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Old 28th February 2009, 02:54 PM   #71
hafp is offline hafp  United States
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luxury54,
Awsome posts on your trails and results. Could you please post some pictures of your work when you have the time.

Did the +5v connect to the pin 20 mod on the CS4397 chip yesterday.
I tapped off pin 28 of the CS8416 chip pin, which measured +5.02vdc and ran a wire to the 47k resistor connected to pin 20 of the CS4397.
Do not hear anything negative from this test hook up.

Would you guys recommend a better +5vdc tap I should use to supply the the vcc for pin 20.

Cheers.
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Old 28th February 2009, 04:46 PM   #72
johnm is offline johnm  United Kingdom
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Is this pin20 mod only for the CS4397 models are does it apply to CS4398 too?

Cheers
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Old 28th February 2009, 05:56 PM   #73
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guys,take a better look ,we were discussing about pin20 of the CS8416 receiver chip for lowest in-band jitter and not the DAC's pin20 - do not make this mod on the dacs cause you might damage them
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Old 28th February 2009, 09:53 PM   #74
hafp is offline hafp  United States
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luxury54,
Thanks for the clarificaion; my bad on the last post, which should have said:

Did the +5v connect to the pin 20 mod on the C8416 chip; tapped off the lead going to pin 28 of the CS4397, which measured +5.02vdc; ran a wire from there to a 47k resistor connected to pin 20 of the CS8416.

With that being corrected, is the +5vdc supply line for this mod critical. Would it be better to take it directly from the +5vdc power supply regulator rather than taking it from a tap on the board, like I did above.

Cheers.
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Old 28th February 2009, 10:28 PM   #75
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Quote:
I have simulated the LP filter with component values as described above. Althought I can't verify a roll-off at 13kHz, but there's a strange 3dB dip around 10 kHz, while the -3dV roll-off is at 43 kHz. The dip is worse when changing R8/R9 from 36k to 22k.
I've just had another go at simulating it and I agree. Something goes wrong with the shape of the filter with the component values we have found to be fitted. Not sure I can explain why but it doesn't work at all.

Quote:
The values described by the Cirrus AN gives a very nice straight line from 5Hz to 48kHz and a steep roll-off at 50 kHz. This is the way I will go, rather than removing the filter all together (by removing all the 1nF cap's as I have it now).
Simulated this too and I agree again! Perfect filter shape. 0.1db down at 20KHz, 3db down around 50KHz. I will be replacing everything with these values next time I get the soldering iron out.

To clarify, that is:

R8, R14, R15, R16 = 13k7
R10, R11 = 3k32
C36,C37 = 1nF
C32, C34 = 220pF

With all the caps except C32 removed it's 0.5db down at 20KHz with a 3db point at 63KHz. The common mode rejection starts to suffer at high frequencies (probably too high to matter) because the filtering that remains is unbalanced.

Kevin
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Old 28th February 2009, 10:41 PM   #76
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So, this is what I've ended up with:

Click the image to open in full size.

Kevin
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Old 1st March 2009, 06:22 AM   #77
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Kevin,

With what opamp you're using? NE5532, LM4562 or AD826? Let us know the results on the actual circuit. It's getting more interesting.

Fred
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Old 1st March 2009, 09:40 AM   #78
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Quote:
Originally posted by hafp
luxury54,
Thanks for the clarificaion; my bad on the last post, which should have said:

Did the +5v connect to the pin 20 mod on the C8416 chip; tapped off the lead going to pin 28 of the CS4397, which measured +5.02vdc; ran a wire from there to a 47k resistor connected to pin 20 of the CS8416.

With that being corrected, is the +5vdc supply line for this mod critical. Would it be better to take it directly from the +5vdc power supply regulator rather than taking it from a tap on the board, like I did above.

Cheers.

yes,i think is a good solution to take that 5v directly from one of the regulators...i will try that myself since on my board cs8416 is fed also with 3,3v
i think would be a better solution t change that small 3,3v regulator to a 5v regulator because cs8416's datasheet says that it can accept voltages up to 5v
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Old 1st March 2009, 11:33 AM   #79
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With what opamp you're using? NE5532, LM4562 or AD826? Let us know the results on the actual circuit. It's getting more interesting.
I'm still using the 5532 currently but I plan to upgrade that. Had a rummage this morning and I haven't got any 220pF caps to try the new filter.

Will have to put an order in for some bits, including some better Op Amps.

Quote:
yes,i think is a good solution to take that 5v directly from one of the regulators...i will try that myself since on my board cs8416 is fed also with 3,3v i think would be a better solution t change that small 3,3v regulator to a 5v regulator because cs8416's datasheet says that it can accept voltages up to 5v
Beware that on my board the CS8416 is fed from two +3.3v supplies so it might not take kindly to being pulled up to 5v. It would be worth checking what it is powered by first, although I doubt it would do any harm through a 47k resistor. In addition, one of the 5v supplies (i believe there are two) drives the DAC so be careful that you don't connect the 8416 to that. I would imagine the 8416 is quite a noisy device and not something you want polluting the DACs power rail.

I'm not sure if there's anything to be gained by running the 8416 at 5v. It could well be that it's less noisy on the lower voltage. Only one way to findout I guess. Try it and see if it sounds any different.

Kevin
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Old 1st March 2009, 04:11 PM   #80
hafp is offline hafp  United States
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Great information from luxury54 and Kevin.

Yeah, the voltage to the CS4316 has me a little bit confused too; but the +5dvc to pin 20 via 47k resistor works pretty well.
One DAC schematic I have of the CS8416/CS4397 has pin 21 of the 8416 being supplied with a +5vdc; another schematic has that same pin supplied with 3.3v, along with pin 23.
Thus my asking the question of where would be the best place to tap the 5v power.

What Kevin notes about keeping the DAC power separate to prevent noise from getting back to the CS4397.

Will change the power tap and let you know how it goes.

Cheers.
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