VSR 5 U Microphone Preamplifier. Operating Manual

Transcription

1 VSR 5 U Microphone Preamplifier Operating Manual

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4 Contents Contents Page Introduction 5 The Power supply 5 The Signal Path and Operating controls 6 Notes on EMC, Ground Lift Switch 9 Specifications 12 Safety Information 13 Warranty, EMC, Declaration of Conformity by Schalltechnik Dr.-Ing. SCHOEPS GmbH 4

5 Introduction / The Power Supply Dear customer, Thank you for choosing the SCHOEPS VSR 5 a very high-quality, low-noise, low-distortion stereo microphone preamplifier. Its special features: The central gain element in each channel is a differential amplifier with current feedback. The module used in the VSR 5 was inspired by the ultra-low-noise Valley People Trans-Amp LZ, developed in the 1970s. The two channels of the VSR 5 are completely separate from one another. Thus there are two each of all the operating controls. The gain is selected by means of a 21-step rotary control which can be set in 3 db steps from unity through 60 db. Each channel has a pushbutton switch for: phantom powering polarity inversion mute a 40 Hz low-cut filter an 80 Hz low-cut filter a 120 Hz low-cut filter All the pushbutton switches have LEDs to indicate their status. When the unit is turned on and the pushbutton switches are not activated, the LEDs glow at low intensity. When phantom powering is turned on or off, the outputs are muted for about four seconds. Output levels are indicated in 3-dB steps by means of a 20-level LED meter. The display thus has a range of 57 db. A clip LED lights at signal levels above +20 dbu. Since this is ca. 8.5 db below the maximum output voltage of the preamp, clear warning is given before overload occurs. The carefully chosen gain parameters of the VSR 5 also ensure that this LED would light in the event of any possible overload of the input circuit. The electronically balanced inputs and outputs are on the rear panel. Two independent outputs, each with its own circuitry, are provided for each channel. Behind the robust aluminum front panel, the chassis is stainless steel which guarantees high mechanical stability and resistance to environmental influences. It also shields the circuitry from electrical and electromagnetic fields. The Power Supply The power supply uses a built-in socket connector for a standard, three-wire AC power cord (IEC/EN C14). The operating voltage is set to 230 Volts at the time of delivery. If needed, the power supply voltage can be changed on the rear panel either by hand or with a screwdriver. The power on/off switch is also on the rear panel. LEDs in the front-panel switches signal that the unit is powered on. Depending on their settings, the LEDs will be lit either dimly ( off ) or brightly ( on ). The internal power supply uses three generously-sized toroidal transformers. The required DC operating voltages are provided by linear circuitry. Power-Line Fuses The power-line fuses of the VSR 5 are soldered to the circuit board of the power supply, and are not externally accessible. A burned-out fuse would generally indicate a defect in one or more components, and fuses should thus be replaced only after a careful check of the unit by qualified service personnel. If a fuse burns out during the warranty period, the 5

