BK Stereo Amplifier 7250 User Manual

Reference 7250/7260  
series II  
Five/Six Channel Amplifier  
OWNER’S MANUAL  
B & K Components Ltd.  
P/N 13007 Rev.0004  
 
Table of contents  
Safety Precautions  
Purpose and function  
Design and construction  
Features  
page 2  
page 3  
page 3  
page 3  
Rear panel view  
Rear panel description  
Level controls  
page 4  
page 4 - 6  
page 5  
Inputs  
page 5 - 6  
page 6  
Outputs  
Control Muting  
page 8 - 9  
page 7  
System installation  
Making the connection  
Troubleshooting  
Care and cleaning  
Specifications  
page 7 - 8  
page 10  
page 10  
page 11  
page 12  
Warranty  
Accessories included: Manual and Power cord  
Page 1  
P/N 13007 Rev.0004  
 
SAFETY PRECAUTIONS  
PLEASE READ BEFORE INSTALLING  
WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS UNIT  
TO RAIN OR MOISTURE.  
The lightning flash with arrowhead, within an equilateral triangle, is intended to alert the  
user of the presence of uninsulated “dangerous voltage” within the product’s enclosure  
that may be sufficient magnitude to constitute a risk of electric shock to you.  
The exclamation point within an equilateral triangle is intended to alert the user of the  
presence of important operating and maintenance (servicing) instructions in the literature  
accompanying the unit.  
Ÿ
Ÿ
Observance of polarity is essential. Double-check connections before turning the  
amplifier on. The amplifier can be damaged if polarities are incorrect.  
Damage can occur to your speakers if the power rating* of each individual driver is  
exceeded by the amplifier. Make sure that all the drivers in your speaker system  
are capable of handling not only the power being delivered by the amplifier, but  
the energy that is likely to be generated during strong passages.  
Ÿ
Ÿ
Turn amplifier ‘off’ before plugging in or unplugging input and speaker cables!!!  
The Reference 7250/7260 series II is equipped with raised feet so that continuous  
ventilation can be maintained. They help to keep acoustic feedback into the  
amplifier at a minimum. They also provide a measure of protection against  
scratching any surface the unit might be resting on. Do not alter or remove them.  
Ÿ
Ÿ
Do not stack anything on top of the amplifier (preamplifier, processor,  
source...etc.).  
Leave at least 2-3 inches clearance from the top of the amplifier to the next shelf,  
component, etc., to insure proper ventilation.  
* If you are at all unsure of what the speaker ‘ratings’ are, contact your dealer.  
Page 2  
P/N 13007 Rev.0004  
 
The Reference 7250/7260 series II purpose and function  
The Reference 7250/7260 series II is a high current, five/six channel power amplifier. It  
is designed to be used in all types of audio or audio/video systems.  
Design and construction  
The Reference 7250/7260 series II utilizes high quality electronic circuitry to achieve an  
environment wherein a detailed, transparent, and highly musical sound can be realized.  
The high quality parts complement includes state-of-the-art solid state devices, 1% metal  
film resistors, computer grade electrolytic power supply capacitors, and a high capacity  
toroidal transformer.  
The Reference 7250/7260 series II operates class A predriver and AB high current  
MOSFET power output stages. It is capable of reproducing the most demanding audio  
signals at rated power levels.  
Features  
Toroidal Transformers -  
Discrete Circuitry -  
Efficient, high current, shielded transformer.  
More accurate and three dimensional reproduction of  
source material.  
Class A Predriver -  
Improves low level detail for smoother, more musical  
sound.  
AB MOSFET Output Stage - For efficient linear power delivery and protection from  
thermal overload  
Gold Plated Connectors -  
1% Metal Film Resistors -  
High Current -  
Improved connections for better sound and minimized  
signal loss and degradation.  
Low noise resistors for better sound and a greater  
degree of repeatability.  
Ability to reproduce demanding recordings.  
Computer Grade Capacitors - Large capacity computer grade electrolytic capacitors for  
extended low frequency control and improved dynamics.  
Fused Outputs -  
Provides protection from accidental shorting of amplifier  
outputs.  
Heavy Duty Binding Posts - Improved current carrying capacity and ease of use.  
Page 3  
P/N 13007 Rev.0004  
 
