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Monoblock / Bridged amplifier explained

Audio Neophyte

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I'm fairly new to the deep dive into the audio world, though I already have built a fairly nice system. My next move will probably be an upgrade in amplifier(s). When reading posts to various audio sites, I have read some confusing posts regarding monoblock amps and/or bridged amplifiers. I originally understood that employing two monoblock amps in a system would generally, all things relative price-wise, etc. produce improved sound by powering each channel by a separate amplifier. But some posts seem to adamantly argue that the use of two monoblock amps is a bridged amp system that increases power but degrades sound in several ways. Or are bridged amplifiers different than running two monoblocks? Should I just consider a similarly well-thought of stereo amplifier for the upgrade? Any clarity (not crazily technical) from this site would be greatly appreciated. Hope I explained the issue adequately. Thanks.
 

Blumlein 88

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Welcome to ASR.

An amp can be monoblock and not be bridged. Some stereo amps can be bridged for more power into a single mono channel.

If properly designed the topology likely has no real consequences for listening.

More than that might get somewhat more technical than you want. The main takaway being you can bridge some stereo amps to monos. Or you can have an amp that is just one channel, and it not be bridged.
 

nerdstrike

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My experience of the low to medium market is that while in theory you can get awesome discrete amplification for practical money, the discrete pre-amps that provide balanced outputs are surprisingly expensive. When you combine the two it's hard to come in cheaper than some really good integrated options.

If you absolutely must have 500 watts per channel, then monoblocs away.

There might be more options on the US that make it a more attractive approach... Either way, don't expect miracles from having more power on tap. You may gain nothing but excessive headroom!
 

restorer-john

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A bridged amplifier differs in that each amplifier handles the same signal but in opposite polarity. Then the output is taken from the two "hot" terminals with no reference to ground. So you obtain twice the voltage swing over a load. That translates to a huge increase in power. However, each amplifier "sees" half the impedance of the load, which often reduces the theoretical quadrupling of power significantly.

A bridged amplifier generally has slightly higher noise floor than the same amplifier unbridged. Unless the two amplifiers are very carefully matched in all parameters, you will get a rise in distortion from unbridged to bridged (BTL- bridge tied load) operation.

Monoblock amplifiers are simply an amplifier in a separate box for each channel. It sounds serious and tough and is really just a term the audio community invented. A monoblock amplifer can be any topology including a bridged pair operating as one amplifier.

You could have a pair of stereo amplifiers each running BTL mono, one for each channel (L/R) and you could call them "monoblocks".

My preference is a large pair of conventional amplifiers (say 200+200@8R) which can be bridged (>600w@8R) if you need to. You have options then down the track.
 

Colin James Wonfor

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Most folk who build these also are aware of the increased current in the output devices at high power levels, and thus more heat. So beware when using a cheapo amp in bridge mode.
 

DonH56

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As said above, bridging and monoblock are not in general the same.

Monoblock = one amplifier channel
Stereo = two channels
Multichannel = more than two channels

Any amp can be "standard" or "bridged". As @restorer-john said, to make a bridged amplifier you take two channels and run them in opposite polarity. That means when the signal at one amp is +1 V, the other is at -1 V, so the difference is +1 - (-1) = 2 V and that is what is applied to the speaker. You have twice the voltage and four times the power, in theory. In practice, most bridged amps are limited by heat, power supply, and such to somewhat less than 4x the output power. As @Colin James Wonfor implied, each channel of the amplifer now "sees" half the load, so to a bridged amplifier an 8-ohm speaker looks like a 4-ohm load. Twice the current is needed, and you are using two channels instead of one, so a bridged amplifier tends to run hotter than a non-bridged amplifier. The output impedance of the amplifier is also roughly doubled, thus the damping factor (load/amp impedance) is halved. And so forth.

Any amplifier may or may not be bridged internally. Bridging is common in amplifiers with limited voltage supplies, like car radio amplifiers and battery-powered (portable) amps and powered speakers. A stereo or multichannel amplifier may have a bridged mode wherein you combine two channels to create a single higher-powered amplifier using an internal circuit to generate the opposite polarity output. A stereo amp may convert to a mono (bridged) amp, a four-channel amp could be converted to a two-channel bridged amp, and so forth.

An "easy" way for manufacturers to create a monoblock is to take a stereo amplifier and add the internal inversion circuit, put a new chassis around it, and now you can sell either a stereo amp or monoblock that is essentially the same "stuff" inside the box.

HTH - Don
 

Hayabusa

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I'm fairly new to the deep dive into the audio world, though I already have built a fairly nice system. My next move will probably be an upgrade in amplifier(s). When reading posts to various audio sites, I have read some confusing posts regarding monoblock amps and/or bridged amplifiers. I originally understood that employing two monoblock amps in a system would generally, all things relative price-wise, etc. produce improved sound by powering each channel by a separate amplifier.

One big advantage of two mono blocks is that you can place them very close to your speaker and thus make your speaker wire very short.
 

pma

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Compared to SE output amplifier, the same bridged amplifier in theory gives 4x more power and 2x more output voltage. The current load to output devices is 2x higher so the SOA is to be investigated before one connects the amplifiers in the bridged mode. In other words, as if one used 2ohm load instead of 4ohm in normal mode, speaking about power load of the output stage. Sometimes the bridging of "normal" amplifiers is tricky and leads to oscillations, the result of added loop inductances of output power grounds. Real world experience, no guessing.

bridge_elinst.jpg

Basic schematics



amptest_bridge_pma1.jpg


Test of bridged modules
 
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DonH56

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And here I thought "double-down" was dead except for cards and drinks... :)
 

Colin James Wonfor

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It was called Wicked Beast because the user could with a selection of switches change from Balance to Un-Balance, and select what Bias Mode the needed i.e. a few Watt A Class or a lot more A Class, it was designed to stop the heatsink getting 50C at any cost, in most cases it sat at 48C max. No burned fingers.
So cold winters night it would runner harder into A in position RED (Led Color)
 

restorer-john

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it was designed to stop the heatsink getting 50C at any cost, in most cases it sat at 48C max.

A real power amp isn't even warmed up at 50 degrees C.

Derating is for babies. Go hard, go hot, or go home. ;)
 

Colin James Wonfor

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Yep babies with soft hands washed by Elves Soup Liquid, so go Suck a Elf, Yes the big amps got much to hotter 1800W heat each channel, 3 banks of caps each bank 1.5F only 2 transformers at 2KW each and mere 180Kgs in Granite.
 

pma

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