Hi
I need help on how to buffer spdif output signal to coax from the usb chip.
Last week i got one of usb sound card (around $10US) and when with my curiousity I opened it up. What if found is it use CM108 from cmedia as usb-dac chip.
I trace the datasheet of the chip and be able to find out the pin for spdif out; however, I don't know how to build a buffer of its output, or can I simply solder them to a RCA plug. Searching through this site, I saw some thread show diagram for PCM2704 using C 1uf seried with R220K thread 62537. Can I use the same technique with this CM108?
Reference
CM108 datasheet
I need help on how to buffer spdif output signal to coax from the usb chip.
Last week i got one of usb sound card (around $10US) and when with my curiousity I opened it up. What if found is it use CM108 from cmedia as usb-dac chip.
I trace the datasheet of the chip and be able to find out the pin for spdif out; however, I don't know how to build a buffer of its output, or can I simply solder them to a RCA plug. Searching through this site, I saw some thread show diagram for PCM2704 using C 1uf seried with R220K thread 62537. Can I use the same technique with this CM108?
Reference
CM108 datasheet
Attachments
Hi Guys,
Be very careful when adding a non-isolated SPDIF output to a USB bus device - I've just destroyed my Sony VGN A170 motherboard (taken out the Southbridge device). Apparently there’s insignificant grounding on the Intel 82801 - high currents can flow though the USB data lines due to earth leakage currents flowing from the "Isolated" laptop supply though the USB - DAC - Amplifier "Ground" connection.
The CM108 can provide a bit accurate SPDIF output (Pin 1), but you must disable the internal mixer Pin 38 Low) – then set the Windows mixer to flat setting, no effects and Max Volume.
I confirmed Bit accuracy by replaying a HDCD WaveFile with no decoding problems.
Use Optical or isolation transformer otherwise you could be in the same boat as my Sony Motherboard.
The only problem with the CM108 SPDIF / Windows USB Audio streaming is that it only outputs SPDIF (Data) while “Playing” so the DAC will be going in and out of “Lock” continually – can be annoying to hear the DAC’s Mute relays click with the inevitable Loudspeaker “thump” just to replay a half missing “Mouse Click” while surfing… However I’m sure I was one of the few to have a USB connected Pink Triangle Dacapo DAC with HDCD filter on Skype!!! – ER just moments before I blew my Southbridge…..
Not to mention Sony does not provide replacement motherboards (A8068822A) for my 14 month old machine
John
Be very careful when adding a non-isolated SPDIF output to a USB bus device - I've just destroyed my Sony VGN A170 motherboard (taken out the Southbridge device). Apparently there’s insignificant grounding on the Intel 82801 - high currents can flow though the USB data lines due to earth leakage currents flowing from the "Isolated" laptop supply though the USB - DAC - Amplifier "Ground" connection.
The CM108 can provide a bit accurate SPDIF output (Pin 1), but you must disable the internal mixer Pin 38 Low) – then set the Windows mixer to flat setting, no effects and Max Volume.
I confirmed Bit accuracy by replaying a HDCD WaveFile with no decoding problems.
Use Optical or isolation transformer otherwise you could be in the same boat as my Sony Motherboard.
The only problem with the CM108 SPDIF / Windows USB Audio streaming is that it only outputs SPDIF (Data) while “Playing” so the DAC will be going in and out of “Lock” continually – can be annoying to hear the DAC’s Mute relays click with the inevitable Loudspeaker “thump” just to replay a half missing “Mouse Click” while surfing… However I’m sure I was one of the few to have a USB connected Pink Triangle Dacapo DAC with HDCD filter on Skype!!! – ER just moments before I blew my Southbridge…..
Not to mention Sony does not provide replacement motherboards (A8068822A) for my 14 month old machine
John
Thank for the info JohnW
Sorry for the problem you got there, may be I am lucky with the direct wiring from the chip.
I've been using CM108 for month now with my NOS DAC TDA1541 (spdif use cs8414) and Cal Lab GAMMA. I connect spdif directly from the chip pin cause I cant find schematic on how to buffer it.
It is good to know that CM108 has bit perfect output. Currently, I play music through foobar2000 with kernal streaming mode and TTA plugin and you are correct that it will output signal when play.
For the other, please beware of the problem JohnW has suggested.
Sorry for the problem you got there, may be I am lucky with the direct wiring from the chip.
I've been using CM108 for month now with my NOS DAC TDA1541 (spdif use cs8414) and Cal Lab GAMMA. I connect spdif directly from the chip pin cause I cant find schematic on how to buffer it.
It is good to know that CM108 has bit perfect output. Currently, I play music through foobar2000 with kernal streaming mode and TTA plugin and you are correct that it will output signal when play.
