Why aren't bridged amps more popular?

[@rainbowmat8204]

Thank you so much Paul for answering my question

[@Paulmcgowanpsaudio]

My pleasure. Thanks for asking.

[@honeyken316]

In commercial sound systems for theatre and cinema is a reason to use the same model of 2 channel amplifier for horns and then bridge the amplifiers for use with the bass speakers that require much more power. That way you can have the same model for two channels of sound or bridge the channels for bass loads.

[@mysock351C]

In car audio bridged class-D is pretty much becoming the only show in town due to the high power requirements, esp. once you get above about 4kW. Saves a lot of components and space getting rid of the negative rail in the power supply section. In home hifi bridging linear discrete amplifiers is quite difficult due to the feedback and DC offsets, not to mention you have all the power and space you need since it can just be a big metal box plugged into the wall. With that said, most subwoofers are usually running bridged class-D since the small increase in distortion is of no concern.

[@GTILOUD]

Korean half bridge are very popular, the only advantage of the Brazilian or Chinese full bridge is the price $$$ they're cheap.

[@joakimsafstrom8405]

It is an amazing thing You are doing with this series, it truly shows Your passion :)

[@chucktyler4057]

I've run a pair of identical Hafler amplifiers in bi-amped set-up driving Magnepans for years. One day I decided to tinker with this setup just to try out the bridging switch on the back of each amp. I also have a Bryston preamp that I left out for expediency, just using the gain switches on the front of the amps. Oh my goodness! The music just bloomed into something incredible! I hate to have to fault the preamp. Magnepan themselves use Bryston. So I'm thinking the lack of stereo crosstalk might be the key.

[@music3121]

He is only one person who knows everything in audio .Thanks Sir

[@georgecan1999]

Many years ago I had a vintage Marantz 4070 quad amplifier which it had a 4 channel / 2 channel switch, that amp was sounding really magical in 2 channel mode which is bridged ( floating ground) but the spec wasn't 4 times of the watts

[@Mark-lq3sb]

Learning something should *never* be boring.

[@HenriVerhage-tf6lb]

I run 2 mono blocks. The best sound I heard to this day.

[@gordthor5351]

"Why aren't bridged amps more popular?" Because they are a sacrifice to sound quality. A properly designed high powered mono block can have finesse and brute power. A bridged stereo amp will always sacrifice quality for quantity.

[@EscapeRealityMedia]

Great comment That’s what I wanted to hear

[@davidclark6896]

I bridged a Crown 1000 in a rack system for my bass guitar. Sounds awesome! The best I remember the tech had to wire the speakon connection differently. Coming from the amp to the cabinet can only be a certain way.

[@Frisenette]

This is a brilliant explanation. It puts things into clear words that I have so far only understood in a murky way. Please *do* go on for hours!

[@cornwallonline]

Paul, why is it necessary to bridge an amplifier just because you want to use all NPN output transistors? Compound feedback pair (Sziklai) amps don't have to be bridged to function - yes, the other part of the pair is a PNP, but the actual output transistors are NPN (al la Quad 405) . Do you use a cunning design to eliminate the compound pair? (but that then necessitates bridging two amps)

[@Radar23]

Always the best information

[@Enigma758]

Is the BHK amplifier quasi-complementary?

[@promo130]

and you cut the damping factor of the amp in half wen bridged

[@jukkamaljanen6644]

There is an error in the video: bridging amplifiers doubles the power, it does not quadruple it. That should be obvious by plain logic, 100 W + 100 W = 200 W. Technical reason is within the halved apparent load (impedance), which is mentioned in the video.

[@marklowe7431]

4x is correct in theory however most will not achieve

[@nix9409]

It's just Ohms law, assuming constant R, doubling the voltage doubles the current, that is 4 times the power. Assuming source can deliver and components handle.

[@jukkamaljanen6644]

Yes I have since then learned a great deal about bridging. A worthwhile mention is that when bridged, many amps are specced for doubled loads (Ohms) compared to single-ended, making it only double powered. That speaks for the fact that those amps are not designed to handle so much power.

