VIHYB Mic Preamp

My prototype VIHYB mic preamp is shown above. VIHYB stands for Variable Impedance Hybrid Microphone Preamplifier. I will soon be building and selling enhanced versions of this unit. Please stay tuned to this page for more details. For now, here are some of VIHYB's features:

• Selectable input coupling and impedance: Each channel has a 6-position rotary switch for your choice of either capacitor coupling (6600 ohms) or five transformer-coupled settings (nominally 250, 625, 1000, 1700, or 2500 ohms).
• Mono Bridged Mode: With the flip of a switch, the normally 2-channel VIHYB becomes a mono mic preamp with a balanced signal path from input to output.
• Short, high-quality signal path: Sealed relays with gold contacts handle all signal switching functions (including polarity, mode, and impedance). Each channel's relays share a compact ground-plane PCB with the solid-state gain stage and part of the tube circuitry.
• Hybrid Gain Structure: The first stage is solid-state, using a Burr-Brown INA103 instrumentation amplifier IC. A three-position toggle switch sets its gain at 0, 20 or 40 dB. The second stage uses one triode of a selected USA-made N.O.S. 5687 tube and has continuously variable gain up to 22 dB. Thus, overall gain is 0-62 dB in three ranges. The other triode of each channel's 5687 is used in cathode follower mode as a low-impedance output line driver.
• External power supply: VIHYB uses an external power supply so that the preamp itself may have an uncrowded layout in a rack-efficient one-rack-unit enclosure. This also eliminates magnetic coupling between the power and audio transformers as a source of noise. Each external power supply can serve up to two VIHYB rack modules (four channels).

Back to Custom Mic Preamp Main Page

Back to Clark Huckaby Main Page

Copyright 2005 Clark Huckaby. All rights reserved. Commercial use of this content without first obtaining the expressed permission of Clark Huckaby is prohibited by law. Distribution of copies beyond personal use and/or re-posting of this page is prohibited by law.