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AlanH  
#1 Posted : Tuesday, August 16, 2016 4:28:07 AM(UTC)
AlanH

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Hi,

I have built a dual Buffalo III dac. Both dac kits are powered by one LCDPS, which receives its 9v from the transformer purchased from you. I have 2 Legatos, powered by 2 Placid HDBPs. All this is housed in a 2u rack unit. Not cooled but it is vented. It has been running for about 18 months with no problems - lovely sound, I use it every day for extended periods. However it does get very hot and the other day I had a look inside and noticed the LCDPS heat sinks in particular were pretty hot. Just about okay to rest the back of my finger on, but marginal. They have also gone rather purple in colour. The heat sinks on the Placids were not so hot and are still black. LCDPS is delivering a very consistent 5.25v per rail.

Should I be concerned about the LCDPS?

Cheers,
Al

Edited by user Tuesday, August 16, 2016 4:47:54 AM(UTC)  | Reason: Not specified

Russ White  
#2 Posted : Tuesday, August 16, 2016 11:49:29 AM(UTC)
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What is the input voltage to the LCDPS?
AlanH  
#3 Posted : Tuesday, August 16, 2016 11:54:26 PM(UTC)
AlanH

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Both rails read 10.3vac for the LCDPS input voltage.
avr300  
#4 Posted : Wednesday, August 17, 2016 6:52:43 PM(UTC)
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allow me to write:


which turns into (10.3*1.4)-1.4 ~13vdc (check yourself at the main cap)

The regulator has to drop 13v -> 5.25v @ aprox. 450mA = 3.5w heat for each rail.

The AC is a bit on the high side. For 5.25v dc_Vout you need as little as 6vac. It will considerable reduce the heat.

Btw, what is your mains? 220v or 240v ?
AlanH  
#5 Posted : Wednesday, August 17, 2016 9:18:38 PM(UTC)
AlanH

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I think I understand. Mains voltage is nominally 230v. Which is producing 10.3vac at the secondary input. Which in turn is producing just over 13vdc at the regulator, which is just a tad too high to drop to the required output of 5.25vdc. Hence the excess heat.

So if I change the transformer to a lower output one of 6vac, am I okay with all other spec the same? Or should I be looking to keep the current about the same, and therefore go for one with a load rating of 15VA...?
AlanH  
#6 Posted : Saturday, August 20, 2016 2:28:21 AM(UTC)
AlanH

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So I swapped the 9v transformer for a 6v one (30VA). All seemed fine with the LCDPS output at 5.25vdc. However, when I connected the dacs the LCDPS output voltage dropped to 4.6vdc and I was not able to correct this with the adjustment pots. The voltage was stuck at 4.6vdc and again, heat sinks became very hot. So I've gone back to the 9v transformer for the time being.

I'm probably missing something obvious. Advice would be greatly appreciated...
avr300  
#7 Posted : Saturday, August 20, 2016 4:24:16 PM(UTC)
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Please post a picture of the lcdps. Does it have 4 power resistors?
AlanH  
#8 Posted : Saturday, August 20, 2016 7:59:52 PM(UTC)
AlanH

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Pics...
LCDPS-1

LCDPS-2

Would really appreciate a quick reply - I'm using the unit this evening in a bar, all being well...

Cheers,
A

Edited by user Saturday, August 20, 2016 8:21:45 PM(UTC)  | Reason: Not specified

AlanH  
#9 Posted : Sunday, August 21, 2016 2:54:43 AM(UTC)
AlanH

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For pics, see previous post. AC measures 242.3v.

Should I stop using the dac for the time being? It will have been this way since I first built it over a year ago. Obviously I need to address the heat problem, but is it that serious I need to sort it out before I use it again? I understand that if the sinks are hot they must be doing their job, I'm just not sure how hot is too hot.

Difficult to shut the dac down - it sounds too nice!
avr300  
#10 Posted : Sunday, August 21, 2016 11:22:40 AM(UTC)
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Please measure:

cut.jpg (41kb) downloaded 21 time(s).

(No need to panicking. The DAC has been ok for long time and will continue to be ok. We just want it cool down a bit).
AlanH  
#11 Posted : Tuesday, August 23, 2016 12:58:07 AM(UTC)
AlanH

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Both V1 and V2 = 13.7vdc
Both rails the same
Brian Donegan  
#12 Posted : Tuesday, August 23, 2016 12:33:36 PM(UTC)
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I think you were just fine with the original transformer. The heat is caused by the current draw of the DACs. If you can touch them, they are most likely under 50c. The discoloration is normal over time.

I don't think there is anything to fix.
Russ White  
#13 Posted : Tuesday, August 23, 2016 5:21:24 PM(UTC)
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I tend to agree. You could go with less voltage it the inputs - but I think you will be just fine. :)
AlanH  
#14 Posted : Wednesday, August 24, 2016 3:20:24 AM(UTC)
AlanH

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Thanks so much for the reassurance guys, have a great day :-)
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