[@nix9409]

In reality it is more like x2-3.

[@bondalero0074]

I miss the days of Zed Audio built amps in my early days; what happened to them; where did the go! I recently picked up (2) Down4Sound JP8 amps to slave/strap in near future! Using just one right now on (1) Skar 10” DDX in DvC2 at 1 ohm in a factory Skar Box REALLY “Shaking Foundations!” Can’t wait to get my Big “3” together so I can slave both JP8’s on a pair of Skar 12” EVL subs just to experience what you spoke of! “Thank You” for your knowledge!”#JP8🔥💪”BlueBeast”#SkarSubs(ServemyTaste)#🔊❤️

[@gordiefrench5342]

Paul as you teach us it is not boring Thank you for what you do

[@steenj938]

Always a pleasure to watch your channel Paul 🙏👍 Greetings from Denmark 🙂

[@Paulmcgowanpsaudio]

Thanks for watching!

[@zertex2830]

Do you have a channel where you go and explain stuff in way more detail? Nice video!

[@rondriver6028]

Bridging amplifiers is mainly used in commercial set ups, dj's would employ amplifiers that are bridged in order to get sufficient power and volume, but it would make no sense for someone having a bridged amplification at home because you don't get the same sound staging stereo imaging and bass output that a single amplifier would give you, and you certainly don't need the extra wattage in small domestic settings.

[@phillipmoore6295]

My McIntosh MC 7300 Amp can be bridged from 300 watts stereo to 600 watts mono. So I could buy another one and use them as bridged mono blocks.

[@scarmenl]

The other thing I found with brigded amps is that you get to hear negatives of the amps all out of ratio to the increased power. Sadly in my esperiance it tends to show the negatives far more.

[@H-77]

That's probably due to the reduced load impedance. Typically, distortion rises as load impedance decreases.

[@skip1835]

- may have already been mentioned in the comments - - should be pointed out, not all amplifiers can be bridged - - the Bel Canto ref600M's is an example, no can do

[@janinapalmer8368]

Very well explained .... yes I remember making a bridge amp using LM3886. These amp chips run on +_ 37v rails but in bridge mode they can only run on +_ 28v to keep the chip within its thermal limits

[@claytonwalters5715]

N channel is a reference to MOSFETs not Bipolar (NPN). MOSFETS are preferred for higher power applications because they have a negative gain to temperature coefficient. This allows them to be stacked in parallel increasing the current capability. Trying to do this with bipolar devices can result in thermal runaway.

[@H-77]

MOSFETs tend to have that same positive temperature coefficient when used at reasonable currents. They also are prone to hot-spots on the die, leading to a very quick failure. So while people like to run around saying that "MOSFETs don't suffer from secondary breakdown!!", it isn't really true. IR has a good application note on this, where they discuss the pitfalls of using modern MOSFETs in linear applications. It is possible (lots of people build amplifiers around HEXFETs, for example), but that doesn't mean they are without pitfalls. A well-designed BJT amplifier will not have any issues with thermal runaway, but the temperature compensation (especially in EF triples) can be a real pain to get right and can be annoyingly complex. Lateral MOSFETs do not exhibit this behavior, and really are pretty much immune to secondary breakdown. The downside is that they're really expensive and somewhat difficult to get, so you might as well just use a bunch of BJTs or regular switching MOSFETs. Like everything in engineering, it's a tradeoff.

[@christianm.6105]

I am new here. Its good to see this Channel. And Channels from the Bridge are get right when the Sound its very well have a robust impedence. Thats right. To reduce Hold up time of Sound to the Hardware.

[@HareDeLune]

Welcome to the channel! : )

[@bass305-HCCA]

In car audio, you can't tell the difference in sound quality between the two. Good video sir.

