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Old 2nd February 2006, 09:46 PM   #1
Nordic is offline Nordic  South Africa
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Default 3.3V PSU to drive PCM2706 USB DAC

Hey guys can you point me in the right direction to make a 3.3V regulated PSU suitable to drive the above DAC..
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Old 2nd February 2006, 09:56 PM   #2
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You might take a look at what I did for the pcm2707: http://www.ecp.cc/NOS-USB-DAC.html

It essentially uses a cap, a resistor and a choke before the transformer, then another cap and resistor after the transformer all for cleaning the AC. Then it uses a rectifier with 100pF snubber caps, a 1800uF cap + a .1uF film cap to smooth, a LM7805 to preregulate, then a 680uF cap, then a high quality LDO 3.3V regulator and then 0.1uF ceramic bypasses next to any pin powered. There should probably be a small film cap before the second regulator, but I ran out of space.
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Old 3rd February 2006, 08:00 AM   #3
Nordic is offline Nordic  South Africa
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Wow, sounds extreme...
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Old 3rd February 2006, 09:48 AM   #4
Nordic is offline Nordic  South Africa
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So there's no way of running this from penlights untill my transformer arrives?
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Old 3rd February 2006, 09:56 AM   #5
lineup is offline lineup  Sweden
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Quote:
3.3V PSU to drive PCM2706 USB DAC
Build a simple 3-4 transistor 3.3V regulator.
Use 3x1.5V batteries to give regulator input at 4.5V.

How much current does a PCM2706 take?
...........................

Datasheet says supply at 3.3V:
min 3.0 Volt, max 3.6 Volt
and typical supply current 23 mA

This is a lot of current, for using battery supply.
They will be empty in a short time.
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Old 3rd February 2006, 11:06 AM   #6
Nordic is offline Nordic  South Africa
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I have some 1700mAh NIMH 1.5 penlights....
Can you point me towards a diagram for that transistor regulator please?
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Old 3rd February 2006, 05:33 PM   #7
Franz G is offline Franz G  Switzerland
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Why not use 4 to 5 of this 1.5V NIMH in series, followed by a 1000uF cap, regulated with LM317 as described in the datasheet (variable voltage). Add a 470uF cap after the regulator and preload the circuit with a bleeder resistor with at least 5mA eg. 680 Ohm.

Works great. The PCM2706 is sounding best with 3.9 to 4VDC. Works for months in my setup.

As soon as the DAC is working (try it first with windows and be happy when the system begins to configure a human interface device and an audio device), I recommend you to download (all for free, just google) the following software:

- ASIO4ALL: the better sound system than the basic windows software.

- Exact Audio Copy: to make perfect rip off from CD

- LAME: to integrate in EAC as converter

- foobar: the player software.

Happy ears!
Franz
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Old 3rd February 2006, 06:07 PM   #8
lineup is offline lineup  Sweden
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Quote:
Originally posted by Franz G
Why not use 4 to 5 of this 1.5V NIMH in series, followed by a 1000uF cap, regulated with LM317 as described in the datasheet (variable voltage). Add a 470uF cap after the regulator and preload the circuit with a bleeder resistor with at least 5mA eg. 680 Ohm.

Works great. The PCM2706 is sounding best with 3.9 to 4VDC. Works for months in my setup.
LM317 needs a voltage across input-output of something like 2.5-3 Volt to work.
If you set output at 4.0 Volts, batteries must hold like 6.5-7 Volt.
This means 6-7 NiMH cells.

Why a discrete transistor based regulator is better.
You can make a custom lowdrop regulator.
The difference between input and output voltage is very low.


I have designed such a regulator using 3 small signal transistors.
My design goal was low dropout voltage and very low supply current consumption.
This to save battery.

At no load my transistor regulator works at only 0.150 mA ( 150uA ) supply current.
And at 50 mA output, output is kept at 5.00 Volt as long as input voltage is more than 5.20 Volt.
Dropout = 0.20V at 50 mA.
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Old 3rd February 2006, 06:09 PM   #9
Nordic is offline Nordic  South Africa
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Thanks Franz, had some good news, sounds like I can have my tranny on monday allready and it was only R20, which is like the equavalent of $2.50, I also found a 12Mhz crystal so apprat from PSU I'm all set...

One slight problem is, I couldnt get a 3.3V reg that can work on 8V, so I took a 8V a 5V and a 3.3V, hope it works if I step down with them.
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Old 3rd February 2006, 08:57 PM   #10
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Quote:
Originally posted by Nordic
One slight problem is, I couldnt get a 3.3V reg that can work on 8V, so I took a 8V a 5V and a 3.3V, hope it works if I step down with them.
I don't know why you can't use a 3.3v reg with a 8V input. At 23mA, you only need to dissipate about 1/10th of a watt of heat.

At any rate, the LM317 is not as low noise as some other regulators, so it may not be the best option here. On the other hand, if you use a small inductor and decouple the pcm's pins well, you can get rid of the high frequency noise.
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