stereo power amp question

[Lee Bartram]

say on a Peavey DCP poweramp you only want to use one speaker sometimes. I know you can just do this with no problem to the amp (i was told this by Peavey) but my question is it has a switch that switches it to "bridged mono".what exactley would this do would you use both speaker outputs or only one and would it do anything different at rather than leaving it in stereo mode and just use one speaker.Any advantages to this?

[Adam Sorber]

Lee,
When you bridge a power amp, it makes the amp a singel channel mono amplifier by bridging both stereo amps together and can almost double the power output into one speaker. With this particular amplifer you must only use the red binding posts when you connect the speaker. When running any amp in bridge mono mode, usually 4ohms is the minimum.

[Shane Glover]

Hi Lee

I do not have a Dcp but I do have several CS800's
An 800 puts out 400 watts per side stereo if I remember
correctly. Putting it in bridge mode combines left & right sides and makes it one single channel amp. By doing so it doubles the power to 800 watts.I use one CS 800 in bridge mode for each subwoofer. And one CS 800 in stereo mode to run the two tops.

On my amps you have to have a special cable . One coming from the left side & one coming from the right side to hook up your speaker to.There are alot of other issues concerning 4 ohm and 8 ohm loads. You may want to read up on your amp and see what kind of load it takes in bridge mode.Bottom line is combining both sides of the amp gives you one power source with more wattage.

Hope this helps
Shane

[Shane Glover]

Sorry Adam & I must have been posting at the same time.

Shane

[Jason Hull]

[Lee Bartram]

thanks for the info i really have no plans to do this anyway i just always wondered how and why they were made this way..

[Johnny Thomasson]

You do not want to use just one side of a stereo amplifier; it is likely to damage the unused side. Bridge it to mono, even if you don't have a speaker with the correct impedance.

So that's why channel B of my stereo Cerwin Vega power amp went south!

[Pit Lenz]

Jason Hull wrote:

You do not want to use just one side of a stereo amplifier; it is likely to damage the unused side. Bridge it to mono, even if you don't have a speaker with the correct impedance.[/i]

Respectfully, I beg to differ.
Jason, where did you learn that from?
Could you please explain how the unused side would be damaged?
We´re talking transistor amps here, right?
In my book the speaker´s impedance should not be lower than the amp´s minimum requirement (higher is OK, but you loose wattage).

I use a powered speaker cab with a Crate PowerBlock inside, constantly set to bridge mode and have a switch in the back that toggles the speaker connections between left channel hot/cold and left hot/right hot (aka bridged out), depending if I want to use it in quieter or louder environment.
If I use the left side only mode, the right side remains unloaded.
The 8-Ohm speaker meets the min impedance requirement of the bridge mode, of course.
Never had any issues with that...
Also all of my PA amps (conventional transistors or class-D) never complained about "running on empty".

A tube amp, of course, is a different beast!

[Dave Beaty]

Hi Lee,
One word of caution; if you switch many stereo amplifiers to the bridged mode, be very careful NOT to allow either of the speaker leads to come into contact with chassis ground, they need to be "floating". There will be a voltage differential present between the speaker connections and power supply ground (which may also be chassis ground). Shorting these connections together will damage many amps. Additionally, in high voltage versions, the user can get at least a mild shock if touching a speaker lead and ground at the same time, whether a signal is present or not.
Dave

[Pit Lenz]

Lee,
to answer your initial question:
In stereo mode each side of the amp works separately.
That means that each input is positive against ground (on unsymmetrical inputs) and the speaker output is hooked up pos (red) and ground (black).
Let´s assume that a stereo amplifier can produce an output of 50 Volts on each side (measured pos versus ground).

In bridge mode, the right input is hooked up though a phase reversed circuit to the same left input.
Therefore the right channel´s output is phase reversed, too.

If you hook up the speaker between the two "pos" (red) posts, it is now not only driven by the left channel´s 50 Volts against ground as before, but by the left 50 Volts against the right -50 Volts, giving a total possible power headroom of 100 Volts.

Besides Dave´s important warning in his reply above, another thing to consider is that the minimum speaker impedance load requirement of the amp sides add up (it doubles in this case).


Here you will find a more detailed and illustrated explanation by Peavey itself.

I hope this could help to explain a bit.
pit

[Jason Hull]

Like Mr. Thomasson, I learned the hard way.

[Brad Sarno]

Hi Lee,
One word of caution; if you switch many stereo amplifiers to the bridged mode, be very careful NOT to allow either of the speaker leads to come into contact with chassis ground, they need to be "floating". There will be a voltage differential present between the speaker connections and power supply ground (which may also be chassis ground). Shorting these connections together will damage many amps. Additionally, in high voltage versions, the user can get at least a mild shock if touching a speaker lead and ground at the same time, whether a signal is present or not.
Dave

HEED THE WISDOM!!

Brad