6 The Signal Path and Operating Controls unit must be returned to the factory or its warranty will be voided. The Signal Path and Operating Controls Inputs The XLR sockets of the electronically balanced inputs are on the unit's rear panel, labeled Balanced Input. The inputs accept balanced or unbalanced audio signals. The contact assignment follows the international standards: Pin 1 = Ground Pin 2 = (+) Phase Pin 3 = (-) Phase Phantom Powering Most condenser microphones require phantom powering in order to operate. The VSR 5 supplies this at its inputs. It can be turned on and off with the front panel P48 switch. The open-circuit voltage is 48 Volts in keeping with international standards, provided via a pair of 6.8 kω resistors on pins 2 and 3 of the input sockets. In most conventional microphone preamplifiers, turning the phantom powering on or off causes a change in low-frequency voltage at the output, which can be audible as a loud noise, and can cause harm to other equipment. In the SCHOEPS VSR 5 an automatic muting circuit avoids this problem. The circuit activates for 2.5 seconds whenever phantom powering is turned on or off, as indicated by a red LED in the Mute switch. The status of the P48 switch is automatically stored. When the preamplifier is turned on, phantom powering will be activated if it was on when the unit was last turned off. Note: When phantom powering is turned on, pins 2 and 3 of the respective input socket will carry 48 Volts DC. If this should be connected to a line-level input, damage can be caused. Mute Switch The output of each channel can be muted for any length of time by pressing its Mute switch. The switch is illuminated in red as long as this function remains activated. The status of this function is automatically stored when the preamp is powered off. Polarity Switch When recording with multiple microphones, e.g. miking percussion such as a snare drum from above and below simultaneously, signal cancellation can occur due to the conflicting phase relationships. Problems can also occur when microphone or cable connectors are incorrectly wired. A simple test (and also a solution) is provided by the Polarity switch, which allows the user to invert the signals of the corresponding channel. When activated, the LED in the switch will glow brightly. balanced microphone output +phase -phase screen VSR 5 input socket X The plug housing should not be connected to the cable shield (pin 1), since this can cause a ground loop. For best protection from electromagnetic disturbance we recommend the use of SCHOEPS' special XLR-3 cable, e.g. K EMC 10 U (10 meters). Connecting to the inputs of the VSR 5 6

7 Operating Controls Front-panel features of the VSR 5 with phantom powering enabled and a microphone connected, normal polarity, outputs muted, and 80 Hz selected as the cutoff frequency of the low-cut filter. This function is carried out by means of high-quality relays rather than placing any additional electronic components in the signal path. Gain Control The gain of each channel can be set in 3 db steps from unity to 60 db by means of the 21-position rotary gain control on the front panel. The precision of this setting is within ±0.3 db throughout its entire range. Low-Cut Filters To remove inaudible frequencies as well as disturbing noise such as popping, wind or microphone handling noise without affecting the desired signal, the SCHOEPS VSR 5 offers three switch-selectable low-cut filters with 40 Hz, 80 Hz and 120 Hz cutoff frequencies. The currently active cutoff frequency is indicated by the bright white illumination of the corresponding switch. Only one filter per channel can be active at a time. The frequency can be changed simply by pressing the corresponding switch. Each filter can also be deactivated by pressing its Phantom powering is turned off. Phantom powering is turned on, but no microphone is connected. Phantom powering is turned on and a microphone is connected. 7

8 Operating Controls Note: During production, the reference level of the 0 db LED is set to +6 dbu. Here the 80-Hz low-cut filter has been activated. button a second time. The filter selection is stored when the preamplifier is turned off, and is set automatically the next time the unit is turned on. Level Indicator The signal level indicator of the VSR 5 consists of 21 LEDs including a Clip LED. The level is indicated in steps of 3 db. The range from -48 to -15 db is shown in green, the range from -12 to -3 db in yellow, and the LEDs for 0 to +9 db are red, as is the Clip LED. A full-wave DIN PPM peak detector drives the display with an attack time of <10 ms and a decay time of 0.5 seconds per 20 db. Clip Indicator The red Clip LED has a fixed reference voltage. It begins to blink at levels above ca. +20 dbu, thus giving a warning before there is any possible overload. Outputs The SCHOEPS VSR 5 is equipped with two separate electronically balanced XLR outputs per channel. The gold-plated XLR output sockets are on the rear panel of the unit. In accordance with international standards, the layout is: Pin 1 = Ground Pin 2 = (+) Phase Pin 3 = ( ) Phase Note: The VSR 5 has floating, servo-balanced outputs. Thus if either pin 2 or 3 is grounded, the output levels will remain the same as in balanced operation. VSR 5 output socket X balanced input Do not connect the plug connector's housing to pin 1. VSR 5 output socket X unbalanced input Do not connect the plug connector's housing to pin 1. In this case pin 3 must be connected to pin 1 (ground), since pins 2 and 3 of the output from the VSR 5 are floating. Connecting the inputs and outputs of the VSR 5 8

