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Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
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Old 13th September 2017, 09:42 AM   #261
Coris is offline Coris  Norway
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Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
This is the XLR output on 205. Also all the outputs it have these diodes to ground, as similar components placed on the signal lines/path.
My guess is the diodes connected in between signal line and ground are meant as ESD protection.
A ferrite bead (placed on all the outputs signal lines) are meant to lower or filter out high frequency residual signals.

Any comments, more opinions, thoughts about such design and how safe is to simplify it, or remove these (in my opinion) too many components in the final signal path.
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Old 13th September 2017, 01:18 PM   #262
dmusoke is offline dmusoke
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Coris:

Why add non-linear components in the signal path? Diodes leak! When inactivated (reverse biased), they have a residual temperature dependent leakage current, small as it may be, but there, contributing to the distortion of the signal.

Also, you said you added diodes on the signal lines to ground? Assuming the output signal is AC coupled, this limits the output +ve/-ve swings to 0.6v. Is this what you want?

IMHO, remove these diodes and just have a 100 ohm current limiting resistor in series with the output signal for protection. Its noise contribution is negligible. The audio system is a closed environment. The output of your board will go into the input of an amplifier or pre-amplifier. Both are closed systems where chances of ESD damage from the user or equipment are extremely small or non-existent. Remember that output stages of opamps already have great ESD protection (+/- 2000V HBM or greater). The same for the input sections of amplifiers, so no need to over-design this board.

Same goes for the ferrite bead. Remove it as I believe its not necessary. The high-frequency residuals that you are concerned about have mostly been digitally filtered out by the ESS-90x8 chips. Look at its datasheet and you'll see many IIR filter options that can be engaged to filter out any sampling artifacts. The DAC has many filter slopes available to the user, namely fast roll off and slow roll off. This is where most of the filtering occurs and because the ESS chip is an 8x oversampling DAC chip, these artifacts are further removed in frequency from the output signal. You input a 44.1kHz PCM signal, the DAC chip oversamples that to 352.8 kHz, so the first Nyquist image will be centered at 352kHz. The IIR filters then attenuate this image to at least 100 dB, depending on the filter slope chosen. You only need a gentle first or second order output filter in the DAC output section to further limit the sampling artifacts, but remember that most of the filtering work has been done by the ESS dac chip itself.

The case is even better if you have higher resolution sources. A 192kHz PCM input signal to the DAC is oversampled to 1.536 MHz. Then, this first Nyquist image at 1.5MHz is attenuated by at least 100dB at mentioned earlier, depending on the filter type chosen in software. Like I said before, you now only need a gentle output filter to further attenuate these less than 100dB images at 1.5MHz even further.

Also, don't forget that the capacitance of good output interconnect (several pF) cable forms a filter pole with the input impedance (>10Kohm) and input capacitance of your preamp/amplifier(several pF at least) and that provides extra filtering.

Assuming a 10pF lumped capacitance (Cable + Input Amp Capacitance) and 10k impedance, the generated filter has a 3dB point of about 1.6MHz. Higher values of input impedance, say 100kohm which is very typical in preamps and amplifiers, will have this pole now at 160 kHz. Now, that's the true bandwidth of your system from Oppo output to the amp input. That's what the amplifier sees. So the already <-100dB suppressed Nyquist images at 352Khz to 1.6MHz, further filtered by the DAC output filter, then further filtered by the cable capacitance, amp impedance, and amp capacitance, do not pose a threat to the system as a whole.

I hope you can see that I have proven that there no need to 'help' the system with further filtering and/or protections. You'll make things worse, all in the name of 'protecting' the equipment downstream. There's an old political saying here in the USA that has an acronym of K.I.S.S ... keep it simple stupid

Good luck!

David
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Old 13th September 2017, 02:16 PM   #263
Coris is offline Coris  Norway
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Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
Please do not misunderstand me (maybe my previous post/text it not expressed very well what I was intended).
The picture above and that design is the original Oppo approach for the 205 audio analogue outputs. The pictured circuits are not my mod or any of my improvements... Actually, my opinion is that such things it cannot be "improvements" at all, but opposite...
I also asked for opinions and comments on the original Oppo design. I personally do not like such diodes or ferrite beads into the signal path, but I try to understand what Oppo was thinking when they did so...

Last edited by Coris; 13th September 2017 at 02:25 PM.
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Old 13th September 2017, 02:37 PM   #264
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Coris:
I'm sorry for it was my mistake and my misunderstanding ... I thought it was mod you had made and were in process of evaluating.
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Old 13th September 2017, 04:46 PM   #265
Coris is offline Coris  Norway
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Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
Quote:
Originally Posted by dmusoke View Post
Coris:
I'm sorry for it was my mistake and my misunderstanding ... I thought it was mod you had made and were in process of evaluating.
There is all right. At least my previous text it was not so specific as well...
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Old 15th September 2017, 01:03 PM   #266
Coris is offline Coris  Norway
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Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
Default Wrong information...

The marked caps on this picture are not AC coupling caps, but it have a different function on board. I did not yet figured out which function it may be... Their minus pole is tied to GND.
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Last edited by Coris; 15th September 2017 at 01:23 PM.
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Old 15th September 2017, 01:41 PM   #267
Coris is offline Coris  Norway
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Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
These caps mentioned in my above post, are a part of the monitor/reset/mute section on board and it should not be replaced, but with similar value and voltage rating.
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Old 15th September 2017, 02:49 PM   #268
dmusoke is offline dmusoke
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Makes sense...probably AC coupling cap is the one in the midst of those 2 large 2200uF caps, which are probably used for de-bouncing the switch.
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Old 15th September 2017, 03:30 PM   #269
Coris is offline Coris  Norway
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Oppo new UDP series players - 203/205 - Discussions, upgrades, modifications
The AC coupling caps (Silmic 100/16v) are all the rest of the marked caps in that picture, except the ones I mentioned. The small (dimensional) ones in between (220/16v) are filtering caps for opamps positive power rails.
Actually these AC coupling caps it should be an unpolarised type. Much better without (bypassing it), if the connected amplifier it can accept DC coupling (into 10mV offset). Before bypassing it, one should measure the DC offset before the caps, to ensure the offset is acceptable for the connected power amp/preamp.
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Old 17th September 2017, 06:26 PM   #270
justubes is offline justubes  Singapore
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Quote:
Originally Posted by Coris View Post
The AC coupling caps (Silmic 100/16v) are all the rest of the marked caps in that picture, except the ones I mentioned. The small (dimensional) ones in between (220/16v) are filtering caps for opamps positive power rails.
Actually these AC coupling caps it should be an unpolarised type. Much better without (bypassing it), if the connected amplifier it can accept DC coupling (into 10mV offset). Before bypassing it, one should measure the DC offset before the caps, to ensure the offset is acceptable for the connected power amp/preamp.
If the preamp inputs have a cap there , a straight wire bypassing the output caps will no longer be an issue.
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