The SkeletonDAC - Page 12

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 

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

Quote:

Originally Posted by Frodo 

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.

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

Quote:

Originally Posted by scootsit 

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.

Quote:

Originally Posted by tomb 

Quote:

Originally Posted by scootsit 

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?

Quote:

Originally Posted by cobaltmute 

Quote:

Originally Posted by scootsit 

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

Quote:

Originally Posted by scootsit 

Quote:

Originally Posted by cobaltmute 

Quote:

Originally Posted by scootsit 

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?

Quote:

Originally Posted by tomb 

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.

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.

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
 

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.

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

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.

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.