Rear Panel View  
1. AC fuse holder  
4. Amplifier control muting input/output  
2. AC Input receptacle  
3. Speaker outputs  
5. Level controls  
6. Inputs  
7. Speaker fuses  
Rear panel description  
1. AC fuse holder -  
Holds the AC Line fuse. This fuse is a 15 Amp / 250 Volt  
Slow Blow fuse. Replace with same type and value fuse only.  
2. AC Input receptacle - For attaching the supplied AC power cord to the amplifier.  
3. Speaker outputs -  
For connecting the speakers to the amplifier. Explained further  
on page 6.  
4. Amplifier control muting input/output -  
To provide remote switching of mute on/off of the amplifier.  
Explained further on pages (8 - 9).  
5. Level controls -  
6. Inputs -  
For adjusting the input level of each channel into the amplifier.  
There are five/six level controls on the back of the amplifier.  
One level control for each channel.  
For connecting signal patch cables (interconnects) from the  
preamplifier to the amplifier to pass signal. Pages (5 - 6).  
Page 4  
P/N 13007 Rev.0004  
 
7. Speaker Fuses - Protection against amplifier damage in the case of shorted speaker  
wires. Replace fuse with same value 6 AMP SLOW BLOW only!  
IMPORTANT!  
Level controls  
When using the level controls, first start with them turned all the way up (clockwise).  
Then adjust them according to your system requirements to match the sound level  
coming from each speaker. This is a rough adjustment for matching different driver  
impedances. Any fine tuning should be done by the preamplifier  
Example: When using 4 ohm and 8 ohm speakers together, the 4 ohm may sound louder  
than the 8 ohm at a given volume level. The level controls on the amplifier are used to  
match the speakers volume levels. Clockwise will increase the output. Counter  
Clockwise will decrease the output.  
Inputs  
RCA type connectors accept line inputs from the preamplifier’s output connectors. There  
are five/six input connectors, one for each channel, that may be used to connect the  
amplifier to the preamplifier.  
RCA cable connector  
Page 5  
P/N 13007 Rev.0004  
 
Here is a typical preamplifier to amplifier setup:  
Outputs  
Five way binding posts are provided. One pair for each channel. They are designed to  
accept a banana-type plug or spade lug connector (shown below) and are color coded for  
easy identification. The positive (+) post should always be connected to the speakers (+)  
jack. The negative (-) post should always be connected to the speakers (-) jack.  
Spade connector Banana jack  
Here is a typical amplifier output setup:  
Page 6  
P/N 13007 Rev.0004  
 
System Installation  
There will most likely be a number of cables involved in the installation of your home  
entertainment system. Preplanning is essential in order to maximize system efficiency.  
We recommend the following as a means of helping you reach that goal:  
§
§
§
Make a diagram of your proposed system by laying out the relative location of each  
component in the system. Then lay out the proposed cable runs between them.  
Number each cable and record its length on the diagram for future reference.  
Cable runs are critical in that they must be kept away from sources of power  
radiation (amplifiers, power cords, heaters, etc...). For safety reasons, they  
should also be kept out of traffic areas.  
The process of optimizing the system will include the type of cable, the length of the  
run, and the obstructions it must deal with along its run. Your dealer can advise you  
on the products available and their relative merits. If building custom length audio  
cables is not your strength, your dealer should be able to help you with that as well.  
§
When possible, use a separate AC power line for the amplifier, one that is not  
shared by any other household component. Important!  
Tip: Take a piece of string (longer than the longest cable run) and mark it at each foot of length. Then do a  
mock cable run using the string, dressing it neatly along the way. Count the divisions to the next full foot,  
and add one foot to allow for some movement of the components. This will provide you with the ideal cable  
length.  
Making the connection  
§
§
Before doing anything, insure that the power switch on the amplifier’s front panel is  
in the ‘off’ position.  
Again, it is recommended that you locate a separate AC power outlet for the  
amplifier, one that is not shared by any other audio component in the system or  
any other house hold component. This will eliminate the possibility of the  
amplifier ‘modulating’ the power being supplied to the component and  
compromising the signal originating from that component.  
§
§
Locate the AC power cord provided with the amplifier and plug it into the power  
input receptacle in the rear panel. Do not connect it to the AC power source yet!  
Connect the audio cables from your preamplifier’s output to the corresponding input  
connector on the amplifier.  
Page 7  
P/N 13007 Rev.0004  
 
