Balanced Audio Technology VK-55 User manual

VK-55
WARRANTY REGISTRATION FORM
Unit Serial Number: _______________________________________
Customer Name: _______________________________________
Address: _______________________________________
_______________________________________
Date of Purchase: _______________________________________
Purchased From:
Dealer Name: _______________________________________
Address: _______________________________________
_______________________________________
IMPORTANT NOTE:
In order to receive the full five year product warranty, please mail this
completed form together with a copy of your sales receipt to Balanced Audio
Technology at the address below, within thirty days of purchase.
Failure to do so will result in the product being warrantied for one year
from the date of manufacture.
1300 First State Blvd. Suite A Wilmington, DE 19804
Tel: [phone] Fax: [phone]

VK-55
Balanced Power Amplifier
Owner's Manual
1300 First State Blvd. Suite A Wilmington, DE 19804
Tel: [phone] Fax: [phone]

Introduction
Thank you for your purchase of the Balanced Audio Technology VK-55 power amplifier.
Please read this owner’s manual to obtain the full benefit of the VK-55 in your system.
This manual provides you with necessary safety information and operating procedures for
this exceptional unit. For more technical information on the circuit design, please read
the Balanced Audio Technology VK-55 White paper.
WARNINGS:
To prevent the possibility of serious injury, electrical shock, or fire:
DO NOT operate with the bottom cover removed.
DO NOT expose to rain or moisture.
DO NOT defeat the ground power-plug.
DO NOT replace fuses with anything other than the same type and rating as supplied by
the factory.
Package Contents
Included in the box should be the following:
Description Quantity
VK-55 Power Amplifier 1
6C33C-B Output Tubes 4
6SN7 Signal Tubes 4
Power Cord 1
Torx Wrench (T-10) 1
Spare Cover Screws 5
Spare Fuses 3
Owner’s Manual 1
Save all the packaging materials in a safe dry area for the unlikely event that you need to
return the VK-55 to the factory for service.

Installing Tubes
The signal 6SN7 tubes can be installed in any of the four sockets. Output 6C33C-B tubes
are marked 1 to 4, and should be installed in that order, left to right, when viewed from
the front of the unit.
Physical Placement
It is recommended that you provide open space above the unit for proper ventilation, with
no electronic components placed directly overhead.
Mount the unit on a hard surface with proper ventilation underneath. Avoid placing the
unit directly on a carpeted floor.
Connecting the VK-55 to Your System
For Balanced Preamplifiers:
Use balanced XLR interconnects. The left and right channel input connectors are clearly
marked on the back panel of the VK-55.
Note: The VK-55 XLR inputs are wired as follows:
Pin 1: common/ground
Pin 2: positive
Pin 3: negative
For Single-Ended Preamplifiers:
Single-ended preamplifiers have RCA connectors. The VK-55 power amplifier is
designed to work with either balanced or single-ended preamplifiers connected to its inputs.
All that is required to connect a single-ended preamplifier with RCA connectors to the
VK-55’s inputs is the optional balanced to single-ended adapters. These adapters are
available from Balanced Audio Technology at a nominal charge.
For Speaker Connections:
The speaker connectors are clearly marked on the back panel of the VK-55. There are
several sets of output taps marked LOW, MEDIUM and HIGH for connecting a variety of
speakers to the VK-55. Please note that some experimentation may be required. Try
each output tap until you find the one that gives the most balanced performance in your
system.

Operating the VK-55
Normal operation of the VK-55 requires simply turning the unit on. There are no meters
to connect, bias setpoints to remember, or drifting bias points to adjust. Please read the
Autobias Feature section for more details.
Turning the VK-55 On:
The power switch is located at the front of the unit. As tubes warm up, their green LED
bias indicators will turn ON indicating their readiness. Different tubes can take different
times to get ready, but normally all four LED’s should be ON after about one minute.
Conditions such as low line voltage and tubes’ age can delay the readiness of the tubes.
Turning the VK-55 Off:
The unit can be turned Off at any time (even while playing). If needed, please wait at
least 30 seconds before turning the unit ON again.
Autobias Feature:
The VK-55 implements a sophisticated autobias circuit that automatically compensates
for tube aging and line voltage fluctuations, as well as marginal mismatching of tubes.
The successful operation of the autobias circuit is noted by individual LED’s that glow
visibly next to each output tube when viewed from the top of the chassis. A total of four
LED’s should light up to indicate proper operation of the circuit. If one of the LED’s
fails to light up (after the unit is warm), there could be two reasons for this problem:
1. The particular output tube is defective. In this case replacing this tube with a
known good one should turn the LED ON.
2. The amplifier was overstressed and the protective fuse inside opened. These
fuses protect output tubes from overloading. There are two fuses accesible
through the top of the unit. Please refer to the section on replacing fuses for
correct ratings.

