catsspat's new toy


I can't even remember exactly why I chose the name "animephile" for my site, and to be honest, I don't even like the name, but I don't have a better idea nor do I care enough to bother changing it. Still, I don't think I've really ever talked about my audiophile hobbies on this site, so I'm introducing my new $200 toy.

First thing I did when I got it, was to open it up, of course. Note that chip on the left with "DAC" written on it isn't the DAC. It's probably a programmable ROM or something. Yeah, it's an oxymoron. "Erasable Programmable READ-ONLY Memory"

Opamps are all JRC (Japan Radio Corporation, now known more as NJR, New Japan Radio) version of 5534. They're certainly not at Burr-Brown 604 or 134 series levels, but they're pretty good and I'm not going to bother changing them out. DAC is AKM's AK4393VF, often used in professional equipment. I think just about all professional soundcards use AKM's DACs. These days, PCM is so well understood, I don't believe that fancy and outrageously priced DACs really get you anything much. By the way, AK4393VF is capable of 192kHz conversion. Apparently, the older versions of the SuperDAC used earlier version(s?) of the DAC. I see AK4528VF on one of the pictures. I think many of these AKM DACs are pin compatible, so it's not surprising that they kept up with the newer models. I'm not sure if the rest of the DAC is capable of handling 192kHz sampling rate, though, and I can't test it because I don't have anything that outputs such.

Board is completely covered with ground-plane, all opamps are powered with bypass caps for each, and from what I can tell, most, if not all, of the resistors in the signal path are 1% metal film type. So far so good.

Now we look at how it's powered. There are the standard 7815/7915 pair for the opamps. If you've ever worked with audio opamps, you should know these by heart. Main filter caps are only 470uF, but for this use, it should be fine. Ceramic caps are used as bypass. Well done.

You'll see a 7805 on the right. All of the digital logic and the DAC itself are powered by 5V. As soon as I saw this, I noticed that the 7805 regulator was getting its power from the same unregulated input as the 7815 regulator. Why not feed it 7815's regulated output?

So far, it's not too bad. Obviously, this isn't going to pass as a "high-end" equipment, but who cares as long as it does the job well?

VERY IMPORTANT: Note that there are no heatsinks, and also note that 7915 isn't even screwed onto the chasis.

Now, we get into the ugly side. This thing is powered by a 9V AC brick rated for 1A. Huh? 9V AC? That means, its peak swing voltage will only be 12.73V. Even considering the common overvoltage on these brick transformers, it can't possibly reach 17-or-so volts required to properly regulate to 15V. In fact, I measured little over 10V RMS, leading to little over 14V peak. Peak to peak is 28V, of course, but we need to generate 30V peak to peak, and those regulators will lose a bit over a volt! What the heck?

Easy, right? I'll feed it 16V AC instead. Looking at the pre-regulation filter caps, I noticed that they were rated for 35V. Good! They should handle it just fine. But uh-oh. Filter cap for the 7805 is only 16V. Easy. I cut off the diode path for that and instead fed regulated 15V to 7805, as can be seen below.

It started up with 16V AC power, and was playing music just fine, but I was noticing how hot the regulators got. This is to be expected since I've increased the junction voltage. Whatever it was getting minus 15V, times output current, must be dissipated as heat. These regulators have thermal protection so I wasn't worried about them while I was fooling around with higher voltage power supply. Then POP! The capacitor right next to the 7915 blew up. Remember how 7915 was free standing? The regulator itself can handle a lot of heat , but the capacitor next to it couldn't.

Then it hit me. They're feeding it 9V to keep those regulators fully on all the time. Transistors are most efficient when they're fully on or off, so when they're fully on, they do not generate much heat. Those opamps have over 100dB of power supply noise rejection, so feeding them noisy power isn't likely to be noticeable at its output. Dang! Forget "high-end." I wouldn't do this even on a consumer-grade equipment.

For your viewing enjoyment, here's the blown cap.

What to do? Use an external power supply. I built this one many many years ago. It has one 35V 4700uF cap for each swing, and the bypass caps are expensive polypropylene types. Yeah, I know better now to use ceramic caps for that, but hey, that was a long time ago. Later supplies I built for my active crossovers are even more insane, with 11,000uF for each swing (22,000uF total, just to feed one active crossover requiring probably less than 200mA). By the way, the regulators I used here are Motorola premium variety.

I removed the regulators from the board and cut away the diodes. 5V regulator is now being fed from the regulated 15V as I mentioned earlier, so no problems there. Here, I'm just testing to make sure everything is kosher. Power button no longer works, but who cares?

Everything put back together with 3-pin connector sticking out at the back. I'm done! Yeah!

So, does it sound better? I'm not sure. As I said, those opamps have very good PS noise rejection. But I just couldn't live with that kind of iffy engineering, so I had to fix it up.

Oh, in case you don't know, I rarely listen to my CDs directly. They're all ripped into -q6 Vorbis Ogg files and are played from a fan-less computer through M-Audio Audiophile 2496. If I'm not mistaken, that card has the same DAC as this unit. Unfortunately, it is inside a PC with more than one switching power supplies affecting it. I can only hear the power supply noise coming out of the soundcard if I pump up the preamp volume while nothing is playing, but that still didn't seem like a good idea. With this setup, computer is isolated completely and I hear absolutely no switching power supply related noise reaching the speakers, even with the preamp set to maximum volume. Mind you, with my pre at max, we're talking about 24dB gain. Let's not get into why the gain is so high.

Basically, for mere $200 and some soldering iron handy work, I'm very happy with the result.

Any questions?