Fivefish Vt-73 User manual

FiveFish

Studios

VT-73 Hybrid-Tube Mic Preamp Kit

Assembly Guide

No part of this document may be reproduced, either mechanically or electronically, posted online on the Internet,

in whole or in part, without the expressed, written permission of FiveFish Audio. This document is solely provided

to the kit builder of the VT-73 Hybrid-Tube Mic Preamp.

veshaudio.com

Assembly Guide Revision 1.2 - 201760804

Dear Customer,

ank you for purchasing our VT-73 Hybrid Tube Mic Preamp Kit.

Great care has been taken to make this assembly guide complete and as accurate as possible.

Our goal is to make your assembly work easy and trouble-free, and deliver to you a working,

reliable, and high-performance mic preamplier.

is assembly guide is a work in progress and we’re continually working to improve it. As

always, we welcome the input of the DIY community if you have any comments, suggestions,

or additional information that you think will be helpful for inclusion in this assembly guide.

If you have any questions that are not covered by this assembly guide, please feel free to

Sincerely,

FiveFish Team

FiveFish

Studios

FiveFish Audio www.veshaudio.com

GENERAL

This assembly guide must be reviewed for familiarization

with safety markings and instructions before assembly of

the Mic Preamp kit.

BEFORE APPLYING POWER

Verify that all components and parts are inserted in the

right location and correct orientation. Visually inspect

that there are no cold solder joints, or short-circuits.

The WARNING sign denotes a hazard. Pay attention

to the procedure, instructions, or the like, which if not

correctly performed could result in damage to your

equipment, electronic component or personal injury.

SAFETY CONSIDERATIONS

Any interruption or disconnection, or lack of connection of

the protective earth terminal/safety ground may cause a

potential electric shock hazard that could result in personal

injury. (Grounding one conductor of a two conductor outlet

is not sufcient protection).

This mic preamp module is designed to be plug-in into

an API 500 series rack or compatible unit. DC Power is

supplied by the 500 series rack to this module.

It is strongly suggested that you use a lab power supply

the rst-time you power your mic preamp project. If

you made any mistake during assembly of this kit (for

example: components inserted in wrong location, wrong

orientation, short-circuit in your soldering job, etc.) you will

not be subjecting the built-in power supply of your rack

to the problem, and avoid damaging your power supply.

If you don’t have a lab power supply and instead will be

using your rack to power directly this project the rst time,

I recommend using an extender card with built-in fuses

to protect your rack power supply from accidental shorts

or over-current. (The in-line fuses will blow if there is

overcurrent or short-circuit condition, thus protecting the

rack power supply).

GENERAL INFORMATION

1. DESCRIPTION

The VT-73 Mic Preamp Kit is a Hybrid Solid-State/Vacuum Tube mic preamp designed for use with API 500 Series lunchboxes or

racks.

The VT-73 design uses a high-performance THAT amplier chip as the primary First Stage amplier. This allows us to have a very

quiet, balanced input front end without the need for an Input Transformer. Voltage gain for the First Stage is set using a single-turn

potentiometer to allow for a wide and continuous range of dB gain. There is also RFI input and output protection and built-in 48V

short-circuit protection to protect the preamp from damage.

The output of the First Stage is fed to the Second Stage Tube amplier, for additional signal processing. This Second Stage also

generates the Second-Order Harmonics added to our original signal. Second Stage output is controlled by a second potentiometer

that can limit the output level of the Mic Preamp. A Third Stage amplier allows for an optional +12dB Signal Boost, and also drives

our Output Transformer for a Balanced Output.

The VT-73 uses separate push-button switches for 48V Phantom Power, -20dB Pad, Polarity Reverse, and Gain Boost. The kit

builder can also wire optional 3mm LED indicators for each switch to indicate when the function is enabled.

The VT-73 requires a dual power supply (+/-15V to +/-18 Volts) and +48Volts for phantom power for proper operation.

2. TOOLS & EQUIPMENT REQUIRED

A few basic tools and equipment are required to assemble this kit. These basic tools are not supplied with the kit.

2.1. Soldering Iron and Lead - We recommend a temperature adjustable soldering iron. DO NOT USE A 100 WATT

SOLDERING GUN. A small to medium-sized soldering tip is required to solder the small parts. You may use Lead-free or

60/40 lead-based solder.

2.2 Cutter - You will need a cutter to cut component leads and wires.

2.3. Solder Sucker Pump - If you made a mistake and need to desolder a component, you’ll need one.

2.4. Multitester - Used for measuring resistance, continuity, and voltages.

2.5. Magnier & Lamp - I recommend a clean and well-lighted space for your assembly area.

2.6. Other Tools (not required, but nice to have) - Component lead bender, vise, tweezers, wire stripper.

3. ASSEMBLY GUIDE

BEFORE YOU BEGIN: Pick a clean work area where you can leave your work-in-progress unattended if you need to.

