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This is the all-important front end to the twinQ

2

. Its job is to accept 

any type of microphone, instrument or other source of audio 
signal, and make it loud enough. Microphones need rather a lot of 
amplification, while guitars, keyboards and CD players need less. 
Mics need to be connected to low impedance inputs, while 
instruments prefer high impedance inputs. To ensure correct 
impedance matching, the inputs are split into an XLR connector 
for Mics, and 1/4" jack "Line" and "INSTRument" connectors for 
everything else. A switch on the front panel decides which input 
connector is active, the XLRs or the 1/4" jacks. The LED next to 
the switch lights to show that the Line inputs (jacks) are selected:-

'LINE' switch out (LED off) = "Mic"
'LINE' switch in (LED on) = "Line" or "Instr"

The Mic input is transformer balanced and the Line input is 
electronically balanced. Note: although the Line input is not 
normally used for microphones, it can also be suitable for some 
high output unbalanced microphones, such as battery powered 
Electret types. The front and rear panel Mic inputs (XLR) are 
balanced and wired as follows:

Pin 2: + (hot)
Pin 3: - (cold)
Pin 1: ground

The Line input (jack) is balanced and wired as follows:

Tip: + (hot)
Ring: - (cold)
Sleeve: ground

The front panel Instrument jack is balanced and wired as follows:

Tip: + (hot)
Sleeve: ground (NB: use a mono jack plug).

Note that if something is plugged into the Instrument input, 
anything plugged into the rear panel Line input will be cut off.

Phantom power

Most high-quality studio mics are "Phantom Powered", which is 
to say they have electronics inside them, which get their power 
from the preamp. Most mics require a supply of 48 volts, so 
Phantom Power is often labelled "48V". The '48V' switch turns 
this power on and a red LED lights when active. When switching 
the Phantom Power on, quite a loud thump may be produced, so 
it is a good idea to turn down the Output Gain (or to momentarily 
select the Line input), when pressing the '48V' switch.

When using dynamic or older ribbon mics, do not turn Phantom 
Power on. It probably won't do any harm but it certainly won't do 
any good, so leave it off! Consult the microphone handbook if you 
are unsure what kind of mic you have.

The main control, labelled 'INPUT GAIN', covers a range of 
microphone amplification from 18dB to 60dB. In many other 
preamps the action of the "Gain" control is rather uneven, with the 
40dB to 60dB range being crammed into the last 1/6th of a turn. 
All Joemeek preamps use a specially designed control that 
ensures smooth operation over the whole range of rotation, with 
extra sensitivity in the crucial 25dB to 45 dB range.

Microphone inputs up to +4dBu can be accommodated without 
distortion (+24dBu by using the 'PAD' switch).

The (0) symbol next to the 35dB mark, means unity gain, or 0dB, 
for a signal in the Line input. For Line inputs the range of gain 
adjustment either side of this mark, is +22dB, -19dB. For the 
"INSTRument" input the gain range is 0dB to +40dB.

The microphone input transformer is permanently assigned to 
the "Mic" Input. The 'IRON' switch optionally sends the "Line" 
input through the transformer, to add some colouration to Line 
sources.

The 'PEAK' LED 16dBu, which is 6dB below clipping, so 
occasional brief flashes are OK but if it's on all the time you need 
to back off the Input Gain!

'HPF' means "high-pass filter". Mainly for use with microphones, 
this helps remove stage rumble, handling noise and "pops". The 
LED lights when active.

Technical stuff

Very low noise - does it matter? Yes and no, it all depends what 
you are doing - what really matters is "signal-to-noise ratio". All 
electronics produce a certain amount of background noise - it's in 
the nature of things. Providing there is only a relatively small 
amount of noise, the signal will cover it up, or "mask" it. So 
providing the signal is much bigger than the noise, you won't be 
aware of the noise. In other words the "signal-to-noise ratio" 
needs to be a big number, ideally such as 80dB or 90dB.

