bridging NAD amplifiers

1ShotBill

I'm looking to power a pair of Polk RTA 12C speakers with my NAD 2400THX power amp and a NAD 7400 integrated. Since the speakers are 4 ohm rated, is it possible/advisable to bridge the 2400 & 7400 together, or should I just use the 7400 as a preamplifier only? (The 2400 is considered to be a "companion" power amp, according to the 7400 manual.) I've never bridged amps before. My concern is the impedance. Is it safe to bridge these considering the speakers are rated at 4 ohms? The manual for the 7400 states "If you are in bridged mode, we recommend that the speakers have a nominal impedance of 8 ohms and that the impedance switch is set to 4 ohms (normal). The Impedance switch is automatically set to this position when the Bridged Mode is selected". What do they mean by "nominal" impedance of 8 ohms?

F1nut

Is it safe to bridge these considering the speakers are rated at 4 ohms?

Absolutely not.

What do they mean by "nominal" impedance of 8 ohms?

It means that the speaker's impedance generally resides in the 8 ohm area, but can dip higher or lower in certain frequency ranges.

disneyjoe7

By Bridging amps they see half the speaker load, so if 4 ohms the amps sees 2 ohms.

1ShotBill

So far one voter against bridging and another in favor. Any other opinions? If the amps will each 'see' 2 ohms, I don't see what the problem would be. I'm told the RTA 12C speakers need real clean power behind them to hear the true potential... which is what I was thinking with the bridging plan.

heiney9

No!! Plus you can't bridge the integrated and still use it as a pre. Also, I have no idea what you mean by this to bridge the 2400 & 7400 together, it makes no sense. Disneyjoe's post is NOT in favor, so that's 2 no's and I'll throw in a hell no.

H9

heiney9

1ShotBill wrote: »

If the amps will each 'see' 2 ohms, I don't see what the problem would be. I'm told the RTA 12C speakers need real clean power behind them to hear the true potential... which is what I was thinking with the bridging plan.

It means the amps will go poof trying to drive a 2 ohm load they aren't even close of capable of doing. Pay up your homeowners insurance with extra fire protection, you might need it if you try it.

11tsteve

i am in no way recommending bridging, but NAD did manufacture the 7400 to be bridgeable, and has instructions in the manual to use the 2400 as the amp for driving the right channel.

(3) In the bridged mode the power-amplifying
section of this receiver will normally be used to drive
your Left speaker, while a separate amplifier such as
a NAD 2400 will drive your Right speaker.
In that case, leave in place the upper jumper or
cable that connects PRE-OUT to MAIN IN in the left
channel. Disconnect the lower (right-channel) jumper
and connect a cable from the lower PRE-OUT jack to
the appropriate input jack on the power amplifier that
will be driving your Right speaker. (If you are using a
NAD 2400 in bridged mode, you will connect to its
upper (L) input.)
Note that in the bridged mode, both the 7400 receiver
and the companion 2400 power amp are driven
through the upper (L) input jack, regardless of which
speaker is being driven.
(4) Disconnect any speaker wires from both the
SPEAKERS A and SPEAKERS B terminals. Select
the cable from the speaker that is to be driven by the
bridged 7400. Connect its "positive" conductor to the
L+ terminal and its "negative" conductor to the R+
terminal in the "B" group only. DO NOT connect any
wires to the black terminals (R- and L-). The "A" group
terminals are not operational in the Bridged mode.

my question is... if this is really that bad of an idea, why do so many mid-fi makers offer this feature? I honestly don't know enough about the subject and am curious as to if there is a high failure rate?

FTGV

heiney9 wrote: »

It means the amps will go poof trying to drive a 2 ohm load they aren't even close of capable of doing.

Thermally stressed if driven hard yes,going poof ,not likely.

heiney9 wrote: »

No!! Plus you can't bridge the integrated and still use it as a pre.

Sure you can by simply removing the shorting links between the pre out /main in connectors.

chandler9a

Honestly, one of those 2400 amps should run a pair of 12C's just fine by itself, not that more clean power would hurt any. I too would say no to the bridging idea...

FTGV

chandler9a wrote: »

Honestly, one of those 2400 amps should run a pair of 12C's just fine by itself, ..

Agreed.

disneyjoe7

1ShotBill wrote: »

So far one voter against bridging and another in favor.

Hmm.... NO HELL NO sorry my Favor isn't ok to do that. You will damage the amp the amp may damage the speakers. You wouldn't be happy later.

