Bob Carver Black Magic 25 Stereo Manuale utente

CORPORATION

Operating Manual

c06-09-22

The lightning ash with arrowhead, within

an equilateral triangle, is intended to alert

the user to the presence of uninsulated

“dangerous voltage” within the product’s

enclosure that may be of sucient magni-

tude to constitute a risk of electric shock

to persons.

The exclamation point within an

equilateral triangle is intended to

alert the user to the presence of

important operating and maintenance

(servicing) instructions in the literature

accompanying the appliance.

WARNING - TO REDUCE RISK

OF FIRE OR ELECTRICAL

SHOCK, DO NOT EXPOSE

THIS EQUIPMENT TO RAIN OR

MOISTURE.

NO USER-SERVICEABLE

PARTS INSIDE.

REFER SERVICING TO

QUALIFIED PERSONNEL

ONLY.

CAUTION: To reduce the risk of

electric shock, do not expose

this appliance to rain and

moisture. Do not expose this

device to dripping or splashing liquids

and no object lled with liquids, such as

vases, should be placed on the device.

IMPORTANT SAFETY INSTRUCTIONS!

PLEASE READ THEM BEFORE OPERATING

THIS EQUIPMENT.

1. Read these instructions.

2. Keep these instructions

3. Heed all warnings

4. Follow all instructions.

5. Do not use this apparatus near water.

6. Clean only with a dry cloth.

7. Install in accordance with the Bob Carver Company instructions.

8. Do not install in close proximity to heat sources such as radiators,

heat registers, stoves, replaces, or other apparatus (including

other ampliers) that produce heat.

9. Do not defeat the safety purpose of the polarized or grounding-

type plug. A polarized plug has two blades with one wider than the

other. A grounding type plug has two blades and a third grounding

prong. The wide blade or the third prong are provided for your

safety. If the provided plug does not t into your outlet, consult an

electrician for replacement of the obsolete outlet.

10. Protect the power cord from being walked on or pinched

particularly at plugs, convenience receptacles, and the point where

they exit from the power amplier.

11. Only use attachments/accessories specied by Bob Carver

Company.

12. Use only with the cart, stand, tripod, bracket, or table

recommended by Bob Carver Company. When a cart

is used, use caution when moving the cart/apparatus

combination to avoid injury from tip-over.

13. Unplug this apparatus during lightning storms or when

unused for long periods of time.

14. Refer all servicing to qualied service personnel. Servicing is

required when the apparatus has been damaged in any way, such

as power-supply cord or plug is damaged, liquid has been spilled

or objects have fallen into the apparatus, the apparatus has been

exposed to rain or moisture, does not operate normally, or has

been dropped.

15. Do not expose this equipment to dripping or splashing liquids, and

ensure that no objects lled with liquids, such as vases, are placed

on the equipment.

16. To completely disconnect this equipment from the AC mains,

disconnect the power supply cord plug from the AC receptacle.

17. The mains plug of the power supply cord shall remain readily

operable.

18. Connect mains power supply cord only to a mains socket outlet

with a protective grounding connection.

19. If possible, save the shipping carton that contained your Crimson

275, as well as the individual tube boxes.

Quick Start Guide

1. Locate the seven vacuum tube boxes, four large

and three small.

2. Place the Black Magic 25 according to the ventila-

tion suggestions on page 6 of this manual.

3. Carefully insert the tubes into their sockets

following the diagram at right and the further

details on page 6 of this manual.

4. Connect the outputs of your preamplier/DAC to

the RCA inputs of the Black Magic 25. Make sure

that the gain/volume control on your pream-

plier/DAC is turned down. See page 8 for more

hook-up instructions.

5. Connect the output terminals of the Black Mag-

ic 25 to your loudspeakers. See page 8 for more

details.

6. Connect the IEC power cable between the Black

Magic 25 power socket and the wall receptacle.

7. Power up your preamplier/DAC.

8. Flip the Black Magic 25 rear panel POWER switch

to ON.

9. Wait two minutes for the tubes to warm up.

10. Activate your music source and slowly advance

the volume control on your preamplier/DAC.

