[Steve Eddy]

Here's a practical example of a bridged output audio amp:
I have a Bryston 2B-LP stereo power amp.
60 Watts/ch @ 8 Ohms
100 Watts/ch @ 4 Ohms
Manufacturer does not recommend using this amp to drive 2 Ohm loads.

A few years ago I needed to press it into service to drive the centre channel in my home theatre system.
There is a stereo/mono switch on the rear of the amp.
This bridges the two channels together, so now I have 200 Watts @ 8 Ohms.
Approx. twice as much voltage, approx. twice as much current into 8 Ohms and twice the slew rate! And approx. 4 times as much power! Yippee!

Sure. But that's only because all you had was a bridgeable 60 watt amp. My point is that the same thing could have been accomplished with a non-bridged 200 watt amp.

Arguably I needed twice the slew rate as I now have twice the output voltage!

Just because you're outputting twice the voltage doesn't mean you need twice the slew rate. The slew rate of each amplifier channel may be very high, so that they could easily double (or more) their voltage swing without any slew limiting. The same topology can be used to produce amplifiers with a wide range of power outputs. You just need to change the gain, supply voltage, the number of output devices and the amount of heat sinking.

And bridging two amplifier channels doesn't change the slew rate of the individual amplifier channels. They still have the same slew rate they did before bridging. You only get the doubling of voltage because one is driven with a signal of opposite polarity and the differential voltage between the outputs has doubled.

The downside is the mono (i.e. bridged) configuration is not recommended for driving 4 Ohm loads. Yes, there's a downside.

That's only because the individual amplifier channels wouldn't be able to dissipate that much power. That's a function of design choice, not bridging.

So the "twice as much voltage, current and slew rate, and four times as much power" statement is true, but is rather misleading too.

Yeah, but as I said, compared to what? A non-bridged amp can also deliver twice the voltage/current of a bridged amp, twice the slew rate, and four times as much power. Sure, if all you have is a particular amp, that's one thing. But I'm talking about what's possible in the marketplace.

Furthermore, this amp (whether used in stereo or as a mono bloc) has balanced inputs (i.e. differential inputs) so, assuming it's receiving a signal from a balanced output pre-amp, and you are using a balanced interconnect, the input will reject common mode noise (within a limited bandwidth, of course).
BTW, the input stage converts the signal into a Single Ended signal, which then drives the power amp stage.

Other amps may have different configurations, YMMV.

Yeah, it's pretty common to have a balanced input, do everything in between single ended, and then balace the output, if you're talkingbabout line level gear, or just continue the output single-ended in the case of headphones or loudspeakers.

se

 

[robrob]

I didn't ask you to explain any safety reasons. I said forget about safety.

 
Steve, you may not be aware of this but other people will read my post.

 

[Steve Eddy]

Steve, you may not be aware of this but other people will read my post.

If it was intended for other people, then why did you quote the question I put to you? You quoted the question, but never answered it. I'm sure other people will be left rather confused.

se

 

[camusmuse]

Thanks for all the info guys.  Alot to digest and mull over. 
 
About bridging amps...there are always trade offs.  You may get twice the voltage, twice the current, but like you said 8ohm is as low as you can go.  Of course the actual impedance changes "real-time" with the source material and speaker design so that 8 may drop to 4 and run your amp into protection or pop a fuse.  I dont know Bryston amps personally, but I do know they are quality.  I would bet you could actively cool that thing and run it pretty "hot".  SQ will suffer though...  When you bridge and use the minimum speaker impedance, you are pushing the amp to its "limits".  Same as running stereo in 4 ohms(same 200 watts right?)...no real difference in power, just how it is used.  I would rather run a higher impedance speaker and get more headroom in the amp and better SQ.  If you want twice the power, buy another amp.  Four times, buy three more.  Just how I see it...and have experienced it.
 
