Running DAC from SMPS

mourip · 3rd October 2006, 01:36 AM

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

singa · 3rd October 2006, 07:25 AM

Hi,
Recheck the usb dac maybe a "short" somewhere;are the components mounted the right way?Any solder shorts,Power connection correct,Polarity?

mourip · 3rd October 2006, 11:40 AM

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.

morpheus82 · 3rd October 2006, 11:44 AM

could be a problem of input capacitance of the dac?

mourip · 3rd October 2006, 12:02 PM

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!

janneman · 3rd October 2006, 12:04 PM

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

poynton · 3rd October 2006, 12:27 PM

Hi.

Don't forget that some smps like to see a load (ie minimum current.)

Andy

clem_o · 3rd October 2006, 01:12 PM

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!

djQUAN · 3rd October 2006, 01:20 PM

what about when switching the supply on, the DAC switch already turned on?

mourip · 3rd October 2006, 06:57 PM

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!

3rd October 2006, 01:36 AM	#1
mourip diyAudio Member Join Date: Apr 2004 Location: Washington, DC	Running DAC from SMPS 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

3rd October 2006, 12:04 PM	#6
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	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 __________________ /Another new issue: Linear Audio Volume 3!

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3rd October 2006, 07:25 AM	#2
singa diyAudio Member Join Date: Apr 2004 Location: near	Hi, Recheck the usb dac maybe a "short" somewhere;are the components mounted the right way?Any solder shorts,Power connection correct,Polarity?

3rd October 2006, 11:44 AM	#4
morpheus82 diyAudio Member Join Date: Oct 2004	could be a problem of input capacitance of the dac?

3rd October 2006, 12:27 PM	#7
poynton Magneto the Gravity Man diyAudio Member Join Date: Mar 2005 Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)	Hi. Don't forget that some smps like to see a load (ie minimum current.) Andy

3rd October 2006, 01:12 PM	#8
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	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!

3rd October 2006, 01:20 PM	#9
djQUAN diyAudio Member Join Date: May 2004 Location: manila	what about when switching the supply on, the DAC switch already turned on?

3rd October 2006, 06:57 PM	#10
mourip diyAudio Member Join Date: Apr 2004 Location: Washington, DC	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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