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Old 7th November 2008, 06:40 PM   #1
fraserh is offline fraserh  United Kingdom
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Default High frequency noise

I've asked a few friends and none of them can hear this, but it's driving me nuts!!! I have a new DAC from Derek Shek but the psu he sent me omits a HF noise (at the socket, not at the dac) It has a a switch on the plug to switch between various voltages- is it safe to try them all and see if it goes away?? Outputs is 800mA

thanks
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Old 7th November 2008, 08:12 PM   #2
Dr_EM is online now Dr_EM  United Kingdom
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Must be a SMPS, try and swap it for a linear, this wil sort this problem
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Old 7th November 2008, 11:59 PM   #3
fraserh is offline fraserh  United Kingdom
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I thought that would be the problem, i've heard of that before with that kind of supply... I have a linear one kicking about but it's slightly different:

3V DC, 1000mA

the original one is set to 12V 800mA- but i've heard that the 1000mA might result in an improvement anyway, it's the lower DC output i'm concerned about
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Old 8th November 2008, 02:49 AM   #4
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Hello fraserh, without knowing the DAC requirements, it's hard to say what will happen with using a lower voltage. I would suspect that the DAC circuit would not be happy with the lower voltage, but it's hard to say without specs. Having extra current available from a PS is not going to cause any problems. If the circuit doesn't need the current, it won't draw that much. But if there is a little extra there, that can be a good thing at times.
So, if you can post some specs on the DAC, we could probably answer better what supply to use. I can agree that it's possible that an SMPS will create some HF noise. Bloody things are a double edged sword. They are much more efficient, and if designed well they can work great. But like anything else, if it's cheap, it probably isn't very good.

Peace,


Dave
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Old 8th November 2008, 03:40 AM   #5
fraserh is offline fraserh  United Kingdom
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I can't find a schematic for the DAC but if it's any use here's the photo i could take of the guts if that helps? The inputs from L to R are: DC, optic, input switch and coax

Click the image to open in full size.
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Old 8th November 2008, 04:28 AM   #6
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definitely an SMPS. I checked the sigtone website. - Nice little DAC, btw.

Since he states it is 100-240v 50/60Hz it is certainly SMPS (autoranging) Sounds like a cell phone charger I have. Whenever I plug in to charge the phone, the supply emits a little high frequeny "whine". He should swap this out for you. I don't care for my phone, but it's unacceptable for a piece of audio equipment. The supply shouldn't do that, so it's a bit of a lemon though it probably meets all it's functional requirements.

Not uncommon in very cheap switch mode supplies. Something not well damped resonating with the switching frequency. A slightly "off" inductor most likely.

oh, and 3v isn't going to cut it. Most likely the circuit will need at least 9v to operate. Depends on the power regulator scheme and the voltage specs of the active parts.

As Dave said, higher current capacity from the supply won't hurt, and can only help most likely. I think you'll need to get within a volt or two of the 12v it requires. Be careful about going over hard to know how it would like that. (really, a 12v supply shouldn't be too hard to find)

-Chris
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Old 8th November 2008, 04:35 AM   #7
fraserh is offline fraserh  United Kingdom
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Thanks so much, everyones helpful round here! I'll get a hold of a decent linear 12V 1000mA supply then. I think i might email him as well just to let him know: it's definitely very noticable- at least to my ears.
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