Replacing Fuses:
WARNING: Please turn the unit OFF and disconnect the power cord before
proceeding.
There are three fuses in the VK-55. The main Slow-Blow fuse (10A rating for 110-
120VAC line voltage and 5A for the 200-240VAC range) is located on the unit’s back
panel. The two 3A Fast-Acting protection fuses are mounted on the VK-55 printed
circuit board and can be acsessed through the holes in the amplifier top plate.
If the pilot LED on the front panel goes out, try replacing the main fuse on the back panel
with the same type fuse.
If one or more of the autobias LED’s has gone out, turn the unit off and wait for few
minutes before proceeding, allowing the internal electrical charge to Remove and replace
the blown fuse with the 3A Fast-Acting type.
In either case, if the unit still fails to operate properly, please contact the factory for
professional service.
Factory supplied fuses should only be replaced with the same type and rating parts.
Replacing Output Tubes:
To maintain the optimal performance of your unit, replace the 6C33C-B output tubes only
with matched sets available from Balanced Audio Technology. If only one tube fails,
then just one pair needs to be replaced.
Please do not substitute any random tube as a replacement. Although the automatic
bias circuit in the VK-55 will accept virtually any random set of output tubes, the unit
will not be guaranteed to meet all of its performance specifications under such conditions.
Finally, the determination that a single tube replacement is prudent rests solely with the
customer, based on actual hours of use for the particular set of tubes. The factory
assumes no responsibility for possible performance decrease under such conditions.

Servicing:
The Balanced Audio Technology VK-55 should require no service other than tube
replacement to maintain its high performance. Please direct any further service inquiries
to the factory.
Cleaning:
To remove dust, occasionally wipe the front and top surfaces of your VK-55 with a damp
soft cloth. If fingerprints appear, you may use a mild, non-alkaline soap solution. Do not
use abrasive cleaners, as they may damage the fine finish of the unit.

VK-55 Limited Warranty
Terms and Conditions
1. Limited Warranty
Upon receipt of the attached warranty registration form, Balanced Audio Technology warrants the purchased
product to be free from manufacturing, materials, and workmanship defects for five years from date of original
purchase, excepting vacuum tubes, subject to the following conditions. Failure to return the enclosed
warranty registration form together with a copy of your sales receipt within 30 days from original
purchase will result in a warranty period of one year from the date of manufacture.
2. Vacuum Tubes
The 6SN7 vacuum tubes (including replacements under warranty) are warrantied for one year from the date of
the original VK-55 purchase. The output 6C33C-B vacuum tubes are warrantied for ninety days.
3. Limited to Original Purchaser
This warranty is for the sole benefit of the original purchaser of the covered product, and may not be transferred
to a subsequent purchaser of the product.
4. Conditions and Limitations
This warranty is subject to certain conditions and limitations, as follows. This warranty is void and inapplicable
if the product has not been used in accordance with the instructions found elsewhere in this manual, or if it has
been misused or abused, damaged by accident or neglect, or in transport once in possession of the purchaser.
The warranty is also void if the product has been repaired, modified, or tampered with by anyone other than
Balanced Audio Technology or its specifically authorized agents.
5. Remedy
If this product contains a materials, manufacturing, or workmanship defect that cannot be repaired at the
dealership where the product was purchased, it must be packed in original packaging and returned to Balanced
Audio Technology via insured freight, at the owners expense. If replacement packaging materials are required,
they will be supplied by the factory at a nominal charge. Returned products must be accompanied by a
written description of the defect, and a return authorization number (available from the factory via
phone or fax). Upon receipt of defective product, Balanced Audio Technology agrees to repair the product
without charge for parts (except vacuum tubes if the unit is more than one year old), or labor. The product will
then be returned via prepaid, insured freight, with carrier at the sole determination of Balanced Audio
Technology. This constitutes the purchasers sole remedy.
6. Design Changes
Balanced Audio Technology reserves the right to modify its products or change specifications at any time
without obligation or liability to previous purchasers.
7. Miscellaneous
Any implied warranties relating to the above product shall be limited to the duration of this warranty. This
warranty does not extend to any incidental or consequential costs or damages to the purchaser. This warranty
gives you specific legal rights. You may also have other rights which vary from state to state.