Hi!
My name is Greg Norman. I work at Electrical Audio.
I'm here to show you how to calibrate a Studer A820 Multi-Channel tape machine.
It's like a 24-track and a 16-track, it's just the same.
Anyways, get your fingers ready... you've got a lot of buttons to press!
[clunk, clunk.]
Fist thing you need to do is to clean and dust the machine.
Sometimes I like using a Swiffer duster to clean some of the dust off of the planes of
it. Keep it away from the moving parts, though.
Then, clean with alcohol that has 90% or better, soak a Q-tip in it,
and clean the tape guide path.
But I like to start with the heads first.
Clean up the center of the head, where the gap is, don't go to the sides because there's
some conductive epoxy you could rub off with alcohol.
You need that.
Make sure when you're done cleaning, your Q-tip's nice and spotless - it doesn't have
any grime on it. If it has grime on it, just get another Q-tip and repeat the process.
Whoo. Yeah!
The Studer 820 has a feature to clean the capstan motor: when no tape is loaded, you
can press the button "PLAY", and the capstan motor starts spinning.
Now for sure you wanna make sure the Q-tip isn't soaking wet cause alcohol can drool
down into the bearings and ruin them. So, just a little bit of dampening is good enough,
and you just hold the Q-tip against the capstan motor as you slowly go down.
And that'll be clean. Just hit "STOP" when you're done.
So the first thing we're gonna do is check the azimuth on both the Record and Repro heads.
That can be done by playing a test tape, like the one I have loaded here - the MRL test
tape that we're going to be using.
We're gonna record at 15 IPS, CCIR EQ, that's we use a lot of times here at Electrical.
But I'm gonna play back the 1 K tone first, do the rough adjustment of the azimuth
for both heads.
Then I'm gonna play the 10 K tone and do the fine adjustment of the azimuth for both heads
- or, at least, check it, see if it's off.
You need a 2.5mm Allen wrench to do this, and there are two access holes in the editing
block, above the head block.
Playing off the repro head first, "ALL REPRO", hit "PLAY",
[1 kHz tone plays]
and gently insert the Allen wrench until it finds its seat.
And I'm looking over at the oscilloscope, and I'm adjusting so that both waveforms
line up with each other.
Now, I'm using the outputs of track 2 and track 23 to do this, going to the oscilloscope.
So I'm going to to to the sync head. That's the hole to the left for the record/sync head,
and I'm gonna adjust that... very gently... looks good.
Now I'm going to play the 10 kHz tone to do the fine adjustment.
I'm still on the sync head, so I'll adjust that first.
[10 kHz tone plays]
That looks good... oh, that's nice!
Now I'll go to the repro head, and fine-adjust that.
Again, the repro head access hole is to the right of the record head.
Oh, that's nice and good, too!
So both heads can be done at the same time because you can play back from both heads
separately.
So now we're gonna do the playback electronics for both the repro and sync heads.
A couple of things that you need to have set up in advance: you have to have the right
calibration tape with the right tones on it. In this case, we're running 15 IPS, CCIR EQ,
so I have those tones ready to go.
And you need to change the meter mode from Peak (if it is in peak) to VU mode. And there's
a soft key in the software to make that change.
The way you can tell if it's in peak mode is by looking at the row of lights on the
meter bridge, and seeing where it lines up with the scale.
In the yellow scale is the peak scale. The white scale is the VU scale. So the row of
lights should line up with the the "0" of whatever scale you're in.
So I'm gonna switch it from peak mode to VU mode.
We have a soft key programmed just for that.
...and you can see the meter lights move.
So now we're in VU.
And now you wanna do your repro calibration from that point.
Then I go to the software alignment section over here on the meter bridge and press
"AUTOPAR ALIGN" (auto-parameter align), and go to "REPRO LEVEL".
And I check on the LCD screen to make sure that it says "0.0". Now, that number means
- that represents what this row of lights is. So right now, this row of lights represents
0 VU.
You might have noticed that when I switched to "AUTOPAR ALIGN" you saw the row of lights
move again to a new mode, and THIS mode is a high-resolution mode. So now it's zoomed-in
to show you more specifically what the level is.
And I'm at "REPRO LEVEL" and I'm going to press "PLAY" and play back the 1 kHz tone
[1kHz tone plays]
...and hit "STORE/START"
And the machine does all the rest - it aligns all 24 channels in one go.
It's like "upside-down Missile Command"...
... for you old people.
So, that just finished the repro level alignment of the repro head.
So I'm gonna go to the sync head and do the same thing so the sync head is also aligned
to the test tape.
[1 kHz tone plays]
Press "PLAY", 1 kHz tone, it's still "REPRO LEVEL", hit "STORE/START",
and it calibrates itself.
This would normally take 15 minutes to do with all the little trimmer screwdriver trim
pots on an old machine. But thanks to 20 or 30-year-old technology we can just stand here
and watch it.
OK, both the repro level of the sync head and the record head - I'm sorry - the SYNC head
and the REPRO head have been calibrated.
Now we're gonna do the "REPRO TREBLE" and play the 10 kHz tone
[10 kHz tone plays]
...and hit "STORE/START".
This might take a little bit longer than the 1 K tone.
So, sometimes when you're playing back the tones, you run out of tone, and you
have to rewind and start over again, and this machine has a feature where you can just locate
to the point where you just started from, hit "PLAY", and it'll continue
where it left off.