§
Connect the wires from your speakers to the appropriate outputs on the amplifier. It  
is absolutely essential that you observe correct polarity in these connections.  
Example: If you connect your left front output of your preamplifier to channel 4 input on the amplifier,  
remember to connect your left front speaker wires to channel 4's outputs. Always observe polarity when  
connecting speakers, connect amplifiers (+) to the speakers (+) and amplifiers (-) to speakers (-).  
§
§
Double check all connections.  
Connect a playback unit (CD, VLD, Tuner, etc...) to the preamplifier. Turn the  
volume on the preamplifier to minimum. Turn on the preamplifier, then the  
amplifier (in that order). Set the source on the preamplifier to the playback unit  
you’ve just connected. Turn the volume up slowly and listen for music from all  
channels. If this is not the case, double check your installation.  
§
Should you encounter any problems that cannot be traced to the source or the  
material being played, consult the “TROUBLESHOOTING” section on page 10.  
Note: When turning equipment ‘off’, the amplifier should always be turned off first, then  
the preamplifier. When turning equipment ‘on’, the preamplifier should always be turned  
on first, then the amplifier. Before turning anything on, insure the preamplifier is at a low  
volume level.  
Control muting  
A control is provided on each Reference 7250/7260 series II amplifier to allow remote  
switching of mute on/off. The preamplifier’s control output, such as is provided with B&K  
series preamplifiers, can be utilized to provide a control signal to the Reference  
7250/7260 series II. If more than one amplifier is being controlled, the control signal can  
be extended to include each successive unit by simply running a 1/8" MINI - JACK cable  
from the CTRL OUT connector of the first amplifier to the CTRL IN connector of the next  
unit (commonly referred to as ‘daisy chaining’). An example of how to connect two  
amplifiers is illustrated in figure E.  
Page 8  
P/N 13007 Rev.0004  
 
If a source other than a B&K series preamplifier is used to control multiple amplifiers,  
only the control output voltage from the source is critical. It must be within the range, as  
indicated on the rear panel, 5-24 volts DC is required. The amplifier will provide each  
successive amplifier with a control voltage of 12 volts DC for reliable operation. The  
amplifiers control output may be used as a source of 12 VDC @ 125 mA for other user  
applications as well. DO NOT POWER MOTORS WITH THIS CIRCUIT.  
If the control function is desired, each unit in the system must remain connected at all  
times and the control must be enabled. To enable the control function, the CTRL  
ENABLE button must be out for each controllable amplifier in the system. For more  
information on the amplifiers output status under various control conditions, refer to the  
following table.  
@ CTRL IN  
Button position  
Output status  
@ CTRL OUT  
Signal  
Signal  
No Signal  
No Signal  
OUT  
IN  
OUT  
IN  
Sound  
Sound  
Mute  
Signal  
Signal  
No Signal  
Signal  
Sound  
* Note: The control voltage is for muting control only. Each amplifier must be connected  
to its own source of AC power in order for it to operate.  
Page 9  
P/N 13007 Rev.0004  
 
Troubleshooting  
PROBLEM  
POSSIBLE CAUSE  
POSSIBLE SOLUTION  
No sound  
1. Reconnect power cord  
2. Check AC switch or fuse  
3. Check for shorts or  
overloading  
1. Power cord not plugged in  
2. Power off at AC source  
3. AC power inlet fuse blown or  
faulty  
4. Control switch in the wrong  
position  
(‘on’ LED not illuminated)  
4. Place control switch in  
proper position  
No sound on some or all  
selected channels (‘on’  
LED illuminated  
1. Speaker leads loose or faulty.  
2. Line stage to amp cables loose 2. Tighten, repair or replace cable  
or faulty.  
1. Tighten, repair or replace cable  
3. Source to line stage cables  
loose or faulty.  
3. Tighten, repair or replace cable  
4. Line stage or source not  
correctly selected.  
4. Check all switch settings  
5. Speaker fuse blown  
6. Level controls adjusted  
improperly  
5. Check all speaker fuses  
6. Re-adjust level controls  
Sound lacks direction,  
bass weak  
1. Speakers connected out of  
phase  
1. Check connections making sure  
that cables are connected (+)  
to (+) and (-) to (-)  
Loud hum or buzz on one 1. Poor ground connection in inter-  
1. Check all connectors and repair  
as necessary.  
or more channels  
connect cables.  
Channel sounds distorted 1. Blown rail fuse  
and low in output  
1. Replace blown rail fuse inside  
amplifier  
** Note:If unit continues to blow power inlet fuses, DO NOT USE A HEAVIER  
FUSE!!, have it serviced.  
Care and cleaning  
Under normal use, the amplifier will not require any special care. Over time you may  
wish to clean the exterior of the unit by wiping it with a damp cloth to remove any dirt or  
dust that accumulates on it. Do not let any liquid enter the amplifier through the vents in  
the top cover. You may clean the connectors on the back panel with isopropyl alcohol  
annually.  
Page 10  
P/N 13007 Rev.0004  
 
