[Harry Manback]

An O2 should drive every Grado headphone on the market perfectly. As for whether there is a benefit? That depends on what you currently use, but as Rrod said, Grados aren't terribly hard to drive.

Thanks for the info folks. Right now I mostly use my iPhone 5. Then either my sound blaster x-fi usb or the cmoy I built.

I appreciate the advice.

 

[castleofargh]

 

  Must have been something wrong with it. Apple would have fixed it if it was under warranty. I've had Macs going all the way back to the Lisa. Never a problem. No sound in the Lisa though!

Some quick googling indicates that this is a common issue with several generations of macbook, especially when the macbook is plugged in (which indicates it could be something like a noisy ground or power supply when running on AC power, combined with an audio circuit with an inadequate ability to reject noise from the power supply). It's very common on other laptops and other mobile electronics too, since high noise rejection isn't really required when running on battery (batteries give a very clean and stable power supply), and mobile chargers tend to prioritize small size and efficiency over low ripple and noise.

my "mobile" charger is a massive 1kg brick for my "portable" laptop(3.4kg). I have had zero noise added when plugging it in to charge, and for the very first time thanks to your post I feel like maybe I should be happy for the huge power converter.
thank you for that moment of optimism.

 

[00940]

  1) What electronic gadgets come after the DAC chip?

 
There are four functions that possibly need to be adressed after a DAC.
 
-1- Current to voltage conversion: some (not all) ICs do not produce a voltage output but a current output. Typical example: the pcm1792-4-8 serie from TI. 
-2- Filtering: a typical DA process require a reconstruction filter. It also produces high frequency aliases and noise. These must be filtered out.
-3- Balanced to unbalanced conversion: a lot of modern DAC output a differential signal. This allows to sum the outputs and get rid of the common noise, achieving better performances.
-4- Buffering: most DAC are not realizing their performances if directly connected to an amp with low input impedance. A buffer stage prevents the DAC to see an external load.
 
This said, different functions can be performed by the same active circuit. It is also common to see ICs which integrate different function onboard (digital filter, DAC, current to voltage conversion for example). A DAC like the PCM5102 has everything onboard (almost, it needs a small external passive filter). And, finally, the power supply for the DAC and the analog stage has also to be taken into consideration.
 
You can have btw some auxilliary functions also performed, such as DC offset removal through a servo or muting or unbalanced to balanced conversion or volume control.
 

 2) How can these gadgets affect sound quality, and how bad would they need to be for the effect to be audible?

 
Well, here are some ways you could mess up. It's not an exhaustive list
 
- badly designed analog filters;
- an analog stage which is not able to cope with the HF garbage at the output of a DAC;
- a current to voltage converter in effect unable to drive the low impedance filter networks needed for low noise;
- unproper decoupling, not taking into account pcb parasitics and resonnance effects or using unproper parts;
- a lack of proper analog filters which lets HF noise into the signal chain, possibly affecting the proper operation of amplifiers down the road;
- unproper PCB layout, mixing analog and digital ground returns currents.
 
How bad those problems need to be... that's a tough question. Badly designed filters will directly affect FR, so that's quite easy to determine. HF pollution on the other hand might be very setup dependent. In any case, from a designer perspective, the goal should be to come close to the DAC's datasheet specifications, no reasons not to. 
 
 
edit: to give a practical example. Here is the output stage suggested by the pcm1794 datasheet. That's for one channel and doesn't have the power supplies of course. U1 and U2 are serving as both 1 and 2 in the list above. U3 as 2, 3 and 4.
 
 

 

[RRod]

Thanks for such a detailed reply! My feeling is that something like "an analog stage which is not able to cope with the HF garbage at the output of a DAC" is what people mean when they talk about having a "bad" analog stage, so I guess that would involve the U1 and U2 stages above.

 

[Greenears]

 
I just wanted clarification on the components of the "analog stage" that DAC-distinguishers like to use as argument points. If it's just a little pre-amp stage, then I can't honestly see how any good unit would screw that up badly, considering how good amps can be for little $. My background is in math, so I'm all fine talking in the digital domain and when equations are around, but I have no idea exactly what electrical components come after the DAC chip. My measurements have told me that whatever they are, they aren't mucking up anything on the DACs I have at least.

 
The state-of-the art 24 bit DACs are differential current mode outputs.  A couple of op-amps are needed to convert to single-ended voltage and low-pass filter.  It's roughly 10 resistors and caps.  The DAC makers provide the reference design online - it's straightforward.  It's pure analog, no clocks.