[@kenwebster5053]

Not out of phase Paul but "inverted" phase. There is a difference in meaning here. Many 2 channel PA amps have the capacity to be wired in a 1 channel (mono) bridged mode. You do have to be cognisant of the amp/speaker power and impedance matching. Passive speaker cable is part of the impedance matching question. It makes no sense using an amp with a high damping factor and nobbling that capability with long thin cables. 30 years in PA have proved to me that the Ethan Winer crowd are simply widely missing the mark on true sound reinforcement because of this issue. There is no need to make peoples ears bleed to fool them into thinking your sound is good. Simply setup correctly so it actually is good! In rough terms, it makes no sense to use a high damping factor amp and nobble that capacity with pathetically long thin high impedance cables....

[@marianneoelund2940]

Also, it makes no sense to seek a high damping factor amp, to use with drivers and crossovers that have several ohms of copper resistance. We need superconducting voice coils.

[@kenwebster5053]

@@marianneoelund2940 I disagree, because damping factor is source impedance divided by load impedance. Therefore, you can only have a high damping factor is the load impedance is several hundred to a thousand times higher than the source impedance. Therefore, there must be some load, enough to constrain current and power to reasonable levels for the equipment used. If the speakers impedance is too low, your amp goes up in smoke. The deal with all this is impedance, not DC resistance. The XO is an impedance device, not a resistive device. Yes, it has some resistance as all conductive devices do, but not a whole lot. Its basically a low and high pass filter built from capacitors and inductors. These are the 2 main electrical properties that produce the impedance required to perform the frequency filtering task. The alternative is to do that filtering at the signal level and drive the speaker transduces with separate amps. That is sometimes done using DSP of course but it a lot more expensive than putting XOs in the speaker cabinet as just stereo 3 way would require 6 separate power amplifiers, instead of the traditional 2. DC resistance is not a huge deal in speaker cables. it's just some insertion loss that can be compensated with more gain. Cable impedance can be a problem as it reduces the amplifiers control over transducer excursions (distortion). Much like if your cars hydraulic systems has air in the lines, reducing the precision & effectiveness of your steering and braking etc.

[@marianneoelund2940]

@@kenwebster5053 Ken, what you need to understand is that the copper resistances in the crossover and drivers *is effectively part of the source impedance.* The mathematical model is an external series resistor representing the copper resistance, with the speaker coils then treated as resistanceless. The same modeling approach is used for motors, transformers, inductors and many other devices, whenever copper losses have a significant impact on the analysis being performed. An 8 ohm speaker will typically have around 3 ohms of copper resistance, sometimes slightly more. Since damping factor, not surprisingly, is about damping, the total resistance in the circuit must be taken into account. It is not the amplifier's output impedance alone, which determines the system damping factor; it is the amplifier's output impedance, plus speaker cable resistance, plus the speaker's copper resistances. The latter dominates, thus system damping factor rarely exceeds 3. This is still true in a multi-amplified system where the drivers connect directly to the amplifier outputs.

[@kenwebster5053]

​@@marianneoelund2940 It's a constant part and therefore not relevant to filtering. Only reactance is relevant to filtering. Even it were relevant to distortion, the issue is load by source impedance & High end amplifiers have such low output impedance to make this negligible. At the end of the day, you have to run electricity through wires. Copper is an economical low resistance conductor and the length of wire in an XO inductor coil is pretty negligible in the scheme of things. You have to have something to do the job. What practical alternative are you suggesting?

[@marianneoelund2940]

@@kenwebster5053 The wire resistance in a driver voice coil is *not* negligible. It enforces an upper limit for the system damping factor, which as I already stated, is only around 3 at best. I'm not suggesting any practical alternative, just pointing out the folly of believing that amplifier damping factors in the hundreds or thousands have any practical meaning. Similarly, the expense of massive speaker cables is wasteful in most cases. Very few owners are aware of this.

[@jecelabayata-he1vn]

Sir how many speakers I can use if I am using bridge mode in my amplifier? Thank you.

