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Old 14th May 2010, 05:34 PM   #11
Joris is offline Joris  Netherlands
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Hi Nick,

Thanks for the pictures! I wish my DAC looks like that, very neat pcb!

The fonts on the chip are OK, also the date corresponds with the production location (HSH for Holland, unless marked TAIWAN on the left side)
So the chips are OK.

As those chips seem very reliable to me (never seen one broken), it must have something to do with the receiver (DIR9001?)
I use CS8414 myself, but maybe we can find some problems that need to be solved.

I guess you already know what I'm going to ask now: Are all the supply voltages correct?

You can measure them with a simple digital multi purpose meter. But since you bought this in the first place, you've probably got one of those and know how to handle one. (If not, I'll help you)

Have you contacted the seller of the DAC already? Maybe he has got some valuable information about these types of problems...

Best regards
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Old 14th May 2010, 05:37 PM   #12
Joris is offline Joris  Netherlands
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Hi Nick,

Just another idea:

What about the digital filter? (SAA7220)
Under it seem to be some DIP-switches to change from OverSampling (OS) and Non-OverSampling (NOS), try removing the chip and put the switches into NOS mode, this might solve your problem.

Best regards
Joris

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Old 15th May 2010, 06:06 AM   #13
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I have tried the switches, no differences.
The noise is very easy to hear if I turn down the volume at the digital side. When halfway up volume control in itunes, the sound is very noisy, and at minimum volume in itunes the sound is very distored and increadibly noisy.

Compared to my 100usd "707 super usb dac" (cs4398) this dual tda1541 sounds warm, natural, but with much less resolution and much narrower soundstage.

I didn't buy it on ebay, I bought it locally in China, as I live here. The seller's english is very limited, as is my chinese. Maybe the best solution would be to send it back to him. But I would maybe expect him to say that it is working perfectly, as it is producing sound, and at loud levels the noisy is not overwhelming.
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Old 15th May 2010, 06:46 AM   #14
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Quote:
but it's quite apparent already that it is quite noisy when there are some quiet music
If photographs are correct, one yellow 470pF DEM oscillator cap is missing on the left chip.
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Old 15th May 2010, 06:57 AM   #15
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Quote:
Originally Posted by -ecdesigns- View Post
If photographs are correct, one yellow 470pF DEM oscillator cap is missing on the left chip.
That is indeed so. The seller said it should be this way for optimal operation, even if the schematic showing it there.
Can that cap make this big of a difference? From the schematic it is between leg 16 and 17 of the tda1541. (C42 in schematic)
Of course I should try to insert one. Can I temporarily try with a bigger size cap if I have ?
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Old 15th May 2010, 07:21 AM   #16
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Use the DEM circuit from the schematic, one oscillator cap on each TDA1541A. You can temporarily use different DEM cap value (330pF ... 1nF), value determines DEM oscillator frequency. The higher the cap value, the lower the DEM frequency. DEM clock typical frequency is around 200 KHz.

Make sure to remove wiring (if present) on the solder side between both chip DEM oscillator circuits (pins 16 / 17).

Attempts to "synchronize" two DEM oscillators this way is very likely to fail / produce unpredictable results.

Yes the DEM oscillator can make such a big difference as it directly affects 6 MSB bit errors of both channels.
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Old 15th May 2010, 07:32 AM   #17
Joris is offline Joris  Netherlands
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Hi Nick and ecdesigns! (Nick, this man's a legend according 1541)

I overlooked the cap, but it is obviously necessary to work good,
to find out whether that's the problem, only place the DAC with the cap and
remove the one without it, if you haven't tried so already.

Best regards
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Old 15th May 2010, 08:20 AM   #18
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I tried inserting a 0.1uf cap, and the sound became more distored than ever. It's the same type of noise/distortion I had before, so it seems likely that it has something to do with this cap. I should get hold of another 470nf cap to try, or could I change both caps to 0.1uf for now? The 0.1uf caps I have is quite big with long leads, will that pick up lots of noise?

Thanks!

Last edited by Nick122147; 15th May 2010 at 08:30 AM.
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Old 15th May 2010, 09:11 AM   #19
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First check if pin 16 and / or 17 of TDA1541A chip #1 and pin 16 and / or 17 of TDA1541A chip #2 are inter-connected through PCB traces, wires or capacitor (attempt to synchronize both chips). Remove these inter-connections first, so you end up with the circuit shown in the schematic.

0.1uF (100,000pF) cap value is too high (use 330pF ... 1nF like I suggested). Make sure to use small cap size and shortest possible connections to pins 16 and 17 (few millimeters). Long wiring easily picks-up interference that can degrade DEM oscillator performance.
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Old 15th May 2010, 09:36 AM   #20
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Thanks!
The seller says that I should not install this 470p, as they two 16 leg of the tda1541 are connected together, would need to cut this connection. So basically what you are suggesting to do. I think I will try this, because the present solution is not good.

Why would he make it like this in the first place? Can it work as is?
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