© 2000-2007 CORNELL Musical Equipment Design & Development 1
Custom 40
&
Custom 80
Owner’s Manual
DC Developments
Musical Equipment Design & Development
Unit 13 Rosshill Industrial Park, Southend-on-sea, Essex SS2 5PZ England
Tel/Fax +44 (0)1702 610964
www.dc-developments.com
© 2000-2007 CORNELL Musical Equipment Design & Development 2
CONTENTS
Introduction 3
Construction and Design 3
Technical Design 4
The Pre-amplifier
The Output Stage
Controls 5
Specifications 6
Valve Replacement 7
Block Diagram 8
Mains Transformer Connections 8
Please read all instructions before operating the amp!
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 earthed. Use the correct mains cord.
If you require any further information regarding the Custom 40 or Custom 80
amplifier, or any other CORNELL products, please do not hesitate in contacting us
(details on front page).
© 2000-2007 CORNELL Musical Equipment Design & Development 3
Introduction
Thank you for choosing a Cornell Custom 40 / Custom 80 amplifier.
Your amplifier employs valve technology, and is hand built to the highest standards.
Only top quality components are used in our amplifiers, so that you can enjoy years
of trouble-free use.
Please take time to read this manual, to ensure that you get the best from your
Custom 40 / Custom 80 amplifier.
Construction and Design
Virtually all modern amplifiers are built using printed circuit boards, which helps to
speed up production and keep down costs. There is, however, one major drawback
with printed circuits - conductor tracks that connect components together often run
very close to one another, creating a small capacitance. The result of this in a
guitar amplifier is a substantial loss in both high frequency response and harmonic
richness.
Cornell amplifiers are designed to avoid this by having point-to-point wiring
throughout. Components are mounted onto a specially designed component board
which is then sealed, using a conformal coating to prevent noise and the reduction
of component life caused by moisture penetration.
The hand wiring, carried out by our highly-trained staff, takes time but ensures that
each of our amplifiers performs to the highest standards of reliability and sound.
The stainless steel chassis holds our specially-designed transformers, and chassis-
mounted (rather than circuit-board mounted) valves (tubes).
Such attention to detail ensures a very close reproduction of the full harmonic
spectrum of your guitar’s pick-ups, resulting in a pure, natural sound that will turn
heads at any venue and/or that records superbly.
© 2000-2007 CORNELL Musical Equipment Design & Development 4
Technical Design
The Pre-amplifier
The Custom 40 / Custom 80 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 BASS and TREBLE controls work over the entire frequency range of your
guitar, allowing for increased amounts of low and high frequency adjustment.
The Output Stage
The Custom 40 / Custom 80 amplifier output stage is Class AB1, which means
that the grids of the output valves are controlled by a negative bias voltage.
The method used in biasing greatly affects the tone of the amplifier.
Should the bias be set too high, then crossover distortion occurs and is constantly
present in the sound of the amplifier, creating a ‘fuzzy’ tone. If the bias voltage is
set too low, then the valves might start to glow red, which will considerably reduce
their life and result in expensive replacement.
It is recommended that a qualified engineer re-biases the output valves when
replacements are first used.
The output transformer of the Custom 40 / Custom 80 has a small, independent
winding that picks up the signal being produced in the final stage of the
amplification process. As the winding is in the output transformer itself, it will
exactly reproduce the signal appearing at the speakers. This output is used to feed
the line output, reproducing the sound of your guitar as accurately as possible.
This output is isolated from the chassis, ensuring that no earth loop (and the
resultant hum) can be produced when connected to a mixer or external power amp.
© 2000-2007 CORNELL Musical Equipment Design & Development 5
Controls
1. Input - Hi & Lo
Both inputs offer high impedance connections for instruments.
The Hi input provides 6dB more gain than the Lo input.
2. Volume
Adjusts the overall volume of the amplifier.
3. Bass
Adjusts the amount of low frequency boost.
4. Treble
Adjusts the amount of high frequency boost.
5. Mains Indicator
When illuminated, this shows that the valve heaters are on, and that there is
power to the amplifier.
6. Standby
Connects power to the valves for operation. Use standby mode for breaks in
usage (eg, between performance sets)
7. Output Switch
Output LOW position operates the power of the amplifier at 1/4 of its normal
output. Output HIGH position returns the amplifier to its full output.
8. Line Output
The 3-pin male socket on the base of the chassis next to the output valves is
a 600 Ohm line output, for use with a mixer or external power amplifier.
Pins 2 and 3 are ‘live’ (balanced output) and pin 1 is chassis earth.
9. Impedance Switch
The switch at the base of the chassis, next to the line output, is the impedance
switch. This switch should be pointing inward for normal use (8 Ohm internal
speakers only, or 8 Ohm external speakers with the internal speakers
disconnected) and should be switched to point outward for use when an 8
Ohm extension cabinet is used in parallel with the internal speakers (or some
other combination totalling 4 Ohms). Using the correct impedance selection
enables the amp to deliver maximum power to the speakers.