11. Enjoy! If you don’t hear any sound, turn off your

preamp/DAC and Black Magic 25, and re-check

your connections, or contact Bob Carver Corpo-

ration at Bob Carver Company

6260 E. Riverside Blvd. #11 | Loves Park, IL, 61111

email: Jim@bobcarvercorp.com

12AT7

EL-34, KT120,

KT88, or 6550’s

DO NOT MIX

TUBE TYPES!

12AT712AX7

R L

OUTPUTOUTPUT

R INPUT L –

RIGHT –

LEFT

+ AC INPUT

–

“I personally wish to thank you for choosing my

Black Magic 25 amplier. It has truly been a labor of

love, incorporating many of the sonic improvements I

developed for the Silver Seven 900 and Crimson/Raven

350, as well as those from previous designs. Along with

the help of my wonderful staff, we believe that we have

created both a sonic masterpiece and an excellent value.

“It’s time to start enjoying years of musical

enjoyment! But rst, please take the time to read

through this brief manual to get the most

from your Black Magic 25.”

• Ample power for speaker loads from 2 ohms

to 16 ohms, the musicality of premium

vacuum tubes, and the accuracy and pristine

specications that come from Bob’s 50+years of

design expertise.

• Bob’s “listen to the room” innovation. Facilitated

by a special current feedback loop, it allows the

amplier to ‘hear’ the room’s reverb, along with

its unique sonic signature. Each room plays its

own tune, and this amp uses the speaker as a

microphone by using the speaker in reverse to

listen to the room,thereby allowing a portion

of the room acoustic to be expressed through

the main speakers.The room becomes an

integral part of the music in a way no other

Thank

You!

Why

we’re

so proud

of the

Black

Magic

amplier allows. Sound is more majestic, more

realistic, and the sound stage is larger and more

compelling.

This phenomenon is impossible to achieve with

normal solid-state amplier designs, whose low

source (output) impedance effectively shorts

out the speaker’s ability to accomplish this feat

• DC Restorer circuit, an exclusive to Bob Carver

designs, keeps the output tubes running cool,

prolonging their life to beyond 50 years!

Other amplier tubes operate at a very high

idle power to keep distortion low, frequency

response extended, and for other technical

reasons.The downside is that tube life is

drastically shortened, about three to six years at

the most.Worse yet, tube performance begins

to deteriorate as soon as the amp is turned on.

In addition to extended tube life, Bob Carver

Company’s DC Restorer eliminates the need to

purchase expensive matched tubes for the Black

Magic 25.

• Unique transformer design delivers enormous

power through an increased turns ratio, with two

extra interleaved windings, each bilar wound

on a core of highest quality, grain oriented,

silicon steel (Bob’s term for it is admantine.

Google it. ) with a pure nickel center section.The

secondary’s are wound with oxygen-free copper

wire and 98% pure silver wire for the critical

internal connections.

Record This Important Information

For possible insurance claims or factory repair,

please record the serial number, purchase date

and Bob Carver Company Dealer name in the

spaces provided.

Serial Number: _________________________________

Purchase Date: _________________________________

Dealer Name: __________________________________

________________________________________________

Technical Assistance

Your Bob Carver Dealer welcomes questions

about your Black Magic 25 and any other brands

that may be part of your system. If you or your

Dealer wish additional help concerning a

suspected problem, we’re here for you.

Bob Carver Company

6260 E. Riverside Blvd. #116

Loves Park, IL, 61111

email: Jim@bobcarvercorp.com

Customer Service

We are proud of the fact that we support

our ampliers far longer than any of our

competitors.Your new Black Magic comes with

a FIVEYEAR tube and service warranty!

If it is determined that your amp needs

repair, you should rst contact your Bob Carver

Company dealer. If you cannot located the

dealer, contact us and we will provide you with

a Return Authorization. For assistance, contact

us at the phone and email addresses above.

Our Limited Warranty is on page 12 of this

Manual.

Placement and Cooling

Cool air is drawn from under the chassis by the

heat from the tubes acting as an air pump, and

exhausting the warm air out the chassis through

the vents.

Place the amp on a hard surface. Do not place

the amplier on a carpet without something hard

for it to sit on like a piece of nice glass cut to the

same size as the unit.This will allow the feet to do

their job by keeping the bottom raised, allowing

unimpeded airow.

