[FredClark]

A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

[William Eckle]

On 7 Sep 2007 22:36:30 GMT, FredClark wrote:

A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

Hi Fred:
It doesn't mention bridging in the manual, check:
http://www.adcom.com/prod/shopdispla...&prodid=1 182
For the manual for the GFA-545

-=Bill Eckle=-

Vanity Web Page at:
http://www.wmeckle.com

[jwvm]

On Sep 7, 6:36 pm, FredClark wrote:
A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

Why do you want to do this?

[rcs3]

On Sep 7, 6:36 pm, FredClark wrote:
A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

Some amps are designed to be bridged and others are not. I'd check
with Adcom tech support on your amps. I have a pair of older NAD with
switches for bridged mode. There is also a specific way to connect
your speakers and pre-amp! Be sure and check with Adcom on how to do
this.
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Rick

[jwvm]

On Sep 8, 8:47 pm, rcs3 wrote:

snip
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Actually, the power is nearly quadrupled if the power supply can
provide sufficient current. The impedance does not change but because
the load voltage is doubled, the current will also be doubled. The
current doubling is cause for concern since it could damage the the
output transistors or result in higher power dissipation that could
cause longterm problems.

[Bob]

"rcs3" wrote in message
...
On Sep 7, 6:36 pm, FredClark wrote:
A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

Some amps are designed to be bridged and others are not. I'd check
with Adcom tech support on your amps. I have a pair of older NAD with
switches for bridged mode. There is also a specific way to connect
your speakers and pre-amp! Be sure and check with Adcom on how to do
this.
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Rick
I have never heard that bridging and amp halves the speaker impedance. You
don't wire the speakers differently when the amp gets bridged..the speakers
remain the same and the amp sees the same load. If I'm wrong on this
explain how the change occurs.
Bob

[Chung]

Bob wrote:
"rcs3" wrote in message
...
On Sep 7, 6:36 pm, FredClark wrote:
A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.
Some amps are designed to be bridged and others are not. I'd check
with Adcom tech support on your amps. I have a pair of older NAD with
switches for bridged mode. There is also a specific way to connect
your speakers and pre-amp! Be sure and check with Adcom on how to do
this.
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Rick
I have never heard that bridging and amp halves the speaker impedance. You
don't wire the speakers differently when the amp gets bridged..the speakers
remain the same and the amp sees the same load. If I'm wrong on this
explain how the change occurs.
Bob

But the amp does not see the same load in bridging as in single-ended.
To see this assume the speaker is R ohms. Let's say one amplifier is
outputting V volts. In the single-ended case, current is V/R. In the
bridged case, because the speaker's other end is connected to an
amplifier, that other end actually sees a voltage of -V (instead of
ground). Therefore the current drawn from the amp is 2V/R. Hence
effective resistance is R/2 (current is V divided by R/2).

Put some numbers in. Say R=8 ohms. Your amp is delivering 8V into the
speaker. In the single-ended case, current = 8V/8ohm =1A. In the bridged
case, the voltage across the speaker is 16V (since the other amplifier
is delivering -8V), and therefore current into speaker = 16/8 =2A. So as
far as the amp is concerned, the speaker looks like 4 ohms since 8V will
draw 2A.

[Norman M. Schwartz]

"Bob" wrote in message
...
"rcs3" wrote in message
...
On Sep 7, 6:36 pm, FredClark wrote:
A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

Some amps are designed to be bridged and others are not. I'd check
with Adcom tech support on your amps. I have a pair of older NAD with
switches for bridged mode. There is also a specific way to connect
your speakers and pre-amp! Be sure and check with Adcom on how to do
this.
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Rick
I have never heard that bridging and amp halves the speaker impedance. You
don't wire the speakers differently when the amp gets bridged..the
speakers
remain the same and the amp sees the same load. If I'm wrong on this
explain how the change occurs.
Bob

Some many years ago I redeployed a pair of bridgeable stereo Adcom GFA-555s
using each to drive the R and L panels of a Magneplanar Tympani IVa. (Later
on I acquired a pair of Bryston 7B-STs to do the same job.) The Adcoms
(which I still own) did the job admirably; great sound at any volume
setting. They never ever clipped, shut down or burning any fuses, (speaker's
or amp's).

[Randy Yates]

jwvm writes:

On Sep 8, 8:47 pm, rcs3 wrote:

snip
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Actually, the power is nearly quadrupled if the power supply can
provide sufficient current. The impedance does not change but because
the load voltage is doubled, the current will also be doubled. The
current doubling is cause for concern since it could damage the the
output transistors or result in higher power dissipation that could
cause longterm problems.

I agree that the power is quadrupled:

P = V^2 / R

and so

P1 = V^2 / R
P2 = (V + V)^2 / R
= 4 * V^2 / R
= 4 * P1.

However, the impedance seen by the amplifier output stage, at least
in the ideal case, is reduced by two, precisely because of the
increase in output current you described. Algebraically,

Rl = V / I,

where Rl is the load impedance seen at the output of the power amp,
V is the output voltage of the power amp, and I is the current
running through the power amp.

