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The SkeletonDAC - Page 12

post #166 of 209

I can't see any reason why it would not be safe.

The output is capacitor coupled so no DC can make

it in or out.

 

Cheers!

Quote:
Originally Posted by Frodo View Post

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

post #167 of 209
Quote:
Originally Posted by Frodo View Post

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.

post #168 of 209

Would it be okay to use transformers instead of capacitors on the SkeletonDAC?

post #169 of 209
Quote:
Originally Posted by scootsit View Post

Would it be okay to use transformers instead of capacitors on the SkeletonDAC?

Maybe - but just keep in mind that this a phenomena limited to that CISCO switching power supply on the SSMH.  It got more than one of AMB's Gamma 1 DACs, too.

post #170 of 209
Quote:
Originally Posted by tomb View Post

Quote:
Originally Posted by scootsit View Post

Would it be okay to use transformers instead of capacitors on the SkeletonDAC?

Maybe - but just keep in mind that this a phenomena limited to that CISCO switching power supply on the SSMH.  It got more than one of AMB's Gamma 1 DACs, too.


Oh, I was referring more generally. I want to use some step down transformers, I've been using them (from Radio Shack) instead of an amp with IEMs, to boost the current, and I've had good results. I want to drive some IEMs directly off of the SkeletonDAC, could I replace the caps with transformers, since both should block DC, right?

post #171 of 209
Thread Starter 
Quote:
Originally Posted by scootsit View Post

Would it be okay to use transformers instead of capacitors on the SkeletonDAC?

I can't see it would be an issue. The only thing I can think of would be size of the transformers that you could find.
post #172 of 209
Quote:
Originally Posted by cobaltmute View Post

Quote:
Originally Posted by scootsit View Post

Would it be okay to use transformers instead of capacitors on the SkeletonDAC?

I can't see it would be an issue. The only thing I can think of would be size of the transformers that you could find.

http://www.head-fi.org/t/553094/continued-sidetrack-discussion-from-tiniest-portable-amp-i-can-build-nikongod-microtransformer-based-impedance-step-down-box

post #173 of 209
Quote:
Originally Posted by scootsit View Post

Quote:
Originally Posted by cobaltmute View Post

Quote:
Originally Posted by scootsit View Post

Would it be okay to use transformers instead of capacitors on the SkeletonDAC?

I can't see it would be an issue. The only thing I can think of would be size of the transformers that you could find.

http://www.head-fi.org/t/553094/continued-sidetrack-discussion-from-tiniest-portable-amp-i-can-build-nikongod-microtransformer-based-impedance-step-down-box


Given the 1k+ impedance of the input side of transformer (the output side is ~8z), there should be no roll-off on the bottom end, right?

post #174 of 209
Quote:
Originally Posted by tomb View Post

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.


Thanks, I will be using the FSP025-DYAA6 from http://tinyurl.com/b55uhgp when I build the SSMS it was just $8.50 on eBay, if there are any problems I will post.

post #175 of 209

Hi, finished my DAC last night, the 2704 went down well, I flooded the pins and the wicked off the excess solder. I tried the wipe method first but I just couldn't get it to work.

In fact the most difficult (and time consuming) thing was getting the surface mount components out of those tiny packets, is there an easy method? I couldn't find information on the internet. confused_face(1).gif

 

I was a bit shocked at first when I plugged in my HD 595s and then ATH-M50s directly and noticed the lack of bass. However after I actually read though the website and forums and realised I would need to change the caps it sounds great. Currently using some 220uf 100v KMG caps that I had laying around, but I will order some better quality ones later today, I have quite a large case so I welcome any suggestions.

 

I have one question, I want to use The Skeleton as a desktop DAC with my Starving Student amp (I'm going to leave it permanently connected, to hopefully reduce the risk of blowing the chip), I want to use an on/off switch. I use one with the Alien DAC I previously built and it is very useful with the Mac, flick the switch and you go from headphones to built in computer speakers immediately and back again without having to change any settings.

 

Is it possible to add an on/off switch and if so, where can I connect it?

 

Many thanks, Andy
 

700

700

post #176 of 209

I think an on-off switch will involve cutting a trace on the PCB - probably the one between the USB pin that leads to the +5V pad just ahead of the mini-USB jack.  Then you'd wire an SPST switch to the mini-USB jack pad and the +5V pad on both sides of where you'd cut the trace.

 

Just a guess - maybe cobaltmute has another suggestion.

 

As for removing SMD parts from the packaging: tweezers.  Use the same ones you use for placing the parts.  The pointed ends are very handy for pulling back the film covering of the SMD parts packages.  Then you just flip the parts out on your building board.

post #177 of 209
Thread Starter 
If you insert the switch in the 5V line that would be the best bet.

Take the 5V lime from the cable, run it to the switch and then to the board.
post #178 of 209

Duh!  Make the split in the wire, not the trace.

 

post #179 of 209

Hi, Thanks for such fast responses, probably not the most elegant solution, but in the end I just removed the Mini USB connector bent pin 5 out horizontally (so it was sticking out the back of the connector) and wired the switch between that and the 5v pad, then soldered the connector back onto the board.  A blob of hot glue should stop the wires pulling on the pin until I get it all safely back in the case.

post #180 of 209

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.
 


Edited by Frodo - 11/27/12 at 5:57am
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