[@delamalasie]

naim power amp use all NPN but i think the negative is connected to ground

[@milkman100001]

why do we see normal cheap cables in the background to test / adjust and set the high quality products when we are told all the time that we have to purchase cables that cost thousands.?

[@VladoT]

I do test and adjust amplifiers using regular cables instead high-end ones and yes, more expensive (speaker and signal) cables improve the sound later on. On the other hand investing thousands in cables is only justified in rare cases when you have very expensive (house money) system. On regular (few thousand) systems having invested a few hundred in cables and few thousand does not make any audible difference. But using a regular cheap cables - yes, you can hear the difference.

[@H-77]

Well... because you're listening to people who want to sell you something. We're dealing with such low frequencies (well below 100 kHz), so the transmission line characteristics of the cables being used is of minimal concern. I have seen zero evidence that anyone can actually tell the difference in a double-blind test. Furthermore, there are no measurable differences at the frequencies we are using this equipment at. One very good reason to not use such fancy cables on the bench is that they are often very thick and stiff, which is really annoying since it tends to make lighter-weight equipment slide around.

[@EscapeRealityMedia]

Can I bridge two same crown amps that have different wattage one is 450 and the other is 300 or something like that?

[@davidtomsett]

Robustly, like the D’Agostino Relentless amps!!

[@claytonwalters5715]

Don't attempt to bridge amplifiers that are not designed to be bridged. When you bridge amps the voltage across the load (speakers) doubles. As Paul stated, the power draw by the speakers increases by a factor of 4 because power is a squared function of voltage. But that increased power comes from the amplifiers and if split evenly then the power draw has doubled on each. Due to market forces, engineers will generally not design an amplifier for power levels it is not intended for.

[@markallen6384]

Sorry about this off topic question..I have a old Marantz SR4200 receiver and old Klipsch RF35 tower speakers with a center speaker. As this receiver is 5.1 capable and I have only 3 speakers would it be possible to use the unused rear channels and add them to my front and left speakers(front left and rear left receiver channels into the 1 front speaker and same with right side speaker). Would I short out my receiver or damage speakers?

[@chadbarker4023]

Where them damn speakers? What's Chris B doing? Can u do a show and give an update please or I'm going to buy some Bose 901s! Oh wait, I already own a pair in the basement. Hahahaha

[@jamesplotkin4674]

Use those 901's to hold up expensive stuff in case of a basement flood ;-)

[@juliaset751]

Very good explanation. Paul did it again.

[@darthbubba866]

Didn't answer the question. Are bridged amps more complex to manufacture? Sound worse? Less stable? Can only drive speakers above "X" ohms? Too expensive to the end user? He was asking about market penetration, not technical stuff.

[@clydeblair9622]

Excellent

[@Patrick_AUBRY]

So reference monitor with XLR input are bridge amplifier?

[@H-77]

Not necessarily. XLR is just (usually, but not always) a balanced input. What amplifier that drives depends on the choices made by the engineers who designed it.

[@toysforboysrc]

Can someone answer me what is ADAPTIVE FEEDBACK GLOBAL MODULATION TECHNOLOGY This is Alpines technology but I need to know what this tech does for the four channel D class Alpine. There’s just no content on this matter, only the scientific jargon on the chalk board, but nothing that explains how this will affect mids & highs ?

[@stephens2r338]

Bridged amps offer 4x the power but with 4x the noise and 4x the problems. In reality it still has 2 channels with the same issues a regular 2 channel amp has only now you have 4 channels to work with. It's not mono. It's a cheap fix no matter the retail price to offer 2 amps with lots of power using smaller amps.

[@ragextico]

So I have a full bridge amp and there’s 2 positive and 2 negative outputs. How do I hook up one subwoofer with one set of speaker wire to get the most wattage?

[@CDJF1]

It should tell you on the back of the amp near the spkr teminals how to hook up for bridge mode. Usually the positive spkr wire goes in to ch. 1 positive and the neg. spkr wire goes in ch.2 positive.