I used to do car audio as well(was MECP certified at 17y/o), and while I love my high current "cheater" car audio amps, when you push them to ultra low impedances...ie.....1/2ohm mono....you can definitely hear a SQ difference and not a good one.  If you dont know.... a cheater amp is one that is rated at say 22wx2 at 8ohm, but it is "stable" down to 1ohm or lower, wiring multiple drivers to achieve probably 400-500 watts on a regulated ps.....unregulated, you can go even lower but again active cooling of some sort is a must.  They made these amps so you could compete with "44 watts"(0-50w class), and have a decided advantage because you are running a high current amp that really puts out much more power than your "competition".  Of course everyone followed suit and made high current amps...Orion's Concept series were the pinnacle for me.  Rated at like a 1/4watt, but really put out around 1000 or so(all depends on how much "battery/alt" juice you can supply).  High current was created for the competitions...some of us run them "cool" and get fantastic sound quality.  Not as loud, but much much better all around.  Plus you dont have to worry about melting your amp....literally...lol. 
 
My verbose point is.....all you are going to do is wear you amp out faster.  Heat kills...  Right now my bedroom system is a rather odd setup up, but it isnt really for music..its for pink noise for sleep/meditation.  Two parasound Zamps, each bridged; but I am using old Bose roommate speakers(1 or 2ohm single 4" speaker per speaker.  They were meant to be full range and have their own built in high current amp.  Well the amps died pretty regularly, so I have a "few" broken pairs.  Back to bedroom...you'll love this...lol....I have the 4" 1ohm in series with a Peerless 10" 8ohm woofer(each for right and left channels) to actually bring up my impedance to keep my amps cooler(produce LESS power).  No crossovers at all, just "lucky"

natural roll off and some room tuning/speaker placement with a portable RTA.  Mid-fi for sure, but I cant sleep without some sort of "noise"...but thats a different story.  Does TV fine, but it really could use a tweeter for music("Aint got highs, Aint got lows; Must be Bose"...lol)
 
The more I read over the comments above it seems that we all have fundamental disagreements, or at least on my part, misunderstandings from my lack of expertise.  Maybe I will figure it out one day, then I can play with the "big kids"....til then I will most likely go back to lurking.  I hate to waste your time on my whimsical misgivings about electronics. 
 
All I was trying to do was hook up a Conrad-Johnson MV-52 as a headphone amp...just....STILL...waiting on cable so I can run that EL34 based "box of gold" to my cheapo Beyers...dont worry I wont call it "balanced" ever again.  Probably going to sell the CJ anyway(why I am making my "not balanced" four conductor cable able to use a SE three conductor 3.5mm input jack or any other "termination".  The CJ sounded great on my modded Maggies....CJ PV-1 as the pre....  maybe I should just go back to full size speakers...

   Thanks again for trying to school me.....just too far out of my comfort zone I suppose....

 

[Sonic Defender]

  Well, when I was doing all my trials on different headphone amps vs. different speaker amps with the (HE-6).  I and a few others found more times than not the speaker amp had what it took to get the HE-6 to sound listenable.  
 
I now have the 560 but I don't have all the headphone amps I had before, so I can't really do the same comparison as before.   
 
So you have to do some grunt work and come up with your own conclusion.  Just like headphone amps, all speaker amps sound different so you have to get the one that fits your tastes.  
 
One of the good things about already owning speaker amps and / or vintage receivers -  you might have a gem and don't even know it.  Chances are if the NAD sounds good with speakers it should do a good job with the 560.
 
Do you already have this?
 

Hi preproman, the cable manufacturer you had suggested said this when I told him I preferred to not have any resistance added into the cable:
 
"You can do that, but the issue arises when then amp isn't running at optimal power state."
 
What do you think about that? My instinct tells me to just have no resistance added to the cable. Your thoughts, and other members of course, are appreciated.

 

[Wildcatsare1]

Hi preproman, the cable manufacturer you had suggested said this when I told him I preferred to not have any resistance added into the cable:

"You can do that, but the issue arises when then amp isn't running at optimal power state."

What do you think about that? My instinct tells me to just have no resistance added to the cable. Your thoughts, and other members of course, are appreciated.
[/quote

Mark, perhaps that is why the good Docter uses the HiFiman Adapter, even with SS Amps.

 

[wuwhere]

 
Hi preproman, the cable manufacturer you had suggested said this when I told him I preferred to not have any resistance added into the cable:
 
"You can do that, but the issue arises when then amp isn't running at optimal power state."
 
What do you think about that? My instinct tells me to just have no resistance added to the cable. Your thoughts, and other members of course, are appreciated.

