HD REFERENCE Operating Manual
Fredenstein HD Reference Preamplifier The Fredenstein HD Reference microphone preamplifier utilizes a completely new approach to microphone level amplification. Many in the recording industry are now using 96 kHz or 192 kHz sampling rates while tracking, but still using equipment, which cannot provide the frequency response or bandwidth provided by modern A/D converters. The HD Reference overcomes these limitations and yields a new sound quality.
Fredenstein HD Reference Preamplifier Installation: Electrical Safety Warnings: Do not open the enclosure, hazardous voltages are present inside! There are no user serviceable parts inside. Refer servicing to qualified personnel. Do not expose this appliance to rain and moisture. Do not block any ventilation openings. Do not install near heat sources. Protect the power cord from being walked on or pinched.
Fredenstein HD Reference Preamplifier The input impedance of the HD Reference is natively 200 kOhms (200,000 Ohms) and can be reduced to 1KOhm (1000 ohms) or 300 Ohms by activating the LOW-Z functions. With both 1K and 300 pressed, the input impedance is approximately 230 Ohms. The initial 200 kOhm input impedance avoids loading the microphone output transformers and yields, in some cases, sonically superior results.
Fredenstein HD Reference Preamplifier when possible. The most common use for high pass filters is to reduce unwanted rumble from air conditioners or from outside sounds when acoustic isolation tends to be be less than perfect. High pass filters can also help reduce leakage from other sources when the the instrument has minimal low frequency information, and the leakage mostly exists as low frequencies.
Fredenstein HD Reference Preamplifier Unfortunately, standard audio test equipment is unable to cover the complete range of the HD Reference. The frequency response of the HD: 10Hz to 50kHz within 0.1 dB at ALL gain settings, -3dB at 2Hz and 900 kHz. At most gain settings, it becomes even flatter. Figure 1: Frequency response.
Fredenstein HD Reference Preamplifier Figure 2 Figure 3: Total Harmonic Distortion. This graph shows the 1 kHz THD as the input signal is stepped over a 86 dB range. Two gain settings are shown, 0 dB and +40 dB. Even with 40 dB of gain, distortion is typically near -100 dB which translates to 0.001%. You can see a smooth gradual climb after the output passes +5 dBu on the +40 dB gain setting. Figure 3 Figure 4: THD&N Ratio. Changing the measurement to “percentage” and allowing for “noise”.
Fredenstein HD Reference Preamplifier Figure 4 Figures 5, 6, 7 show the harmonic levels at various output levels with the 40 dB gain setting and a 250 Hz input (chosen for a centered graph). Figure 4 at 0 dBu output, Figure 5 at +10 dBu output, Figure 6 at +20 dBu output which is near where many A to D converters overload. Notice 2nd harmonic at 500 Hz and 3rd at 750 Hz and nothing above 7th. Tube circuits often display similar harmonic signatures.
Fredenstein HD Reference Preamplifier Controls and Operation: Rotary Control: GAIN : Gain Control from 0 to 64 dB in 1dB steps Pressing the Gain Knob Mutes the output and the Gain Display Blinks Output Peak Level Indicator: -18dB to +20 dB, 2 dB steps (0dB = +4dBu) Switches: P48 : +48 Volt Phantom Power when lit POL : Reverse Output Polarity when lit LOW Z 300 LOW Z 1K 300 Ohms Input Impedance when lit : 1000 Ohms Input Impedance when lit With neither 1K and 300 pressed, the input impedance is
Fredenstein HD Reference Preamplifier Gain Control: Rotary Encoder sets the Gain in 1 dB steps which are displayed next to the knob. Pushing the Knob activates an immediate MUTE. This control as with all others can be remote controlled POL – Polarity Control: Pushing the POL switch selects the polarity, when lit (blue), the output polarity is reversed. Otherwise the true, non-reversed, polarity is selected (normal operation).
Fredenstein HD Reference Preamplifier (Will not apply to next revision with a single PCB) There is another LED on the Gain Display between the 2 digits that is used to indicate if a preamplifier board is set to an invalid address. This is an internal setting that should be properly set by the factory. Channel 1 needs to be set with both dip switches set to “ON”. Channel 2 needs to be set with 1 to “OFF” and 2 set to “ON”. “ON” is towards the back of the PCB and “OFF” towards the front edge.
Fredenstein HD Reference Preamplifier manual to have some space above and below in the rack. Think about how hot a 15 watt incandescent lightbulb gets. The Commander Remote Control The Commander Remote Control unit looks very similar to the HD Reference and notably ALL of the controls are included. Only the meters are missing on the Commander, as there is no audio involved in this box to meter. In the control room, one typically uses the meters of the recording device.
Contact Info: Fredenstein Professional Audio by Orion Communication 7F-1, No. 582, Ruei Guang Rd. Neihu District Taipei 114 Taiwan Phone : Email : Web : + 886-2-2657-2618 info@fredenstein.com www.fredenstein.