[@bloodcarver913]

Bridging an amp also generates more noise than running in SE mode. The uV will rise.

[@PebblesChan]

I can see why stereo amps are driven in bridge mode but with the complexities properly addressed, can’t you also join multiple amps even with different gains in phase to get an increased output?

[@mysock351C]

No, not unless they are meant to be bridged. With linear amplifiers there will be DC offsets, as well as feedback (typically, but thats another story). Anyway, getting to the point, if you bridge two linear amplifiers directly, the resulting DC offset of each amp will unbalance the differential input of the other its attached to, resulting in substantial current flow, and also distortion. If its bad enough, it could even damage the output stages. Normally in bridged ICs they will either be class-D, or specifically built to be easily bridgeable (e.g. TDA1554, and others) via connecting the internal amplifiers together on the PCB. In car audio whole class-D amps can also be bridged together, but this requires that the clock signals of each amplifier be synchronized to prevent phase issues and idle tones, among other things.

[@PebblesChan]

I said if you properly addressed the complexities. A simple way could be galvanically isolating the inputs and outputs so that the amplifiers are effectively just voltage sources with accompanying series resistors connected to the loudspeaker and handling the increased series resistance.

[@mysock351C]

@@PebblesChan Joining two separate amplifiers can be quite challenging to say the least. Galvanic isolation would be difficult due to the large inductance needed for the transformers while still having the necessary high frequency response. The easiest way to achieve DC blocking would be to use capacitors at the outputs. To get a lot of capacitance, this can be done using what's called a bipolar capacitor, which consists of two electrolytic capacitors and two diodes capable of handling the current requirements. This works identically to a non-polarized capacitor by offsetting the voltage each capacitor sees so it does not see a significant reverse bias. But there are other issues to consider as well. You are joining two amplifiers with separate power supplies, so that invites both DC and AC ground loops, even if the amplifier does not have a specific connection to ground. The transformers have quite a bit of parasitic capacitance and it can potentially allow unwanted signals to get into the audio. You would need to have external star-point grounding to ensure there are no loops. The amplifiers also have to be very well balanced gain-wise to work properly or the audio will have an offset, which can cause issues with audio and the loud speakers. You also still have the same issues with the feedback. While the capacitors will block the DC, there is a possibility of imbalances at audio frequencies as well. If one amp unbalances the other, there will be substantial current flow due to how much gain margin there is. Even a few mV can cause several amps to flow as the amplifier attempts to balance its differential input. Lastly you will also need an external phase inverter for one of the amps. This could be as simple as a center tapped audio transformer, but for best results it should be op amps so the fidelity is not unduly compromised. It could work, but care would be needed if you're to avoid spontaneously decapping all the output transistors. But still better to buy amps made to be bridged rather than having a maze of wiring and circuitry dangling off the back. With that said, it is often done in car audio even with non-bridgeable amps, but life is easier there as everything is on one supply (12V) and the amps are usually class-D, so there's less risk of interactions. But there are still often issues.

[@mysock351C]

@@PebblesChan Talking about this reminds me of when I tried this as a kid to get more power before I knew any better. There was "audio" when I turned it on, but lots of sparks and smoke coming off the speaker wires. Everything survived, but still amusing to think back on it. Edit: In all honesty it was probably because I hooked it up wrong and shorted something out. Hooked up correctly there probably would have just been some DC offset.

[@H-77]

Yes, in theory you could. In practice, it is likely to result in one (or more) blown amplifiers.

[@janinapalmer8368]

What determines how good or bad a bridged amp setup sounds is how you derive the inverted signal ... in my humble opinion you MUST use a low gain low noise op amp to provide a true balanced output to drive the amp modules

[@SomeTechGuy666]

Ground is probably NOT the same as the ground in the well. The "ground" you refer to is probably the center tap on the transformer secondary. I doubt it is connected to household ground. This would be easy to test.

[@H-77]

Usually those two grounds are tied together (very intentionally at one specific point!) for noise reasons.

