JVC HR-XVS20 distorted linear audio?

[hodgey]

This otherwise nice SVHS deck I have has an issue, something is causing noise and distortion on the linear audio. Hi-fi works fine. I have a Samsung SV-6123 Hi-Fi VCR that has very similar symptoms, and on that one it happens with the mechanism from two different decks so I don't think it's a head issue. Has anyone experienced something similar and have any idea what could cause this sort of noise?

The sample is from the JVC, with a sample from the same tape form a JVC HR-J658 (which sounds fine) for comparison.

[lordsmurf]

All I hear is differing hiss patterns and muffling. Both files have it, especially this hiss.

JVCs do that at times. Even Panasonic can do it. All VCRs do it to some extent, on various tapes.

There is a reason it happens, and I've read about it before in my VCR repair/tech books from Capelo and Beeching. Some to do with the compensation circuits. I don't remember the specifics anymore.

[Kaos-Industries]

Quote:

Originally Posted by hodgey

This otherwise nice SVHS deck I have has an issue, something is causing noise and distortion on the linear audio. Hi-fi works fine. I have a Samsung SV-6123 Hi-Fi VCR that has very similar symptoms, and on that one it happens with the mechanism from two different decks so I don't think it's a head issue. Has anyone experienced something similar and have any idea what could cause this sort of noise?

The sample is from the JVC, with a sample from the same tape form a JVC HR-J658 (which sounds fine) for comparison.

Did you ever get this fixed? I'm looking at one of these very decks for a relatively good price but I'm hesitant at the fact that it's not in the buying guide's recommended models, and is already a VCR/DVD combo device when I would already be using a ES-15 DVD for passthrough.

[latreche34]

Quote:

Originally Posted by lordsmurf

There is a reason it happens, and I've read about it before in my VCR repair/tech books from Capelo and Beeching. Some to do with the compensation circuits. I don't remember the specifics anymore.

Yes, The automatic audio gain control, The two samples sound similar to me with the exception that the second sample is louder, In the service manual there is an adjustment for the master gain if it's very low, but the audio AGC is built in the VCR and cannot be disabled, I believe some high end VCR's with Dolby or DBX circuits don't have this feature and they produce a much cleaner linear sound especially from home recordings.

[timtape]

I'm an audio tape guy. Much of the problem here is probably audio head azimuth mistracking. Consumer video formats like Beta and VHS are particularly vulnerable to it. Believe it or not, recorded azimuth patterns can vary from tape to tape and can seriously degrade the audio clarity.

The issue is not so much the background noise (that is always there) but the muffled audio makes the background noise seem to have risen. It's the audio that's down. It can sound weak, distant, hollow, and probably has a lot to do with people's negative opinions of the linear sound track. It's often not played at its best.

Many VCR's have a front panel video tracking control, but no unmodded VCRs that I'm aware of have an accessible audio head azimuth control. If they did, it would be easy to tweak it and find out what it can do to the linear sound's clarity. Adjusting audio head azimuth is kind of the audio equivalent of adjusting the picture tracking control.

Attached pics of a home baked azimuth adjuster on my AG- 7350 made about 10 years ago. It's not flash but it works without having to open up the machine each time a tape is played and poke around with a screwdriver. I made the mod to make tuning in the azimuth quick, easy and safe. Whenever I transfer my tapes or someone else's tapes I adjust audio head azimuth for each tape. The large cardboard ring helps protect the delicate adjuster from accidental damage.

[lordsmurf]

Quote:

Originally Posted by timtape

Believe it or not, recorded azimuth patterns can vary from tape to tape and can seriously degrade the audio clarity.

I knew everything you've stated, but the added details are much appreciated.

[timtape]

Quote:

Originally Posted by lordsmurf

I knew everything you've stated, but the added details are much appreciated.

No problem. I might upload a couple of audio examples from commercial pre recorded movies on VHS. Many had HiFi stereo tracks but also linear stereo tracks. Some had Dolby B encoding on the linear track and some no encoding. I only have a few examples but a VHS copy I have of the Clint Eastwood movie "In the Line of Fire" has particularly good sound on both tracks. At their best, these duped VHS tapes have excellent sound and sometimes you have to know what to listen for to even notice the difference.

[latreche34]

The reason why I don't recommend messing with the VCR alignment is that some people don't know or don't have the right tools to do it and they end up messing the whole head stack, Because if they change the head tilt they risk pushing the tape against the guide and they get tape curling without noticing it, If they change the head tilt in the perpendicular direction they get lip-sync problems and possible some tracking issues. If someone knows what he is doing like yourself that's fine but not for everyone.

[hodgey]

Quote:

Originally Posted by Kaos-Industries

Did you ever get this fixed? I'm looking at one of these very decks for a relatively good price but I'm hesitant at the fact that it's not in the buying guide's recommended models, and is already a VCR/DVD combo device when I would already be using a ES-15 DVD for passthrough.

