Parallel Mono

[babebambi]

A lot of 2-channel amps (either power amp or amp head for bass or PA) can run bridge mono (as in serial).

How come we don't see any running parallel mono? Can anybody explain what it takes to run such operation?

Edit:
I mean "parallel mono" as in running two amps into ONLY ONE load, in order to get more current. Similar in the objective (to get more power), but different in implementation to "bridging", which also runs two amps into one load, but to get higher voltage swing.

I am NOT talking "dual mono", where two amps with same signal running into two separate loads.

[BassmanPaul]

While this can be done it's not the usual way of bridging two channels. The main problem is that the output points of both channels have to match exactly. If they don't, one channel is going to be fighting the other to keep its output where it thinks it should be. This is an easy way to burn out an output stage.

[babebambi]

Paul, thx for the info.

About the two parallel channels having to match precisely - I don't see that being more difficult or more trouble than the two bridged (serial) channels matching. Perhaps I am over looking something?

I did find some more info here on the Wiki. But I still don't understand why the serial bridging is so much more popular than parallel bridging. One being useful for high impedance load and the other useful for low impedance load.



In some sense, I think parallel would make a bit more sense:

Smaller loads (such as 210/115/112) are more often than not with higher impedance (8ohm) nowadays; vise verse, large loads (215/610/412) tend to be lower impedance (4ohm).

An 2-channel amp could then be optimism to run 8ohm on each channel with the small cabs, and mono parallel to run those large cabs.

Where as bridge mono (serial) would run against the market trend of the cabs. Remember how odd it is to match cabs to the original Eden WT800/600/500.

[billfitzmaurice]

Originally Posted by babebambi

But I still don't understand why the serial bridging is so much more popular than parallel bridging. .

Because series bridging results in higher wattage ratings, and what sells amps is watts.

[babebambi]

Originally Posted by billfitzmaurice

Because series bridging results in higher wattage ratings, and what sells amps is watts.

Bill, thx for the wise words. But I am still not entire sure.

Let's use the original WT800 as example again.
It's 400w each channel into 4ohm and 800w into 8ohm bridged.

If it were designed to be 400 watt per channel into 8ohm
(this could be more expensive to build? but then it doesn't have to supply as high a current, so less beefy component somewhere?)
It will still give the same 800w, only into (IMO a more useful/realistic) 4ohm parallel mono...

Which is more efficient to run a large load?
(let's assume we can make it any impedance)
High current or high voltage?

And which is easier/cheaper to built?
Amp with high current or amp with high voltage?

[BassmanPaul]

If you look at the specs of most stereo power amps they are fully capable of driving 2Ω per channel all day. In series bridge, at a moment in time, if one channel is going positive say 20V and the other is going negative 18V the difference would not be noticeable.

However if those nodes are connected together in parallel bridge to drive a low impedance load, then the 20V channel will be trying to pull the 18V channel to 20V and vice versa.

[billfitzmaurice]

Originally Posted by babebambi

If it were designed to be 400 watt per channel into 8ohm
(this could be more expensive to build?

It would be.

High current or high voltage?

That entirely depends on the load impedance.

And which is easier/cheaper to built?
Amp with high current or amp with high voltage?

High current is less expensive, so if you need higher voltage to drive a higher impedance load it's less expensive to series bridge two channels to double the voltage than to use higher voltage components in a single channel. Bridging is a complicated issue, and should only be undertaken with attention paid to voltage swing, current and load impedance. Few users understand those relationships, all they know is watts, and considering watts alone can cause problems.

[babebambi]

Originally Posted by BassmanPaul

If you look at the specs of most stereo power amps they are fully capable of driving 2Ω per channel all day. In series bridge, at a moment in time, if one channel is going positive say 20V and the other is going negative 18V the difference would not be noticeable.

However if those nodes are connected together in parallel bridge to drive a low impedance load, then the 20V channel will be trying to pull the 18V channel to 20V and vice versa.

Paul, so you are saying parallel bridge is A LOT MORE sensitive to mismatch than serial bridge? I got to read up on this, can you point me to some material online? Thx.


BTW, all this ? comes up after I tried a MC2102 as a power amp for my bass rig, haha ridiculous, I know. The MC2102 allows operation in stereo/serial/parallel AND put out the same power in 2/4/8 ohm - thus I can serial bridge into a 4ohm load, and I can also choose to parallel bridge into the same 4 ohm load; and I started to wonder which is better.

[babebambi]

Originally Posted by billfitzmaurice

It would be.
That entirely depends on the load impedance.

High current is less expensive, so if you need higher voltage to drive a higher impedance load it's less expensive to series bridge two channels to double the voltage than to use higher voltage components in a single channel. Bridging is a complicated issue, and should only be undertaken with attention paid to voltage swing, current and load impedance. Few users understand those relationships, all they know is watts, and considering watts alone can cause problems.

Now that makes a lot of sense. Thx Bill.
The work of the mighty marketing department again.

[Bob Lee (QSC)]

Some Crown amps (such as the Macro-Tech Series) can do that. It does require using a jumper between the two + (red) output terminals.

[Vic Winters]

Originally Posted by Bob Lee (QSC)

Some Crown amps (such as the Macro-Tech Series) can do that. It does require using a jumper between the two + (red) output terminals.

Micro-Tech too.

[Jerrold Tiers]

The problem with parallel mono is that you also need a lower impedance speaker... So if each can drive 2 ohms, then to get double power, you need to go to ONE ohm...... doubling the number of speakers, although they don't have to handle much power each.

But if you do BRIDGE mono, you need 2x impedance, not 1/2 impedance. So you can use a single 4 ohm speaker system. That's much more available, and is practical on a power basis too, since most any 500-600W speaker is very usable with a 1200W amp..

[babebambi]

If an amp allows operation in stereo/serial/parallel AND put out the same power in 2/4/8 ohm - thus I can serial bridge into a 4ohm load, and I can also choose to parallel bridge into the same 4 ohm load.

Which would be better?
Doesn't matter? Doesn't make a difference?
Depends? ... on what?

[Bob Lee (QSC)]

Originally Posted by Vic Winters

Micro-Tech too.

I thought so but wasn't sure. Thanks.

[billfitzmaurice]

Originally Posted by babebambi

If an amp...put out the same power in 2/4/8 ohm -

You'd have a tube amp that probably can't be bridged.

[babebambi]

yeah, that's a tube amp
it is also able to bridge and parallel mono
(the manual has instructions to use all three modes)
safe operating impedance is 1-4 ohm parallel and 4-16 ohm serial
but I am interested to understand which way to get to 4 ohm is better ...