Bryston 4B NRB User Manual

4B NRB/NPB OWNERS MANUAL

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STEREO POWER AMPLIFIER

GENERAL DESCRIPTION

Bryston's 4B stereo power amplifier consists of two amplifier modules, each with its own ±85v
power supply, which can be operated independently or combined (MONO mode) to form a single
800 watt amplifier (8i2 load) in a 3 rack height chassis. Operated independently (DUAL mode)

each channel can deliver 250 watts into SQ (or 400 watts into 4Q). Each of the two amplifier
modules use 8 of Bryston's custom power transistors for a total of 16 output devices per 4B.

POWER CONSIDERATIONS

The 4B employs truly massive power supplies which can draw prodigious amounts of current from
the line when the music demands it. In addition, every Bryston amplifier contains exceedingly

high quality dedicated circuitry in its power supplies to reject RF, line spikes and other power line

problems. For these reasons the 4B should NOT be connected to the accessory power outlets in

a preamp NOR into such devices as power bars or line conditioners. It should be plugged into its
own socket in the wall outlet (with the power switch in the OFF, or OUT, position).

In general, if your preamp has a three prong grounded line cord you can avoid local ground loops
which could cause hum or noise in the system by plugging the preamp’s line cord into the same
wall outlet next to the power amp.

CLIPPING INDICATORS

The 4B amplifier uses a pair of 3 colour LEDs with green indicating power on and red indicating

actual overload or distortion. Yellow appears dynamically at the threshold of clipping to indicate

caution in proceeding to higher power levels. As long as the LED is green, or green and yellow

with only very brief red flashes, the waveform is reaching full power only at the highest musical

peaks. Once the indication contains a substantial red content it should be considered as a sign

that the level is too high and may cause speaker damage if allowed to continue.

The clip-sensing circuit in the 4B uses an AC comparator to detect any source of signal distortion

including clipping, short circuits in cabling, excessive DC or supersonic signals, whether at input

or output, etc. Most conditions which could cause the red LED to light for more than a moment or

two can be dangerous to your speakers and should be corrected immediately.

SPEAKER POWER HANDLING & FUSE PROTECTION

Most speakers will safely absorb an undistorted musical signal up to the full power capability of

even large amplifiers like the 4B (DUAL mode). However, once the signal starts to be clipped the

distortion by-products generated by the overdriven signal can result in very high power levels fed

to the smallest and most fragile of the speaker's components (it should be noted that an amplifier

is quite capable of distorted power levels of twice the undistorted rating and that all the excess

power goes to the high frequency driver). It is also quite possible to damage the woofer by

causing it to exceed its excursion limits and impact against the back of the magnet by doing such
things as turning up the bass control on a preamp and playing music quite loud. This is especially
true with amplifiers which can develop full undistorted power down to extremely low frequencies

as all Bryston amplifiers can. Many speaker manufacturers recommend series fuses to protect the
drivers in case of accidental (or even wilful) overload. If you wish to use fuses follow the

manufacturers recommendations since even what seems like a small increase in current rating on

a fuse will result in large increases in power allowed. Example; A 3 amp fuse will allow about 70
watts but a 4 amp fuse will nearly double this to about 130 watts and a 5 amp fuse will allow 200

continuous watts.

It should be emphasized that almost any amplifier is capable of inflicting damage on
almost any speaker if used in a thoughtless or abusive manner and that Bryston cannot be

responsible for speaker damage caused in this way.

BRIDGED OPERATION (MONO mode)

When operated in BRIDGED (MONO) mode the two internal amplifier sections are operated

out of phase and the load is connected between the two HOT (RED binding post) terminals
with no connection to ground. The two amplifier sections operate together to form a single
push-pull amplifier with double the normal output voltage. In this mode the amplifier can
generate output voltages of greater than 60v(rms) into loads as low as 8 ohms thus producing

output power levels exceeding 800 watts (rms).

N.B. Only the left channel input is used in MONO mode.

