Cornell Acoustic Setup guide

CORNELL AMPLIFICATION
OWNERS
INSTRUCTION MANUAL
Acoustic Amp
D.C.Developments
MUSICAL EQUIPMENT DESIGN & DEVELOPMENTS
Unit13 Ross hill Industrial Park Sutton Road Southend-on-Sea Essex SS2 5PZ
Telephone [phone]

INDEX
1. INTRODUCTION
CONSTRUCTION & DESIGN
2. TECHNICAL DESIGN
3. CONTROLS
4. THE SPECIFICATIONS
5. TUBE REPLACEMENT
& VALVE FAILURE
Please Read all instructions before operating unit!
If you require any further information regarding the Acoustic amplifier or other
CORNELL products, please do not hesitate to contact us.
CORNELL EQUIPMENT DESIGN & DEVELOPMENT
www.dcdevelopments.com Telephone [phone]
WWW. DCDEVELOPMENTS.COM

INTRODUCTION
Thank you for choosing a Cornell Acoustic amplifier.
Your amplifier employs valve technology. It is hand built to MOD standards. Only top
quality components are used so that you can enjoy years of professional use.
Please take time to read this manual, to ensure that you get the best
from your amplifier.
Amplifiers of today try to offer a wide range of tones and sounds resulting in a mass of
controls that can confuse even the most enthusiastic fiddler.
The result of this is that most amplifiers of today sound the same with a noticeable loss of
natural tone that can only be reproduced by simple design and point to point wiring.
Before Operating your amplifier Please Read these Important Safety
Instructions.
Do not operate or use close to or in wet, damp, conditions, keep away from liquid.
Do not operate or use close to any Heat sources such as radiators, power lighting,
Cooking stoves, fires, or any direct source of heat.
Do not cover or block any ventilation openings. These may be on the top or on the back.
This product must be Earthed. It will come with a 3 pin plug or 3 pin outlet connector
It is for your safety that all terminals are used and go directly back to the wall socket.
Speaker Output.
There is a risk of electrical shock from the speaker output terminals.
Never operate the amplifier without the speaker outlet being connect to the correct
speaker impedance.
Servicing.
Refer All servicing to a qualified service person.
Should a problem occur make sure the amplifier is un-plugged and not connecter to a
mains supply then Contact a service person.
We do recommend that you change the valves yourself, should you attempt to change a
valve remember to disconnect the unit from the wall so no mains voltage is present in the
unit. Remember Valves are hot and can burn the skin so always allow 10 to 15 minutes to
them to cool.
WARNING:
TO PREVENT DAMAGE, FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS UNIT TO
RAIN OR MOISTURE.
NO USER SERVICEABLE PARTS INSIDE, REFER SERVICING TO QUALIFIED
PERSONNEL ONLY.
THIS UNIT MUST BE EARTH GROUNDED.
P.1

TECHNICAL DESIGN
Making bespoke guitar amplifiers and with the advent of acoustic guitars it is no surprise to
get a request for a quality custom acoustic amp. Not having made one before i was
surprised that the main request was to simply amplify the tone from the expensive guitars
that the customer owned. What was more surprising there seem to be next to nothing on
the market that was not full of digital effects and numerous controls that coloured the
natural tone.
Virtually all modern amplifiers are built using printed circuit boards, which contain conductor
tracks that connect components together, these conductor tracks often run very close to
one another. When this happens a small capacitance is produced between them, the result
of which is a substantial loss in both high frequency response and harmonic richness.
The Cornell Acoustic amplifier is designed to avoid this by having specific point to point
wiring.
Components in the amplifier are mounted on a specially designed board using eyelets and
Turret Tag’s that are hand riveted onto the board where the components are mounted.
These components are then sealed using a conformal coating to prevent noise and
reduction of component life caused by moisture penetration.
The steel chassis holds specially designed, interleaved, transformers, wound with
impregnated paper. The design ensures a very close reproduction of the full harmonic
spectrum of your guitar’s pick-ups.
The cabinet is made of a rigid construction using high quality Pine and Ply wood. The
covering is both heavy duty and burn resistant, The cabinet is handsomely finished and
features original fittings.
The pre-amp is designed to be simple in use, and yet produce the wide range of sounds
that the musician of today expects from a professional amplifier.
The ‘Tone controls are designed to work over the entire frequency range of your guitar,
allowing for increased amounts of low and high frequency adjustment.
The Output stage.
The output design is a Class ‘AB’ and is achieved by means of a negative voltage applied
to the grid of the output valves,
Cathode bias resistors are also employed to stabilise current flow throughout the life-time of
the valve. The voltage across each resistor will vary with the valves characteristics. When
these voltages are equal, then each valve is drawing the same amount of current and the
valve set is ‘matched’ resulting in maximum output and long life.
P.2

