Hello all,
I've recently completed populating the PCB for my 12AU7 SSMH, and now I'm ready to put it into an enclosure (assuming that it all works okay)
I purchased a 48v switch mode supply off Trademe (basically Ebay for kiwis) which was listed as "delta electronics". Little did I know, it turns out that it's the same Cisco branded supply that's been reported as having issues with a floating ground output that goes above ground potential in certain operating conditions, and can fry sources connected to the SS.
This is the supply I have: http://www.diyaudio.com/forums/attachment.php?attachmentid=388347&stc=1&d=1387346363
I was considering what I could do to make this supply safe to use with the SSMH, and my Skeletondac which I'm currently using as my primary source, and thought, it would be pretty easy to just tie the output ground to the ground pin of the mains outlet. Would there be any problem doing this? I assume this would eliminate any issues with transients showing up on the ground rail of my amp, but could it interfere with the switching circuitry? I have little experience with switchers, beyond building a few circuits using the 34063...
I was already considering opening up the supply to augment the filter caps and add in some inductor based filtering to clean up the supply as much as possible. So grounding the output at the same time wouldn't be any hassle for me.
If anyone could shed some light on whether my idea is workable or not I'd really appreciate it. I don't really want to buy another supply for now, as I paid a decent amount for this one, and don't mind opening it up to tweak it a little bit if it's possible to do.
Thanks for reading this!
Chris
I've recently completed populating the PCB for my 12AU7 SSMH, and now I'm ready to put it into an enclosure (assuming that it all works okay)
I purchased a 48v switch mode supply off Trademe (basically Ebay for kiwis) which was listed as "delta electronics". Little did I know, it turns out that it's the same Cisco branded supply that's been reported as having issues with a floating ground output that goes above ground potential in certain operating conditions, and can fry sources connected to the SS.
This is the supply I have: http://www.diyaudio.com/forums/attachment.php?attachmentid=388347&stc=1&d=1387346363
I was considering what I could do to make this supply safe to use with the SSMH, and my Skeletondac which I'm currently using as my primary source, and thought, it would be pretty easy to just tie the output ground to the ground pin of the mains outlet. Would there be any problem doing this? I assume this would eliminate any issues with transients showing up on the ground rail of my amp, but could it interfere with the switching circuitry? I have little experience with switchers, beyond building a few circuits using the 34063...
I was already considering opening up the supply to augment the filter caps and add in some inductor based filtering to clean up the supply as much as possible. So grounding the output at the same time wouldn't be any hassle for me.
If anyone could shed some light on whether my idea is workable or not I'd really appreciate it. I don't really want to buy another supply for now, as I paid a decent amount for this one, and don't mind opening it up to tweak it a little bit if it's possible to do.
Thanks for reading this!
Chris
Attachments
"floating ground output that goes above ground potential in certain operating conditions??"
What exactly you mean? Looks like you have one ground, then positive output, which is +48 and then another GROUND which, under certain conditions, would become floating? Looking at the picture I can tell you that there are only two wires at the end. PLUS and MINUS.
I used to design PWM power supply and can tell you that it is impossible. PWM controller collects its information ( in our case it is output voltage feedback directly from the output (+ and GND), sometimes before or after inductive element, to make close loop feedback control simple and easy to operate). By saying that, PWM controller constantly monitors its +48 DC output (it is single output power supply, so it monitors only one single channel) and, if there is something wrong (again, it depends on particular design) it must trigger an alarm.
About making it better. It is really difficult to implement. Output voltage has broad variety of harmonics, that is a result to be a PWM power supply. And normally, inside PWM power supply we have ONE huge inductor, and few little ones.
The big one is calculated to have contentious current (again, it depends on design) and have nothing to do with filtering output voltage.
The little ones are put in place to filter high frequency noise, put in place to filter output voltage. This is where we can play with elements.
But my opinion, if you need clean +48 DC output, go for AC transformer and bridge+capacitor. No digital noise at all.
What exactly you mean? Looks like you have one ground, then positive output, which is +48 and then another GROUND which, under certain conditions, would become floating? Looking at the picture I can tell you that there are only two wires at the end. PLUS and MINUS.
I used to design PWM power supply and can tell you that it is impossible. PWM controller collects its information ( in our case it is output voltage feedback directly from the output (+ and GND), sometimes before or after inductive element, to make close loop feedback control simple and easy to operate). By saying that, PWM controller constantly monitors its +48 DC output (it is single output power supply, so it monitors only one single channel) and, if there is something wrong (again, it depends on particular design) it must trigger an alarm.
About making it better. It is really difficult to implement. Output voltage has broad variety of harmonics, that is a result to be a PWM power supply. And normally, inside PWM power supply we have ONE huge inductor, and few little ones.
The big one is calculated to have contentious current (again, it depends on design) and have nothing to do with filtering output voltage.
The little ones are put in place to filter high frequency noise, put in place to filter output voltage. This is where we can play with elements.
But my opinion, if you need clean +48 DC output, go for AC transformer and bridge+capacitor. No digital noise at all.
Ahhhhh, my brain was a bit too switched off when I made that post I think. I'll try and explain the situation more accurately...
What I understand is the negative output on the power supply is normally ground referenced, but there's a chance in some circumstances for it to have a transient show up on it and damage devices on the input. I assume because they are ground referenced (ie. usb dac) and it pumps current into the dac chip if its not isolated by a buffer or similar.
My understanding of the issue isn't too good, mainly because I haven't been able to find a whole lot of info on it, at least explained in a manner that makes sense to me.
Here's a couple ideas by others, in case my understanding of the issue is flawed so you can check it out yourself:
What I understand is the negative output on the power supply is normally ground referenced, but there's a chance in some circumstances for it to have a transient show up on it and damage devices on the input. I assume because they are ground referenced (ie. usb dac) and it pumps current into the dac chip if its not isolated by a buffer or similar.
My understanding of the issue isn't too good, mainly because I haven't been able to find a whole lot of info on it, at least explained in a manner that makes sense to me.
Here's a couple ideas by others, in case my understanding of the issue is flawed so you can check it out yourself:
http://www.diyforums.org/SSMH/SSMHoverview.php said:
http://www.head-fi.org/t/445851/starving-student-blows-up-dacs (by dsavitsk) said:
Just curious if you were able to find a fix for the problem? I have Cisco PS and SSMH boards on the way and I would not want to fry my source once I get everything up and running. The SSMH power up sequence already asks to wait before plugging in headphones and unplugging them before turning the amp off.
Fred, thanks for replying. For now, I have a cheap Chinese DAC which if I lose, it will not be the end of the world. But once I get the setup up and running, I will definitely upgrade to a better DAC. Hopefully, the SS will play nice with whatever I have.
I was just checking with OP if maybe there is a way to modify the Cisco power supply to reduce the possibility of frying the DACs.
I was just checking with OP if maybe there is a way to modify the Cisco power supply to reduce the possibility of frying the DACs.
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