Believe it or not, I have heard people say this... "I aligned this machine a couple of years ago...why should it need it so soon again?" This attitude has been a continued source of amazement to me.
The fact that analog machines are living in an environment, which changes with humidity, temperature, and age, one would think that logic dictates that these machines need maintenance regularly. But, nooooo, this document has to explain why analog machines need regular care.
Here is an analogy:
When you buy a car you...
Drive it from the showroom floor and put gas in it only when it needs it for the rest of the life of the car, and until you decide to sell it. and...
Magically, oil is injected into the oil pan in precisily the correct incremenets when car needs it and (of course) the oil is somehow transformed from dirty fluid into a clear smooth lubricating substance... and...
Over the course of 3-4 years, your tires somehow manage to re-tread themselves with new tough fibers, resisting all forms of road conditions, including nails, glass, and construction. and...
Every week, the weather is PERFECT and it RAINS in exactly the correct amount at EXACTLY the right time with the wind following at exactly 15 MPH with the only elements in the breeze being pure oxygen... dust free so that you never have to worry about washing your car...
If this sounds like a fantasy, your right...it is!
The only way your analog machine will stay aligned is if You do it... and you do have to do it!
- Degauss the tape recorder heads.
- Clean the Heads , Pinch Roller , and the Capstans.
- Physically Align the Reproduce Heads.
- Electronically Align the Reproduce Electronics.
- Physically Align the Record Heads to match the alignment of the Reproduce Heads.
- Bias the tape machine's record electronics to match the particualar type of tape you are using.
- Adjust the Record Electronics. to match the Reproduce Electronics
- Record a Known Audio Source and monitor the output using first your ears, then your test gear.
Explanation of Terms:
Physically Align the heads
By "physically align" I mean, that the actual physical orientation (the rotation of the heads left, right, up, down, back, and forth) in relation to the tape contact, must be calibrated. This orientation is usually represented as Azimuth , Zenith and Wrap
To properly physically align the heads of an analog tape recorder, you must first know what correct alignment is.
Theoretically, perfect tape head alignment is the optimum orientation of the tape head to the tape that provides the most information to the tape head available from the tape.
This usually means that the Tape Head Gap is 90 degrees perpendicular to the tape path.
Many people use Calibrated Test Tapes as a reference to align the tape heads. Although these tapes are expensive, they are the most convenient and accurate way of calibrating the Azimuth , Zenith and Wrap of tape recorder heads.
How to properly Degauss an Analog tape recorder's heads
Ok, I know I'm gonna get some flak about this one, but here goes...
You don't have to buy an expensive tape head de-magnatizer to degauss your tape recorder's heads.
What I use is an easily available Radio Shack bulk tape eraser. You can buy these for less than $50 (US) from your local store. And it works just fine!
In the following, when I say "de-mag unit", I mean the bulk tape eraser that you can buy from Rat Shack.
Here is what to do:
Make sure your analog tape recorder is off and unplugged from it's power source.
If your analog tape recorder's outputs are plugged into your console, turn your console off for (your speaker's) and your safety's sake.
Make sure the switch on the de-mag unit is set to the off position.
With the de-mag unit off, bring the de-mag unit as far away from the tape recorder heads as possible and then and only then turn the de-mag unit on.
Do NOT turn the de-mag unit OFF unit you are back at this starting position. Failure to do so WILL cause you to your analog tape recorder's heads! (and this is bad)
Slowly, and I mean SLOWLY, bring the de-mag unit in closer to the analog tape recorder heads.
The speed at which you bring the unit to the heads should be approx 12 inches every 5 seconds (or slower).
If you don't know how slow that is, just go as slow as you can, and that will probably be slow enough. If, you're on any drugs (especially SPEED) you'll NEVER get slow enough.
Your movements should be very smooth with no jerking. As close to a slo-mo film shot as possible.
As you approach the tape recorder's heads, slow down even more. Make this motion very smooth and very slow!.
Slowly, as you get closer to the heads, bring the de-mag unit up to each one of the three tape recorder heads. (erase, record, and playback). Make SURE you do NOT make any jerky motions as this will cause these actions to Magnatize the heads.
