HHB Circle 5A User manual

Version 5.1 03.01.02 Page 1
Service manual
HHB Circle 5A
Powered Monitor speaker
with V3 electronics
Manual: Version 5.2 23.12.2001
This manual is subject to change without notice.
Always check with HHB that you are using the latest version.
Also available as an Adobe Acrobat V4 file.
When printing this file, for clear sharp pictures on a black & while laser, it may be necessary
to adjust your printer driver’s ‘Print half tone’ settings. If you have a 600dpi printer, setting the
half tone to around 45 lines per inch will give a clean sharp image, where as the default -
around 60lpi may give a dark image to pictures..
WARNING! DANGER OF ELECTRICAL SHOCK
Opening mains operated equipment like the HHB Circle 5A incurs a risk of electric shock.
DO NOT attempt to open this equipment unless you are qualified to do so, have the
necessary test equipment and are operating the Circle 5A from an
ISOLATED POWER SUPPLY.
Ensure that only the correct mains voltage is applied, as marked on the module.
NEVER OPERATE OR OPEN THIS SPEAKER IN DAMP OR WET CONDITIONS AND
NEVER ALLOW IT TO BE USED OUTSIDE. ENSURE THAT ALL POWER AND SIGNAL
CABLES ARE IN PERFECT CONDITION AND ARE CORRECTLY FUSED.
IF IN DOUBT, CONTACT HHB IMMEDIATELYBEFORE PROCEEDING.

Version 5.6 07.04.02 Page 2
Contents
Page 1: The cover and warning
Page 2: (This) index page
Page 3: Section 1.0: External arrangement and
comments on connectors/controls
Page 4: Section 2.0:
General arrangement, notes on testing
Page 5: Section 3.0:
Access to the Circle5A electronic module
Page 6: Section 4.0:
General inside views of C5A module
Page 7: Section 4.1
Close-up view of C5A module’s circuit boards
Page 8: Circuit diagram: C5AIPM input board
Page 9: Circuit diagram: C5APAM’s rectifier/PSU/mute circuit
Page 10: Circuit diagram: C5APAM’s active filters
Page 11: Circuit diagram: C5APAM’s power output circuit
Page 12: Parts list
Page 13: Fault finding
Page 14: Modifications and updates
Information contained in these pages is the intellectual property of Harbeth Audio Ltd.
© Harbeth Audio Ltd. 1997-2002 All rights reserved.

1.0 External details
This is a view of the external controls on the
Circle5A.
1.1 Master Volume Control
The function of the Master Volume
control is really that of a sensitivity control - to scale
down excessive input signals. In a set-up where the
signal level is scaled so that set to maximum (fully
clockwise) an input of 0.775VdBV, on the loudest
peaks, will fully drive the power amplifiers. Since
many sources give a signal under normal pro-
gramme that is significantly greater than 0.775V, it is
expected that in most situations the Circle 5A’s vol-
ume control wil be set to about half way i.e. 12
o’clock. This would apply in many studio’s where the
‘+4’ signal reference is the maximum. Note: as you
will observe from the circuit diagram, the volume
control follows the input buffer stage, and the input
amplifier will overload and distort if the input signal is
excessive whatever the volume control is set to.
1.2 Input sockets and selector switch
There are two input connectors: a master input, an
isolated XLR following thenormal European wiring
convention:
Pin 1 = shield (ground*)
Pin 2 = Live, hot, + signal
Pin 3 = Cold, -, return signal
* Pin 1 is connected to the ground of the C5A’s
electronics. There is no connection from the audio
ground to the mains (safety) ground. The metal
panel is the only part of the C5A’s electronics that is
connected to the mains ground.
Also provided is a secondary input: a Phono (Cinch,
RCA) connector for unbalanced systems. The centre
pin is signal +, and the connector case is the ground.
The phono plug’s case is connected to the C5a’s sig-
nal ground, not the mains (safety) ground. Neither
input is transformer isolated, and therefore care
must be taken to eliminate hum loops.
The selector switch selects which of th two inputs is
fed to the input buffer IC.
Connect to EITHER the XLR or the phono, not both.
Only use the mains cable supplied. Replace the
mains fuse with the correct type. The Circle5A must
be earthed at all times, and is not suitable for use
outdoors.
Version 5.6 07.04.02 Page 3
External view of C5A’s version 3 panel

