. Headphones are between 12 Ohms and 600 Ohms normally. To drive such low impedance loads require a far higher current output stage. But it also requires a far higher output voltage. A typical 300 Ohms headphone needs around 10Vrms to produce the sort of dynamic range they are capable of. A 32 Ohms headphone would need around 4Vrms.

 

So the 2Vrms output of a line amplifier stage will need to be increased via a higher gain in order to obtain the output voltage required to drive a set of headphones. And that's just for the increased voltage swing required. If you add to that that a headphone driver also needs a higher current from the headamp stage, then a simple opamp output is going to let you down in terms of frequency response under load. Bass will be the first victim.
 


Edited by Baxide - 7/9/13 at 2:27am
post #718 of 857
Quote:
Originally Posted by Baxide View Post

Assuming that the basic DAC chip output is the more common 2Vrms and the CD line input of your amplifier is 2Vrms then the line output op-amp only needs to be of unity gain and be an impedance match for between 22K to 100K amplifier inputs.

A headphone output amplification stage needs to be able to drive a far lower than 22K impedance. Headphones are between 12 Ohms and 600 Ohms normally. To drive such low impedance loads require a far higher current output stage. But it also requires a far higher output voltage. A typical 300 Ohms headphone needs around 10Vrms to produce the sort of dynamic range they are capable of. A 32 Ohms headphone would need around 4Vrms.

So the 2Vrms output of a line amplifier stage will need to be increased via a higher gain in order to obtain the output voltage required to drive a set of headphones. And that's just for the increased voltage swing required. If you add to that that a headphone driver also needs a higher current from the headamp stage, then a simple opamp output is going to let you down in terms of frequency response under load. Bass will be the first victim.

 

Respectfully, I disagree on a few points.

The M-DAC can be used as a digital pre-amp.
There are a lot of pre-amps out there that can output 10 Vrms.
There are a lot of analog pre-amps out there that have a gain of 10 or 20 or 30 dB. This is fairly typical.

You don't match the impedance to a 10 kOhm load. This is a low frequency signal, not RF, i.e. the signal is much lower than 1 MHz. The ideal pre-amp would be an ideal voltage source, i.e. have zero output impedance.

If you design the pre-amp output stage to output enough current and with a low enough output impedance, then you can also use the pre-amp out to drive headphones.
There are also a lot of pre-amps which are designed to drive 600 Ohm loads. Sure, this is overkill, but there are many out there designed to drive a 600 Ohm load.
post #719 of 857

With an average closed loop gain of 30 for a 100W amp I would be expecting to see a massive amount of signal clipping at anything above 4Vrms from a preamp. So 10Vrms won't be doing much good to the power amp output stage.

 

Preamps require a certain amount of impedance matching with a power amp. To suggest otherwise is fallacy. A low output impedance from a headphone amp might be useful for headphones, but not for a pre/poweramp connection link. You are not driving a difficult power amp input after all.

 

Sure there are opamps with 600 Ohms output impedance. The NE5532/5534 were the first to be manufactured and widely used. But that doesn't make it a good output stage for headphones. I can't think of a single opamp offhand that has a 600 Ohms output impedance and a high enough current output to drive a set of decent headphones. 

post #720 of 857
Quote:
Originally Posted by Baxide View Post

With an average closed loop gain of 30 for a 100W amp I would be expecting to see a massive amount of signal clipping at anything above 4Vrms from a preamp. So 10Vrms won't be doing much good to the power amp output stage.

 

Preamps require a certain amount of impedance matching with a power amp. To suggest otherwise is fallacy. A low output impedance from a headphone amp might be useful for headphones, but not for a pre/poweramp connection link. You are not driving a difficult power amp input after all.

 

Sure there are opamps with 600 Ohms output impedance. The NE5532/5534 were the first to be manufactured and widely used. But that doesn't make it a good output stage for headphones. I can't think of a single opamp offhand that has a 600 Ohms output impedance and a high enough current output to drive a set of decent headphones. 

 

If you are saying that a gain of 20 or 30 dB is excessively high for a pre-amp, or not necessary, then I agree. The pre-amp may clip at an output of 10 Vrms, but obviously you just turn the pre-amp volume down to a reasonable listening level.

I agree, the average power amp needs on the order of 1-3 Vrms at the input to drive it into clipping. Anything else from a pre-amp is excessive. Call it pre-amp headroom, if you like.

 

I don't see any reason why an output impedance of (for example) 1 Ohm for a pre-amp driving a power amp would be a problem. Sure pre-amps often have an output impedance of approx. 100 Ohms (usually some insurance to keep the pre-amp stable when driving very capacitive interconnects), but I can't think of any technical reason why you would not want to drive a power amp with an input impedance of 50 kOhms with a pre-amp having an output impedance of 1 Ohm.

 

There are a lot of headphone amp manufacturers who use an Op Amp like the NE5534 to drive the headphones:

the Grado

the CMOY

iBasso, etc, etc.

The NE5534 does not have an output impedance of 600 Ohms. It's less than 1 Ohm Closed Loop;  0.3 Ohms at a gain of 30 dB

It can output up to 38 mA.

25 mA into a 32 Ohm load is 20 mW, more than enough to drive a Grado SR-225i to 110 dB SPL.


Edited by Chris J - 7/9/13 at 3:08pm
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