If you just hit "STOP", everything stops and it just resets to zero, nothing was achieved.
So, I'll show you what that looks like.
[10 kHz tone plays]
I have to hit "STORE/START" again to restart the calibration process.
And then, let's say we're running out of 10 K tone and I need to rewind and play more.
I'll hit "Locate" and then "PLAY" and you can see that it's all frozen, and it picks
up where it left off.
And the "REPRO TREBLE" has to be done for the sync head and the repro head.
[fast-forwarding sound]
So the sync electronics have been calibrated.
You can see the level on the meter bridge
is right up along that row of lights.
I'm gonna switch from the sync head to the repro head and do the same thing.
Playing 10 K,
[10 kHz tone plays]
calibrating "REPRO TREBLE".
[fast-forwarding sound]
OK, the treble has been adjusted for the repro head.
And that's all you need this test tape for - you're done with the repro.
Alright, you're done with the MRL tape. You can spool that off.
And load a fresh reel of tape for your session.
We're just grabbing a scrap piece of tape from the studio for demo purposes.
So before you start any recording adjustments, you wanna make sure that the Dolby HX Pro
is switched off.
You can find that button here, but in order to make it change state you have to "SET ENABLE",
press the button. And you can see the light came on. So I'm gonna "SET ENABLE",
turn it off.
Ok, you've got your tape on the machine
that you're going to use for the session.
We're going to do the bias first.
I've gotta arm all of the channels, and select
RECORD BIAS".
To change the bias setting - the overbias setting -
you press "BIAS PRESET",
and it shows in the upper-left-hand display,
what the overbias level is. Right here it says,
"2.8" overbias.
You can use the "M REF" which stands for "Meter Reference" to change that. I'm gonna
change that to "3", "negative 3", meaning "3 dB overbias"
And I'm gonna hit "STORE/START" to save that setting.
When it happens, the "BIAS PRESET" mode disappears and and it goes back to regular-old
"RECORD BIAS" adjustment.
I'm gonna double-check that it remembered it just by pressing "BIAS PRESET" again.
It's there, press it again to get out of that mode, and now we're gonna record a 10 kHz tone,
And then
[10 kHz tone plays]
...do the bias.
It's recording... "STORE/START".
So after the bias is completed, we can move on to the "RECORD LEVEL"
and "RECORD TREBLE" adjustments.
I'll go here, on the keypad, and press "RECORD LEVEL"
and it'll go into the "RECORD LEVEL" adjustment.
And it'll record
1 kHz tone.
[1kHz tone plays]
Hit "STORE/START",
and watch the show.
So exciting.
I wonder if the drummer is any good.
I wonder if it matters if he's any good.
I gotta stop paying attention to what I'm doing,
so I don't get hurt when I don't do it right.
That's done. Let's move on to the "RECORD TREBLE" adjustment.
[14 kHz tone plays]
And that pre-selects a frequency that I don't like using. I like to keep it standard with
other tape machine adjustments where I do the "RECORD TREBLE" at 10 K, 0 VU. So I'm
gonna switch the tone generator to 10 kHz
[10 kHz tone plays]
and at a level of 0 VU.
Some people might look down upon that, but I like it.
After it's set up that way, I hit "STORE/START",
and it calibrates itself, magically.
[fast-forwarding sound]
Alright, treble's done. What I'd like to do now is the final stage of the alignment process,
and that's the "REPRO BASS".
I'll go here and select "REPRO BASS", turn the tone generator on, and select "0 dB",
and change the frequency to 100 Hz.
And you can see what frequency it is on the bottom-left of the screen.
And then hit "RECORD".
[100 Hz tone plays]
Looks pretty close, but I'll hit "STORE/START" and it'll calibrate itself again.
And we'll watch the meters move.
...slowly,
patiently.
[fast-forwarding sound]
So now that's complete, I like to check the bass frequency response by turning the tone
generator down to a lower frequency.
That's 90 Hz... 80 Hz...
60 Hz... 50 Hz...
40 Hz... 30 Hz...
... and now it's off the scale.
And this is a high-resolution meter, so all the way down is 2 dB down, all the way up
is 2 dB up, so it's actually pretty good.
... and that's it.
The machine's ready to go.
OK, sometimes you'll need to calibrate your machine to a different level than the reference
tape level, and I can show you how to do that with the keypad on the meter bridge.
So, go into "AUTOPAR ALIGN" - again, make sure you're in VU mode first.
And go to "REPRO LEVEL", cause you'll be playing back the 1 kHz tone off the test tape.
And let's say you want to be - let's say you wanna calibrate the machine to 3 dB higher
than the reference tape.
You'll wanna make sure that the tone on the reference tape play back 3 dB low
on the meter bridge.
So, up in the upper-left-hand corner of the LCD screen here, there's a "0.0" which represents
what this row of lights is.
so 0.0 VU ... dBVU.
I'm gonna use the "M REF" buttons to go down 3 dB.
And now this row of lights means "negative 3 dBVU".
And when you play the 1 kHz tone and hit "STORE/START", the machine will calibrate itself
to that level.
And you repeat the process for the "REPRO TREBLE", playing back 10 kHz.
It'll reset to "zero" up here, and you just have to change that to "negative 3".
Once it's at "negative 3", you press "PLAY" to play the 10 kHz tone, hit "STORE/START",
and it'll calibrate itself for that, and the repro electronics for that will then be set
up for 3 dB lower than whatever the reference tape was set for - or recorded at.
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