1ShotBill

For those who say the 7400 integrated amplifier can't be bridged and that it's not 2 ohm capable, I offer this direct quote from its owners manual: "While the 7400 is conservatively rated at 100 watts per channel continuous power for test tones, its Power Envelope circuit produces upwards of 370 watts per channel of long-term dynamic power for music, with a peak current of 40 amperes for precise control of voice-coil motion with speaker impedances as low as 2 ohms. For still more power, a rear-panel bridging switch converts the outputstage into a mono amplifier rated at 200 watts continuous power and 800 watts of tone-burst powerfor music. The companion 2400 Power Amplifier may be added for stereo." http://www.manualslib.com/manual/108996/Nad-7400.html

With all due respect: If I risk burning my house down by bridging these two (companion) amps together, as some here have suggested, why then is it recommended in the manual?

My main question here was not can these be bridged, for I already knew that to be possible. However, what I do want to find out is whether or not it is okay to do so using 4 ohm speakers, since the manual says "we recommend that the speakers have a nominal impedance of 8 ohms". If anyone can specifically speak to this question I would greatly appreciate it.

Secondly, I'm now considering going the preamp route as well since a couple of users here feel the 2400THX is powerful enough to drive the Polk RTA 12C speakers. I am by no means planning to blast this system at high volume levels. Just looking to get plenty of clean power behind the speakers (as many RTA 12 users have recommended on this forum) to bring out their best attributes. I'm looking at something along the lines of a 1700 or 1130 if I don't go the 7400 integrated (bridged) route. In any case, I'd prefer something with a good phono-pre built in.

monepolk

Actually everyones reply was that it was not a good idea to bridge them for a 4 ohm load.

F1nut

For those who say the 7400 integrated amplifier can't be bridged and that it's not 2 ohm capable, I offer this direct quote from its owners manual: "While the 7400 is conservatively rated at 100 watts per channel continuous power for test tones, its Power Envelope circuit produces upwards of 370 watts per channel of long-term dynamic power for music, with a peak current of 40 amperes for precise control of voice-coil motion with speaker impedances as low as 2 ohms.

That's in stereo mode, not bridged.

However, what I do want to find out is whether or not it is okay to do so using 4 ohm speakers, since the manual says "we recommend that the speakers have a nominal impedance of 8 ohms". If anyone can specifically speak to this question I would greatly appreciate it.

Again, absolutely not.

heiney9

1ShotBill wrote: »

For those who say the 7400 integrated amplifier can't be bridged and that it's not 2 ohm capable, I offer this direct quote from its owners manual: "While the 7400 is conservatively rated at 100 watts per channel continuous power for test tones, its Power Envelope circuit produces upwards of 370 watts per channel of long-term dynamic power for music, with a peak current of 40 amperes for precise control of voice-coil motion with speaker impedances as low as 2 ohms. For still more power, a rear-panel bridging switch converts the outputstage into a mono amplifier rated at 200 watts continuous power and 800 watts of tone-burst powerfor music. The companion 2400 Power Amplifier may be added for stereo." http://www.manualslib.com/manual/108996/Nad-7400.html

With all due respect: If I risk burning my house down by bridging these two (companion) amps together, as some here have suggested, why then is it recommended in the manual?

My main question here was not can these be bridged, for I already knew that to be possible. However, what I do want to find out is whether or not it is okay to do so using 4 ohm speakers, since the manual says "we recommend that the speakers have a nominal impedance of 8 ohms". If anyone can specifically speak to this question I would greatly appreciate it.

Secondly, I'm now considering going the preamp route as well since a couple of users here feel the 2400THX is powerful enough to drive the Polk RTA 12C speakers. I am by no means planning to blast this system at high volume levels. Just looking to get plenty of clean power behind the speakers (as many RTA 12 users have recommended on this forum) to bring out their best attributes. I'm looking at something along the lines of a 1700 or 1130 if I don't go the 7400 integrated (bridged) route. In any case, I'd prefer something with a good phono-pre built in.

Obviously we don't know what we are talking about. Best way to find out is to try it. Go ahead bridge them both together and see if it's possible. Be sure and test it playing loud too.

1ShotBill

So how then do I connect them in 'stereo' mode (not bridged)? Maybe I'm not using the correct nomenclature here. Or, is the reason this is not possible due to the fact that my speakers are not 8 ohm? What I would really appreciate here is an answer that clearly explains why this is not possible... rather than a "hell no" or "absolutely not". Clearly I'm not understanding something here and would like to know what that is. Please enlighten me. And I say that without any sarcasm.

Any alternatives such as certain NAD pre-amps to use with the 2400THX would be spectacular! Units I'm considering are the 1600, 1130, 1300. Thoughts on these?