10. Mains Fuse
The fuseholder contains the mains fuse for the amplifier. The mains fuse
protects the amplifier from electrical faults.
Replace a failed fuse only with the same type and rating.
Do not operate the mains switch without a 30 second delay between
operations. There is an internal thermistor to reduce mains surges. This
protects the amp and helps to ensure a long life for the components. The
thermistor works by introducing a resistance in the circuit when the power is
switched on. Within a few seconds the thermistor heats up and its resistance
reduces, allowing the full current to flow into the mains transformer. After
switching off the amp, it takes a few seconds for the thermistor to cool down
and to return to its initial, protective resistance value.
© 2000-2007 CORNELL Musical Equipment Design & Development 6
Specifications
POWER Custom 40 ....................... 230 Volt AC, 50Hz, 120 Watts
115 Volt AC, 60Hz, 120 Watts
Custom 80 ....................... 230 Volt AC, 50Hz, 280 Watts
115 Volt AC, 60Hz, 280 Watts
FUSES Custom 40 ........................ 1 Amp, 240v Slo-blow for the 230v model
2 Amp, 120v Slo-blow for the 115v model
Custom 80 ........................ 2 Amp, 240v Slo-blow for the
230v model
4 Amp, 120v Slo-blow for the 115v model
INPUT IMPEDANCE ...................... Hi - 2.2 MegOhm: Lo - 136 kOhm
CONTROLS .................................... Volume, Bass, Treble
(Reverb optional extra)
LINE OUTPUT ..……..……………... Coil tapped from output transformer
600 Ohms at 0.25 Watt
OUTPUT Custom 40 ..................... 40/10 Watts
Custom 80 ..................... 80/20 Watts
SPEAKERS Custom 40 ................ 1 x Tone Tubby (8 Ohms)
with 8 / 4 Ohms impedance selector switch
Custom 80 ………..... 2 x Tone Tubby (16 Ohms each, in parallel)
with 8 / 4 Ohms impedance selector switch
CABINET .......................................... Pine shell & plywood baffle. Tweed covering.
Leather handle. Rubber feet.
SIZE Custom 40 .......................... Height: 18in (450mm) [480mm inc. feet/handle]
Width: 23in (585mm); Depth: 9.5in (240mm)
Custom 80 ........................... Height: 20in (510mm) [535mm inc. feet/handle]
Width: 26in (660mm); Depth: 10in (254mm)
WEIGHT Custom 40 ...................... 52 lbs / 23.5 Kg
Custom 80 ....................... 74 lbs / 35 Kg
OPTIONS (on request) .................. Choice of speakers, colours,
custom modifications
© 2000-2007 CORNELL Musical Equipment Design & Development 7
Valve Replacement
Valve life varies, depending upon playing style and application. Power valves have
a much shorter life than pre-amp valves, which can last for years. In order to
maintain the optimum performance of your amplifier, the valves should only be
replaced with the same types of valve, as specified below.
The Custom 40 amplifier has three pre-amp valves (12AX7/ECC83) and two power
valves (6L6). The Custom 80 has the same pre-amp valves and four 6L6 output
valves.
Warning
When changing valves, ALWAYS unplug the amplifier, and remember that the
VALVES ARE HOT! Wait for the valves to cool, or replace the valves when
the amplifier has not been used for several hours.
Valve Line-up
Mains
Transformer Output
Transformer
6L6 6L6 ECC83 ECC83
Front panel
ECC83
© 2000-2007 CORNELL Musical Equipment Design & Development 8
Custom 40/80 Block Diagram
INPUTS TONE
CONTROLS
Hi
Lo
BASS TREBLE
Output
Stage
8 Ohms
Line Output (XLR)
VOLUME
2
1
3
Speaker Output Jacks
Output Transformer
Mains Transformer Connections
(only to be altered by qualified personnel)
HT
Bias
Htrs
A
B
C
D
E
F
Fuse
Thermistor 1
2
For 240v A/C Mains
Connect 1 to A (Blue)
Connect 2 to F (Brown)
Join C & D (Black/Red)
B & E (Yellow/Orange)
- no connection
For 115v A/C Mains
Connect 1 to A&D (Blue/Red)
Connect 2 to C&F (Black/Brown)
(T 4 Amp Fuse)
B&E (Yellow/Orange)
- no connection
For 100v A/C Mains
Connect 1 to A&D (Blue/Red)
Connect 2 to B&E (Yellow/
Orange)
C&F (Black/Brown)
- no connection
BLUE
YELLOW
BLACK
RED
ORANGE
BROWN
Neutral
Mains
Switch
Live
4 Ohms
/
