How to do Self-power for USB dac pcm2706? - diyAudio
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Old 22nd September 2005, 06:22 AM   #1
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Default How to do Self-power for USB dac pcm2706?

Hi,
I have a USB kit with PCM2706/TDA1543 dac on hand. The schematics is as follows:
http://www.audioworkshop.com.hk/download/AW_D3.pdf

I have already replace the usb power for the pcm2706 and pull the power from the lt317 using a tl431 for 5v. There is some improvement after this mod but I can improve this further by using the self-power mode.
I tried to convert the circuit for pcm2706 for self-power mode but failed, got a "malfunction usb device error". Here is what I did:
1. cut the trace and put the P-sel pin to ground
2. connect the Host pin to USB power with 1M resistor to ground
3. connect all voltage pins to a 3.3V power.

Is there anything else I missed? Thanks in advance.

BTW, this dac sound very good, (direct out to a NI gainclone without buffer)
I will stack another 1543 on top for my next tweak.
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Old 24th September 2005, 01:57 AM   #2
Franz G is offline Franz G  Switzerland
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Do you feed in 3.3V in VCCP/Pin 2 ?

Franz
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Old 24th September 2005, 05:59 PM   #3
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Pin 2? yes, 3.3v to all V pins. Vdd, Vbus, Vccl, Vccr, Vcom, Vccp.

Host pin 5V from usb. Psel to ground.
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Old 24th September 2005, 06:51 PM   #4
cyteen is offline cyteen  England
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This is one of the implementations I've come across which might be helpful with regard to which pins require 3.3v for self power.
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Old 24th September 2005, 06:58 PM   #5
cyteen is offline cyteen  England
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This is the other one:
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Old 24th September 2005, 07:05 PM   #6
Franz G is offline Franz G  Switzerland
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I finished my first PCM2706 DAC some days ago, to play with different modes.

But, I did not realize, that FSEL must set high to use the internal DAC, same setting as for SPDIF-out.

In the link from audioworkshop you pointed to, Chuck, I found the little comment about FSEL (J2 in this circuit) and got my DAC playing now.

BTW: I found, the chip is sounding better with 4V (actually trying 4.3V ) than with 3.3V.

Franz
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Old 25th September 2005, 02:22 AM   #7
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Thanks for the circuit, Cyteen.

It seems the Vcom, Vccl, Vccr do not need to be connected to 3.3v, that
strange.
I recheck the datasheet, Vcom don't need to be connected but Vccl, Vccr should be connect, this pin is for the dac/analog output.

Hi Franz, good work, yeah the Fsel needs to be selected between SPIF out or internal dac. Are u using the self-power mode?
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Old 25th September 2005, 12:56 PM   #8
Franz G is offline Franz G  Switzerland
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I could drastically improve the sound of the first version, by

- decoupling the Vccl/Vccr from the digital voltages by CLC-filter 1000uF/330uH/1000uF

- replacing the 0.022uF MKT caps in the I/V conversion by sowjet MKP's. This caps are a key part, when using internal DAC.

- adjusting the voltage to 3.99VDC (by listening, with regulated supply).

It's sounding definitively better than anything else I heard out of a PC!

Franz
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Old 25th September 2005, 02:44 PM   #9
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Franz, did you set the Psel pin high or low (to ground).
Yes, they very good by itself.
I also add your decoupling, but just couldn't bypass the internal regulator.... hey, what am I saying, you are using it in self-power mode, otherwise, you couldn't set it to 3.99v!

Could you tell me which of the V pins are connected to your 3.99v (that is a pretty precise voltage)
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Old 25th September 2005, 04:28 PM   #10
cyteen is offline cyteen  England
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That makes sense now I think about it, the above were for i2s only operation. I was forgetting the D3 has the option of either i2s to the tda1543 or the internal DAC.

I have one of these kits on its way, should be with me in a week or so.

One of the other suggested tweaks is to replace the 12Mhz crystal with a Crystek C3390 XO clock.

Any other comments you have about the build would be appreciated.
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