9 Notes on EMC, Ground-Lift Switch Notes on EMC (Electromagnetic Compatibility) This section is admittedly rather long in proportion to the rest of the manual. Please be assured that, as a rule, the VSR-5 will not have problems with interference even if you don't memorize all the details which we are about to present. However, in the rare event that a problem with hum or radio-frequency interference does occur, we want to offer enough information to be of real help. A summary of how to proceed: 1. Set the Ground Lift switch to the Hi-Z position. That setting will prevent interference in most circumstances, and is recommended as the default. 2. Use microphone cables that make no connection between the XLR-3M connector housing and pin 1. Only the shield of the cable should be connected with pin 1 at either end of the cable. For best results, use the SCHOEPS cable K EMC_U. 3. Whenever the outputs of the VSR 5 are connected to one or more items of other equipment, only one unit should have a direct connection between its circuit ground and AC safety ground. Thus, if necessary, a ground lift switch on one of the units should be set to the ground position. (This does not apply to battery-operated equipment, nor to AC-operated equipment that is completely isolated from the electrical safety ground and carries the symbol.) 4. Power all equipment that is connected to the VSR 5 from one common AC power outlet. Detailed description In the development of the VSR 5, emphasis was placed on first-rate audio characteristics but also on a corresponding degree of immunity to radio-frequency interference (RFI). Filters for this purpose have been built into the inputs and outputs, but these protective measures can reach their full effect only if suitable cables are used. To guarantee the best possible protection from RFI we recommend using special SCHOEPS XLR-3 microphone cable such as K EMC 10 U (10 meters) oder K EMC 20 U (20 meters). This cable is distinguished by: being RF-proof due to its high degree of shield coverage conduction of any RF picked up by the shield to the chassis of the unit to which the cable is connected, by means of condensers in the output plug not through the connection of pin 1 with the connector housing; this avoids ground loops small diameter robustness non-twisting (important when hanging microphones) flexibility even in cold weather Ground-Lift Switch In conventional XLR-3 cables pin 1 and the plug housing are often connected together. This can offer a certain amount of protection from electromagnetic fields. In that case the setting of the Ground-Lift switch is immaterial since it is bridged by the connection in the cable plug. But the connection of pin 1 with the connector housing can create ground loops which can cause hum when several pieces of equipment share the same protective AC ground. (What a ground loop is and what causes it is shown on the following page.) Thus the option exists to separate the circuit ground from the chassis ground by setting the Ground-Lift switch to the LIFT position. For this to have any effect, however, the connection in the XLR plug of the cable between pin 1 and the 9

10 Ground-Lift Switch Unit without ground-lift switch VSR 5 U Conductive chassis Conductive chassis Circuit ground 1 2 Connection by way of the house AC safety ground Circuit ground C* GND HI-Z LIFT Connector housing The red dashed line is a ground loop. As in the windings of a transformer, magnetic fields-- either from power supply transformers or due to differences in chassis potential among connected items of equipment cause current to flow at 50 or 60 Hz. Ground-lift switch * Bypass capacitor for RF; the SCHOEPS K EMC _U cable also has bypass capacitors in its XLR plug Cable shield The origin of ground loops I Hum current connector housing must be interrupted, and this can again lead to problems with RFI. To avoid both RFI and ground loops at the same time, we recommend the use of the SCHOEPS K EMC _ U cable. In the connectors of this cable there is no DC connection between pin 1 and the housing; thus no ground loops can occur. RFI on the other hand is conducted to chassis ground through condensers built into the plug connector. This provides RF protection despite the lack of a DC connection from pin 1 to the chassis. So that the Ground-Lift switch does not create a ground loop, do not set it to the GND position when this type of cable is being used. The HI-Z position of the Ground-Lift switch is designed to bridge the difference in ground potential among pieces of equipment that are connected to power outlets some distance apart, without causing hum problems. Safety is maintained by keeping the chassis of the VSR 5 connected to AC safety ground regardless of the Ground-Lift switch setting. Avoiding ground loops The greater the size of the loop encompassed by the relevant equipment, the greater the effective AC magnetic field radiated by transformers or electrical conductors, and the stronger the induced hum is likely to be. Thus to the extent possible, all interconnected equipment that uses three-wire AC power cords should be powered from the same outlet. This will minimize the ground loop area and thus the resulting hum. 10