A glass shop can make such a base plate and

in colors if you wish. A nice dark gray, smoke or

opaque black looks beautiful. It should be at least

a quarter of an inch thick.

We also don’t recommend placing the Black

Magic in a tightly-enclosed cabinet without

sufcient ventilation.Allow at least 18 inches of

free space above the amplier.

12AT712AT712AX7

EL-34

KT120 or

KT88 or

6550’s

DO NOT

MIX!

Inserting the Vacuum Tubes.

The Black Magic comes with three small and

four large vacuum tubes: Two 12AT7’s, one 12AX7,

and four EL-34 output tubes.

Press the tubes into the bases (sockets) gently

so that you don’t bend the pins.

The bases for all three small tubes are identical,

so take care to make sure that the 12AX7 is in the

middle socket.

Tung-Sol in their innite wisdom has

congured their tubes’ black, central base

hole to be slightly different than our

conventional tube bases. Look carefully

so that you line up the raised portion

of the tube’s central base with the “key

way” on the tube base.

key way

More About the Tubes.

The output tubes do not need to be matched,

as the sound of the amp does not at all depend on

matched output tubes.That’s because the DC re-

storer circuit eliminates the need to match tubes.

The only caveat here is that the output tubes

should all be the same type and vintage.

Looking at the amplier from the front, left to

right: the rst tube is a 12AT7, then a 12AX7, and

nally a second 12AT7.We ship Black Magic with

EL34 output tubes. However, you can substitute

KT120’s or any of the popular derivatives such as

KT88, KT90, or KT100. The mighty 6550 may also be

used.

Why we can offer a 5-year warranty

on Black Magic 25 tubes.

There is a meter on the front of the amplier

which can indicate the health of the tubes — get a

bad reading, get free tubes!

As with our more expensive ampliers, Bob

employs his unique twist on a DC restorer circuit

which has two main benets —lower distortion

without dissonant side effects and extended tube

and amplier life.

Our ampliers simply do not run hot. Like their

more expensive siblings, they are the coolest

running tube type ampliers ever, allowing you

to actually touch the tops of the output tubes and

never be burned!

The internal temperature of our ampliers

is a bit warmer than the inside of your mouth

resulting in an extremely long lifespan.

Due to the unique design, all the components

in the amplier undergo much less stress than in

conventional designs.

And, due to the efciency of the concept, our

transformers can be lighter and, despite Bob

Carver specifying esoteric steel for their cores, it

helps us sell a $4000+ amplier for under $3000.

As with his legendary Sunre® tracking power

supplies, the bottom line is that you may expect

our ampliers to outlive any other brand, and our

extended warranties underscore that fact.

We warrant the Black Magic for a full ve years;

that’s the amplier and the tubes! We love the

fact that our nest competitors warrant their

tubes for three months. It’s all about economics.

If your tubes tend to fail, limit the warranty. A

manufacturer has no option; they must. Since

our tubes last for years, it costs us nothing to be

heroic.

Perhaps even more importantly, not only do the

tubes no longer fail every two or three years, they

do not degrade sonically as all tubes must when

boiling away in every one of our competitors

ampliers — a truly remarkable accomplishment

and typical for Bob Carver,Absolute Sound

Magazine Hall of Fame designer.

General Operation.

Bob has intentionally made the Black Magic

extremely simple to operate. Volume (gain) is

determined by your preamplier or DAC.

Tube biasing, using the rear panel control, is

optional and will be covered on page 9 of this

manual.

That’s all there is…except for connecting your

sound source, loudspeakers and line cord.

Speaker Connections.

It is very important to use speaker cables of the

correct diameter in order to reduce power loss. It

is not within the scope of this manual to discuss

all of the esoteric cables available.

The Black Magic 25 speaker terminals will

accept spade lugs, banana plugs or bare wire.

If using bare wire, remove half an inch of

insulation and tightly twist the wire strands

together.They may also be “tinned”with solder

before insertion into the center hole in the

speaker terminal.

From the rear view: the black binding post is

common, and the red post is two or four or eight

ohms.The power curve is quite at, hence the taps

may be used for one or two ohm speakers, or for

sixteen ohm speakers.

L R

R L

OUTPUT

Input Connections.