INPUT CONNECTORS

The 4B NRB is supplied with two pairs of input connectors: unbalanced RCA/phono and a

combination - 3 pin balanced XLR (pin 1 is ground, pin 2 is POSITIVE & pin 3 is NEGATIVB &

3 conductor balanced 'A" phone (TIP is positive, RING is negative & the sleeve is ground) ­jack with fully discrete active input circuitry. A toggle switch allows selecting between balanced

or unbalanced inputs. (The NPB has only the balanced XLRM" jacks).

All input connectors (except phone jacks) are gold plated and should be used only with quality

gold plated input cable connectors as a poorly plated connector will eventually corrode through

the gold flash. Bryston makes cables with appropriately heavily plated, high quality connectors,

available through your dealer.

OUTPUT CONNECTORS

The 4B is equipped with four binding post terminals (2 red, 2 black) which can accept either

standard banana plugs or bare wire. Refer to the rear panel hookup diagram and to the

descriptions of DUAL and MONO operation for details on how to connect speakers to these

terminals. Since the binding posts are gold-plated we recommend gold-plated banana plugs be

used for the lowest distortion.
N.B. Do not attempt to remove the red or black connector nuts from the binding post

connectors. They are not removable and atternpting to force them off may break the
connector or strip the threads.

OUTPUT CABLES

For some time there have been available on the market special speaker cables constructed for
extra high current and low loss and distortion. These cables will cause no difficulty or instability

with any Bryston amplifier. In fact, we recommend that low inductance cables be used for the

smallest loss of signal between amplifier & speaker.

GROUNDING and the GROUND SWITCH

The left most switch on the rear panel is a GROUND LIFT switch. It is connected between the
chassis ground (including the third prong on the power line cord) and the signal ground. This
switch is normally left in the
installation, or an unusual grounding situation with a preamp using a three wire power line
cord, will cause a ground loop between the signal ground and the chassis ground. This switch

will allow the elimination of the resulting hum in such cases without resorting to a "cheater"

plug by switching to the separated position 3Tl. Note that this switch does not disconnect the
chassis from the third prong on the power line cord which must be left intact for safety reasons.

connected position Occasionally a multi-amplifier rack

(3)

cuss 2 WIRING PERMITTED

CABUGE DE CUSSE 2 PERMIS

HOOKUP TOR DUAL

(STEREO) OPERATION

250W/80 250W/80

GNO(-)

HOT( + )

HOOKUP FOR MONO

(BRIDGED) OPERATION

800W/8n min.

WARRANTY

Bryston products are warranted to be free from manufacturing defects for a minimum of twenty years
from date of original purchase, including parts, labour and return shipping to the first and all subsequent
owners. Warranty coverage is automatic and commences with the date of the original dealer’s bill of sale
(which is the sole proof of purchase date).
In the event of a defect or malfunction Bryston will remedy the problem by repair or replacement, as we
deem necessary, to restore the product to full performance. Warranty service may be obtained by
returning the unit to any Bryston retail dealer. If it cannot be returned to a Bryston dealer, write or call:

BRYSTON SERVICE USA.:

70 COVENTRY ST. SUITE #5

NEWPORT VERMONT

U.S.A. 05855

PHONE: [phone]

FAX: [phone]

E-MAIL: [e-mail]

I or failure of the product or any component part was caused
by damage (not resulting from a defect or malfunction) or abuse while in the possession of the customer,
tampering by persons other than factory-authorized service personnel, or failure to follow Bryston
operating instructions. This warranty gives you specific legal rights and you may also have other rights
which may vary from province to province or from state to state.

BRYSTON SERVICE OUTSIDE CANADA & the USA:

CONTACT YOUR LOCAL DISTRIBUTOR

OR

CHECK OUR WEB SITE AT: [e-mail]

E-MAIL BRYSTON DIRECTLY: [e-mail]

FAX BRYSTON DIRECTLY: 705-742-0882

PHONE BRYSTON DIRECTLY: 705-742-5325

BRYSTON LTD., 677 NEAL DRIVE, P.O. BOX 2170, PETERBOROUGH, ONTARIO CANADA K9J 7Y4