Reference 7250/7260 series II SPECIFICATIONS  
Power rating: 8 ohms  
4 ohms  
200 watts @ 1 kHz  
375 watts @ 1 kHz  
Frequency response  
Input sensitivity  
THD (S+N)  
5 Hz - 45 kHz  
1.4 Volts  
0.09 % @ 1 kHz  
Input impedance  
Damping factor  
Current (peak to peak)  
Slew rate  
33.2 k ohms  
450  
75 Amps  
14 V / usec  
Dynamic headroom  
S/N (A-weighted)  
Voltage gain  
1.2 dB  
95 dB  
28  
Line voltage  
120/220/240 VAC switchable  
17"(w) X 19.25"(d) X 7.25"(h)  
70 lb  
Dimensions (O.A.)  
Weight  
Power consumption  
1830 watts max  
17.5 Amps max current draw  
130 watts @ no input  
Replacement fuses  
Line -15 Amp/250 Volt Slow Blow  
Rails - 6 Amp/250 Volt Slow Blow  
Speaker - 6 Amp/250 Volt Slow Blow  
In-rush - 2 Amp/250 Volt Slow Blow  
Control - .5 Amp/250 Volt Fast Blow  
Page 11  
P/N 13007 Rev.0004  
 
Limited Warranty  
B&K Components Ltd., referred to herein as B&K, warrants your B&K equipment against all defects in  
material and workmanship for a period of five years from the date of purchase. This warranty applies only  
to the original purchaser and only to equipment in normal residential use and service. Defective equipment  
must be returned to B&K, prepaid, accompanied by sufficient payment to cover the cost of return shipping  
and handling, and will be repaired or replaced at the discretion of B&K whose decision as to the method of  
reparation will be final.  
This warranty shall not apply to any equipment which is found to have been improperly installed, incorrectly  
fused, misused, abused, or subjected to harmful elements, used in any way not in accordance with  
instructions supplied with the unit, or to have been modified, repaired or altered in any way without the  
expressed, written consent of B&K. This warranty does not apply to the cabinet, the remote controller, or  
appearance items such as the faceplate, control buttons, or display lenses, nor does it cover any expenses  
incurred in shipping the unit to and from the manufacturer’s service depot.  
No warranty, implied or otherwise created by State law shall extend beyond the terms of this warranty and  
B&K shall not be liable for any incidental or consequential damage arising out of a defect in material or  
workmanship of the unit during the terms of this warranty or thereafter. Some States do not allow the  
exclusion or limitation of incidental or consequential damages and the foregoing exclusions may not apply to  
you.  
This warranty gives you specific legal rights. Your may also have other rights which vary from State to  
State.  
No agent, representative, dealer or employee of B&K has the authority to increase or alter the obligations or  
terms of this warranty.  
B&K Components Ltd.  
RETURNING EQUIPMENT  
No equipment may be returned to B&K Components Ltd. Without a RETURN AUTHORIZATION. Should  
you find it necessary to return equipment to B&K, for any reason, a RETURN AUTHORIZATION (RA)  
number must be issued by B&K in respect of the equipment being returned. You may request an RA  
number by calling B&K at the numbers below. We ask that you provide the following information at that  
time.  
1.Your name, address, and phone number.  
2.The model and serial number of the equipment being returned.  
3.A description of the problem being experienced.  
Your call will be referred to a Technical Service Representative who will work with you to resolve the  
problem. If it is determined that the unit must be returned for repair, an RA number will be issued.  
B&K Components Ltd. 2100 Old Union Road, Buffalo New York 14227  
1-800-543-5252 or 1-716-656-0023  
Page 12  
P/N 13007 Rev.0004  
 
B&K Components, Ltd 2100 Old Union Road Buffalo, New York 14227  
P/N 13007 Rev.0004  
 
B&K Components, Ltd.  
2100 Old Union Road  
Buffalo, New York 14227  
P/N 13007 Rev.0004  
 

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