2.0 General arrangement
All the signal processing circuitry of the Circle5A
amplifier module is arranged on two PCB’s - one
‘passive’ board, the C5AIPM holds the XLR, selec-
tor switch, volume control and phono socket. This
is connected to the C5APAM (filter/PSU/power
amp) board via a 6 way wire loom. There are no
user-adjustable parts.
Although mains voltages do not appear on the
PCB, but care should be taken when examining
and working on the module, since the secondary of
the mains transformer (25-0-25 AC) is connected to
the bridge rectifiers and smoothing capacitors on
the board. These store considerable energy, and
are capable of creating a spark many minutes after
the C5A’s mains power is removed.
The very low level of self noise generated in the cir-
cuitry means that, at idle, there is an extremely low
level of background noise generated in the circuitry.
If the C5A is powered up the front panel power-on
LED fitted to the tweeter face plate just above the
bass unit will glow green, indicating that the speak-
er is powered and awaiting a signal. If the power-on
LED is the illuminated, by definition, the PSU is
working, and the two LED’s on the C5APAM will be
glowing, confirming that the +/- 12V rails are opera-
tional.
To minimise power-on and power off ‘thumps’
appearing at the drive units, a circuit detects the
presence of mains 50/60Hz cycles, and should the
mains disappear (either because the user has
intentionally or unintentionally switched off the
speaker or because of mains supply failure) the
C5A will revert to muted mode a virtually instanta-
neously and the audio output circuitry will switch
off, and programme will not be heard.
The power-on LED is driven from the rectified regu-
lated supply rail, and is a positive indication that the
transfromer, rectifiers and smooting capacitors are
functioning correctly.
The bass unit is directly driven from a pair of IC
power amolifiers in bridge push-pull mode. The
tweeter is driven from one one IC.
NOTE CAREFULLY:
DO NOT CONNECT EITHER OF THE BASS OUT-
PUT TERMINALS TO GROUND SINCE THIS MAY
DESTROY ONE OR BOTH BASS POWER IC’S.
THIS WILL REQUIRE THE REMOVAL AND
REPLACEMENT OF ONE OR MORE POWER
IC’S, A DIFFICULT AND EXPENSIVE TASK.

Sec 3.0 Removing the Circle 5A’s
active module from the cabinet
It is absoluletely essential that before removing
the module you have the necessary tools, a
clear space, and sufficient uninterrupted time to
work. Rushing leads to mistakes, and mistekes
can be dangerous and impair the excellent
performance of your Circle 5A speakers.
An isolated mains PSU is essential for your
electrical safety: be sure you never work on
equipment directly connected to the mains sup-
ply. Ensure that the mains supply is discon-
nected
and removed from the module, and is not
reconnected until the module has been fully
refitted.
We suggest that you cover your work bench
with a soft material to protect the underside of
your Circle 5A’s from scuffing during
removal/replacement of the module. Also be
aware that the module is heavy and that once
the screws are loosened, it will tend to drop
downwards, and that the heavy aluminium
panel of the module will readily chip the softer
wood of the cabinet, exposing the white MDF
board under the black paint. You will need two
screwdrivers:
3.1: A 3.0mm cross head screwdriver of the
‘Superscrew’ or ‘Pozidrive’ NOT Phillips type.
The Superscrew type has 4 thin grooves into
which the Superscrew screw driver securely
locates. If the Phillips type is used, the screw-
driver will ‘mash’ the heads, and then it may
not be possible to remove the module from the
cabinet.
3.2: A larger size (M4, 4mm, No.2)
‘;Superscrew’ or ‘Pozidrive’ screwdriver.
Section 3.3: Removing the screws
Please follow these instructions exactly. Failure
to do so may well destroy your cabinet and/or
module.
First, using your smaller Superscrew driver,
check that the screwdriver makes a positive fit
to the screws marked 1,2,3,4. Applying as little
force as necessary, unscrew (anti-clockwise)
the four corner machine screws in the order 1,
2, 3, 4.
These screws locate in metal inserts trapped in
the inside of tha cabinet, and the alignment of
the module and the cabinet is precise.
Then, using the larger screw driver, remove the
screws A, B, C, D, E and, as you loosed screw
F, expect the module to drop down. Be ready
tocatch it!
The module can then be removed a short
distance from the cabinet, as the internal con-
nections to the module are on short flexible
wires. Be ready to carefully note the colour
coding and position of the wires that connect
the module to the woofer, tweeter and LED’s.
NB: This photo is of the earlier module,
but the screw arrangement is identical

There are four function blocks in the C5A elec-
tronic module:
C5AIPM: a small PCB carrying the XLR,
phono,volume control and selector switch. This
is secured to the panel by the nut of the vol-
ume control and the two M3 nylock nuts that
secure the XLR socket.
The input signal, once selected by the user
switch is sent to the C5APAM
MAINS TRANSFORMER:
The mains primary is connected directly to the
user’s mains off-on switch. The single sec-
ondary is connected to the C5APAM. The
transformer’s mains operating voltage is not
adjustable; various voltages are available for
different market conditions.
Sec. 4.0 General view of C5A module viewed from the inside
Version 5.6 Page 6

Section 4.1 Close-up views of
inside of C5A module
C5AIPM:
note air holes are sealed with
hot glue.
Wire loom connecting C5AIPM to
C5APAM
C5APAM

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