We can compute I as

I = (V + V) / R,

where R is the [ideal] load impedance of the speaker. Then

Rl = V / ((V + V) / R)
= R / 2.
--
% Randy Yates % "With time with what you've learned,
%% Fuquay-Varina, NC % they'll kiss the ground you walk
%%% 919-577-9882 % upon."
%%%% % '21st Century Man', *Time*, ELO
http://home.earthlink.net/~yatescr

[Serge Auckland]

"Bob" wrote in message
...
"rcs3" wrote in message
...
On Sep 7, 6:36 pm, FredClark wrote:
A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

Some amps are designed to be bridged and others are not. I'd check
with Adcom tech support on your amps. I have a pair of older NAD with
switches for bridged mode. There is also a specific way to connect
your speakers and pre-amp! Be sure and check with Adcom on how to do
this.
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Rick
I have never heard that bridging and amp halves the speaker impedance. You
don't wire the speakers differently when the amp gets bridged..the
speakers
remain the same and the amp sees the same load. If I'm wrong on this
explain how the change occurs.
Bob

When you bridge-connect a stereo amp, you connect the 'speaker to the two +
terminals only, leaving the negative terminals unconnected. You then arrange
for the two amplifier halves to be driven in anti-phase, either with a
couple of op-amps, or more easily with a centre-tapped transformer. This
assumes that each stereo half is a conventional amplifier, i.e. one that
that loudspeaker -ve connection is at ground. Some high-power amplifiers
(like some Musical Fidelity) are already bridge connected internally, so you
can't then bridge connect again.

As you double the voltage across the load, you quadruple the power, so a 100
watt 8 ohm stereo amplifier becomes a 400 watt into 8 ohm bridged mono
amplifier. Each stereo half then is driving 200 watts into 4 ohms. All this
assumes that the amplifier is "perfect" and you get a doubling of power
going from 8 ohms to 4 ohms. Most amps will be a little off perfection, so
typically, a 100 watt/8 ohm stereo amp will give 350-370 watt/8 ohm bridge
connected. Clearly, if the load is lower than 8 ohms, each half of the
stereo pair will see less than 4ohms when bridged, so you need to be sure
that the amp is happy into 4 ohms or less before bridging.

S.

--
http://audiopages.googlepages.com

[rcs3]

On Sep 9, 11:25 am, "Bob" wrote:
"rcs3" wrote in message

...

On Sep 7, 6:36 pm, FredClark wrote:
A newbie at seperates and recenty aquired an adcom preamp tuner with a
couple of adcom gfa-545 stereo amps. My speakers a Magnepan SMGa's.
My question is can each of the stereo amps be bridged to mono? If so,
I need direction on wiring.
Thx in advance.

Some amps are designed to be bridged and others are not. I'd check
with Adcom tech support on your amps. I have a pair of older NAD with
switches for bridged mode. There is also a specific way to connect
your speakers and pre-amp! Be sure and check with Adcom on how to do
this.
Just remember with bridged amps the power is doubled and also the
speakers impedance is effectively halved as see by the amplifier. a 4
ohm load looks like a 2 ohm load, etc. With speakers like the Maggies
that may be a problem.

Rick

I have never heard that bridging and amp halves the speaker impedance. You
don't wire the speakers differently when the amp gets bridged..the speakers
remain the same and the amp sees the same load. If I'm wrong on this
explain how the change occurs.
Bob

Bob, I was referring specifically to the way my NAD amps are bridged.
The right pre-amp out goes to one amp's right main in. The left pre-
amp out goes the other amp's right main in. The speaker connections
only use the L+ and R+ connections, they do not share a common ground.
this is simalar to running two speakers in parallel. In this type of
setup the amp "sees" a 8 ohm load as 4 ohms, or 4 ohms as 2 ohms. That
is why I advised Fred to check with Adcom on this type of setup.

Rick

[jwvm]

On Sep 9, 8:29 pm, Randy Yates wrote:

However, the impedance seen by the amplifier output stage, at least
in the ideal case, is reduced by two, precisely because of the
increase in output current you described.

We have an English problem here because "amplifier" is a fuzzy term in
this context. When two amplifiers are bridged, the result is a single
more powerful amplifier. The load impedance for this new amplifier is
the same as for the unbalanced configuration. I agree that each
individual amplifier channel will now see an effective load that is
only half as large as previously. If Rick's wording was altered from

"the speakers impedance is effectively halved as see by the
amplifier."

to

"the speakers impedance is effectively halved as see by each
amplifier."

the ambiguity would have been removed.

[Randy Yates]

jwvm writes:

On Sep 9, 8:29 pm, Randy Yates wrote:

However, the impedance seen by the amplifier output stage, at least
in the ideal case, is reduced by two, precisely because of the
increase in output current you described.

We have an English problem here because "amplifier" is a fuzzy term in
this context. When two amplifiers are bridged, the result is a single
more powerful amplifier. The load impedance for this new amplifier is
the same as for the unbalanced configuration. I agree that each
individual amplifier channel will now see an effective load that is
only half as large as previously. If Rick's wording was altered from

"the speakers impedance is effectively halved as see by the
amplifier."

to

"the speakers impedance is effectively halved as see by each
amplifier."

the ambiguity would have been removed.

I agree. The "total amplifier" will see the same impedance while each
"channel amplifier" will see half the impedance.
--
% Randy Yates % "Rollin' and riding and slippin' and
%% Fuquay-Varina, NC % sliding, it's magic."
%%% 919-577-9882 %
%%%% % 'Living' Thing', *A New World Record*, ELO
http://home.earthlink.net/~yatescr