I have a oppo 93 that I've been repairing from PS failure. The 5vdc regulator that feed the 3.2and 2.5v regulators failed. At that time it somehow caused those additional regulator to output a, well, distorted wave form(an ramping component on top of the DC), but maintained their dc ratings measured by a DVM. However after repairing the 5v regulator, this strange output remained, so I also changed out those regulators also. Now the PSs outputs look quite good. I also though that these regulators(317s) were quite indestructible been internally protected.
Problem;. Now that the unit plays there is a detectable distortion especially in voices when accompanying bass notes. Yet when a disk with a sweep (20-20k) is played the scope shows a perfect output wave sweep. Intermodulations distortion?
Any ideas?
Problem;. Now that the unit plays there is a detectable distortion especially in voices when accompanying bass notes. Yet when a disk with a sweep (20-20k) is played the scope shows a perfect output wave sweep. Intermodulations distortion?
Any ideas?
If a scope shows a problem with what is supposed to be regulated DC, then that's a sufficient reason to troubleshoot. No need for distortion analysis to know there is a problem.
Sometimes a ramping waveform is really a short section of an exponential that looks relatively straight. If it its frequency is related to the AC line frequency or to SMPS frequency then it might suggest a problem with filter caps or with a load drawing too much current.
Sometimes a ramping waveform is really a short section of an exponential that looks relatively straight. If it its frequency is related to the AC line frequency or to SMPS frequency then it might suggest a problem with filter caps or with a load drawing too much current.
Thanks for the reply. I have remedied the many regulated dc supplies. All appear functioning correctly with little hash. Fixed them.
The problem that exists is a notable "clipping" distortion, especially in voices, but not all the time. I've scoped output while play sine waves and sweeps 20-20k with no clipping on either the waveforms or anomalies on the PSs. I've also measured/scoped the +- inputs(ac&dc) to the output opamps(both channels) with no signs of distortion and identical measured values. Replacing the output opamps made no difference. I'm starting to suspect the Dac chip, CS4382A. I'm at a loss, where to go now?
How are you playing music, over USB, CDs, other? Does the intermittent clipping problem occur with all sources?
Good question! I've only been using disks. Using another player results in no distortion, proving it's not in the rest of the system. I'll try a USB stick using the same files today. I played a Chris Jones disk containing some lower bass/voice combination. The clipping noise is in both voice and bass note, but I cant see PS issues during this to explain that clipping noise(?). Just a side note, the DC offset on the output didn't change when I switched from an OPA2132 to a OPA2107. Exactly the same offset, 8.2mv/.3mv on both opamps without discernable differences in the +- inputs to each channel from the CS4382A(during a sine wave steady state play). I though that strange....
Tried a usb stick play, still distorting. Additionally, the usb play mode(in the back) is rather dull relative to disk play. The disk is made from the same files as the stick!
And you say the distortion is intermittent, or does it reliably occur under any conditions, say, for example, at some particular point in a piece of music? Also, if intermittent how often does it occur, how long does it continue, and does it occur when playing certain frequencies, and or when higher volume levels are being played back, etc.?
The distortion does repeat at the same points in play. It's not continuous throughout a track. It seems to mostly affect lower register voices. I know this seems strange, and it's got me baffled. I proven it to not to be any part of the rest of the system. It is most notably during louder voice passages. Heavy Bass notes also tend to clip. Scoping the respective PS points at the chip pins(opamp, dac, regulator output) during these times shows no disturbance to the flat line DC. I've changed all the caps in these supplies, regulators, even the output opamp. No joy! And yet it sounds wonderful between those distortion points....
Could the Oppo outputs be overloading the input circuitry of the following component?
Try a -6dB attenuator between them.
Can you actually see with a scope the Oppo outputs clipping? If not, it could be overloading.
Try a -6dB attenuator between them.
Can you actually see with a scope the Oppo outputs clipping? If not, it could be overloading.
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The oppo is feeding a SET with a 100k input. Should be good. Using sine waves there is no clipping at any time, any freqs, 20-20k. I've tried watching the signal of the tracks at the player output that distort. As you know it's rather difficult to discern wave form distortion with a complicated wave pattern. If I hazard a guess, the bass portion "may" appear to soft clip at the peaks but I don't know if a bass guitar (in the track bass notes) has that characteristics. Again, the voice distortion is always on just portions of passages every time it's played, not through the entire track. Most of track the sound of the music is better than my Meridian player. Very simple acoustic music doesn't have this apparent problem. Would higher modulated disk/music play a part in this?