So how do you achieve that in practice? The trick is to keep the 
microphone as close to the sound source as possible without 
overloading it, so as to get as much signal out of it as possible. 
Then you set the Gain control to give only as much gain as is 
needed to get a decent level into the recorder.

Of course when there is no signal going on, you may hear the 
background noise of the electronics. In that case, given the 
amount of gain in a typical studio monitoring system, this noise 
"floor" should ideally be in the region of -80dBu or lower, in order 
for it not to be noticed.

The twinQ

2

 microphone preamplifier uses state-of-the-art 

electronics and has an equivalent input noise of around -127dBu 
(with a 150ohm input load). Despite all the hyperbolae and 
obfuscation, the theoretical best possible performance with 
silicon-based electronics is about -131dBu. So the preamplifier 
used in the twinQ

2

 and all other Joemeek products approaches 

this limit. To improve significantly on this would require highly 
specialised electronics and probably a vat of liquid Nitrogen to 
cool it!

The maximum gain available from the preamp is 60dB, in which 
case the noise floor will be -67dBu. This is actually quite noisy - if 
you record that noise onto a digital recorder and play it back you 
will definitely hear it. In practice of course, you do not record and 
play back "silence" and the rest of the mix will probably be more 
than 70dB louder than this noise and will mask it completely. Even 
so it is generally a good idea not to use gains greater than 40dB or 
50dB and indeed, it should rarely be necessary to do so.

Preamplifier

8

Содержание twinQ2

Страница 1: ... 20 10 15 10 0 4 oo dBu 4 20 10 15 10 0 4 oo dBu 0 15 15 9 9 6 3 3 6 dB MAKE UP GAIN 8 20 0 3 16 12 5 dB MAKE UP GAIN 8 20 0 3 16 12 5 dB 0 15 15 9 9 6 3 3 6 dB 0 3 3 2 0 1 1 sec 0 3 3 2 0 1 1 sec 10 5 50 100 1 ms 10 5 50 100 1 ms 0 15 15 9 9 6 3 3 6 dB 0 15 15 9 9 6 3 3 6 dB 0 15 15 9 9 6 3 3 6 12 12 dB 0 15 15 9 9 6 3 3 6 12 12 dB LF FREQ 650 40 400 200 150 85 50 Hz LF FREQ 650 40 400 200 150 85...

Страница 2: ...e direction of and distributed exclusively by JOEMEEK is a registered trademark of PMI Audio Group PMI AUDIO GROUP USA 1845 W 169th Street Gardena CA 90247 toll free 877 563 6335 fax 310 323 0900 UK Unit 4 Minerva Court Woodland Industrial Estate Torquay TQ2 7BD tel 44 0 1803 612700 fax 44 0 1803 612009 email info joemeek com www joemeek com ...

Страница 3: ... or when unused for long periods of time 14 Refer all servicing to qualified service personnel Servicing is required when the apparatus has been damaged in any way such as power supply cord or plug is damaged liquid has been spilled or objects have fallen into the apparatus the apparatus has been exposed to rain or moisture does not operate normally or has been dropped 15 Apparatus designed with C...

Страница 4: ...uipment will be disposed of by local authorities collection systems Statement of RoHS Compliance PMI Audio Group manufactures complete electronic products which are covered by the European Union s Removal of Hazardous Substances directive 2002 95 EC RoHS This directive seeks to eliminate toxic substances from the manufacturing process such that when equipment is disposed of at the end of its life ...

Страница 5: ...former In addition low noise Burr Brown OPA2134 audio amplifiers are used throughout the signal path headroom is increased and power consumption is reduced Since 2003 the Joemeek product range has been designed by renowned audio electronics engineerAllan Bradford With his background in physics and over 30 years experience with the design of instruments mixers processors and amplifiers Allan s uniq...

Страница 6: ...hese two sockets at a time INSTRument input high impedance input Plugging in here overrides anything plugged into the Line or Mic inputs PREAMP GAIN sets the amount of audio amplification Too little gain and the sound will be too quiet too much and the signal could become distorted PEAK LED lights 6dB below clipping HPF high pass filter Mainly for use with microphones this helps remove stage rumbl...