For the other, please beware of the problem JohnW has suggested.
goda_takeshi,
Apparently the insignificant grounding issue is known to effect the Intel 82801- which is used in Laptop computers only…
I bought my Laptop as a ‘Gray import’ from HK – and I’m currently in Prague, the VGN series is apparently for the domestic US market only - So it’s not serviced in Europe – so for anybody who is unlikely enough to face similar problems with Sony servicing Nexttronics (speak with Chris) where able to help – with first class service.
http://www.nexttronics.com/index.html
For 'Bit accuracy' with the CM108, Pin 38 must be tied Low (disable the internal mixer)
USB has very poor Phase Noise performance, and is not helped by the large pulsing Earth leakage currents and high levels of RF introduced by the PC – also the absolute sampling rate is determined by the PC’s internal clock – so expect large PPM errors, which drift about like a drunken sailor, and vary wildly between computers.
John
Apparently the insignificant grounding issue is known to effect the Intel 82801- which is used in Laptop computers only…
I bought my Laptop as a ‘Gray import’ from HK – and I’m currently in Prague, the VGN series is apparently for the domestic US market only - So it’s not serviced in Europe – so for anybody who is unlikely enough to face similar problems with Sony servicing Nexttronics (speak with Chris) where able to help – with first class service.
http://www.nexttronics.com/index.html
For 'Bit accuracy' with the CM108, Pin 38 must be tied Low (disable the internal mixer)
USB has very poor Phase Noise performance, and is not helped by the large pulsing Earth leakage currents and high levels of RF introduced by the PC – also the absolute sampling rate is determined by the PC’s internal clock – so expect large PPM errors, which drift about like a drunken sailor, and vary wildly between computers.
John
I'm using one of these CM108 USB adapters but I don't have SPDIF on my amp. Will disabling the mixer as you describe improve the sound quality in that case? I'm getting a significant amount of hiss and some digital clicking sounds.
I saw another suggestion elsewhere to try adding a 47uF capacitor on the power supply lines so I might try that as well...
I saw another suggestion elsewhere to try adding a 47uF capacitor on the power supply lines so I might try that as well...
virus
i downloaded this file , and while installing , i got a virus , so please check the download before installing!
i downloaded this file , and while installing , i got a virus , so please check the download before installing!
Hi !
I make a small MIDI-synth on ARM-computer with an external sound card C-media 108 (CM108).
It found that my soundcard gives a pretty nasty distortion. I make the test file 44100/16 PCM. I tried to play a file on all available headphones and players (PMP, PC, laptop), including CM108 connected to desktop and laptop. Effects and resampling disabled. In general, having tried all, came to the conclusion that the blame CM108. Search in Google for a similar problem - did not find anything except this thread.
The test file is a 440 Hz sine tremolo envelope.
Represent a distortion on hearing chattering like membrane (limiting, resonance, but without increasing the amplitude), and appears only when the signal levels of about -54db. Not to say that at higher levels of signal distortion is not quite, simply, probably, heard them worse. I thought, at first, that is aliases and connects BH3540 IC for experiment (has a built-in low-pass filter), but without effect. Also tried grounding pin 38.
I recorded the distortions via Mic-In of CM108 itself.
Test file: http://forum.vegalab.ru/attachment.php?attachmentid=239320&d=1434099023 (must be 100% volume)
And that's what I hear: http://forum.vegalab.ru/attachment.php?attachmentid=239321&d=1434099070
I had little amplifyed the signal and filter it. When test signal level increasing / decreasing around the -54db (<64 and >63 in DAC values) overtone disappears then it appears.
I can not understand - whether the chip I got broken, or bad PCB routing. Or it is correct operation of this chip ?
Sorry for bad english.
I make a small MIDI-synth on ARM-computer with an external sound card C-media 108 (CM108).
It found that my soundcard gives a pretty nasty distortion. I make the test file 44100/16 PCM. I tried to play a file on all available headphones and players (PMP, PC, laptop), including CM108 connected to desktop and laptop. Effects and resampling disabled. In general, having tried all, came to the conclusion that the blame CM108. Search in Google for a similar problem - did not find anything except this thread.
The test file is a 440 Hz sine tremolo envelope.
Represent a distortion on hearing chattering like membrane (limiting, resonance, but without increasing the amplitude), and appears only when the signal levels of about -54db. Not to say that at higher levels of signal distortion is not quite, simply, probably, heard them worse. I thought, at first, that is aliases and connects BH3540 IC for experiment (has a built-in low-pass filter), but without effect. Also tried grounding pin 38.
I recorded the distortions via Mic-In of CM108 itself.
Test file: http://forum.vegalab.ru/attachment.php?attachmentid=239320&d=1434099023 (must be 100% volume)
And that's what I hear: http://forum.vegalab.ru/attachment.php?attachmentid=239321&d=1434099070
I had little amplifyed the signal and filter it. When test signal level increasing / decreasing around the -54db (<64 and >63 in DAC values) overtone disappears then it appears.
I can not understand - whether the chip I got broken, or bad PCB routing. Or it is correct operation of this chip ?
Sorry for bad english.
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