I am not trying to offend anyone here in this forum. I new to this and and doing my best to educate myself. Thanks

DaveHo

You can't bridge them because the speakers are 4 ohm & the amps will fry. You can't use both amps in a bi-amp configuration, the 12C's don't support it. Bottom line, you can't use both amps if you're going to be powering 12C's. Don't know how to say it any more straight forward than that.

1ShotBill

Thanks DaveHo! I really appreciate that explanation.

I will now start my search for a nice NAD pre-amp with a good built in phono-pre that I can connect to my NAD 2400THX power amp.

Thanks again to everyone who did their best to help me out!

pitdogg2

DaveHo wrote: »

You can't bridge them because the speakers are 4 ohm & the amps will fry. You can't use both amps in a bi-amp configuration, the 12C's don't support it. Bottom line, you can't use both amps if you're going to be powering 12C's. Don't know how to say it any more straight forward than that.

let me expand on this a little.
Earlier in the thread this was mentioned. Forget Bi-Amping this is just Bridging Mono. since both speakers are 4ohm when the amps are bridged they each will see a 2ohm load(speaker) instead of 4 ohm. Then as you play music they will dip lower >2ohm so the amp may see a direct short and will just stop working(protection mode) not to mention you will have much more noise(distortion). So in this case to get more power you get none at least not for very long.

FTGV

1ShotBill wrote: »

What I would really appreciate here is an answer that clearly explains why this is not possible... rather than a "hell no" or "absolutely not". Clearly I'm not understanding something here and would like to know what that is. Please enlighten me.

The issue is the potential for thermally stressing the ouput stage of the amplifier.The lower the impedance the more current that is required.Since bridging the amplifier increases the available voltage swing and current it's easy to see that if you push the bridged amp hard into lower impedances it will put greater demands on the output transistors,thus they will be running much hotter.If the heatsinks are not able to disipate the extra heat generated it's certainly concievable it could lead to eventual failure with a poorly designed amplifer.Do I think your NAD will instantly vapourize if you run it bridged?As I stated previous not likely for a few reason's.First while in bridged mode it will have the potential for considerably greater output it's highly unlikely one would want to push it anywhere near those limits.Also the NAD designers are clever folk's and will have included thermal protection.

1ShotBill

I just realized that although I do not yet have a preamp to test out my recently acquired NAD 2400THX power amplifier, I can still test it by connecting my Cambridge Audio phono pre directly. Since the 2400 has L/R level adjustments on the front I am able to control the volume during testing. Let me just say that now it's connected, I have no need for more power. I only got to about 8-O'Clock on the level adjustment before my wife shouted up the stairs at me to "TURN IT DOWN!". Ha! Can't wait to crank it up a bit later today when the neighbors are out to work. While bridging sounded like a cool idea, it's totally unnecessary here. Still searching for a nice preamp with a good phono pre.

ZLTFUL

So you have a standalone phono pre (pretty much every Cambridge phono pre I have heard is pretty dang nice for the money) and you want a preamp with an integrated phono pre? Why?
My experience shows that while they are out there, a standalone phono pre is going to provide you with a better sound.
There are several technical reasons for this but we will skip them for now.

If it were me, which it isn't but if it were, I wouldn't pidgeonhole myself into finding a pre with a decent phono stage. I would simply focus on finding a decent pre and keep using the Cambridge phono pre.
This will open the preamp door much wider.
Since you are just getting rolling, take a look at the NAD XX20 preamps. There are some nice options in that line and while they do come with phono stages, I wouldn't make that your primary focus.

tonyb

Bridging in general is usually an idea best left as just an idea.

Glad your digging the new amp, now just be careful with that volume dial. Everything has limits. Hate to see you pop a tweeter on those speakers. Listen closely, when you start to hear the music get congested or start to collapse, back off the volume dial. Adding an amp doesn't mean you can crank on the volume dial, just sayin'. Enjoy the new toy and welcome to the club.

1ShotBill

ZLTFUL wrote: »

... take a look at the NAD XX20 preamps. There are some nice options in that line and while they do come with phono stages, I wouldn't make that your primary focus.

Great idea! So I have the opportunity to by a nice 7020 locally (missing it feet) or pick up a 7020e (which has the digital tuner) elsewhere. Is the "e" model just as good of a preamp as the non-e version? There's also a NAD 3020 floating around out there.

Lastly, any idea if the NAD 1130 is as good of a preamp as the 20 Series? (Phono pre inputs aside)

ALL212

heiney9 wrote: »

Obviously we don't know what we are talking about. Best way to find out is to try it. Go ahead bridge them both together and see if it's possible. Be sure and test it playing loud too.

