Cornell Custom 80 Owner's manual

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

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).

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.

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.

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.

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

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

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

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