TAB-Funkenwerk V78M Tube Mic Preamp

V78M Single Channel, Tube Microphone Preamplifier with Split Input Sensitivity and Gain

Overview

The TAB Funkenwerk V78M is a single channel, tube driven mic-preamplifier constructed to handle signals as low as ribbon microphones all the way to the hot line level signals used for mastering your final recording. Based on circuit designs of the pre-eminent tube mic-preamplifiers manufactured by Telefunken, the V78M uses the same set of transformers that we designed for the highly esteemed TAB Funkenwerk V72S. The unique aspect of the V78M is the split sensitivity and gain control that enables the flexibility to deal with the most challenging recording problems and providing the head room and sound character to make a 57 sound like a 47! The V78M is constructed as an enclosed plug and play unit in a 19" one rack space enclosure.

Technical Data

Polarity reverses via relay with switch and indicator on the faceplate
100 Ohm ground resistive switchable

This unit is shipped with NOS tubes made by Telefunken AG and/or Philips/Valvo. The V78M may be operated with an EF86/6267 in the first stage and an EF80/6BX6 in the second stage if replacement tubes are unavailable. Please note an EF80 reduces the output level by several dB's and will change the sound character.

Construction and Mode of Operation

The preamplifier utilizes a split control system featuring an Input Sensitivity adjustment knob coupled with a Make-Up Gain knob. This allows the user to set the system up in either the historic V72 setting or overdrive the input transformer to add harmonic and frequency distortions to create your own sounds. The Input Sensitivity knob allows the user to switch between -60 to +6 dB in six positions (-60 / -40 / -20 / -10 / 0 / +6dB) depending on the type of microphone or buss level being input into the V78M. The Make-Up Gain knob allows the user to switch between 22 to 60 dB by 3dB increments over 11 steps, with the last two settings increasing by 6 and 8 dB respectively (22 / 25 / 28 / 31 / 34 / 37 / 40 / 43 / 46 / 52 / 60).

Amplification and noise floor are rated at an optimum, therefore with wide range, the influence of the amplifier on the signal-to-noise ratio (dependent on the input signal itself) remains far below 1 dB. The noise level component of the input tube is unimportant and generally does not require selected tubes. However, when the tubes are in need of being replaced they should be replaced with NOS tubes of western manufacturing origin. The output stage, having relatively small gain, is provided with a strong low impedance tube (EF844s) to drive any kind of resistive, inductive or capacitive loads.

All of the transformers are custom built, high quality NI/FE/CO transformers that are resistant against stray fields and are magnetically screened with a multi-layer Mu-Metal shield. Low sensitivity against ring is guaranteed by shock mounting the input stage. In spite of the compact mounting of this enclosed unit, the development of heat remains within permissible limits. The wide open frequency response is designed to protect the entire acoustic range and resolution of the recorded instrument, and is inter-modulation stable to meet acoustical requirements.

Suggested Settings

These suggested settings are for input sensitivity vs. clipping with reference to 20/1K/20K Hz at 0dB gain.

• +6dB max input 23dBu (10V): mix buss, two bus, etc.
• 0dB max input 17dBu (5V): mix buss, two bus, etc.
• -10dB max input 12dBu (3V): high output modern condensers like TLM types, etc.
• -20dB max input 6.6dBu (1.643V): condensers like U47, M49, KM5x, KM8x and modern counterparts
• -40dB max input 0dBu (0.775V): standard dynamics (SM57/58), dynamic condensers like C12(a), C60, and modern ribbons
• -60 dB max input -8.5dBu (0.2945V) vintage ribbons and low output dynamics

These settings are suggestions with reference to 0dB-0.775V. The V78M was designed for sound-forming by over or under loading the preamplifier input, enabling the V78M to sound like many different mic-pre's in one box! The V78M's input transformer can withstand input levels up to +30dBu without becoming damaged.

All technical specs are given with the Input Sensitivity at -60dB and the Make-up Gain at 40 dB. Not only does this setting replicate the historic V72 specs used during countless classic recordings at EMI and other studios but also when changing the input sensitivity over the make-up gain, the frequency and harmonic distortion specs change as well. Which is precisely why we built the V78M with the split controls in the first place.

1. Power Hookup: Provides power to the V78M via standard monitor cable from a three prong outlet.
2. 100 Ω (Ohm) Ground Switch: 100 ‚Ѷ resistive buffer switch in between the audio and chassis ground
3. XLR Output: Standard XLR connector with 600 Ω output impendence, Pin 2 Hot.
4. TRS Output: Hooked up to XLR Output in parallel, Tip Hot.
5. TRS Input: Hooked up to XLR Input in parallel, Tip Hot.
6. XLR Input: Standard XLR connector with adjustable input impedance, Pin 2 Hot.
7. Input Sensitivity Switch: Six position rotary switch that sets the input sensitivity/impedance
8. Low Cut Switch: Switchable 120Hz high pass filter with 6dB per octave.
9. +48V Switch: Activates the built-in microphone voltage supply with a 5 second ramped timing circuit
10. Polarity Reverse Switch: Reverses the output 180 degrees via relay
11. Makeup Gain Switch: Eleven position rotary switch that sets the output gain
12. Power Switch: Energizes the unit with either 115V/50Hz or 230V/60Hz.

Getting Started

1. Make sure the V78M power switch on the front panel is down.
2. Turn the Input Sensitivity knob (the one on the left) all the way up to the right at +6dB.
3. Turn the Make Up Gain knob (the one on the right) all the way down to the left at 22vdB.
4. Flip the three switches in between the knobs (Low Cut, +48V, and Polarity Reverse) to the down position.
5. Plug the AC cable into the back of the V78M and then into a working AC outlet.
6. Plug a microphone cable into the XLR Output jack on the back of the unit (center of panel) and plug the other end into the mixing console, snake channel or recording unit.
7. Plug another microphone cable into the XLR Input jack on the back of the unit (right side of panel) and plug the other end into your microphone or microphone power supply unit.
8. Flip the power switch on the front panel to the upright position. The light above the switch should turn on.
9. Start experimenting!

Maintenance Requirements

This unit must be sent to TAB-Funkenwerk every two years for routine maintenance checks. It is necessary to check all voltages and functionality of the vacuum tubes. Customer pays only for the shipping and handling.

Warranty Information

If the maintenance requirements are maintained the unit has a limited warranty of 5 years. Otherwise, the warranty will void at the end of the first two year period. This warranty covers all parts & labor, except vacuum tubes. Customer pays for any shipping and handling charges. Warranty period starts on the date of sale from the dealer. Dealer's invoice is referenced as the warranty slip so please retain the original receipt for your unit.

All specifications are subject to change without notice, and this manual may contain errors which we will happily edit as they are pointed out. V71D, V72S, V72M, V76M, V77M, V78M are all trademarks of TAB-Funkenwerk. V72 and TAB-Funkenwerk are registered trademarks at the USPTO. All Copyrights 2009, TAB Funkenwerk. Other product names mentioned may be service marks, trademarks or registered trademarks of their respective companies and are hereby acknowledged. The V78M is designed by Oliver Archut and is made in the USA.

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