TWIN MIC AMPS WITH LIMITERS FOR DIGITAL VIDEO CAMERAS Type GSTN1

The GSTN1 is a compact audio front end for digital video cameras. Designed to attach underneath a video camera the unit offers two independent mic/line amplifiers each with a limiter. Each input is transformer balanced, is switchable between mic and line level, has a gain control and a limiter indicating LED. The unit is powered from the digital video camera.

The original GSTN1 was optimised for use with the Sony PD100 & VX1000 cameras.

A new version of the GSTN1 is now available designed to be compatible with the VX2000. When used in conjunction with a modification to the VX2000 (undertaken for a fee by a department of the BBC (contact details on request)) this new GSTN1 offers a superior sound than Sony's professional DVCs. Please quote GSTN1 (VX2000) when ordering.

Another additional new feature that is available for the GSTN1 is the inclusion of a a headphone socket & 3.5mm jack plug on flying lead that are directly connected. The concept behind this is that camera operators have been know to break 3.5mm headphone jacks plugs in the cameras headphone socket, it is then an expensive operation to take the camera to bits and mend the socket. Now the camera operator can plug their headphones directly into our GSTN1 and when they break their headphone jack they can either easily replace the socket on the GSTN1 or remove the flying lead that plugs into the camera and continue with plugging a different pair of headphones directly into the camera, a much cheaper solution than taking cameras to bits. Please note when ordering this is an additional extra cost option (£18).

FREQUENTLY ASKED QUESTIONS FOR THE GSTN1

VIEW OF GSTN1

#     2 Independent Limiters with Limit indicating LEDs    #
#     Mic/ Line Switchable      #
#     Powered from Camera     #
#     Independent gain controls for each channel      #
#     Transformer balanced inputs on XLR connectors      #
#     Audio Output on stereo 3.5mm Jack      #
#     Power Input on 2.5mm Jack     #

GSTN1 (Original Version) Specifications

Output line up level      = -45dBu
Limiter knee                  = 4 to 8 dB above line up

Input line up levels        
    Mic at minimum gain      = -45dBu
    Mic at maximum gain     = -70dBu
    Line at minimum gain      = +10dBu
    Line at maximum gain     = -15dBu

Maximum input before clipping
    Mic at minimum gain    = -8dBu
    Mic at maximum gain    = -33dBu
    Line at minimum gain    > +26dBu
    Line at maximum gain    = +21dBu

Frequency response
    40Hz to 20kHz        = +1 / -2 dB

Noise measured at output
    Mic at any gain        < -80dBu unweighted Quasi peak

Power requirements
    +5V to +12V at approx 25mAs

Weight    300 grammes

Size     (LxWxH) (excluding knobs) 115 x 61 x 35mm

View of GSTN1 Attached to Sony PD100

THE FOLLOWING OPERATING INSTRUCTIONS ARE REPRODUCED WITH THE KIND PERMISSION OF 'SMART VENTURE'

GUIDE TO USING THE GSTN1

Switching on:
There is a power switch at the front of the box. It may be just an on/off on the earlier boxes, or a 'tip'/'ring' switch on later boxes. Just choose the option to get a green power light on the rear of the box. The switch can be left on, as the box will go on and off with the camera.

Setting up:
If you're plugging in mics through the Glensound, you must not operate the camera in auto sound level. The box replaces the auto function in the camera for external mics.
From experience, a VX 1000 needs its sound level to be in manual and on "2". Look in the viewfinder to get this exactly on 2, not on the LCD at the back.
On the PD100 go into the menu and get into audio levels. Select manual, and level select. On the bar graph, turn it right down, then go up 3 clicks on the wheel (3 steps on the graph). Press menu to clear the screen.
The unmodified VX 2000 needs its level at seven clicks up from zero. Use the button on the rear of the camera.
The modified VX 2000 just needs the menu setting to 'manual', and adjusting the level makes no difference.
Once this has been done, you don’t need to change the camera settings at all, unless a battery has been off the camera for more than about 5 minutes.
The 'red light' on the camera should never light if the camera level is correct, even if you shout into the mics.

