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Old 15th May 2010, 10:58 AM   #21
Joris is offline Joris  Netherlands
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Hi Nick,

It could work, but both the capacitors are needed.
I've had mine connected just like this, only with 2 caps.
First try without the link, you can always try to connect them later, it slightly betters the sound.

Best regards
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Old 15th May 2010, 12:08 PM   #22
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Quote:
Why would he make it like this in the first place? Can it work as is?
He made it like this in an attempt to synchronize both DEM oscillators.

I am pretty sure it cannot work like this. The solution Joris suggested might work but reliable operation cannot be guaranteed (oscillator drift / component tolerances).

My advice, cut the interlink between the chips and use two separate 470pF caps. I am quite sure the noise problem will be solved then.
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Old 15th May 2010, 12:29 PM   #23
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Originally Posted by -ecdesigns- View Post
My advice, cut the interlink between the chips and use two separate 470pF caps. I am quite sure the noise problem will be solved then.
How can I do this? I think I found the traces on the upside of the board. How do I cut them without making too much damage to the surroundings ?
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Old 15th May 2010, 02:45 PM   #24
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How can I do this? I think I found the traces on the upside of the board. How do I cut them without making too much damage to the surroundings ?
The traces on the PCB can be interrupted using a 1mm PCB drill. Drill in the center of the PCB trace. This causes minimum damage to the PCB. You have to interrupt the trace as close to each IC as possible so the remaining piece of PCB trace won't pick up interference.

If you don't mind soldering at the TDA1541A pins you could try to carefully bend pins 16 and 17 so they are outside the IC socket. Then solder a small 470pF cap (1206 NPO SMD cap for example) directly between pins 16 and 17 of each DAC chip. This way you don't have to damage the PCB.
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Old 15th May 2010, 03:47 PM   #25
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Thanks, this seems doable. If I decide to try to bend the legs on the dac, would it be enough to do it with the one dac that hasn't got the cap now?
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Old 15th May 2010, 04:13 PM   #26
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I just started thinking: The DAC was still noisy when running with just the right 1541 (the one with the cap in place). Shouldn't it have been quiet then when not connected to the dac if the other capless dac is the problem ?
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Old 16th May 2010, 08:05 AM   #27
Joris is offline Joris  Netherlands
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Originally Posted by Nick122147 View Post
I just started thinking: The DAC was still noisy when running with just the right 1541 (the one with the cap in place). Shouldn't it have been quiet then when not connected to the dac if the other capless dac is the problem ?
That could be, but there are still lines attached to the cap, so remove those connections to the other TDA first. When those lines are gone it should be OK.
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Old 17th May 2010, 02:20 PM   #28
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I received two 470 pF caps today, and bent the 1541 legs outside the socket (on both 1541's) and soldered them to leg 16 and 17.
No difference!
Still the dac is very noisy at low volume. Also when comparing to the cheap cs4398 dac, the highs are almost none excisting. The bass seems good, but the sound is clearly not good.
This dac should‘t be noisy even at not full digital volume should it? In quiet music I can hear the noise even at full volume, but at 10% volume the noise is very loud. At 60% volume it is annoying.

Last edited by Nick122147; 17th May 2010 at 02:26 PM. Reason: spelling
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Old 17th May 2010, 06:47 PM   #29
Joris is offline Joris  Netherlands
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Hi Nick,

That's strange, this means that the DEM clock (it's an internal DAC clock) is running normally, or that both your TDA's are fried. I schould consider asking the seller for a replacement unit. This DAC shouldn't produce any noise, not even at low volumes...

Best regards
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Old 17th May 2010, 07:56 PM   #30
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Originally Posted by Nick122147 View Post
I received two 470 pF caps today, and bent the 1541 legs outside the socket (on both 1541's) and soldered them to leg 16 and 17.
No difference!
Still the dac is very noisy at low volume. Also when comparing to the cheap cs4398 dac, the highs are almost none excisting. The bass seems good, but the sound is clearly not good.
This dac should‘t be noisy even at not full digital volume should it? In quiet music I can hear the noise even at full volume, but at 10% volume the noise is very loud. At 60% volume it is annoying.
Hi Nick,
I had problems with noise(artifacts like) on my 4XTda1541A (similar schematic to yours). After many hours of testing I've found out that one of the voltage regulator was not working properly , even though when voltages were checked the readings were in order. (when I slightly move the regulator, the voltage dropped suddenly). You should try to check the power supply.

Good Luck,
Sorin

Ps. I've got better results using tubes for I/V stage.
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