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Old 29th June 2008, 05:41 PM   #1
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Angry Sony DTC77ES DAT, distortion on playback

Hi all, My frustration mode is in overdrive! I have a Sony dtc77es DAT recorder ehich has been performing perfectly for a while now but i made the mistake of leaving a tape inside while not in use. The next time I used the machine, playback was severely distorted. I cleaned the heads with a cleaning tape at first then (after only slight improvement) with some isoprpoyl alcohol. This seemed to solve the problem for a while. Now when I play any tape, there is distortion which increases on the louder tracks. The thing that I do not understand is that when I make a new recording, the sound is perfect when switching monitor mode from source to tape. However when I then rewind and play the recording, the distortion is back, but if I then play this tape in my other DAT deck (a dtc690) the distortion has gone! Can anyone please throw some light on this one as I'm hopeful that it is an easy fix.

Thanks in advance.

Richard.
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Old 30th June 2008, 10:39 AM   #2
Mooly is offline Mooly  United Kingdom
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Hi,
See no one has replied ! Never worked on DAT but have worked on thousands of VCR's which use the similar helical scan technique.
It's almost certainly "mechanical" and that unfortunately includes the drum and head assembly (wear) . I am not sure now whether there are separate pole pieces (heads) on the upper drum for recording and playback.
The only 100% sure way to diagnose is to look at the so called R.F. signal or "envelope" coming of the tape with an oscilloscope. This would show any problems such as low amplitude or entry and exit problems of the tape wrap.
Also look closely at the tape itself in good light, make sure there are no lines or creases across the tape surface.
Usually tape path problems ( so called compatability problems ) are to some extent self cancelling when the tape is recorded and played back on the same machine, which makes me suspect head/lower drum wear.
Regards Karl
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Old 30th June 2008, 05:57 PM   #3
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Hi,
Thanks for the reply. The recorder does have seperate record and playback heads so while recording | can toggle between source and tape and both sound fine. It's only when I rewind the tape and play it again that the distortion appears but if I play the tape in my other DAT, the output is fine. I do not understand how there can be a problem if monitoring off tape whilst recording produces a clear output? Now for a hot update! Whilst typing this reply I have played an existing recording and the distortion was greatly reduced, more like vinyl surface noise than distortion. (static maybe? do these machines suffer from that?). I have now played another tape and it is absolutely perfect! Go figure. Any input would be gratefuly received!

Thanks.
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Old 30th June 2008, 06:12 PM   #4
Mooly is offline Mooly  United Kingdom
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Hi,
Erm !! When you are recording I would have thought (99.999%) sure that it's monitored in what if it were a VCR would be called E to E mode as opposed to real time monitoring like a 3 head analogue tape deck. If you record BBC1 on a VCR and monitor it at the same time, it's not the recording you are seeing, just the signal passed through the machine.
How have you cleaned the heads ? They are extremely delicate and must be treated with care. The ferrite material will snap if rubbed in a vertical direction.
Do you have an old tape you can afford to scrap ? there is a way of cleaning heads that will work when all other methods fail

Edit. Static can effect the drum assembly. The drum spinning round on a plastic tape is the perfect ingredient. Some VCR's suffer badly and there have been quite a few mods brought out for affected models. I don't know whether the Sony DAT suffers from this. If you suspect this then with the tape playing hold (very gently) your finger tip on the rim/edge of the ROTATING drum and see if the problem is made WORSE not better. Do not touch the tape or the part of the drum in contact with the tape.
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Old 30th June 2008, 07:46 PM   #5
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Hi Karl,

This machine does have 'real' monitoring, just like a three head analogue tape deck. I have tried a couple more tapes and fresh recordings since my last reply and the deck now seems fine. I can only put this down to a post cleaning glith (whatever that is!) but I will run the machine for a while before putting it back in to full time service.

Thanks for your interest!
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Old 1st July 2008, 07:18 AM   #6
Mooly is offline Mooly  United Kingdom
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Hi Richard ,
Thats great I thought I had better put only 99.999 % sure You learn something everyday. I had never heard of that being done ( real time monitoring on a domestic helical scan machine ).
It sounds like one of the heads was still clogged. I have seen that countless times and even after proper cleaning they still don't repond. I mentioned a way that "always works" certainly with VCR's. When there is nothing else to lose , try this. Play a tape and use your finger to gently rub and press the moving tape against the rotating heads. As I say it's the LAST RESORT, but it works.
Nice machine by the way -- Googled it !!
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Old 2nd July 2008, 03:04 PM   #7
ivoa is offline ivoa  Croatia
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I would like to give my opinion about this problem: when you play VCR tapes, CTL head reads pulses to properly switch between rotary heads. If you are recording on DAT, ctl pulses are also recorded at the moment, and 'real time' listening while recording is not possible in way of 3 head ordinary tape deck.

If ctl head gets dirty you have distortion while listening and clear sound in another device with clean ctl head.

My question is while recording on DAT how it is possible listening recorded signal in 'ordinary' play mode which uses ctl head and rotary head as signal source as they botha are 'busy' with recording of signal?
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Old 2nd July 2008, 05:05 PM   #8
Mooly is offline Mooly  United Kingdom
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Hi,
I had never heard of this on a domestic machine but I think DAT will use something similar to DTF (Dynamic track following) like Video8. The 25 hz control track in a standard VCR is used to sync the capstan, and as you say to derive the 25 hz head switching signal in playback. The "tracking" control on a VCR whether manual or auto normally uses this signal to alter the phase of the capstan and thus maintain lip sync when using the analogue soundtrack at the tape edge.
Regards Karl
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Old 4th July 2008, 02:11 PM   #9
ivoa is offline ivoa  Croatia
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Thanks for explanation.
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