| mourip |
Tonight I tried hooking up an SMPS to my Scott Nixon USB DAC instead of the SLA battery which I had been using. I got the SMPS from EBAY after a few reports that it worked well with a Tripath amp. It is good for about 3 amps at 12v.
Before I hooked it up it measured about 12 vdc output. When I flipped the switch to the DAC the DAC power-on LED flashed briefly but the DAC would not show up on the computer. Measuring the output now showed about 4 vdc. If I disconnect the wires to the SMPS and turn it back on I get 12v. As soon as I slip the switch to power on the DAC it drops to 4v. I do have one extra 1000mf cap added to the power input of the DAC. It looks as if the SMPS is going into a protection state when trying to charge up that cap. I could take it off but there will still be another onboard cap to charge.
Any ideas?
Best,
Paul |
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| singa |
Hi,
Recheck the usb dac maybe a "short" somewhere;are the components mounted the right way?Any solder shorts,Power connection correct,Polarity? |
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| mourip |
| quote: | Originally posted by singa
Hi,
Recheck the usb dac maybe a "short" somewhere;are the components mounted the right way?Any solder shorts,Power connection correct,Polarity? |
The DAC is working fine off of the SLA battery, even after the symptoms I described so I have to assume that it is wired correctly and has no issues.
Thanks for the reply. |
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| morpheus82 |
| could be a problem of input capacitance of the dac? |
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| mourip |
| quote: | Originally posted by raikkonen
could be a problem of input capacitance of the dac? |
That seems most likely. I did add some extra capacitance when I set up the DAC for the SLAs. It was only 1000mf but perhaps the cheapo SMPS did not like charging up the cap. It probably saw it as a dead short for at least a brief time...
Thanks! |
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| janneman |
Do you still have the battery connected when you use the smps? What is the normal battery voltage? If the battery voltage is much lower, the DAC may be protected to overvoltage and may see the 12V as overvoltage.
Jan Didden |
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| poynton |
Hi.
Don't forget that some smps like to see a load (ie minimum current.)
Andy |
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| clem_o |
If it powers up to 12V without load, then it shouldn't be looking for a 'minimum current'.
Probably caused by the heavy filter caps of the DAC - Charge them up first using the SLA battery, then quickly switch over to the SMPS. If that gets the whole thing working, you've confirmed the problem...
Now as to how to go around that... hmmm - charge the filters through the series resistor first, then have a relay short out the resistor after a second or two... ???
Cheers! |
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| djQUAN |
| what about when switching the supply on, the DAC switch already turned on? |
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| mourip |
Thanks for the good tips.
No battery connected when using the SMPS.
First I turn on the SMPS, then I switch on the DAC.
A series resistor sounds like a good idea for troubleshooting. Basically I want to compare the sound of SLA vs SMPS. If I like the SMPS I will probably leave it powered up all of the time. If the resistor works I could use a DPDT on-off-on switch so that I had the resistor in line one way and then out the other.
Anyway I have some good ideas to try...
Thanks! |
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| clem_o |
If you plan to leave the PS on, then yes, the switch would be an economical way of doing things.
The other thing I was considering was using a 12V relay, normally-open type. Power the relay coil through the output of the resistor. The pull-in voltage of a relay usually is around 8V, so once the filter capacitors have charged to about 8V, the relay turns on and shorts out the series resistor.
If that still crashes the SMPS you can always add a few series 1N400x diodes to the relay coil to further 'delay' its turn-on....
Cheers! |
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| clem_o |
| quote: | Originally posted by mourip
If the resistor works I could use a DPDT on-off-on switch so that I had the resistor in line one way and then out the other.
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mourip,
all you need is an SPST switch. Parallel it across the resistor. "on" shorts out the resistor. Using a DPDT will "briefly" disconnect the power... :-)
Cheers! |
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| mourip |
| quote: | Originally posted by clem_o
mourip,
all you need is an SPST switch. Parallel it across the resistor. "on" shorts out the resistor. Using a DPDT will "briefly" disconnect the power... :-)
Cheers! |
Great idea! Thanks. Any idea what a good value would be? |
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| clem_o |
How much capacitance is in that DAC board?
If the SMPS is rated to 3A and puts out 12V, a 4.7 ohm resistor will limit the current to 2.55A into a dead short. A 10ohm resistor would limit the current to 1.2A - that would be a very gentle inrush...
What you need to estimate is the power rating of the resistor - and that depends how long it takes to charge the capacitors...
You could use 2x 1W 10 ohm resistors in parallel. I'd guess that's lots of power headroom. Or a single 1W 10 ohm resistor...
Cheers! |
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| mourip |
| quote: | Originally posted by clem_o
How much capacitance is in that DAC board?
If the SMPS is rated to 3A and puts out 12V, a 4.7 ohm resistor will limit the current to 2.55A into a dead short. A 10ohm resistor would limit the current to 1.2A - that would be a very gentle inrush...
What you need to estimate is the power rating of the resistor - and that depends how long it takes to charge the capacitors...
You could use 2x 1W 10 ohm resistors in parallel. I'd guess that's lots of power headroom. Or a single 1W 10 ohm resistor...
Cheers! |
Thanks for staying with me!
The DAC has a 1000mf cap onboard and I added another 1000mf. Not too bad. I think that your suggestions have me in the ballpark now...
I hope that it sounds better. I would like to leave it on all of the time but could not with battery power, at least not without adding a wallwart and a more elaborate switching setup.
Best,
Paul |
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| clem_o |
Hi Paul,
Somehow I doubt if it will make any difference, sonically - but OTOH if it saves you the trouble of having to recharge an SLA that would make it worth it...
Come to think of it, given the stability of your power provider, you may even decide to forego the SPST switch - just short out the resistor by twisting its legs together... rather ugly but hey, zero cost... Can't do that where I live - power outages are more a norm than exceptions.
Good luck, and let us know how it goes. |
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| clem_o |
Hi Paul,
Somehow I doubt if it will make any difference, sonically - but OTOH if it saves you the trouble of having to recharge an SLA that would make it worth it...
Come to think of it, given the stability of your power provider, you may even decide to forego the SPST switch - just short out the resistor by twisting its legs together... rather ugly but hey, zero cost... Can't do that where I live - power outages are more a norm than exceptions.
Good luck, and let us know how it goes. |
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| mourip |
| quote: | Originally posted by clem_o
Hi Paul,
Somehow I doubt if it will make any difference, sonically - but OTOH if it saves you the trouble of having to recharge an SLA that would make it worth it...
Come to think of it, given the stability of your power provider, you may even decide to forego the SPST switch - just short out the resistor by twisting its legs together... rather ugly but hey, zero cost... Can't do that where I live - power outages are more a norm than exceptions.
Good luck, and let us know how it goes. |
I set it up last night and it worked like a charm. I used a 15 ohm 10w resistor to start up and then flipped the switch to remove(short) it. The sound seems about the same or close enough that it seems worth doing.
Thanks for all of the help!
Best,
Paul |
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| clem_o |
Great to hear!! Enjoy the music!
Cheers
Clem
--- double post msg 16 and 17 - haven't figured how that happened... ???!!
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