Power amp and bridging

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RideTheCrash

RideTheCrash

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I'm running a single 8 ohm cab for vocals. Right now, I don't have a proper power amp for it. Since it's one cab, I'd assume I should bridge the amp to make it mono. If my imaginary amp didn't have a bridge switch, how would I set it up run out of both outputs? Because I assume running one side of the amp, would only give me half the wattage?

I'm sketchy in the way of ohms and watts.
 
I've been playing and recording for over 40 yrs. and I still get confused about that same thing. Must be getting old.
 
If the amp doesn't have a switch to put it into bridged mode, you can't do it. You can always just use one side of a stereo amp, just get one with enough wattage per channel. Then, when you get another speaker, you are all set.
 
Farview said:
If the amp doesn't have a switch to put it into bridged mode, you can't do it. You can always just use one side of a stereo amp, just get one with enough wattage per channel. Then, when you get another speaker, you are all set.
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im not so sure about that.

im inferring its a power amp only, no powered mixer or anything. this only pertains to amps with binding post (banana) outputs; you take the banana and 'bridge' it across the two red (+) posts, therefore, using the two channels. mind you, you can still use two speakers with it, if you're speakers support 4 ohm operation and one speaker has an 'ext' jack, or something equivalent.

the black terminals don't carry any power to my knowledge. i think im pretty much accurate on this, i work in a music store, and im the main in-house tech (ok so its a small establishment...) its done all the time like that here, i have it set up that way with my personal PA rig too. I wouldnt bridge the mains though, i would get a suitable power amp to run it in stereo. Bridging is better for powering subwoofers.

man, farview, we seem to be bumping heads a lil bit huh? first with the pro tools panning question, and now this one???

i love ya man!
 
Not all power amps can be bridged, depends on their design.

"the Black terminals dont carry any power to my knowledge"
Then you dont have much knowledge, as the power put to speakers is AC power, and that requires 2 paths of current flow(i.e. red and black terminals).

When an amp is in the "bridge" mode one of the internal "amps" must have its input inverted then the two amps which are joined at the "Black" terminal now utilize the two "red" terminals as the outputs to the speakers.
So, if an amp is not equiped with a "bridge switch" it probably cant be bridged.

Speakers dont "support any ohm operation" they are what they are.
They have a rating (in ohms) that the amp sees as a "load". Amps are designed to work with a particular "load. Most modern amps now will handle a load of 2ohm per side, or 4 ohm bridged, but not all amps are this way.
You would have to look at the specs of your particular amp.
 
TragikRemix said:
im not so sure about that.

im inferring its a power amp only, no powered mixer or anything. this only pertains to amps with binding post (banana) outputs; you take the banana and 'bridge' it across the two red (+) posts, therefore, using the two channels. mind you, you can still use two speakers with it, if you're speakers support 4 ohm operation and one speaker has an 'ext' jack, or something equivalent.

the black terminals don't carry any power to my knowledge. i think im pretty much accurate on this, i work in a music store, and im the main in-house tech (ok so its a small establishment...) its done all the time like that here, i have it set up that way with my personal PA rig too. I wouldnt bridge the mains though, i would get a suitable power amp to run it in stereo. Bridging is better for powering subwoofers.

man, farview, we seem to be bumping heads a lil bit huh? first with the pro tools panning question, and now this one???

i love ya man!
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Unless you figure out a way to run the positive slope of a signal to one side of an amp and the negative slope to the other side of the amp, it will not be bridged just by using the positives of both channels. You need to have an amp that has the switch. It's been this way since the dawn of time.
 