Its usually easier to troubleshoot something if you can make the symptom stay present rather come and go. If you find a place in the music which is not too complicated, say, maybe where bass distorts and not a lot else is going on, maybe you could use a wav editor to select and copy that part over and over, effectively turning it into a loop. Then you would have a test signal that distorts constantly. Makes it easier to then see what the state of the hardware is during the fault condition. Such as, for example, check for things like power supply voltage sagging, some AC appearing on DC power rails, op amp clipping, etc.
Distortion is often level sensitive. You could also look at the time-domain waveform the wav editor to see if distortion occurs at times when the waveform peaks are especially high magnitude.
One way to check for a level related problem would be to take recording and again using a wave editor, reduce the volume of the whole song by, say, 3dB - 4dB. Save that to a new wave file and burn to CD. Does that version play without distortion?
How about trying a frequency sweep waveform, possibly at different volume levels?
IIUC your player can act as USB dac? If so, then probably worth trying it in that mode. Much easier and faster to send it various test signals.
Another thing to do is try a different amplifier to verify that the distortion is internal to the Oppo.
To summarize much of the foregoing in terms of basic strategy, if you can find a way get the Oppo to distort constantly with a simple test signal then it might be a lot easier interpret scope readings. Also, observing for changes in device behavior as you adjust input and or control variables can sometimes provide useful troubleshooting clues.
Distortion is often level sensitive. You could also look at the time-domain waveform the wav editor to see if distortion occurs at times when the waveform peaks are especially high magnitude.
One way to check for a level related problem would be to take recording and again using a wave editor, reduce the volume of the whole song by, say, 3dB - 4dB. Save that to a new wave file and burn to CD. Does that version play without distortion?
How about trying a frequency sweep waveform, possibly at different volume levels?
IIUC your player can act as USB dac? If so, then probably worth trying it in that mode. Much easier and faster to send it various test signals.
Another thing to do is try a different amplifier to verify that the distortion is internal to the Oppo.
To summarize much of the foregoing in terms of basic strategy, if you can find a way get the Oppo to distort constantly with a simple test signal then it might be a lot easier interpret scope readings. Also, observing for changes in device behavior as you adjust input and or control variables can sometimes provide useful troubleshooting clues.
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Is there a digital volume control on the Oppo? If so, try setting it to a lower level, some cause clipping when at full scale.
Set the scope to a very slow sweep and look for flat tops on the waveform, but not individual peaks,
which are too brief and hard to see, unless you capture and store the waveform.
Kinda like this:
Attachments
Thanks for the help. The digital volume is always on full, but thanks for the reminder. I will give it a try reducing the output amplitude. I believe doing so on this dac chip will tend to cut the bit quality/digital output quality(?). Also, my test disk has multiple freq test bands, mostly -20db level. Maybe output level is the key.
Sorry, my scope is an oldie, no storage capabilities. One track I'm concentrating on appears to have the bass wave portions at the highest amplitude on the scope display. That peak has a rounded leading/trailing edge with flattish top shape. Thus my interpretation of "soft clipping" I've never have seen other flat topping of the other frequencys. As you noted, it's always moving and hard to interpret.
Live test example;
Listening to Maria Mulder " Richland Women" this morning, a simple acoustic guitar, acoustic bass and her voice only, when she says RED her voice distorts. The word following are fine(?), until she says RED again. Baffling?
Sorry, my scope is an oldie, no storage capabilities. One track I'm concentrating on appears to have the bass wave portions at the highest amplitude on the scope display. That peak has a rounded leading/trailing edge with flattish top shape. Thus my interpretation of "soft clipping" I've never have seen other flat topping of the other frequencys. As you noted, it's always moving and hard to interpret.
Live test example;
Listening to Maria Mulder " Richland Women" this morning, a simple acoustic guitar, acoustic bass and her voice only, when she says RED her voice distorts. The word following are fine(?), until she says RED again. Baffling?
Do turn down the digital volume level a few dB and recheck.
Storage is not necessary, set the hor sweep to around 100mS per division and reset the brightness
so you can see the peaks clearly without blooming.