 
A cable with no resistance?

 

[Hun7er]

Did anybody tried with headphone SET amp like Art Audio Jota or Audio Note Conquest ?

 

[preproman]

 
Hi preproman, the cable manufacturer you had suggested said this when I told him I preferred to not have any resistance added into the cable:
 
"You can do that, but the issue arises when then amp isn't running at optimal power state."
 
What do you think about that? My instinct tells me to just have no resistance added to the cable. Your thoughts, and other members of course, are appreciated.

I think when using the 560s you may want that little bit of resistance, but that's just a guess.

 

[Steve Eddy]

A cable with no resistance?

No added resistance, i.e. in addition to the cable's normal resistance.

se

 

[davidsh]

Depends entirely on the amp u are using whether you want any extra resistance of some sort

 

[RAZRr1275]

If anyone's interested in experimenting with using speaker amps for headphones, I have an affordable, but very good option listed in the classifieds here . The Temple Audio Bantam Gold. Reviews and such are linked inside the thread 

 

[Sonic Defender]

Depends entirely on the amp u are using whether you want any extra resistance of some sort

You actually replied to an original post of mine quite some time back now on this subject. You had suggested that based on your calculations my NAD M3 integrated amp should be quite quiet and noise wouldn't be an issue. Since that time different aspects of using a moderately powerful amplifier (180watts into 8ohms, 480watts into 4ohms) with my HE 560 have been discussed. Essentially I am trying to determine whether using an adapter box such as that provided by HiFi Man would impact the sound quality as it does put a great deal of resistance between the signal and the headphone. My research seems to suggest that where possible one should avoid adding resistance in this manner. However, we now of course must consider the impact on the amplifier, and of course the risk to the headphones of just running wires from the speaker terminals directly to the headphones.
 
Personally I am not worried about blowing the headphones, I trust myself to have a safety regiment in place (i.e. I will always turn the volume to zero before applying gain). My new concern is whether or not the amplifier will behave well when driving such a load. I am technically very ignorant in this area and I haven't the slightest clue what the implications for the amplifier performance is when I assume only a very limited amount of range of the volume attenuator will be brought into play with driving headphones. What does the amplifier see as a load in practical terms and how does it change (if at all) the amplifiers performance? Thanks to any and all with thoughts on this to share.

 

[Chris J]

You actually replied to an original post of mine quite some time back now on this subject. You had suggested that based on your calculations my NAD M3 integrated amp should be quite quiet and noise wouldn't be an issue. Since that time different aspects of using a moderately powerful amplifier (180watts into 8ohms, 480watts into 4ohms) with my HE 560 have been discussed. Essentially I am trying to determine whether using an adapter box such as that provided by HiFi Man would impact the sound quality as it does put a great deal of resistance between the signal and the headphone. My research seems to suggest that where possible one should avoid adding resistance in this manner. However, we now of course must consider the impact on the amplifier, and of course the risk to the headphones of just running wires from the speaker terminals directly to the headphones.

Personally I am not worried about blowing the headphones, I trust myself to have a safety regiment in place (i.e. I will always turn the volume to zero before applying gain). My new concern is whether or not the amplifier will behave well when driving such a load. I am technically very ignorant in this area and I haven't the slightest clue what the implications for the amplifier performance is when I assume only a very limited amount of range of the volume attenuator will be brought into play with driving headphones. What does the amplifier see as a load in practical terms and how does it change (if at all) the amplifiers performance? Thanks to any and all with thoughts on this to share.

In ten words or less (more or less)
The power amp won't be fazed by driving a 60 or 600 Ohm load.
You can use the M3 to directly drive your headphones without fear.
Obviously, you can turn your M3 on, play music at a reasonable volume and unplug the speakers mid song and the amplifier will be unaffected.
I've done it myself many times.

 

[Sonic Defender]

In ten words or less (more or less)
The power amp won't be fazed by driving a 60 or 600 Ohm load.
You can use the M3 to directly drive your headphones without fear.
Obviously, you can turn your M3 on, play music at a reasonable volume and unplug the speakers mid song and the amplifier will be unaffected.
I've done it myself many times.

Much appreciated, cheers.