You can only bridge amps that are made to be bridged, and all of those have a switch.
 
ok, so i was indeed mistaken.

i learned something today ;)
 
It is also not healthy to send your speaker two ouputs from an amp. In stereo mode chennl 1 inout feeds channel 1 output. In mono mode, channel 1 inoput feeds both channel 1 and 2 outputs. In bridged the two amps work together from 1 inout signal to create 1 output wattage. This is not the same as plugging channel 1 and 2 outputs into the same speaker.
 
geeeezzzzz

you guys act like it's rocket science.... ANY stereo amp can be mono bridged.... the difficulty is in the input.... all a mono switch does....(go on check the schemo) is route the input to both channels in such a way that they are out of phase ...THAT"S ALL... so assuming you have a balanced input... all you need is to rig a special cablewith one input and two outputs makeing sure that +/- are reversed for one of the outs.... alternatively assuming the amp is unbalanced in if your output is balanced simply use a y cord configured as an insert.... the output of the amp is of course taken ONLY from the "red" terminals... this should give you 2x's the voltage....
on the other hand if what you need is more current... simply run into both inputs and take the output from both sides to the speaker making sure that they are in phase....
 
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yeah, my Tascam PA150 if bridged is 300 Mono/bridged or 150Watt Stereo.

It has a switch. Stereo or Mono/BRDGE

I'm not sure just any old amp can take the bridged current? but I never tried it?
 
COOLCAT said:
I'm not sure just any old amp can take the bridged current? but I never tried it?
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An amp in bridged mono is usually restricted to twice it's minimum per-channel impedance to keep it within it's current limits. An amp that can handle 4ohms per channel stereo will usually be safe only for 8ohms bridged, for example.
 
Give me one instance of where it would require you to run the outputs of two channels to one speaker.
 
i really feel safer just running things at 8 ohms stereo. less can go wrong that way.

one amp per pair of speakers... keepin it simple. throw a crossover into the mix, sure, but keep it even.
 
JCM900 said:
Give me one instance of where it would require you to run the outputs of two channels to one speaker.
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Anytime you want to use a stereo amp in mono and still get it's full power output. Driving subs or bass cabinets is a common application.

Bridged mono for higher impedances, usually above 4ohms EDIT- 4ohms and above
Parallel mono for lower impedances, usually 4ohms or below
 
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All of my amps that have a bridged mono mode are rated down to 2 ohms.
 
xstatic said:
All of my amps that have a bridged mono mode are rated down to 2 ohms.
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2 ohms in bridged mode? I've never seen that. (not that I have seen everything) I've seen 2 ohms in dual mono and 4 ohms in bridged.
 
xstatic said:
All of my amps that have a bridged mono mode are rated down to 2 ohms.
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Not in bridged configuration they're not. Bridged is ALWAYS twice the minimum impedence of the channels not bridged.
The only way your amps are rated for 2 ohms bridged is if they're rated for 1 ohm unbridged and I've only seen a couple of like $15,000 audiophile amps that are rated for a load that low.
Now parallel mono goes down to 2 ohms but not bridged. and not all amps have the parrallel mono set up.

A couple things I haven't seen mentioned ..... personally, I don't like to use one side of a stereo amp and leave the other unconnected from any speaker. Maybe it's just from my tube git amps, but some amps don't like to be hooked up to nothing even if there isn't any signal.

And sometimes amps'll be weird in bridged mode ..... more prone to failure or shutting down.
 
My bad, you guys are right. A lot of my sub amps are wired in parallel mono, and not bridged. I shamefully retract my earlier statement because it was wrong:D
 
Lt. Bob said:
Now parallel mono goes down to 2 ohms but not bridged. and not all amps have the parrallel mono set up.

A couple things I haven't seen mentioned ..... personally, I don't like to use one side of a stereo amp and leave the other unconnected from any speaker. Maybe it's just from my tube git amps, but some amps don't like to be hooked up to nothing even if there isn't any signal.

And sometimes amps'll be weird in bridged mode ..... more prone to failure or shutting down.
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I meant to point out before that many amps today don't run in what used to be parallel mono, like you are talking about, even if they have the switch. Parallel mono output involves feeding the same signal to both channels, putting a jumper between the + outputs, and running a common return. This parallels the outputs, giving you enough current to run low-Z loads in mono. On most amps today that have a parallel switch, only the inputs are paralleled. Paralleling the outputs is never mentioned. Crown Macro/Microtechs are a notable exception, they still have the procedure for paralleling the outputs in their manuals. Basically, they are some of the only amps I'd trust under hard use in bridged or parallel output mode.
 
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