cobaltmute
Headphoneus Supremus
- Joined
- Jul 2, 2008
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The only recommendation that I can suggest is to try and decide what you like.
Quote:Hi, I just wondered, is the Skeleton DAC safe to use with the Millet Starving Student Hybrid? I read that the SSMH had destroyed a few Bantam / Alien DACs.
http://www.head-fi.org/t/445851/starving-student-blows-up-dacs
Use with caution. All of those other DACs had output capacitors, too. The common symptom was a DAC that had the chip directly output (through capacitors) to the SSMH. IOW, there is no buffer, opamp, or other active device between the DAC chip's output pins and connection to the SSMH. Since the SkeletonDAC falls into that category, caution is advised. It's possible that since the PCM2704/5 has a built-in headphone amplifier, that it offers more protection than the PCM2702, which formed the basis for the Alien and Bantam. We don't know that for sure, though.
You should also be aware that the issue was really traced to the CISCO switching power supply used in the original Starving Student. The CISCO power supply seems to have a floating ground and a different potential voltage can develop around the RCA jacks. If you happen to plug in one of the DAC's mentioned and touch the outside of the jacks with the center pin of the RCA interconnects, a discharge will occur that will fry the DAC chip - output capacitors or not.
If you don't use that power supply, then you shouldn't have a problem.
I just wondered if anyone is using bypass caps, and is there any particular value in it?
It's going to be a while before I get new output caps and wondered if using the Wima caps that came with the Skeleton DAC kit in parallel with the Nicon 220uf caps I am using at the moment would be a worthwhile mod. I've read that bypass caps can improve high frequency response.
Wouldn't that floating ground be a possible issue for nearly any source?
There's probably not a person on Head-Fi who would admit that a capacitor would pass DC current
That's a funny way to say it. As you know, a coupling capacitor passes "dc current" while its charging to the potential difference of the 2 points being coupled.
[...] There's probably not a person on Head-Fi who would admit that a capacitor would pass DC current, but nevertheless, it does - under the right conditions. After all, a lethal transient could simply be "interpreted" as the first part of a low frequency sine wave. I don't know - maybe that explanation is invalid, but frying the DAC through a DC discharge at the outputs is a fact and was repeatable (for many people unfortunately). I actually heard the static discharge through my headphones on a couple of occasions when a DAC was fried.
Actually, I tried a bypass combination once based on Dsavitsk's recommendations in his excellent "Notes on Output Coupling Capacitors." It was back a few years ago and the DAC was the AlienDAC, but the same principles apply. If memory serves, I used a couple of Muse ES's at 4.7uf, and bypassed them with a couple of 0.22uf Sonicap Gen II's. It sounded very good ... until I blew it up with a Starving Student amp.Sorry - I guess that's too close to home in this situation.
IOW, yes - I think the right combination of bypassing might yield excellent results if you have the room. However, what I used was definitely one of the specific combinations that Dsavitsk mentioned in his articles. The ES's are known for excellent bass, while the Sonicap Gen II's were known for sparkle. Unfortunately, I think Soniccraft quit making the Gen II's. Anyway, it's worth experimenting and Wima's are usually a great bypass caps in most situations Roederstein box film caps are also a great bypassing cap. Just remember that combinations may vary widely. Bypassing is almost witchcraft and voodoo in terms of predicting the results of various combinations.
DC voltage is simply dV/dt = 0. Any transient would, by definition, not have dV/dt = 0. So a transient is not DC.
The decoupling capacitors block DC, but the moment dV/dt != 0, it will allow current trough. We use this to filter audio signal out of DC bias, since audio signal is everything but dV/dt = 0. The thing is, capacitors work both ways. If there's a change in voltage at the output of the circuit, the capacitor will allow this difference in voltage to flow back trough the circuit. Since the other side of the cap is the DAC chip, this transient discharges trough the chip. If it's not built to handle such current, it fries.
In this case, the static discharge when connecting the DAC to the amplifier causes the voltage at the output of the capacitor to rise (dV/dt > 0). This causes the capacitor to conduct in the opposite direction it's intended to, which applies a voltage to the output of the DAC chip. The reason it fries the chip is probably as simple as it not being tough enough to handle voltages being applied to it's output.
The damage occurs on the rising edge of the transient, as this is when the capacitor conducts.
Hi Guys,
Is the PCB available in the UK? I've looked at Beezar and it looks like it's $10 shipping to the UK, a bit expensive for me.
Due to that I thought I'd have a go at trying to proto-type it on a protoboard with through-hole components - but now I've read the whole thread I can see why I've not got it to to be detected and just spent two frustrating days trying it to no avail. Wish I'd noticed that earlier!
I'm assuming it's due to the through hole components being the problem as stated. I've put the PCM2704 on a SSOP-DIP converter board - is it easy to fry the chip in mounting/reflowing? I was a bit worried about the heat from keep dragging and reflowing to get it right. I'm pretty new to DIYing.
Anyway, looks like I'll have to start properly and try to get the board somehow, if anyone knows a better route than paying $10 for postage please let me know!
So I just built a SkeletonDAC and it's working to great success with 470uF Nichicon KWs as my output caps. I was planning on using earphones directly out of this DAC, but damn, it is really really really loud. I have to lower teh volume down to 1, and then halve the volume in foobar to get to listening volume. How do I reduce the volume on this so I don't risk blowing out my ears? Just put a resistor in the output?