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analogue tape, audio maintenance, education, music, music technology, proaudio, recording, studio technique, tape
This guide was produced for a client back in the mists of time. It features a tape machine with probably more available controls than yours has to tweak, but just ignore the ones you don’t have.
This is excellent as it allows you to set tape azimuth without needing an oscilloscope – and lets face it – who has one of those nowadays!
Materials + tools:
Tape head demagnetiser.
Plastic ‘tweaker’.
2″ Test tape.
Oscillator (in desk or separate) capable of 1khz, 4khz, 10khz, 100hz at +4 dBm or less.
True RMS voltmeter (calibrated in dB’s).
Frequency counter (optional).
Blank reel of tape (same sort you intend to use – preferably from the same batch).
Procedure:
1). Demagnetise the heads.
Turn off the machine!
Danger! – keep demag away from test tape and other sensitive
material – switch on and off well away from everything! Power up the demag and
bring it (slowly) up to the heads. Move it (nearly touching the head) in a zig-zag from top
to bottom and then vertically up the head over the head gap. Move slowly to the next
head and repeat. Now pull it away slowly and when 3′ or more away – unplug.
2). Repro alignment.
Clean the heads. Lace up the test tape, select the 30ips AES section. Connect the
frequency counter to the o/p of any channel of the m/c. Hit play and listen to the
1k tone – if the Freq counter doesn’t say 1k, adjust the speed control until it does! –
(do the same for 15ips – while you’e at it).
Connect the RMS vvm to ch8 o/p. Play the 1k tone. I suggest we set the machine to a
400nWb/m operating level, meaning that a 320nWb/m test tape should read -2dB on
machine meters – or +2dBm on a true RMS one…If needed – set the azimuth at
this point by putting all channels into play and pushing all faders up in centre position
mono. Play the 15k tone. If you now move the head by tweaking one of the sideways
adjusters, you will see a single peak of response. This corresponds to in-phase azi
adjustment.
Do the same for the sync head.
Now select play head and play 1k(level), 15k(hf) and 60hz(lf) and set the response to -2dB
on the vu’s (equiv to +2dBM).
Use the True RMS on ch8 to check this.
(We cannot be sure the machine meters are telling the truth so if we get a channel right
by using the true rms, then we can copy that setting across and be sure it’s right (assuming
the vu’s are OK!!).
Select the sync head and do the same.
3). Rec/Rep alignment.
Clean the heads.
Lace up the blank tape.
Put 8 channels into record.
Replay off the repro (play) head.
Using your Oscillator choose 10khz and set an o/p of around 5dB below 0.
Run the tape in record.
Use the tweaker to reduce bias (anti clockwise) – watch the o/p rise to a peak and then fall.
Increase bias (clockwise) and keep increasing it past the point where the o/p hits a peak
and starts to fall.
Take it ‘over the hill’ 1-2dB (30ips), [3-4dB (15ips)].(You will need the true RMS voltmeter
to do this).
Now put an oscillator input in of 1khz(level) @ 0dB (i.e. +4dBm) – the same should come out.
Ditto at 10khz(hf), 4khz(mf)(if you adjust this you will need to check 10khz again),
and finally 100hz(lf) which should read +1dB (i.e. +5dBm).(M/c meters ok for this).
Now put the next 8 channels into record and do it all again!!
Finally, put all channels in record and listen to the o/p’s individually – there should
be no excessive or different noise on any one track.
Congratulations! Your machine is now lined up and ready to go!
The Author
Howard Turner has over 30 years experience in the studio business, and for the last two and a half decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios.
Further information: +447803666789
web: www.studiowizard.com
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