11 Notes on EMC Cables among the various pieces of equipment should be arranged so that the loop they form has the smallest possible area. As a third tactic, the signal cables of all audio equipment should be kept as far as possible from sources of magnetic fields (transformers, high-current power cables). The Ground Lift switch will have no effect if pin 1 of the microphone cable is connected to its connector housing. In that case a ground loop will be created via the shield contact of the unit's input socket, since this contact is connected to the chassis and thus to the AC safety ground. If hum problems occur, the best approach is to reduce the extent of any ground loop. Should this not help, any existing connection between pin 1 and the plug connector housing of the microphone cable should be cut. But please be aware that doing this can lead to radio-frequency interference, especially if the RF is not bypassed to the chassis by way of a capacitor from pin 1 immediately at the input. c) if an item of equipment with a direct connection between its circuit ground and its AC safety ground is connected to the VSR 5; or d) double-insulated ( Class II ) equipment ( ), if a cable with an extra ground wire is connected. A further possible cause of hum Please note that strong hum can occur if the input of the VSR 5 is left open (i.e. neither a microphone nor any other item of equipment is connected to it) while the Ground-Lift switch is in the LIFT position. This hum does not represent a defect, but results from the fact that the circuit ground is not connected to the chassis under these conditions, which limits the ability of the chassis to act as a shield even though it is connected to the AC safety ground. The hum will disappear if any of the following occurs: a) if pin 1 of any cable connected to the VSR 5 is also connected to its connector housing; b) if the VSR 5's Ground-Lift switch is set to Ground ; 11

12 Specifications Inputs: 2, balanced, electronically floating Phantom powering: +48 VDC (P 48*); can be switched off Resistances: kohms Maximum current: 10 ma (according to standards) Minimum current at which LEDs indicate a microphone at an input: 1.7 ma Input impedance: 8 kohms Input CMRR** at 60 db gain: > 90 db at 1 khz (for typical values see Fig. 1) > 80 db at 15 khz Max. input level: 25.4 dbu (23.2 dbv) at 0 db gain, f = 1 khz Fig. 1, Common-mode rejection ratio Gain adjustment: 0 db db in steps of 3 db Gain accuracy: ±0.3 db Low cut filters (-3 db): 40 Hz, 80 Hz, 120 Hz at 12 db/oct. or off (see Fig. 2) THD+N at 1 khz: % at 30 db gain and 27.5 dbu output level (1 db below clipping) into 100 kohm load (see Fig. 3) Noise (input terminated with 200 Ohms; gain: 60 db, referred to input): dbu ( dbv), unweighted, RMS Fig. 2, Frequency response with 40, 80 and dbu ( dbv), A, RMS*** 120 Hz cut-off frequency dbu ( dbv), CCIR-1k, Q-peak**** dbr dbr k 10k 40kHz k 10k 40kHz Frequency range (gain: 30 db): 12 Hz khz (±0.1 db) 2.5 Hz khz (-3 db) Inter-channel phase difference: 0.0 at 5 Hz 0.0 at 50 Hz 0.0 at 1 khz 0.0 at 10 khz at 200 khz Slew rate of the Core SVM : 10 V/µs at 30 db gain RF filter range (in- and outputs): 3 MHz 1 GHz, see Fig. 4 Max. output level: 28.5 dbu (26.3 dbv) Outputs: 2 2, balanced, electronically floating Output impedance: 50 Ohms Output CMRR*: ca. 60 db (20 Hz 20 khz) Meter range: -48 dbr dbr (adjustable) clipping LED lights up at +15 dbr Power supply: VAC / VAC, Hz Power consumption: 10 VA Dimensions (19", 2U): 485 mm (w) 60 mm (h) 195 mm (d) Weight: 4.70 kg, lbs Case: stainless steel, aluminum Front: gray Nextel finish; front panels: stainless steel dbr Fig. 3, 1 khz, gain= 30 db, 1 db below clipping dbr k 10k 40kHz 10MHz 100MHz 1GHz Fig. 4, noise floor and level of RF interference at 10 dbm and 80% AM modulation at the inputs 12