THE CONTROLS
1. INPUT Hi & Lo.
High impedance input is for instruments without a built in amplifier or high output
Coil type pickups.
Input Hi provides more gain than the Lo input Both Hi and Low inputs can be used
It is not essential to use one type use to your own taste.
2. VOLUME.
Adjusts the gain of the pre-amp and is used in conjunction with the
MASTER control to set the overall volume of the amplifier.
3. BASS.
Adjusts the amount of low frequency boost.
4. TREBLE.
Adjusts the amount of high frequency, the pull switch lowers the frequency.
5. MIDDLE.
Adjusts the amount of mid frequency boost.
6. MASTER
Controls the signal going to the output stage and is after the return loop so will
Adjust any effect output level.
7. MAINS.
When illuminated the valve heaters are on and there is power to the amplifier.
8. STANDBY.
When operated cuts the HT voltage to the amplifier.
9 4 & 8 ohms output
Out-put speaker impedance.
If you have a CORNELL Extension Speaker cabinet set this switch to 4 Ohms.
10 Send / Return FX Loop
Connect the send output to the input on the pedal of the effects unit, the send signal
Is controlled by the volume control. Connect the Return socket to the output of the
pedal or effects unit this is controlled by the Master Control.
MAINS SWITCH operation.
Do not operate mains switch without a 30 second delay between operations.
There is an internal thermistor to reduce mains surges. This thermistor works by
introducing a resistance when switched on, after a few Seconds the thermistor is
heated and the resistance is reduced. When switched off it then takes a few
seconds to cool and retain its resistance before the nexed switch on.
Mains and HT Fuse
The fuse holders contains the mains and HT fuse to the amplifier and
protects the amplifier from electrical faults.
Replace a failed fuse only with the same type and rating.
! 
P.3

THE SPECIFICATIONS
POWER..............................................120 Volt A-C 60hz 140 Watts US Model
230 Volt A-C 50hz 140Watts GB Model
FUSE..................................................T3 Amp for the 120 Volt US Model
T2 Amp for the 230Volt GB Model
HT 250 m/Amp
INPUT IMPEDANCE.................... Input HI 10 Meg Ohm. Input
LO 100k Ohm.
CONTROLS...................................... Pre-amp volume, Bass, Middle,Treble. Master
OUTPUT........................................... 50 Watt R.M.S Class ‘AB’.
CABINET.......................................... plywood. Head
Pine and Ply cabinet
Dimensions
Height. 20 1/2 in 520mm Width. 19 1/2in 485mm Depth. 9 1/2 in 240 mm
WEIGHT.
45 lbs 20.5 Kgs.
OPTIONAL ON REQUEST....... Colours, Speaker cabinet.
P.4

Tube Replacement
Tube life varies depending upon playing style and application. Power tubes have a much
shorter life than pre-amp tubes which can last for years.
To maintain the optimum performance of your amplifier, the tubes should only be replaced
with the same type tubes as specified on the tube illustration below.
When changing tubes, ALWAYS unplug the amplifier and remember that the
TUBES ARE HOT! wait for the tubes to cool or replace tubes when amplifier has not been
used for several hours.
Your amplifier has 5 valves, three pre-amp valves 12AX7 or ECC83,and the phase splitter
is a 12AT7 ECC81, there are also two power valves 5881.
Valve Failure.
When a valve breaks down its internal elements can short. This can cause major
damage to the internal components of the amplifier and also be a possible fire risk.
There are two fuses that will break under fault conditions. The fuse mounted on the back
panel and their are others in the chassis remember to replace the fuses with the same
type and rating.
Remember we are always happy to assist in anyway we can so please do not
hesitate to contact us.
Chassis Valve Line up
Mains
Transformer Output
Transformer
5881 5881 ECC83 ECC83
Front panel
CAUTION CHASSIS SERVICE HOT
P.5
ECC81