UNI-PRE 3 KNOB

Universal Active/Passive Bass Preamp System

Important Note: Before removing any components from the card it is essential to follow the Pre-Installation Checks. Warranty is only valid once checks are completed.

Overview & Technical Specifications

Technical Features

Totally independent active and passive signal paths
Custom designed pots for optimal control placement
Class A FET input stages for great sound quality
Two gain trim preset adjusters (0-12dB each) for pickup matching
Internally adjustable bass control frequency window
Internally adjustable treble shelf frequency
Mid control with frequency sweep (100Hz – 2.5kHz)
Selectable flat response or pre-shaper contour
Modular design with pluggable inter-connections
Screw terminals for all external connections
Plug-in tone caps to allow easy swapping of the cap value for different roll-off Passive Tone frequencies

Dual Active/Passive Signal Paths

Purpose of Dual Signal Paths

The UNI-PRE’s unique dual path system provides separate active and passive signal paths controlled from the same knobs. This is particularly useful for:

Smooth blending: Guarantees totally smooth blend in active mode
Pickup compatibility: Works with non-matched pickups of different types and outputs
Backup option: Passive signal is always available even without battery power
Tonal flexibility: Access to both classic passive tone and enhanced active tone

Technical Specifications

Flat response. Neutral response setting.
Pre-shape. Gentle lift at low and high frequencies, peaking at +4 dB at 40 Hz and 10 kHz.
Pickup gain. Internal trimmers, 0 to +12 dB per pickup in active mode.
Bass control. ±18 dB cut and boost with internally adjustable bass window.
Bass window. Lower frequency filter 20 to 80 Hz, higher frequency filter 40 to 200 Hz.
Mid control. ±14 dB cut and boost with frequency sweep from 100 Hz to 2.5 kHz.
Treble control. ±18 dB with internally set shelf frequency from 1 kHz to 7.5 kHz. Pull for bright, peaking at 10 kHz.

Pre-Installation Checks

Important: Before installation, check that your bass’s cavity is suitable for the UNI-PRE modular system. Ensure there’s adequate space for the separate Volume/Blend and EQ modules, plus wiring connections.

Your Uni-Pre is supplied mounted on a card with a test lead terminated with a 3.5 mm stereo Jack for test purposes. If you are installing into a plate, you can use the spacers as fitted to the card, or if you are mounting directly into the body, there are additional nuts and washers supplied. If you are using metal knobs, it is essential to include the supplied springs beneath knobs for grounding.

Pre-Installation Test Setup

Pre-Installation Connection Diagram

UNI-PRE Controls

Standard Pre-Installation Test Procedure

Turn down the input of your bass rig.
Connect a mono instrument lead between the output jack of the preamp and your bass rig.
Connect a 9v battery to the battery clip on the UNI-PRE system.
Connect the supplied stereo test lead to a high-quality audio player. This mimics a pick-up input to test the functions of the preamp before installation in case there are any pre-existing issues with the pickups or existing wiring.
Turn up the input on your bass rig to a suitable level to check for clean audio.
Turn up the Volume knob and test that sound is coming through your bass rig.
Switch the Active Passive toggle and experiment with the controls to familiarise yourself with the functions shown in the diagram above.

Control & Functions

VOLUME & BLEND STACK

Volume (Upper Knob): Sets the output level for both active and passive paths simultaneously.

Blend (Lower Outer Knob): Sets both the active and passive blend mix for the pickups: ACW for bridge pickup alone and CW for the neck pickup alone. A click midway gives an equal mix of both pickups if they are balanced.

Plug-in Tone Shaping Caps: For additional fine tuning of the passive tone control. These allow easy swapping of the cap value for different roll-off frequencies.

Note: Internal Gain Trims (0-12dB) allow the pickup levels to be adjusted and/or matched for perfect balance.

BASS & TREBLE STACK

Bass (Lower Outer Knob): Bass Boost/Cut or Boost only, set according to Jumper Link on circuit board. Controls the level of low end content according to the ‘Bass Window’ settings on the circuit board. A centre click is included.

Treble (Upper Knob): Boost/Cut knob, controls the higher frequency spectrum according to the setting of the internal Treble Shelf Frequency adjustment. Pull for Bright, adds ‘high end sizzle’ sheen. A neutral setting is provided with a centre click.

MID & FREQUENCY STACK

Mid (Upper Knob): Controls the level of Mid Boost/Cut at frequencies according to the setting of the Mid Frequency knob. A neutral setting is provided with a centre click.

Frequency (Lower Outer Knob): Continuously variable Mid Frequency Sweep from 100Hz to 2.5kHz.

ACTIVE/PASSIVE TOGGLE SWITCH

Location: Mounted on circuit board

Active Mode: Engages active signal path with full EQ control

Passive Mode: Engages passive signal path (always available even without power)

Power: The power is switched on automatically when a MONO JACK is plugged into the Output Jack Socket.