Good grief H9 - take 5 minutes and browse to the link he sent. Or do I have to read it to you..??

The user guide CLEARY STATES and the diagram of the back of the unit CLEARY SHOWS that you can bridge this amp. Insure you set the impedance switch to 4 ohms. I wouldn't try and drive 2 ohm speakers with it at that time. It also CLEARY STATES that you can use a NAD 2400 as the amp for the other channel.

ZLTFUL

ALL212 wrote: »

Good grief H9 - take 5 minutes and browse to the link he sent. Or do I have to read it to you..??

The user guide CLEARY STATES and the diagram of the back of the unit CLEARY SHOWS that you can bridge this amp. Insure you set the impedance switch to 4 ohms. I wouldn't try and drive 2 ohm speakers with it at that time. It also CLEARY STATES that you can use a NAD 2400 as the amp for the other channel.

But that's the part you are missing here. A 4 ohm speaker on a bridged amp *will* present the amp with 2 ohm loads. Remember that a speaker's impedance is NOT constant. It rises and falls based on where the sound that is being played resides in the frequency range, the duration of it's trip to that point...etc...
The user guide does clearly state that the amp is 2 ohm capable but makes no mention of it while bridged.
And this is where the comments of "Don't do it" come from.
Bridging increases the current demand/thermal load on the amp. That stress rises as you place "greater" (read: lower impedance speakers) load on the amp. So you have bridged the amp increasing the stress on it. You now are adding a 4 ohm nominal load which also increases it.
If we were talking about running bridged with an 8 ohm nominal load (which incidentally *is* covered in the user's guide) then the above would be moot. But we aren't.



Bill, the 7020e isn't better or worse than the 7020. Aside from the digital tuner, they are pretty much identical. I have no use for tuners so I wouldn't let the tuner part sway me one way or another.
The 3020 is near and dear to me as that is the pre I use for my 2 channel system. The big thing to look out for is scratchy pots. A De-Oxit treatment negates this concern. I also am not a huge fan of the vertical connectors on the back but definitely not a deal breaker.
I have no experience at all with the 1130 so i can't speak to it.

DollarDave

1ShotBill wrote: »

....
Any alternatives such as certain NAD pre-amps to use with the 2400THX would be spectacular! Units I'm considering are the 1600, 1130, 1300. Thoughts on these?

...

I have 2 1600's, one I use, and one spare. I like them both, but not quite as much as my B&K pre-amps. I have an extra one of those, too. I need to have a closet cleaning party.

I use NAD 2400's with both my NAD 1600 and a B&K PT5 and they have very good synergy.

heiney9

Chill Aaron, never said it couldn't be bridged but IMO, driving what would then be a 2 ohm load would be bad

ALL212

heiney9 wrote: »

No!! Plus you can't bridge the integrated and still use it as a pre. Also, I have no idea what you mean by this to bridge the 2400 & 7400 together, it makes no sense.
H9

heiney9 wrote: »

Chill Aaron, never said it couldn't be bridged but IMO, driving what would then be a 2 ohm load would be bad

Really...:rolleyes:

It will either not allow power to the speakers as it may see it as too small a load - in that case it won't hurt anything. Or it will go into thermal overload if you play it too loud and shut down until it chills. Really no damage if you try it and keep the volume down to a reasonable level.

Why would you recommend, even jokingly, for a fellow Polkie to "Be sure and test it playing loud too."?

Chilled, but disappointed in what I read here...

heiney9

I stand corrected, I wasn't aware one could use the pre-out's and still use the power section of an integrated. The few I've sold or owned were either a pre or power amp not both. I still didn't quite understand what the meant by bridge them together. I loosely assumed connecting the two amps to each other in bridged mode, which I have never heard of. His 12C's are not bi-amp capable so I assumed he didn't mean that way.

I suppose he could have meant to use the power amp (bridged) on one speaker and the integrated as a pre-amp and bridged on the other speaker. One of the issues could have been gain mismatch but that would probably be just one problem amongst others if that was his intention.

Have I explained it sufficiently for you, so you can stop following me around and admonishing my posts?

H9

ALL212

No matter how I try to pick this up I can't find a clean end! :biggrin:

After reading the very few pages of the document provided I didn't have any issues figuring out how it would work. I do agree that hooking up 4 ohm speakers to the bridged setup might cause problems and is probably not a great idea but done conservatively might work quite well.

I would only ask that you spend a bit of time doing some research before posting, whether merely an opinion or statement of fact.

A2