13 Safety Information Safety Information Please observe the following safety advice: Water, Liquids, Moisture Operation of the unit near water or other sources of liquids should be avoided. Please make certain that the unit cannot fall into liquids or that liquids cannot enter the openings in the unit's housing. The unit should not be operated in spaces with high humidity, especially condensing humidity. To preserve your warranty rights, all repairs during the warranty period should be carried out only by SCHOEPS or its authorized representatives. Caution: There is a risk of electrical shock if the unit is opened. Always disconnect from AC power first! Operating Voltage The unit may only be operated with the AC line voltages specified in these operating instructions ( VAC / VAC, Hz). Electrical Safety Ground Please make certain that the unit is connected to electrical safety ground in accordance with regulations. AC Power Cable Make certain that the AC power cable is in good condition. Arrange the AC power cable so that it will not be damaged and so that it does not cause accidents. The unit is shipped with a three-wire AC power cable with a German Schuko plug. On request a three-wire AC power cable for North American use can be provided instead. In some countries the unit must be used with a customer-provided AC power cable. Service / Repair None of the internal parts of this unit require maintenance. Any needed repairs should be carried out only by qualified service personnel. 13

14 Warranty, EMC, Declaration of Conformity Warranty We guarantee our products for a period of twenty-four months, except for batteries. The guarantee period begins on the date of purchase. Please provide your bill of sale in all cases as proof of guarantee; without it, repairs will be undertaken only at the owner's expense. We reserve the right to satisfy all warranty requirements regarding defects of workmanship or materials by means of repair or partial or complete replacement of the product, at our sole discretion. Excluded from this guarantee are defects due to misuse (e.g. incorrect operation; mechanical damage), abuse or Acts of God. This guarantee is nullified in the event of tampering by unauthorized persons or agencies. To secure your rights under this guarantee, send the product with proof of purchase and a precise description of the malfunction, at your expense, either to SCHOEPS (if you are a customer in Germany), or to our representative (if you are a customer outside of Germany). Prior to sending your defective product for repair, please contact your local dealer or distributor for instructions. In exceptional cases you can, by prior arrangement with SCHOEPS, send the product directly to us from a foreign country. However any return shipment must then be prepaid; this tends to cause delays, especially for non-warranty service. Full payment must be made before a repaired item can be returned to the customer. This guarantee does not affect any contractual agreements which may exist between the buyer and seller of the equipment. This guarantee is world-wide. Electromagnetic Compatibility (EMC) This equipment meets international specifications as described in the Declaration of Conformity below. It does not emit interference. It can be used in environments in which interference exists, even if that reduces its effectiveness for its intended use. That is, the unit's functioning may be affected in the worst case by electrical, magnetic or electromagnetic fields, but it will not be damaged. Operation of this equipment in surroundings with high electromagnetic field strengths (e.g. near transmitters) should be avoided. Declaration of Conformity CE-Mark The CE-mark guarantees that all products conform to relevant standards approved by the European Community. The products described in this User Guide comply with current, relevant standards when used with cables from SCHOEPS. Relevant directives: EMC Directive: 89/336/EEC, amended by 92/31/EEC and 93/68/EEC Relevant standards: EN , -2 and those which are referred to by them. 14

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16 Subject to change without notice. Not responsible for errors or omissions SCHOEPS GmbH Spitalstraße 20 D Karlsruhe (Durlach) Tel: +49 (0) Fax: +49 (0) Schall Technik