Control Functions Summary

UNI-PRE 3 Knob Control Functions

ACTIVE MODE FUNCTIONS

VOLUME: Active output level control

BLEND: Active pickup blending

BASS: +/- 18dB Boost/Cut

MID: +/- 14dB with Frequency Sweep

TREBLE: +/- 18dB with Bright pull switch

GAIN TRIM: 0-12dB per pickup

RESPONSE: Flat or Pre-Shape contour

PASSIVE MODE FUNCTIONS

VOLUME: Passive volume control

BLEND: Passive pickup blending

TONE: Plug-in tone caps (optional)

PICKUPS: Direct pickup signal

NOTE: Always available even without battery power

EQ CONTROLS: Bypassed in passive mode

Installation & Connections

Tools & Materials Required

Screwdriver 1.8mm slotted (flat-blade) for connection screw terminals
Hex driver / Allen key 2mm for knob grub screws, also 1.5mm required for Fender style knobs
Soft cloth to protect the instrument surrounding the cavity
New 9v battery

You may also need

Adhesive-backed copper foil for proper grounding
Soldering iron (for grounding connections)
Wire cutters/strippers to prepare the pickup wires
Tools to remove existing control plate etc.

GROUNDING – IMPORTANT!

If you are using metal knobs, it is essential to include the supplied springs beneath knobs for grounding.
All pots shafts need to be substantially electrically grounded.
This is best achieved using adhesive backed copper foil on the internal face the pots are mounted to.
Conductive paint is fine for screening purposes, but DO NOT RELY ON IT to ground the UNI-PRE pots.
Affix an appropriate piece of adhesive copper foil all over the area the pots will be mounted against.
If you cannot find en existing Ground wire you may need to attach a new one to the copper foil as a ‘star’ screening point.
Solder any other ground wires, such as the bridge and pickup cavity screens, close to the star point.

Installation Steps

Prepare the cavity with adhesive copper foil for proper grounding as described above.
Note the arrangement of spacers, washers and nuts as provided on the card. If you are mounting onto a plate you will likely reassemble the parts as provided with spacers. If mounting directly into the body, there are extra nuts and washers provided.
Disassemble the knobs and hardware from the card.
Remove the test lead from the pickup screw terminals.
Set internal jumper links on the EQ module according to desired configuration (see diagram below).
Connect pickup wires to the screw terminals on the Volume/Blend module: HOT (signal) and COLD/GND (ground) for each pickup.
Identify the existing Ground wire within the bass cavity, strip the insulation back 5mm and insert it into the screw terminal of the trailing green wire that is attached to the Jack socket of the uni-Pre.
Mount the potentiometers in the control plate or body, ensuring they are properly grounded to the copper foil.
Before final assembly, test all functions with a temporary battery connection.
Once confirmed working, secure all modules and wiring, ensuring nothing is pinched or stressed.
Fit the knobs. Ensure the upper knobs have a slight gap below for smooth operation. If you have metal knobs ensure the supplied grounding springs are fitted below the upper knobs.

Knob Grounding Springs

Fit on pot shaft with larger coil upwards.

Rubber Washer (Optional for 7mm Shafts)

Volume/Blend Circuit Board Connections & Settings,
Passive Tone Caps & Gain Trims

Volume/Blend Circuit Board Connections and Settings

EQ Module Jumper Settings

Set Bass Control (Boost/Cut or Boost Only), Mid Control (On/Off), and Response (Flat or Pre-Shape) using jumper links.

Warranty Information

Guarantee

Your East product is guaranteed to be free from defects in materials and workmanship for a period of one year from the date of original purchase.

If during the guarantee period your product becomes faulty due to defective materials or workmanship, then the unit will be repaired or replaced without charge for parts or labour at the discretion of East UK, according to the conditions below.

Conditions

The original sales invoice or receipt indicating the date of purchase and sales outlet is presented together with the faulty unit.
The unit was installed competently consistent with the instructions supplied.

What Is Not Covered

Damage due to accident or improper handling, installation or operation.
Defects caused by the instrument or system to which the unit has been installed.
Damage resulting from repair of the unit carried out by non-authorised service personnel.
The costs of transport or shipping costs relating directly or indirectly to the guarantee of this product.

Proper Disposal

To dispose of electrical goods safely, follow these simple steps:

Check Local Rules

Find out if there are any specific laws in your area about disposing of electrical waste. Many regions have special regulations for electronic equipment.

Recycle

Take your old electrical items to a local recycling centre. They can handle many types of electronics and appliances and ensure materials are properly processed.

Donate

If your item still works, consider donating it to a bass player who has yet to discover the wonders of our active bass technology.

Waste Electrical & Electronic Equipment Compliance

East Tone UK comply to WEE/MM6881AA.

By disposing of your electrical goods properly, you help protect the environment!

East UK Customer Service

For technical support or warranty inquiries, please contact:

www.east-uk.com | tech@east-uk.com