Storage is not necessary, set the hor sweep to around 100mS per division and reset the brightness
so you can see the peaks clearly without blooming.
Rayma, your the man. I stepped down the Oppo volume (adjusting the amp volume up to compensate), and after 8 apparent steps down the distortion sound pretty much vacated.
Now for the fix.... This is a new development as previously I've played this same disk/Oppo player literally a hundred times set at full volume without this distortion! I need to absorb the linked pages you sent, but is there a quick heads up I should be aware of where this will lead?
Now for the fix.... This is a new development as previously I've played this same disk/Oppo player literally a hundred times set at full volume without this distortion! I need to absorb the linked pages you sent, but is there a quick heads up I should be aware of where this will lead?
Intersample overshoots often go unnoticed by many people. They are worst when playing back 16/44 at an audio frequency of around 11.25kHz. Based on your description of when the problem happens, its intensity, and the frequencies affected, seems doubtful intersample overs are the whole story.
Both rayma and I were trying to get you to do some tests, including at different signal levels. IME that makes sense based on your description of the problem.
Getting back to it then, IIRC Oppo used ESS dac chips. Is that right for your player? If so, the volume control is usually implemented digitally inside the dac chip. In that case intersample overs might not be helped by volume reduction anyway. IIRC Benchmark attenuated the digital audio before the ESS dac chip in order to prevent intersample overs.
Moving along a bit more, seems more likely that the problem is not in the digital signals before the dac chip. More likely in the analog output stage following the dac chip. Turning down the volume as a test will reduce the peak signal levels in the output stage too.
Both rayma and I were trying to get you to do some tests, including at different signal levels. IME that makes sense based on your description of the problem.
Getting back to it then, IIRC Oppo used ESS dac chips. Is that right for your player? If so, the volume control is usually implemented digitally inside the dac chip. In that case intersample overs might not be helped by volume reduction anyway. IIRC Benchmark attenuated the digital audio before the ESS dac chip in order to prevent intersample overs.
Moving along a bit more, seems more likely that the problem is not in the digital signals before the dac chip. More likely in the analog output stage following the dac chip. Turning down the volume as a test will reduce the peak signal levels in the output stage too.
I have a limited ability to reduce or manipulate a (signal or disk) modulation level. I'm not talking about amplification. My only means is to play what disks I have. By playing the previously Muldur disk(simple acoustic music) was an attempted to reduce the signal total modulation level, my only option. That doesn't reduce the possible peaks. It helped to displayed or demonstrated the distortion, less to listen through. My test disk, no matter what track was played didn't distort(31, 61, 440, 1k, 20-20k etc) in the output.
This Oppo model bdp-93 is equipped with a CS4382A 8 channel dac chip. It does have in chip volume control, 1 db per step. Presently I've have an OPA2107 output opamp in the stereo circuit with all the other surround sound channels opamps disabled, runnings for only 2 channel use.
I have monitored the dac chip differential inputs to the 2107, its PS +- 12 vdc, and both channel outputs. It has never shown any propensity to distort the signals sent to it by the dac, at least with steady state sine wave signals. The only way I know of to compare under music conditions would to have some type of storage(?) differential/dual channel device to compare different strength "in vs out" signals. I don't have that device. But I not inclined to blame this opamp as it the third different (5532, 2132) installed in this position and all output distorted music signals but not under steady state signals. I agree that reducing the dac out will reduce the opamp out also. Any other tests to run for assistance?
This Oppo model bdp-93 is equipped with a CS4382A 8 channel dac chip. It does have in chip volume control, 1 db per step. Presently I've have an OPA2107 output opamp in the stereo circuit with all the other surround sound channels opamps disabled, runnings for only 2 channel use.
I have monitored the dac chip differential inputs to the 2107, its PS +- 12 vdc, and both channel outputs. It has never shown any propensity to distort the signals sent to it by the dac, at least with steady state sine wave signals. The only way I know of to compare under music conditions would to have some type of storage(?) differential/dual channel device to compare different strength "in vs out" signals. I don't have that device. But I not inclined to blame this opamp as it the third different (5532, 2132) installed in this position and all output distorted music signals but not under steady state signals. I agree that reducing the dac out will reduce the opamp out also. Any other tests to run for assistance?