[@ToyotatechDK]

Great explanation

[@FOH3663]

The negative effects of power supply rail pumping can be mitigated via bridging.

[@rutvinchaudhari3185]

Thanks for The video

[@roshanaruna7872]

really explain

[@pennfootball71]

I wish you guys would reverse engineer some audionet amps. They are the best I ever heard! Also Mola Mola! I use the Mola Mola Kaluga's but wish I could buy more American stuff that could beat the Europeans in sound. I haven't found anything yet but David Belles is good for more affordable gear I have heard just not enough power for what I need. I do use American Speakers from YG Acoustics and American cables from Kubala Sosna and have a USA made Rogue Audio Ares phono.

[@CDJF1]

Love my MC275 by McIntosh.

[@com456dj]

Nice Video

[@johnsweda2999]

Why should it be an issue with impedance surely you just put a zobel network on the output to keep the impedance in check

[@marianneoelund2940]

Zobel networks only affect impedance at high frequencies. They are not effective across the full audio frequency range.

[@Paulmcgowanpsaudio]

It's not that easy. It sees half the impedance because there's twice the voltage.

[@hom2fu]

zobel network. when your tweeter sound harsh, put it in and it sound softer.

[@H-77]

The speaker impedance doesn't change, but it's basically being split between the two amplifier modules. The problem is that designing an amplifier to drive 2 ohm loads is hard. Power is equal to (I^2) * R, so it should be easy to see that getting a lot of power at 2 ohms requires a lot of current. The problem is that in order to get a lot of power at 8 ohms, you need fairly high voltage rails, and you quickly run into an SOA (safe operating area) issue in the output stage, which is typically solved by adding more output transistors. Do some google searching for what the inside of a Crest 7001 looks like- you can see just how many output transistors there are for this very reason. Furthermore, even with enough output transistors to handle it, there is still a lot of heat that has to go somewhere, and most audiophiles will reject any amplifier with a cooling fan, so that means big, heavy and expensive heatsinks.

[@marianneoelund2940]

@@H-77 From SOA considerations, it's actually much easier to design a BJT amplifier to achieve a target power level into a 4 ohm load, if it's bridge mode, because the working Vce is cut in half. BJT's safely handle much higher currents at lower voltages. Another approach to ameliorating SOA issues, is stacked output transistors as used in the Dynaco Stereo 400 (a Dave Hafler design).

[@FSXgta]

Because watts are cheap nowadays. You only need bridge if you need LOADS of power.

[@scottdc6971]

BTL never sounds as nice as an SE amp in my experience.

[@wishusknight3009]

I used to have a class A super symmetrical. its total power output was probably not more than 18 watts per channel into 8 ohms and it consumed about 350 watts off the wall at all times. I swear it must have weighed 60 pounds or more. It had a control on it which gave it a user adjustable damping control, so it behaved like a transconductance amp. And this was probably by far the best sounding amp I have ever had or heard. Really wide bandwidth, extreamely articulate and able to match pretty much any speaker you can throw at it. I am really sorry I sold it but we live in hot weather so it was just not practical. It basically needed to stay on continually to stay warm and sound good.

[@ThinkingBetter]

Internally bridged vs. externally bridgeable are not exactly the same. You get more performance for your money with an amplifier that is carefully optimized for outputting the power you need, with or without internal bridging.

[@abrahammutai8073]

I need to reach you by a call

[@nix9409]

"Ground" is just a reference point, it is a most misused nonsensical term in electronics ever.

[@bobross6802]

Push-Pull

[@akhtarizod5802]

Because they sound horrible.

[@dragan3290]

I would love to bridge my Yamaha A-520 amp to power a 15 inch subwoofer! But no I can't. Lol.8 to 16 ohm amplifier driving a 4 ohm? Naaah! I have bridged an old Akai 1980s amp when I was younger and it was loud. My brother uses it now as his garage amplifier.

[@hometheaterfever5]

Ohh. Huh?