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Thread: Basic questions about Oscilloscope, DeMag, MRL..

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    Basic questions about Oscilloscope, DeMag, MRL..

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    Hi all. I've recently picked up an Oscilloscope and am wondering what to do with it. I picked it up because I know you check head azimuth with it, but what else does this thing do? I still need to download the manual for it and dive in but I was wondering what you guys use yours for(if ya got'em)? Can I just make a XLR or TRS cable for this so that it hooks up to my deck? I know absolutely nothing about them other than i should have one and know what it does.

    Second question I have, has anyone here used the Short MRL Test/Reference tapes? The tones on them are 50 100 1k 10k and 16k, and the tapes are available for $299.99 on eBay, is there anywhere that you guys know of to get test tapes cheaper?

    I also, have a Teac E-3 Hand D-Mag. Is this an adequate demagnetizer to use on a Tascam MS-16 and an MCI-JH110B or should I get something like the 'Han-D-Mag'?

    Thank you guys for any input or advice you can offer!

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    Make and model number PLEASE! Is it dual input? If so then yes, it can be used to set azimuth and get track phase spot on.

    Other than that it will not be a of great use except perhaps for signal tracing if you have a fault. A scope is of most use attached to the AUX output of a good milliVoltmeter when it can be a check that signals are not clipping.

    Do not forget that a scope shows you peak to peak values, not rms.

    Dave.

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    What size tape deck? (width) Get a test tape direct from MRL or JRF Magnetics. I just bought one of the four tone 1/2" 15 ips from JRF Magnetics. It's $145. here's the price list: http://www.mrltapes.com/pub043+lf.pdf

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    There are also quite different specs for scope suitable for audio frequencies to scopes for RF - plus loads of different types that can also act as generators - so they can produce a tone, and then superimpose what your tape deck has done to it - like wow and flutter. It's quite a shock to see two sine waves that should be locked together drifting and having a major panic, then doing the maths and discovering the speed drift is incredibly low, but just looks terrible. Reading the damn things can be almost magic.

    The advances in SDR technology have made RF alignment and investigation a lot easier to do - I wonder if there is an audio version of these things (Software Defined Radio) as the various display modes would make frequency response and unwanted artefacts much easier to read.

    You can use a scope in audio systems to see harmonics, phase errors, and if you have any synth VSTIs or even real ones, you can understand what the controls actually do. You can measure accurately, and you can compare two things on a dual trace machine. If it lets you, you can also use left and right inputs to show the deviation away from mono. The left moving the trace horizontally and the right moving the trace vertically. A mono signal is a straight diagonal line. As soon as any width to the stereo field appears you see the line thicken and change. With practice you can even see polarity and phase errors. L and R with one accidentally inverted produces a circle not a straight line. Look up Lissajous Curves on the net. You will also then see familiar images from sci fi movies and old Doctor Who episodes. In the 70s, I used my Ferrograph 722HD reel to reel recorder which had loudspeaker outputs to drive the scan coils on a domestic TV - I just cut the X and Y inputs and connected the to the tape recorder and the results on the screen were wild!

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    Rob, did you ever go as far as feeding audio into the de-gauss coil? Add that to your scan coil drive and get crazy colours!

    Hmm? Whatever happened to "Chromasonics" ?

    Dave.

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    Quote Originally Posted by Chip Whitley View Post

    I also, have a Teac E-3 Hand D-Mag. Is this an adequate demagnetizer to use on a Tascam MS-16 and an MCI-JH110B or should I get something like the 'Han-D-Mag'?
    According to the review at

    TEAC E3 Head Demagnetiser (RM May 93)

    your demagnetiser should be OK for those machines although the Annis Han-D-Mag looks like a more powerful device.
    JRP Music - Audio Mastering and Restoration
    http://www.jrpmusic.co.uk

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    Thanks for all the replies boys. I've had my head buried in cables, patchbays, solder and busy with a baby.

    The scope is a dual input scope - Hitatchi V-650F - so I've got the x and y capabilities. The guy I got it from has a ton of scopes and uses them for audio repair. He knew my intent in getting one so I'm assuming he gave me something capable. What I didn't think to ask at the time, he told me I can order some probes from the internet but how do I hook this thing up to the inputs of a console or deck? Do you rig up your own cables for these? Ideally I'd like to find a good in-depth article on using a scope in a pro-audio situation but I haven't found anything yet.

    In regards to the demag, looking through the MS-16 manual I see the TEAC-E3 Head Demag is actually listed in the manual to use. I've read that manual a good number of times, apparently I need a good number more.

    Thank you all for the help and advice, really appreciate it as this a great forum. Maybe this is a topic for another thread, but are there any other really good reel to reel web forums you guys frequent or like? It seems very tough to find anything for me other than this and the TOMB which isn't really as knowledgeable or reel to reel focused. Thanks all!

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    This may also be a stupid question, but one that I have nonetheless. If I get the two test tapes I need(quarter inch and one inch 15ips), after I've got my machines completely spec'd out, I know they are spot on I've just got them calibrated to the tape and they are recording and reproducing perfectly...

    can I then run the tone being played from the tape into the United Audio Apollo converter, record the tones from the tape onto a DAW and use those tones as reference tones? Could I take my short version MRL tape and then make my own full length tape by looping the recorded tone on the DAW? What exactly are the problems one would run into doing this? Does my deck being a 16 track and not a full track present a problem, or is this something people do and I am late to the party?

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    No real problems at all level for level, but in your DAW, levels are precise, that tiny fraction too much and the waveform suddenly has a flat top, whereas on your reel to reels, experience tells you how far to push. If you run a tone at the maximum you are going to ever record at, in loudness terms, this will give you a good place to set the levels on the digital kit. You, however have to decide your headroom. On the multitrack, levels are important because too much can bleed into the next track, so a mega loud sound on track1, might be leaking slightly into that quiet marimba on track 2? It's like knowing your thrid gear is a bit weak - you can thrash 1,2 and 4 and be easy on 3 once you understand how it works.

    To Dave - damn, never thought of the degaussing coils!

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    Scope leads and probes: These are special, very low capacitance cables of a specific length and almost always terminate in a BNC connector. Scopes have an input resistance of 1 meg Ohm very close tolerance and a low but known capacitance. The probe usually has a tiny trimmer capacitor and it is usual to set that for best square wave (at 20Khz for audio) Such cables and probes have very little influence on the circuits under test, especially when set for "X 10".

    But, for audio purposes, especially signals in and out of a mixer, the source Z is so low that you can simply use single core screened cable and RCA phono plugs and a BNC adaptor (but if you WANT to go mad! Buy some BNC plugs and make your own leads. Just don't complain to me!) .

    Generally however a scope in the audio service world is almost always hooked into the AUX outputs of a mV meter and serves as a superb check for clipping and hum or other nasties.

    Copying test tapes is technically a bad idea because the replay and record machines will not have the same head geometry as the original and therefore there are bound to be inaccuracies at some frequencies and across tracks. Hopefully these will be small and you can correct for them. Otherwise..BLOODY GOOD IDEA! Once copied, put the TTape in a safe or at least a fireproof cash box. Use the copy for day to day checks.
    You could of course make your own test tape from PC generated tones, again not as good as the real thing but so long as you have a known flux level to start with, ok if you don't intend to exchange tapes.

    For interest you could run a 1kHz, 0vu recorded tone through a DAW and clock it on a Real Time Analyser? Don't be TOO disheartened by the ghastly level of distortion products!

    Dave.

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