The red RCA-type input is for the right channel;

black is for the left channel. As with speaker

cables, you have many esoteric options as well

as “conventional”connection cables. At the

very least, use high quality RCA cables with gold

plating and durable cable-to-plug connections.

Cheap cables can fail and lead to frustrating

trouble-shooting — who would ever suspect their

connection cables?

Double-check that “left goes to left”, “right goes

to right”,“plus (red) goes to plus (red)”, and “minus

(black) goes to minus (black)”.

Line Voltage

This amplier may be congured for operation

with 120 volts or 240 volts, 50 / 60 Hz.The change-

over must be performed by qualied personnel.

It is a standard under-the-chassis wiring

conguration.

When used with 240 volts, the AC line fuse must

be replaced with a 1.5 Ampere unit.

Fuses

The rear panel line fuse is a 3 Ampere (1.5

Ampere for 240 volt operation), fast-blow type,

and should be replaced with the same type and

rating if it ever needs replacing. Do not, under any

circumstances, use a “slow-blow” fuse here.

The (rear panel) vacuum tube cathode fuse

(B+) is a 1.0 ampere and

should be replaced with

the same type and rating.

If the fuse blows during

bench testing, it may be

temporarily replaced

with a 1.25 or 1.5 ampere

fuse. Do not, under any circumstances, use a “slow-

blow” fuse here!

Normally, a 1.0 ampere fuse will be perfect for

music because the peak-to-average power ratio of

speech and music is about 10:1. If you nd that the

1.0 amp fuse blows with music, you may replace it

with a 1.25 ampere fuse, or even a 1.5 ampere unit.

Power Switch

Up is ON, down is OFF. There is no power-on

indicator except for the glow of the tubes, so you

will have to remember whether you turned it on

for about 10 seconds until you can see the tubes

glow. It is safe to switch the amplier on and off at

will.

Adjusting the Output Tube Bias.

The front panel incorporates a multi-purpose

meter, one of the purposes of which is as aTube

Bias Meter. IMPORTANT: Turn your preamp volume

control all the way down while performing bias

adjustments.

Use a small screwdriver and adjust the BIAS

control (located on the rear of the

amplier) for 100 mA, after the

unit has warmed up for about 20

minutes.The normal range to use is

from 60 mA to 120 mA, and changes

here will vary the damping factor of

the amplier slightly. More current

increases the damping factor, whereas less cur-

rent provides a softer more tube-like sound.

The design center is 100 mA, and that should be

your starting point if you want to experiment.

It will vary from speaker to speaker, and most

importantly with your taste.

The meter reads the combined current for all

four output tubes, and it is normal for this current

to vary slightly with changes in power line voltage.

Tube Substitution

The output tubes do not need to be matched,

as the sound of the amp does not at all depend

on matched output tubes.That’s because the

DC restorer circuit eliminates the need to match

tubes.The only caveat here is that the output

tubes should all be the same type and vintage.

Looking at the amplier from the front, from left

to right: the rst tube is a 12AT7, then a 12AX7, and

nally a second 12AT7.The output tubes are EL-34.

Any of the popular derivatives such as 6550, KT88

or KT120 may also be installed. Bias adjustment

will be required when changing tube types.

Output tubes must always be 4 of the same type.

No mixing.

Monitoring and Tube Troubleshooting.

Once the idling current has been set, it will

normally not need to be adjusted for several years

unless you want to a) experiment for different

sound; b) if you install different output tubes, or

c) the amplier suddenly starts to sound funny.

If you hear a POP and see a ash, yet the amp

continues to play, you should rst check the

current and then the output tube fuse.

If the fuse blows, the output current will drop to

zero. If the tube fuse blows, replace it WITHOUT

replacing any tubes.

Turn the amp on and monitor the current. If it

climbs to within the range you had set, and if the

amp sounds good, all is well.

Often, an output tube has a speck of dust-like

impurity, which comes into contact with an

internal element, shorting the element, and is

vaporized into gaseous oblivion.The getter, the

mirror-like shiny plating on the inside of the tube

does its job, absorbs the vaporized material and

the tube is new again.All it takes is a new fuse.

If you install a new fuse and it blows again, you

will need to determine which tube is the culprit.

Proceed as follows:

Indice

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