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Old 21st December 2010, 08:18 AM   #381
phrarod is offline phrarod  United States
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I used filter network before in my AN dac and it sounded bad. That's why AN bypassed it eventually. I hope that is not the problem with this board
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Old 21st December 2010, 08:19 AM   #382
la1209 is offline la1209  Hong Kong
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A 330R resistor parallel with a 820pF cap at the output of the AD1865 used in the DAC broad of AN
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Old 21st December 2010, 08:21 AM   #383
phrarod is offline phrarod  United States
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They used different values over the years but yes
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Old 21st December 2010, 08:24 AM   #384
la1209 is offline la1209  Hong Kong
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I think the DAC ASH almost the same as the AN's DAC broad but have a better power supply, or you can install a 0.01uF cap parallel with the IV resistor to see if there any help...maybe the designer here know how to do
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Old 21st December 2010, 08:26 AM   #385
la1209 is offline la1209  Hong Kong
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I think the distortion make with the I/V stage...
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Old 21st December 2010, 08:27 AM   #386
la1209 is offline la1209  Hong Kong
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Do you have another AD1865 and try?
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Old 21st December 2010, 08:35 AM   #387
phrarod is offline phrarod  United States
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I think you helped me locate the problem. The 74H is not outputting the right voltage. I just got off a long very frustrating chat with Quanghao.

If there was an issue with the output the sound would be very different. I believe I have to get the 74H working then deal with the output I/V if they present an issue.

Yes, I ordered this board because it is a copy of the AN board but with better power.

What I need to know is this: If both chips blew up what caused them to blow up in this circuit? I have never blown one of these chips. I know both were working fine. When I put them into the board they both measure exactly the same - being off.

I could order more 74H chips but if the board is blowing them up OR if there is an issue with the PCB then there's no need to order more just to blow them up. Maybe something is shorting to ground in that area?
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Old 21st December 2010, 08:35 AM   #388
phrarod is offline phrarod  United States
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Yes, I tried three AD1865's No change
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Old 21st December 2010, 08:35 AM   #389
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you can remove it?? you connect direct to DAC??

you measure: 74HC04
Pin 1=2.57V
Pin 2 = 2.57V
Pin 4= 5
Pin 6 = 5V
Pin 8,10, 12 = 5V
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Old 21st December 2010, 08:45 AM   #390
phrarod is offline phrarod  United States
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I did remove it once and got the same distortion

I just checked for shorts on the 74H pins. No shorts to ground.

Since the 74H data sheet shows what looks like internal diodes I measured the pins like diodes as shown and the chip measures how a diode would ie readings in only one direction.

So what are the potential areas that would pull down its voltage aside from short to ground which I don't measure?

Last edited by phrarod; 21st December 2010 at 08:52 AM.
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