icon Audio Stereo 25 MK II User Manual

Page 1
icon Audio
Instruction Manual Covering:
Stereo 25 MK II
Ultralinear Push Pull Amplifier EL34 or KT88
Standard version with KT88s
Contents
1 Introduction & Final Inspection
2 Quick Set Up Guide
3 Connecting inputs & outputs
4 Getting the best performance
5 Trouble Shooting
6 Bias Adjustment, Triode mode
7 Valve Replacement
8 Specifications
9 Guarantee
10 Packing Instructions
1 Introduction
Thank you for purchasing the Stereo 25 .
A great deal of care has been taken in the design,
selection of components and production of this
amplifier. We are sure that you will hear the
difference.
In order to get the best out of your amplifier,
please read the enclosed notes. Even if you are
experienced with hi fi please read the ‘quick set
up guide’. Should you be uncertain about
anything to do with your amplifier please contact
us for advice.
Hi fi reproduction is a long chain of events that
includes the recording, editing, mixing etc, before
being transferred to a medium such as LP, CD, or
FM, before being played through your own source
unit, the amplifier and finally loudspeakers.
Your room acoustics will also affect the sound
before it finally reaches your ear. Whilst the
amplifier is arguably the most important part of a
system, it is important to remember that the
weakest link will always affect the final results
when making judgements. And not all recordings
are have a good “balanced” sound, therefore an
amplifier which faithfully reproduces the input
signal will also reproduce imperfections in the
tonal balance and the recording itself. Setting up
and judgements should be made with a ‘clean’
well balanced recording.
The Stereo 25 is a push-pull Ultralinear
stereo power amp, capable of running in
Ultralinear mode (half pentode and half triode).
Using the excellent 6L6/EL34/6CA7/KT66/KT88
valves. These are in semi auto-bias mode which
whilst rarely requiring attention gives maximum
power, cool running and wear indication. The
driver and phase splitting is all triode for best
sound quality and low noise. The pre-amp is a
high quality ‘Passive’ circuit using silver PTFE
audio cable and an ALPS ‘blue’ volume control. It
is sensitive enough to be used with all modern
source equipment having an output of 300mv or
greater. It may also be used as a power amplifier
being driven by a separate pre amplifier. Its
simplicity coupled with point to point hand wiring
without the use of printed circuit boards results in
an open euphoric sound that is wonderfully
detailed and warm sounding. The overall design is
inspired by the Leak Stereo 50 design. The wide
range of output valves that ST25 is capable of
using make it extremely versatile and you can
customise it to your own taste. Recommended
upgrades are Mundorf capacitors and various
output and driver valves.
IMPORTANT!
THIS MANUAL CONTAINS
ESSENTIAL INFORMATION
FOR THE HEALTH & SAFETY
OF YOUR AMPLIFIER. PLEASE
READ & KEEP SAFE AND
REFER TO IF NECESSARY

icon Audio Stereo 25 MK II Specifications

General

Frequency Response	20Hz - 20kHz
Input Impedance	100kΩ
Output Impedance	4Ω, 8Ω
Input Sensitivity	250mV
Power Consumption	120W
Power Output	25W per channel
Total Harmonic Distortion	<0.1%
Valve complement	4 x EL34
Signal to Noise Ratio	90dB

Summary

Introduction and Initial Checks

Final Inspection - Your Guarantee of Quality

Overview of rigorous final inspection and listening tests performed by Icon Audio for optimum performance.

Quick Set Up Guide

Connecting Inputs and Outputs

Bluetooth Operation

Guide for pairing and using the Bluetooth feature on the amplifier.

Using the ST25 as a Power Amplifier

Instructions for operating the amplifier in a pure power amplifier configuration.

Connecting Loudspeakers

Guidelines for connecting speakers, including polarity and cable choice.

Headphone Operation

Information on the amplifier's dedicated headphone circuit and usage.

Getting the Best Performance

Amplifier Dead Troubleshooting

Steps to diagnose and resolve issues if the amplifier appears dead, checking fuses and connections.

Valve Warm-up and Care

Guidance on valve warm-up, lifespan, and cabinet cleaning.

Changing and Upgrading Valves

Guidance on replacing and upgrading valves for better performance.

Trouble Shooting

Distorted Sound Diagnosis

Steps to diagnose and resolve distorted audio output from the amplifier.

Speaker Noise Issues

Advice on identifying and fixing unusual noises or hums from the speakers.

Bias Adjustment and Setting

Hum Problems Resolution

Methods to identify and resolve hum issues experienced with the audio output.

Valve Replacement Guidance

General advice and considerations for replacing amplifier valves.

Bias Checking and Adjustment

Detailed steps for checking and adjusting the bias voltage for optimal amplifier performance.

Triode Operation Mode

Details on the 'Pure Triode' modification and its effect on output.

Valve Replacement and Problems

Valve Replacement Safety

Critical safety precautions related to high voltages and hot valves when servicing.

Detailed Valve Changing Procedure

Step-by-step guide for safely replacing output valves, including bias checks.

Specification and Features

Guarantee and Shipping

Warranty Exclusions

Details on warranty exclusions and conditions for claims.

Packing Instructions