Joemeek VC2 User manual

VC2 1
JOEMEEK TUBE CHANNEL
INSTRUCTIONS
The JOEMEEK TUBE CHANNEL VC2 is a development of historic tried and
tested circuits and designs from the 1960's to the present day, combined in a
single outboard rack unit by acknowledged leaders in analogue technology.
THE JOEMEEK TUBE CHANNEL - WHAT IT IS AND WHY
The JOEMEEK Tube Channel is the result of continuing experimental and
development work carried out over a 2 year period to incorporate the best of
historic design and tube technology as an extension of the development of the
other famous JOEMEEK products; the Stereo Compressor the Studio Channel
and the ProChannel.
It's best to think of the Tube Channel as four separate pieces of equipment:
1) The Microphone amplifier.
2) The Compressor.
3) The Enhancer.
4) The gain make-up.

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The microphone amplifier takes the audio signals from any microphone
and amplifies them up to 'line' level; that is, from a few millivolts, up to
about a volt.
This function is not too difficult and the microphone amplifiers on normal
professional mixers do it quite well; BUT they cut costs and corners. The
JOEMEEK Tube Channel has an uncompromising old fashioned
approach, it uses a transformer at the input and two separate amplification stages
linked to provide lowest possible noise and distortion. By using the finest
components available for the purpose, and with proven high overload amplifier
design developed over many years, the performance is startlingly good.
The JOEMEEK Tube Channel is designed for the best capacitor microphones; it is
particularly good with the Neumann range, the AKG C3000 and C414, Microtech
Gefell, and Audio Technica.
Dynamic or ribbon microphones should be used with the phantom power turned
off, then full advantage can be taken of the extreme low noise performance of this
amplifier.
An unusual function switch is included on the rear panel for historic microphones;
this is an impedance conversion switch to optimise noise performance for elderly
ribbon and moving coil microphones which were designed to operate at 50 ohms.
Pressing in the 'hidden' switch, the impedance of the input is reduced to give an
improved transformer ratio for these microphones.
VOLUME
In normal use the JOEMEEK Tube Channel will work with any microphone and in
any audio environment. However, some capacitor microphones can produce
enormous output voltages when placed close to a loud sound source. To eliminate
any possibility of overload under these conditions, a 20dB pad switch is fitted.
NOISE
The combination of a good specially wound microphone transformer and 1996
spec. amplifiers makes the noise lower than other microphone amplifiers.

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In practice, the only noise audible is the noise from the microphone itself (except the
characteristic tube noise in the line amplifiers).
PHASE SHIFT and QUALITY
It's Fletcher Company theory that 'big' sounds are only possible if the recording channel
keeps the response and phase of the lower frequencies flat and under control. To
achieve this, the JOEMEEK Tube Channel has an extended frequency range down
below 15Hz. This ensures that there are no sudden phase shifts in the low end. The
proof of the theory is that the sound from the Tube Channel is characteristically full
bodied and rounded in character.
Such extreme LF response can often bring its own problems so a 'subsonic' (High
Pass) filter can be switched in with a front panel push-button.
OVERLOAD MARGINS
In the mid 1970s Ted Fletcher designed a range of mixers specifically for use by the
Independent Broadcasting Authority and the BBC. One of the specification clauses
insisted on by them was an extreme overload margin in the microphone amplifier. The
reason was that although momentary overloads (transients) are not audible, they have
an effect on perceived quality. A high overload margin amplifier just sounds better.
Nowadays, many of these notions have been forgotten and 'quality' electronics is
getting rarer and rarer. But the JOEMEEK Tube Channel applies these professional
rules and achieves a clean transparent sound.
Line level inputs are plugged into the JOEMEEK Tube Channel via an XLR connector.
The line input is electronically floating balanced using the 'Superbal' electronic circuit
designed by Ted Fletcher in the mid 70's. The circuit gives excellent rejection of
electrical interference and produces an accurate line level signal.
PHASE
A push button is provided on the front panel to reverse the phase of all audio signals
(mic and line).

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BALANCED AND UNBALANCED
The JOEMEEK Tube Channel is designed to be used in the best larger
studios where most (if not all) interconnections are 'balanced'. Balanced
operation means that the audio is carried on two wires working in opposite
phase. Then should any interference appear on the 'line', it will be
effectively cancelled out. Both of the main inputs (Microphone and Line) and the line
output are accurately balanced to get best advantage from true balanced operation; but
unbalanced operation (for line level signals) will NOT degrade the performance unless
very long cables are used (above 50 metres).
OPERATING THE MICROPHONE AMPLIFIER.
Press in the 'MIC/LINE' switch, (in for MIC and out for LINE). Turn the INPUT GAIN
knob down to minimum then, If you are using a capacitor microphone, plug in the
microphone, then switch on the phantom power by pressing in the 'Phantom' switch.
(Do it in that order).
NOTE. The phantom power supply takes several minutes to reach its working voltage.
Remember to switch on at least 5 minutes before using the microphone.
CAUTION. When using phantom power, DO NOT USE UNBALANCED
MICROPHONES. It will damage (magnetise) the input transformer.
Turn up the INPUT GAIN until sound registers on the VU meter (VU switch in). Do not
let the VU needle hit the end stop too hard or overload may possibly happen. The meter
electronics has been adjusted so that it is normal for the needle to move in the red area.
OVERLOAD MARGIN AND THE VU. METER
For steady tones, the '0' on the VU meter corresponds to approximately 0dBu (Where
0dBu is 0.775v RMS on the line output with the output control set at '0')
This setting of '0' is to allow for the considerable under-read that occurs with all VU
meters with music signals. It is normal for the peaks of signals to go to +10dBu while
the VU meter reads only '0'.
In practice, when the VU meter is peaking at or just above '0' the music signal will be
well within normal limits and will have a significant overload margin.