No, I haven't. On the samsung deck with similar symptoms I have tried to adjust the audio head, which did seem to give a slight improvement in general sound quality, but not much effect on the noise (which is a bit more noticeable than on the JVC). It may be a different issue on that deck though for all I know. I also didn't notice this sort of noise when realigning the audio head on a different panasonic VCR, the sound just got more muffled when the head was out of position. Alignment may have some impact due to the mentioned auto-level-control, but I'm not sure if that's the core issue I'm having, or if bad alignment just makes it worse.

I did have a look at the clips I made in spectrum view in audacity, and you can spot that there is some bands where there is a lot more amplitude on the xvs20 than on the j658:

XVS20
hr-xvs20.png
HR-J658

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There seems to be a lot more noise bleeding through. The amplitude of the waveform is quite similar. The older model seems to have more actual signal in the higher frequency bands too, which could indicate that the head is better aligned I suppose.

I'm planning to try to replace and maybe tinker around a bit with the audio filter components on the Samsung one to see if it has some impact, as I did find that shorting over the paralell inductor + capacitor filter on the output seemed to have an impact on it.

[lordsmurf]

Quote:

Originally Posted by latreche34

The reason why I don't recommend messing with the VCR alignment is that some people don't know or don't have the right tools to do it and they end up messing the whole head stack, Because if they change the head tilt they risk pushing the tape against the guide and they get tape curling without noticing it, If they change the head tilt in the perpendicular direction they get lip-sync problems and possible some tracking issues. If someone knows what he is doing like yourself that's fine but not for everyone.

Part of the problem is that audio heads aren't really adjustable like the video head. So I think this is partially (entirely?) an academic conversation.

[timtape]

Quote:

Originally Posted by hodgey

No, I haven't. On the samsung deck with similar symptoms I have tried to adjust the audio head, which did seem to give a slight improvement in general sound quality, but not much effect on the noise (which is a bit more noticeable than on the JVC). It may be a different issue on that deck though for all I know. I also didn't notice this sort of noise when realigning the audio head on a different panasonic VCR, the sound just got more muffled when the head was out of position. Alignment may have some impact due to the mentioned auto-level-control, but I'm not sure if that's the core issue I'm having, or if bad alignment just makes it worse.

I did have a look at the clips I made in spectrum view in audacity, and you can spot that there is some bands where there is a lot more amplitude on the xvs20 than on the j658:

XVS20
Attachment 12801
HR-J658
Attachment 12800

There seems to be a lot more noise bleeding through. The amplitude of the waveform is quite similar. The older model seems to have more actual signal in the higher frequency bands too, which could indicate that the head is better aligned I suppose.

I'm planning to try to replace and maybe tinker around a bit with the audio filter components on the Samsung one to see if it has some impact, as I did find that shorting over the paralell inductor + capacitor filter on the output seemed to have an impact on it.

The noise can be a combination from different areas. Partly tape hiss. Partly hiss from the playback preamplifier. Partly interference noise from the video electronics and maybe even the motors. On the HR6J58 file there's a tone at about 700 Hz. These noises are constants. Of course there is always tape hiss on the tape but other noises such as the 700 Hz tone are probably not on the recording and no amount of adjusting head alignment for clearest audio will reduce this constant interference noise, but the clearer sound might help to mask it.

When Beta and VHS VCR's first came out from makers like Sony, JVC, Panasonic, there was only linear sound and so I guess they designed the machine to make the most out of that linear sound. As one example, they used proper shielded cable from the audio head to the preamp to keep interference noise out. Later when they added HiFi sound, maybe some slackened off their standards for the linear sound track playback, seeing it now as the "poor relation" to the HiFi track - which it was in some ways but not all. Many later model VHS decks changed to a flat ribbon cable from the audio head - no shielding - so the risk of interference getting in.

Maybe for most users the only way to get the best out of the linear track is to use perhaps a good quality machine which has proper shielded cable from the audio head all the way to the preamp. It might be an older machine without HiFi sound.

Quote:

Originally Posted by latreche34

The reason why I don't recommend messing with the VCR alignment is that some people don't know or don't have the right tools to do it and they end up messing the whole head stack, Because if they change the head tilt they risk pushing the tape against the guide and they get tape curling without noticing it, If they change the head tilt in the perpendicular direction they get lip-sync problems and possible some tracking issues. If someone knows what he is doing like yourself that's fine but not for everyone.

I agree. When I headed the technical side of a large audio tape archiving project, I knew that my staff hadnt even heard of the word "azimuth" let alone ever adjust it. But correcting azimuth on the thousands of tapes was one of requirements of the project to meet IASA standards. So I made it easy for the staff and designed and fitted front panel adjusters on all our transfer decks. Now no dismantling of the tape machine, no tools required. Just two fingers. Like a VCR's manual tracking control.

I wasnt suggesting at all that unskilled people cluelessly dive into their machines and start randomly twiddling head base screws. I've seen enough of that in my own service of tape machines where someone has "had a go". Sometimes the only way to restore proper head alignment is with proper alignment jigs from the factory.