Bi-Amping question: NAD 906

[khaliss]

Hi all! Long-time casual lurker here & a mild enthusiast for low/mid-level audio gear. I recently acquired (locally) an interesting amp on FB marketplace (while browsing for used speakers LOL). It's an old but fully functioning NAD-906 3-channel amp (release year: 1992), each of the three independent stereo power amplifiers within the 906 has its own pair of inputs and outputs.

Base Specs:
* Continuous Average Power Output into 8 OHMS (Min. power per channel, 20 Hz - 20 kHz, both channels driven with no more than rated distortion) ==> 30 W (14.8 dBW)
* Rated Distortion (THD 20 Hz - 20 kHz) ==> 0.05%
* IHF dynamic power (maximum short term power per channel)
> 8 ohms ===> 48 W (16.8 dBW)
> 4 ohms ===> 65 W (18.0 dBW)
> 2 ohms ===> 85 W (19.3 dBW)

This is a very beefy amp, heavier than my new Yamaha A-S701. Currently, I got it hooked up in Bi-amp configuration, driving Mordaunt Short MS912 speakers. This setup is sounding really good by the way, just as good as the Yammy (I think)

Channel-1 pair is wired to the speaker's HF connectors, while Channel-2 pair goes to LF. Channel-3 is not in use, but I'm thinking of putting Channel 2 & 3 in bridge mode... then connecting it to the speaker's LF, that way the amp can supply more power to drive the woofers as needed. Essentially, HF would have 30 watts on tap, while LF 60 watts(?)

My question is: with the double amount of amplification power on tap for the woofers (versus the tweeters), does this mean the volume (as I listen to music) would be "louder" on the LF channel (woofers) and thus it would cause an imbalance to audio between HF & LF?

 

[khaliss]

also, I played around with a "quad" stereo setup last night... added a pair of bookshelves (Definitive Demand D9), and connected them to Channel-3. Suprisingly, the setup sound really good as well LOL, not sure if my ears were just messing with my brain:

 

[DVDdoug]

Maybe...

From the dotted-line it looks like only one channel is used in bridged mode.

What do the specs/manual say about impedance in bridge mode? What's the speaker impedance?

Typically, you have to double the impedance rating since amp is rated for 2-Ohms, probably no-less than 4-Ohms in bridged mode. And since you'll be wiring 2 woofers in parallel, that's half the impedance.

My question is: with the double amount of amplification power on tap for the woofers (versus the tweeters), does this mean the volume (as I listen to music) would be "louder" on the LF channel (woofers) and thus it would cause an imbalance to audio between HF & LF?

A bridged amplifier normally puts-out twice the voltage. That's +6dB louder, and 4-times the power if the voltage "holds-up". 4 times the power means twice the voltage and twice the current... If the amplifier can't put-out twice the current the voltage will "sag", or be limited. That doesn't affect the loudness, only the maximum power or clipping point.

It's POSSIBLE, but unlikely, that the "bridging" switch lowers the gain so the loudness stays matched.

 

[dualazmak]

I assume the latest system setup (ref. post #931 on the project thread) of my multichannel multi-SP-driver multi-amplifier fully active stereo audio rig would be of your interest and reference...

 

[Clmrt]

It's a SIX channel amp, three stereo modules in one chassis.

You are passively bi-amping, meaning you might have more power "potential" this way or that - but it all squeezes through a passive crossover that levels off power relative to the drivers' requirements. No matter what you do for more power, you are still slaved to the passive crossover, which negates anything you do on the amplifier side of things.

 

[khaliss]

It's a SIX channel amp, three stereo modules in one chassis.

You are passively bi-amping, meaning you might have more power "potential" this way or that - but it all squeezes through a passive crossover that levels off power relative to the drivers' requirements. No matter what you do for more power, you are still slaved to the passive crossover, which negates anything you do on the amplifier side of things.

yes, when I say "channel-1, 2, 3", I meant stereo amp pairs, sorry for the confusion. since I only have 4 different connectors on my speakers (2 each for LF & HF), I can only bridge the amp's 2 stereo channels (pairs 2 & 3) to feed the speakers' LF connectors. That would effectively net 60 watts for the woofers (since they would be drawing more power)... then the tweeters (HF) can have remaining stereo pair.

With that, I'm utilizing the entire amp & all of its 6 individual channels to feed the Mordaunt Short speakers... if that makes sense(?) I want the whole amp working, per say LOL