In the previous part of this Alpha Academy series, you were able to read about what a d/a converter is and why you need one. In this part, we’ll look at “external” d/a converters. What is an external dac? And when is it a good idea to purchase one?
As described in the previous article, in every “digital” device with an analog output, there is a d/a converter. In simple sources, it is often nothing more than a dac chip which converts the digital signal to analog. This analog signal goes into an output stage. Simple, but it works.
Now we wouldn’t be enthusiasts if we didn’t wonder how we can improve it. And fortunately, that’s possible! You see, there are also external d/a converters. You connect these to the digital output of the source. The external d/a converter (dac) then takes over the job of converting digital to analog from the internal dac. And in many cases this results in a jump in quality.
Choice
The great advantage of using an external d/a converter is that you have control over the quality and sound signature. Skeptics will say that all d/a converters sound the same, but that is simply not true. Every converter sounds different. And there are many reasons for that, which we will go into more detail later.
To give a hint: jitter, digital filters, noise floor and output stage all affect playback. And that difference is not subtle.
So every dac sounds different. Sometimes it’s a matter of better or worse and sometimes – more often to be honest – it’s just different. Think warmer, more detailed, bigger, etc. It’s up to you to choose a model that you feel suits your taste as well as one that integrates well into your system.
To make an informed choice, it is crucial that you try the dacs at home. A product really has to match. And you won’t know for sure until you have experienced it at home in your own system.
Inputs and outputs
Another thing an external dac can offer is multiple inputs. And perhaps multiple outputs as well. Think single ended and balanced. These cannot always be used at the same time. If you do want to, check that carefully.
Since almost all sources are digital nowadays, it is convenient that you have multiple inputs and that you can easily switch between them. Common digital links are: optical, coaxial, and AES/EBU. We also see BNC, USB and I2S. There are also manufacturers who implement their own interface. For example MSB with their optical link.
BNC and I2S we don’t see that often. In the case of BNC, that’s a shame because it’s a perfect interface. With I2S, the question is whether the standard used is the same as your source. So pay close attention to that! Some dacs offer the option to choose a standard. So do some sources. That again gives some flexibility.
We often get asked what the best connection is. Whether there is some kind of hierarchy you can adhere to. That’s a tough question, but we use the following ourselves:
- BNC and AES – Perfect 75 or 110 Ohm. Already works very well with a decent cable.
- Coaxial RCA – Often not really 75 Ohm. Less jittery than optical.
- Optical – jitter sensitive. Very dependent on the implementation and cable.
- USB – noise-sensitive. Very implementation dependent. Moves clocking to dac.
In the case of USB, it depends on the implementation. The advantage of USB is that the clocking is moved to the dac. If the dac has a very nice clock, this is a big advantage. If the source has a better clock, you nullify it.
So with I2S, the question is whether the standard is the same. We actually never use it because it is such a closed system. The Sonnet Pasithea does have an I2S input, but it only works with Sonnet equipment. I2S can be very nice…And you should definitely try it. But it is rather closed…
Optimal environment
A manufacturer can go all out on the design of a stand-alone dac. Now of course they won’t do that with the affordable models. But with the more luxurious models they will of course do their best to realize the maximum achievable (within the price band). And believe us: the sky is the limit. Just look at brands like Wadax, MSB or, for example, Nagra.
Now there are manufacturers who try to go for the best results with existing dac chips. So although the chip – think of an ESS or for example AKM model – is similar to the dac chip in many decent CD players or streamers, the result of the separate dac is still a lot better.
That has everything to do with the implementation of the dac chip. The power supply is much more stable and quiet, the clocking of the chip is often much better and also the output stage is much nicer implemented. And all this makes the result a lot better: more flow, more control, more air and less sharpness.
Now, a very high level can already be achieved with existing chips from ESS, AKM or Texas Instruments, for example. However, there are manufacturers who want to go even further. Those manufacturers – think dCS, Sonnet or MSB – manufacture their own dac chips. Many go for an r2r setup, or variant thereof. However, there are also manufacturers who go for an fpga setup. Think Grimm Audio with the 1.5-bit dac in the MU2.
Now, a “proprietary dac” does not have to be better than a nice AKM, TI or ESS. However, it is true that a proprietary design ensures that a manufacturer usually knows well how to optimally implement the dac. Think about controlling the volume. In many dacs this is not possible without loss of data. With an in-house design, you can work around that as a manufacturer. And that has its advantages.
When to upgrade?
So with an external dac you get the option to connect more devices AND you can go for a certain sound or performance level yourself. Excellent. But when is it useful? And how do you know when an upgrade is useful?
There is undoubtedly a time when you notice that a certain source sounds less good than other sources. For example, if the CD player sounds a whole lot better that the streamer, then you know that your amplifier and speakers are not the limiting factor.
Now you can go for a completely new streamer. And in many cases, that will be a solution. However, you can also choose to purchase an external d/a converter. One that performs another step above your CD player. You can now not only improve the sound of your streamer, but also the CD player and possibly the TV and other digital sources. Several birds with one stone!
Next Episode
We hope this article has provided some insight into the usefulness of an external d/a converter. In the next installment: bits and sampling rates…Now what is that? And how much do we need?