NAD T757 help required.

[navin advani]

My bedroom install is very compact.

Besides the AVR and the 5 sources (set top box, PS3, DVD/VCD player, Wii and WD Media Player) there is no room for an additional power amp in the cabinet. In addition to this the system will have to work for 2 channel audio and 5.1 HT.

The front speakers will be floorstanding 3 way.

Hence I was thinking of getting the NAD T757 instead of a Marantz 6006 + 2 channel power amp. The idea being to use the bi-amp option of the T757 to drive the front channels woofers with one amp and mid-tweeter section with the second amp.

Question: Does the T757 have an internal crossover that allows me to choose the frequency at which I bi-amp?

I was thinking of bi-amping at say 200-300Hz. Many floor standing 3 way speakers use this has the LF frequecny (Focal's 836V XO is at 250Hz and Electra 1038 is at 230Hz; Paradigm's Signature S8 is at 230 Hz and Studio 100 is at 300 Hz and Revel's F52 is at 200 Hz). This also makes sense in power distribution becuase about 50% of all music's enery is below 250/300hz and 50% is above 250/300Hz (depending on genre).

 

[anm]

try calling Ashish @ lakozy
I spent sometime looking in the manual but could not figure this out.

 

[Ajay Kamath]

Navin, the bi-amp terminals on the speaker will anyway run through the crossover of any bi-amp capable speaker and do the needful. Why do you want to set that from the amplifier? Most of the AV receiver's bi-amp outputs cannot be used as active crossover networks. You can just set the HPF on the speaker channels in a range of 30-200Hz in most instances. I have never seen BPF in any receivers.

 

[navin advani]

Navin, the bi-amp terminals on the speaker will anyway run through the crossover of any bi-amp capable speaker and do the needful. Why do you want to set that from the amplifier? Most of the AV receiver's bi-amp outputs cannot be used as active crossover networks. You can just set the HPF on the speaker channels in a range of 30-200Hz in most instances. I have never seen BPF in any receivers.

So that the HPF and LPF amps do not have to deal with the entire 20-20khz abdwidth. Each need only concentrate on the area designated to it.

Hence if 4 channels of the 757 could be used as 2 LP sections and 2 HP sections with a crossover set at say 200hz. You could then send 20-250hz to the woofer of a speaker and 250-20kHz to the mid and tweeter. Why did I choose 250Hz? Because 250/300 Hz is about the freqency at which music's energy band is split 50/50. Using the amps this way prevents bass amp's clipping from disturbing the mid/hf and also is more efficient as there are no passive (or very few) network components between the amps and the drivers.

However I understand that NAD could no way know what the 4 chanels would be used for so each amplifier actually produces the full range (20-20khz) and the speaker's LPF and HPF networks do the filtering.

BTW Ajay, fancy finding you here.

 

[Flash]

Navin
How about adding a Active crossover into the mix.
Receiver preouts connect to active crossover this is turn connects to Power amp which in turn are connected to the speakers

Each channel of the XO gets the full signal from the Receiver/Source . it in turns splits the signal on the basis of what crossover/ slope you set it at for each channel.
the XO sends the desired freq signals to the PoweAmps channels which in turns amplifies the speakers


I am not too sure if what I just said made any sense . was just THINKING OUT ALOUD.
Pardon me if its all gibberish

 

[navin advani]

Navin
How about adding a Active crossover into the mix.
Receiver preouts connect to active crossover this is turn connects to Power amp which in turn are connected to the speakers

From what I understand (Ajay Kamath would you confirm this) the NAD 757 works like this:

When you choose to use the rear channels as Main channels It sends the main channel signal to 4 amplifer modules (instead of 2). So the same fullrange signal goes to all 4 modules. When you connect a module to the LP section of the speaker it can power the low frequency driver of that speaker and similarly for the HP section.

If we wanted to do what you want to do what I'd need is a front pre out AND front power in. Pre-outs and Power-Ins were available in the old days in many stereo amplifiers. But cost cutting (preouts and power ins cost pennies) as eliminated this feature in most AVRs.

If a "Power in" was available I could have used the pre out, then an active crossover, then use a compact class D amplfier like a Crown XLS for the bass and send the mid-hf to the AVR's amp. But that is a big IF today.

 

[Flash]

From what I understand (Ajay Kamath would you confirm this) the NAD 757 works like this:

When you choose to use the rear channels as Main channels It sends the main channel signal to 4 amplifer modules (instead of 2). So the same fullrange signal goes to all 4 modules. When you connect a module to the LP section of the speaker it can power the low frequency driver of that speaker and similarly for the HP section.

Absolutely correct. It splits it into 4 channels and the full range signal is sent to 4 amp modules.

If we wanted to do what you want to do what I'd need is a front pre out AND front power in. Pre-outs and Power-Ins were available in the old days in many stereo amplifiers. But cost cutting (preouts and power ins cost pennies) as eliminated this feature in most AVRs.

If a "Power in" was available I could have used the pre out, then an active crossover, then use a compact class D amplfier like a Crown XLS for the bass and send the mid-hf to the AVR's amp. But that is a big IF today.

Why would you need Power In ?


since you have 7 channel preouts on the NAD. just hook up the front L+R preouts to a Active XO and attach a class D amp to drive the LF of the speaker
Use the NAD internal amps (2 modules) to send the entire FQ band to the HF of the speaker. let the speakers internal crossover come into play to filter out the unwanted freq that it receives.

Unles offcourse you want to add another power amp into the picture to drive the HF section of the speaker.

Then follow the same method
However in this case . the NAD will be working like a preamp and not using its internal amps
You will however have complete control over what signals your Power Amps receives

 

[navin advani]

.
Why would you need Power In ?.

Use the NAD internal amps (2 modules) to send the entire FQ band to the HF of the speaker. let the speakers internal crossover come into play to filter out the unwanted freq that it receives. .

I do not have space for an external power amp in this system hence my idea was pre-out to electronic XO to power in so each internal power amp has to handle only a limited range of frequencies say 20-300hz and 300-20kHz.

I am trying to negotiate space for a Crown XLS 2000 or Xti 1002 or maybe even an old Carver M1.0t. Do you think the old Carver would still stand the test of time against the new fangled Crowns?

 

[navin advani]

Most of the AV receiver's bi-amp outputs cannot be used as active crossover networks. You can just set the HPF on the speaker channels in a range of 30-200Hz in most instances. I have never seen BPF in any receivers.

Any alternatives to the NAD 757? Denon? Marantz (I am told reliability is an issue)?, Onkyo Integra?

QUESTIONAIRE FOR AVR PURCHASE QUERY

OBJECTIVE:

1. Audio preference (Music / Movies) = 60 % / 30% (10% games).

2. Budget = Rs. 1,00,000

3. Room Size (Lenght x Breadth x Height = 15' x 17' x 9'

4. Source (CD /DVD /Satellite /Other) = CD, PS3, Wii, WDTV, Asus Oplay, Tata HD Set top box.

5. Existing components to be integrated with new purchase (Speaker /Amp /Cables /Equaliser /Other) = DIY speaker using RAAL tweeter, Accuton Mid and ScanSpeak Illumintor bass.

6. Can used AVR be considered (Y/N) = N

7. Other details /preferences = Laid back sound

8. Other query-1 = What 7.1 and 7.2 options are there in my price range?

9. Other query-2 = Need good clean processing, comprehensive room correction (Audessy XT32 or similar), and the ability to bi-amp front channels using rear channels.