Operational use:
Plug your mics in as normal, using the locking XLR inputs. Pull the pugs out squarely, whilst holding the locking catch in, as if you pull at an angle they can be stiff. The mic/line switches work just like the Beach Box, so set as appropriate.
The level controls at the back work rather differently though. They don’t go down to zero, so even at –12, you will get some sound.
To get really great sound, check levels on one mic at a time, by either unplugging or using the mic/line switch to switch of the mic you’re not interested in (assuming your inputs are mic level). Use the meter on the camera to get an averaging half way, peaking to nearly full scale reading. The lights on the box should be flashing quite regularly on peaks in the sound. If they’re on all the time, the level is too high, if they’re never on, the level is too low. It's actually best to go for a too high level if you're unsure.
Usually a Sennhieser gun mic needs the level at –10, a Sony ECM 77 clip mic at +6, and a Beyer gun mic at +10. This is for ‘normal’ speech at a ‘normal’ distance. These figures can only be a guide, and you should treat each situation separately, and take levels as above if you can. However, due to the forgiving nature of the box, going by the above settings will usually get transmittable results.
When using the Sennhieser gun mic on a pole or handheld, switch the bass cut on by sliding the red switch to the right. This will avoid the limiters being triggered by handling noise. A slight bass boost in post production will bring back the low end if need be.
The box isn’t designed to handle every sound level in the world, and if you can’t reduce the level on a loud sound just let the limiters take it, move the mic further away, or use an in-line XLR attenuator. These handy devices look like an XLR plug & socket glued together. By connecting it between the mic and the cable you can reduce the sound level by the amount marked on the side. Have a 10dB and a 20dB in your kit. Contact the dr. for supply details.

GUIDE TO INSTALLING THE GSTN1

The box is an alternative to the well known ‘Beach Box’, and is physically of similar dimensions. It works in a completely different way, with high quality 'limiters' in the box replacing the cameras auto and manual sound adjustments. It will fit the Sony VX 1000, VX2000 and the PD100. Also you can use it on the Canon GL1 (with the menu set to 'mic atten') and to some other cameras. For the very best results on a VX 2000, the camera needs to be modified. Contact Machines Group (67676) to have this done. Order a 'VX 2000 line-in' Glensound box to use with a modified VX 2000, or better still get a complete VX 2000 (with line in mod) /Glensound package from the MTC (64047).

Features:

High quality balanced mic inputs

Individual limiters (with up to 25dB headroom) for each input mean no distortion

No ‘pumping’ of the sound due to quick acting limiter

Lightweight

Camera level is fixed, just use the two easy to access knobs on the box for each independent channel

Reliable construction from established UK Company

Fastening it to the camera:
Depending on what camera you have, there is a choice of two holes to mount the box. The one in the middle is for the PD 100 types, the one towards the front is for  VX 1000 types. The little locating ‘pip’ is unscrewable also, so move this too. The big screw may fall out if the box isn’t attached to a camera, so look after it !  If the screw doesn't fall out, the box has to be dismantled to change positions. See the dr. or a friendly engineer to do this. A 1p piece or a screwdriver is needed to turn the screw.

Connecting it to the camera:
The cables can be pushed into the box to store excess length, or pulled out to give you more.
The small jack plug is for power, and should be connected as follows:

VX 1000: Plug the power lead  in between the phono sockets on the RHS of the camera

Older PD 100: These have the power outlet on the top XLR box, once it’s been modified. This box has to be on the camera to use the earlier Glensound boxes, but it also serves the function of providing a raised mount for a camera mounted gun mic.

Newer PD 100 and VX 2000: Later boxes get the power from the LANC socket, near the headphone socket.

The other cable is for the sound, and should be connected to the camera mic input, or on a modified VX 2000, the phono sockets. There should be a 'dummy' minijack plug or cable in the mic socket of a modified 2000 when you're using the Glensound. Without this, the camera thinks it's on it's internal mic and puts in anti handling noise processing, which you don't want when using external mics.

Recent boxes have a simple internal adjustment which will reduce the output level slightly for the (unmodified) VX 2000 mic input. If this isn't done, you may hear slight distortion on peaks. Contact Machines group if this is a problem.

Power details:
New boxes pick up power from the LANC socket, but older boxes (used on the PD 100) needed a modification to the XLR top box. We recommend getting these older boxes updated by Glensound to use LANC powering as it's a more reliable connection and reduces the bulk of the camera if you're not using a top gun mic.