Keep individual components in their labeled zip bag until you’re ready to solder them. Kit components have been sorted and

labeled for your convenience. The labeled components lessens chances of insertion errors, inserting the wrong component into

the wrong location. Keeping the components in their zip bags also reduces chance of small parts getting lost or misplaced.

Best practice is to solder the smallest and/or shortest components rst. Then solder the taller and larger components next. Big

bulkier components like switches, jacks, big capacitors are soldered last.

NOTE: The photos shown on this assembly guide are Rev.1.1 PCBs.

Your PCB Revision may be later but assembly instructions are

generally the same.

There are ERRATA corrections for the Rev 1.1 PCB version.

Please visit Section 4.0 for details.

Photo of a nished VT-73 Mic Preamp

3.1 Solder all 1/4 watt Resistors.

ERRATA: Solder a jumper wire across RTUBE resistor location.

See Section 4.0 for other ERRATA corrections (R20, R21, R22)

3.2 Solder all Signal Diodes and Rectier Diodes.

IMPORTANT: Diodes must be installed in the correct orientation. Observe where the “white band” is located on the board

silkscreen marking, and orient the Diodes to follow the same direction.

3.3 Solder all Ceramic capacitors.

3.4 Solder the (3) IC Sockets.

TIP: One side of the IC socket will have a notch. Position this notch on the left-side, or on top for use as a guide for Pin1

location.

3.5 Solder the (2) PDIP Relays. Take note of the Relay part number that came with your kit and follow the next step.

IMPORTANT: Insert Relays in proper orientation. Match the “white band” on PCB silkscreen with the Relay’s line markings.

If your kit came with A12W-K Relays, solder the 7812

Voltage Regulator at IC4 location. You can use the heatsink

provided and mount it vertically, or bend the legs and

secure 7812 metal tab with machine screw and nut at on

the PCB board.

If your kit came with A18W-K Relays, Do NOT install the

7812 Voltage Regulator. Instead, solder a JUMPER wire

across pin 1 and pin 3 of IC4 location.

3.6 Solder the 0.1uf WIMA, C24 capacitor (Color Red).

3.7 Solder all small Electrolytic Capacitors. These capacitors have polarity markings, one lead is (+) and the other lead is (-).

ERRATA: Use 47uf/50V for C25 location.

IMPORTANT: Observe the proper polarity when inserting these capacitors. Match polarity with PCB silkscreen markings. All

negative (-) leads of electrolytic capacitors are orientated facing downwards.

3.8 Solder Q1 Transistor.

IMPORTANT: Observe proper orientation and the direction transistor is facing. Follow the PCB silkscreen markings.

3.9 Solder all 3mm LED indicator lamps from bottom of board. These LED lamps are optional and not required.

You can arrange the LED colors any way you want. But for consistency, use the same color arrangement on all mic preamp

kits you’ll build.

A typical color arrangement may be

GREEN - for phantom power switch,

BLUE - for 20dB Pad,

YELLOW - for polarity reverse,

RED - for +12dB Boost

IMPORTANT: LONG LEG of the LED must

be oriented at the BOTTOM position as

shown.

NOTE: LEDs are installed from the bottom.

Bend LED legs as shown on photos.

3.10 Photo showing how the (4) LEDs will show through the Aluminum cut-out panel. Note: Do NOT attach the panel yet.

NOTE: LEDs are mounted at the bottom of the PCB.

3.11 Solder the (4) Push-Button switches. Make sure they’re mounted horizontally level and not crooked or mis-aligned.

TIP: You may use masking tape to hold the switch secure in it’s place while you solder. Solder only one of the switch

terminals and review if the switch is still horizontally level. If everything looks good, solder the rest of the switch terminals.

3.12 Solder all medium-sized 220uf electrolytic capacitors.

IMPORTANT: Observe proper polarity and orientation of (+) and (-) leads.

Table of contents

Other FiveFish Amplifier manuals

FiveFish

FiveFish SK-1DI User manual

FiveFish

FiveFish X-12 User manual

Popular Amplifier manuals by other brands

Sonance

Sonance Sonamp 875D MKII Specification sheet

Clarity

Clarity C120 user guide

Sony

Sony TA-F444ESX Service manual

NAD

NAD D 3020 Service manual

Marantz

Marantz PM6007 quick start guide

Rotel

Rotel RA-931 owner's manual

Philips

Philips TDA6103Q datasheet

Fender

Fender FM25DSP owner's manual

Cary Audio Design

Cary Audio Design SLP-94 operating manual

Custom Valve 80

Custom Valve 80 Traynor YCV80 owner's manual

ASL INTERCOM

ASL INTERCOM iPAM400 product manual

DR. Z Amplification

DR. Z Amplification Prescription ES owner's manual

Pyle

Pyle PP444 user manual

Onkyo

Onkyo TX-904 instruction manual

Marantz

Marantz PM-11S1 Specifications

BRUEL & KJAER

BRUEL & KJAER 2712 instruction manual

BRUEL & KJAER

BRUEL & KJAER 2671-W-001 Product data

Crown

Crown XS500 Operation manual

FiveFish VT-73 User manual

Popular Amplifier manuals by other brands