Panasonic 850 linear audio: hiss and dropouts, cause?

[Koen]

Thanks again.

I can't see anything untoward about the head, not a visible groove as far as I can tell. It looks fine to me but then I haven't been working on these things for five decades. (You must have been dealing with Philips 1500 heads when they weren't yet scarce!)

One thing I did notice earlier today in the course of testing was that with the same tape the problematic 850 gave more distortion on the stereo track than the other 850, so looks as though the 850 we're scrutinising here has had quite some use. I've had it for a couple of years now and must have used it, well, something like a thousand hours? Of course I don't know what happened to it before it ended up in the charity shop where I found it.

I don't care that much about the actual volume of the sound output, but I'm wondering whether the unfavourable signal to noise ratio is a side effect of the A/C head not picking up/not putting through as much dB as it should.

I don't really get all these transfer facilities that have rows and rows of machines in setups where you can't easily access them, precisely because of the A/C adjustment issue. I transfers tapes as a hobby so have tapes from a variety of sources and it's pretty common for tapes to have been recorded on machines that must have been somewhat out of spec. Well, as long as people are happy with their transfers who am I to judge. :-)

[timtape]

Quote:

Originally Posted by Koen

...I don't care that much about the actual volume of the sound output, but I'm wondering whether the unfavourable signal to noise ratio is a side effect of the A/C head not picking up/not putting through as much dB as it should.

Well yes. Apart from the the tape to head contact (including azimuth match to the tape) the other weak link in the chain is the preamplifier immediately after the head. It has a hard job amplifying an at best weak signal off the head. Unavoidably ( at least in consumer formats like Beta/VHS linear audio) it adds some extra hiss of its own. So we want as strong and sharp a signal as possible off the head to mask that preamp hiss. That's part of what azimuth adjusting does.

Quote:

Originally Posted by Koen

I don't really get all these transfer facilities that have rows and rows of machines in setups where you can't easily access them, precisely because of the A/C adjustment issue.

Yes adjusting azimuth is impossible, as well as general ease and speed of maintenance and testing of the decks. The rows of machines sometimes rack mounted might look impressive to the punter looking at company website photos while to a tech like myself it can explain why these machines can be poorly maintained. The owners have made it very hard for themselves to do basic cleaning/ maintenance/ adjustment of the gear. Tape gear was always high maintenance, and now since we're forced to use old gear, it needs even more maintenance and TLC. So why not make it really easy to do the basic day to day "housework". Unfortunately many working in this game seem little more than glorified button pushers re the VCR's and are more comfortable sitting in front of a PC screen with a kb and mouse at hand where they believe they are doing serious media "restoration". But they may have left half the signal still on the tape.

[hodgey]

Quote:

Originally Posted by Koen

Swapping over an entire mechanism is something I've never done before... perhaps it would be asking for trouble if I tried to do that.

It's actually not all that complicated on these newer vcrs, probably easier than swapping ac heads. It's usually just a few screws and disconnecting a few ribbon cables and the whole thing comes out.

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I have a variety of JVC's and while I'm currently using a 7611 (a Digipure one) I generally struggle to see much difference in output between it and much cheaper JVC's, assuming they can be set to edit mode (whereas with Pana the difference between, say, 850/88/1000 and more basic models is quite clear).

As noted, they used the same main video ic in the SVHS and most basic models in the same lineup, the SVHS models simply added an extra IC for the SVHS specific stuff and chroma NR, or in the high end ones TBC/DNR, and S-Video output. (though later JVC used rebadged LGs and some other thing for the most basic ones which are totally different.) So if you are using something external for stabilizing the video one would expect them to look somewhat similar (minus the extra digital noise reduction), I have noted the same thing. The SVHS variants also has this tape stabilizer thing added to the mech but I don't know the effect of it. Panasonic did not share video ics between SVHS and non-SVHS models to the same degree, so the image characteristics differ much more between them.

Quote:

(Come to think of it, I'm not all that impressed with the Pana 88 I got last summer.

These are very notorious for having capacitor issues which impact the image, so that's worth taking into account.

[Koen]

Quote:

Originally Posted by hodgey

...though later JVC used rebadged LGs and some other thing for the most basic ones which are totally different.) So if you are using something external for stabilizing the video one would expect them to look somewhat similar (minus the extra digital noise reduction), I have noted the same thing. The SVHS variants also has this tape stabilizer thing added to the mech but I don't know the effect of it.

(...)

[Pana 88] are very notorious for having capacitor issues which impact the image, so that's worth taking into account.

Yes, I once bought one of these cheap later JVC's that turned out to be rebadged (I recognised the menu from a cheap Aiwa I was once given). Absolute crap. I now know I have to look for the mention of B.E.ST. on the flap to know I have a real JVC in front of me.

I'm one of the ill-advised (well, poor) people using these Pana DMR ES10 DVD recorders to act as a would-be TBC, helps a lot to get a stable signal and adds (too) much of noise reduction. With that in my chain, I do indeed see little difference between cheap and expensive JVC's.

I didn't know Pana 88/200 is notorious for cap issues, thanks for that. Perhaps I'll sell it on one day - I got it fairly cheap, for €70, and may not need to lose all that much money selling it as 'needing refurbishment'. Have used a soldiering iron on occasion but that was just to soldier on a wire... identifying bad caps and replacing them on a PCB seems a lot more complicated!

Chaps, thanks for your input - I may in the not too distant future have a go a experimenting with taking out A/C or even the entire chassis of that somewhat disposable cheap Pana I also have, but this is not likely to happen before the weekend (and may well fail anyway). I'll try to report back if there's any news!