Страница 7: ...ital channel 2 Rear Panel at a Glance 7 x1 x2 44 1k 48k DIGITAL INTERFACE MIC INPUT MIC INPUT LINE INPUT LINE INPUT INSERT INSERT AES EBU OUTPUT OPTICAL OUTPUT SPDIF OUTPUT SAMPLE FREQUENCY WORD CLOCK IN 4dBu OUTPUT 4dBu OUTPUT OUTPUT OUTPUT CHANNEL 2 CHANNEL 1 CAUTION RISQUE DE CHOC ELECTRIQUE NE PAS OUVRIR ENSURE MAINS VOLTAGE AND FUSE RATINGS ARE CORRECT BEFORE CONNECTING MAINS POWER THIS APPAR...

Страница 8: ... by using the PAD switch The 0 symbol next to the 35dB mark means unity gain or 0dB for a signal in the Line input For Line inputs the range of gain adjustment either side of this mark is 22dB 19dB For the INSTRument input the gain range is 0dB to 40dB The microphone input transformer is permanently assigned to the Mic Input The IRON switch optionally sends the Line input through the transformer t...

Страница 9: ...ely than you ever could by hand The compressor is applied in several ways 1 Make Sounds Stand Out Because compressors make loud sounds quieter you can boost the volume of the quiet bits without the loud bits getting even louder That means you can raise the average level of an instrument or vocal in the mix which has the effect of lifting it and bringing it forwards This can actually improve vocals...

Страница 10: ...SLOPE sets the average compression ratio applied to signals above threshold Lower settings anti clockwise have less effect Turning the control clockwise increases the ratio and makes the effects of compression more dramatic At maximum 10 1 the Joemeek compressor effectively becomes a limiter ATTACK sets how quickly the compressor reacts to peaks above threshold Turn this control anticlockwise for ...

Страница 11: ...onics of instruments or make vocals more distinct Increasing or reducing the presence of an instrument or vocal in this way can appear to move the sound forwards or backwards in a mix The HF or treble section is centred at either 6kHz or 12kHz Boosting the 12kHz band gives a sense of air or sparkle to vocals instruments and mixes without boosting harsh upper mid frequencies Alternatively with bass...

Страница 12: ...ze to an external word clock The digital audio outputs are compatible with most digital recorders as well as Digital Audio Workstations and mixers S PDIF format is available from the optical and RCA Phono connectors while the transformer coupled XLR connector provides a balanced AES3 compatible output Highly stable onboard master clocks give low jitter hi fi results Internal sample rates of 44 1kH...

Страница 13: ...ts to read 3dB or 5dB on audio peaks You should now be able to hear the compressor working as the volume diminishes Use the MAKE UP GAIN control to restore the signal to its previous uncompressed level Alter the SLOPE control and listen to how the severity of the gain reduction changes Try changing the ATTACK control and listen for percussive sounds getting louder Reducing the Attack and Release t...

Страница 14: ...AIN control turned up Is the OUTPUTGAIN control turned up Is something plugged in to the INSTRument jack 4 The compressor doesn t work Is the Compressor ON switch in LED on Is the COMPRESS control turned up enough Is the SLOPE control turned up enough Is there enough signal as set by the INPUT GAIN control to drive the compressor 5 Too little or too much compression Turn the INPUT GAIN control up ...

Страница 15: ...ponse EQ Q 0 9 1 6 octaves LF Frequency 40Hz to 650Hz variable MID Frequency 300Hz to 5kHz variable HF Frequency 6kHz 12kHz switchable Nominal output levels 4dBu 10dBv Output impedance 100 ohm Output Level switch 12dB attenuation Noise Floor 85dBu typical with 40dB mic gain VU Meter Analogue movement Power supply 115V 230V ac mains 50 60Hz Power consumption 30W Mechanical 482W x 88H x 220D overall...

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