After slowly moving the de-mag unit across the heads for a few seconds, (usually 5 seconds for each head is sufficient) start bringing the de-mag unit away from the tape recorder heads VERY SLOWLY!.
Once you have brought the de-mag unit as far away from the tape recorder's heads as possible (preferrably back to your original starting point, turn the de-mag unit off.
Stop and get yourself something to drink, or take a smoke break. That is enough stress for the next few minutes. Your tape recorder heads are now de-magnatized! Yeah!
Degauss the analog tape recorder heads. (ask Larry how to do this if you don't know how).
Clean the analog tape recorder heads and capstans and pinch roller.
Put on the analog tape recorder alignment tape.
Locate the 1K tone that exists on the analog alignment tape. There are 2 (two) sets of tones for the analog machine on that alignment tape. Both 15 AND 30 ips exist on the alignment tape. Be sure to find the correct tones for the speed you are wanting to calibrate for!!!
Set the analog tape machine controls to the correct speed and then select 'REPRODUCE' mode on the tape machine remote control. Locate the 1K tone on the alignment tape and push PLAY on the analog tape machine. While playing the 1k tone from the alignment tape, adjust the reproduce playback level trim controls of each track of the analog machine to show the proper playback levels on the analog tape machine playback meters. Valid playback levels are as follows:
+3 for 0 standard operating level (185 nw) +2 for +1 over standard operating level +1 for +2 over standard operating level * 0 for +3 over standard operating level (250 nw) * (NORMAL +3 level) -1 for +4 over standard operating level -2 for +5 over standard operating level -3 for +6 over standard operating level
Rewind the alignment tape to the beginning of the 1K tone. Set the analog tape machine controls on the remote to 'SYNC' and play the 1k tone that exists on the analog alignment tape. Adjust the 'SYNC' playback level trim controls of each track on the analog machine to match (on the analog tape machine meters) the setting selected in step (5).
Locate the 10k signal that exists on the analog alignment tape. Be SURE that it is the 10K tone for the speed that you are calibrating for!!! Set the analog tape machine remote control to 'REPRODUCE'. Push play on the analog tape machine to play the 10k tone found on the analog alignment tape. Adjust the reproduce playback level trim controls on the analog tape machine to make the meters on the analog tape machine match the same levels used in step (5).
Locate the 10k tone that exists on the analog alignment tape. Be SURE that it is the 10K tone for the speed that you are calibrating for!!! Set the analog tape machine remote control to 'SYNC' and play the 10k tone found on the analog alignment tape. Adjust the sync playback level trim controls to the same level used in step (5) (as displayed on the analog tape machine meters)
Repeat steps 5 through 8 until BOTH REPRODUCE and SYNC levels are within +- .5db of tolerance of the alignment tape shown on the analog tape machine!
Remove the alignment tape and place it in a safe place away from stray magnetic fields. Locate the tape you want to record onto and load it onto the analog tape machine.
If you are using Dolby SR, push the hardware bypass buttons IN. These buttons are located at the bottom of each channel of the SR unit. These are the buttons NOT the lever switch! THESE BUTTONS MUST BE IN THE BYPASS (IN) POSITION TO PROPERLY ALIGN THE ANALOG TAPE MACHINE!
Go to the patch bay and patch ALL of the outputs of the ADATs (in this case, channels 1 through 24) to ALL of the inputs of the analog tape machine (channels 1 through 24).
Patch ALL of the outputs of the analog tape machine to ALL of the inputs of the console (1 through 24).
Find the ADAT test tapes that I made and put them into the ADATs. LOAD the SETUP that exists on those ADAT tapes into the BRC. After the BRC has loaded the setup of the ADAT test tapes that I made, goto the 10K tone section of the ADAT tapes and LOOP the section that contains the 10K tones.
Put the analog tape machine into 'RECORD' on all tracks and set the analog tape machine to read 'REPRODUCE'.
Push PLAY and RECORD on the analog tape machine. While the analog tape machine is recording AND while you are looking at the meters on the analog tape machine that are reading the reproduce levels, adjust the BIAS control on the analog tape machine
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31 Mar 2015
1 Apr 2015