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 Post subject: Bridging 2 NAD C272 Amps
PostPosted: Wed Dec 13, 2017 8:16 am 
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Location: Rockwood, ON, CA
Hi Gang,
I have general knowledge on setting a basic stereo system up, but bridging amps are a whole new ball game to me.
I've search YouTube for info., but get conflicting info or just a lot of confusing mumbo jumbo.
I have 2 NAD C272 amps that I would like to bridge.
Can anyone help me as I'm trying to avoid a lot of smoke or possible a fire.....

Sytem is:

2 Nad C272 Amps (150W X 2)
Adcom GTP 500 preamp
DBX 1020 Equalizer/Analyzer
DBX 3BX Dynamic Range Controller
Pro-ject Turntable
Thiel CS 2.2 Speakers (4 ohms / 250W max)

Yes...I know most items are vintage equipment but thats the way I wanted it from the start. ;)

ANY help is and would be greatly appreciated.


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PostPosted: Wed Dec 13, 2017 8:19 am 
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As posted in your other thread 8)

The manual states….

Quote:
“In this mode (bridged), the amplifier sections will react as though the speaker impedance has been halved. Low impedance speakers (under 8 ohms) are not recommended when using Bridge Mode, as these may cause the amplifier’s thermal cutout to operate if played at high levels.”


This means in bridge mode your amplifier will see your 4 ohm Theil speakers as a 2 ohm load. Not recommended. And given Theil does not have the capability to bi-amp, you are stuck using only 1 amplifier.


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PostPosted: Wed Dec 13, 2017 9:20 am 
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I have bridged my 2 NAD 2200's by moving the switch at the back of the amps and running only 1 RCA (L or R) into each amp and following the connection instructions for the speakers which I believe are the 2 red posts. Works well with Maggies that are 4 ohms. YMMV.


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PostPosted: Wed Dec 13, 2017 11:27 am 
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The 2200 is a different amplifier than the C272. The manual for the 2200 does state 4ohm speakers are safe when the amplifier is bridged. The C272 does not recommend this.

Bridging amplifiers are not the same across different brands and or models. Despite the increase in power, one should pay close attention to ensure they are not presenting an impedance to which the amplifier in unable to handle. Failing to do so could result in damaged equipment.


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PostPosted: Wed Dec 13, 2017 12:56 pm 
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sthomas1049 wrote:
As posted in your other thread 8)

The manual states….

Quote:
“In this mode (bridged), the amplifier sections will react as though the speaker impedance has been halved. Low impedance speakers (under 8 ohms) are not recommended when using Bridge Mode, as these may cause the amplifier’s thermal cutout to operate if played at high levels.”


This means in bridge mode your amplifier will see your 4 ohm Theil speakers as a 2 ohm load. Not recommended. And given Theil does not have the capability to bi-amp, you are stuck using only 1 amplifier.


Let me further clarify, as i re-read your response I think I get what you mean.

The amplifier sections (left and right channels) will act (perform) as if speaker impedance was halved. Meaning, they increase current and the output goes up, similar to output in a 4 ohm load into two channels. Or, the power doubles.

Another way to look at it is that each half of the amp is seeing half the load presented to the amp. In other words, a 8 ohm load is seen as 4 ohms to each channel; voltage will double in most cases. This is why not exceeding the recommended minimum ohm is important. For example, your 4 ohm speakers are seen as 2 ohms to each channel.

The amp amp does not change the resistance of speakers because the amp is bridged, it will still represent a 4 ohm load; however your amp determines how it reacts to the load - i.e. Splits it between channels.

Essentially, your issue is the amp is not stable, when bridged, below 8 ohm. Its recommendation is really one amp for each speaker, assuming load is 8 ohm each speaker.


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PostPosted: Wed Dec 13, 2017 2:56 pm 
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JGP wrote:
sthomas1049 wrote:
As posted in your other thread 8)

The manual states….

Quote:
“In this mode (bridged), the amplifier sections will react as though the speaker impedance has been halved. Low impedance speakers (under 8 ohms) are not recommended when using Bridge Mode, as these may cause the amplifier’s thermal cutout to operate if played at high levels.”


This means in bridge mode your amplifier will see your 4 ohm Theil speakers as a 2 ohm load. Not recommended. And given Theil does not have the capability to bi-amp, you are stuck using only 1 amplifier.


Let me further clarify, as i re-read your response I think I get what you mean.

The amplifier sections (left and right channels) will act (perform) as if speaker impedance was halved. Meaning, they increase current and the output goes up, similar to output in a 4 ohm load into two channels. Or, the power doubles.

Another way to look at it is that each half of the amp is seeing half the load presented to the amp. In other words, a 8 ohm load is seen as 4 ohms to each channel; voltage will double in most cases. This is why not exceeding the recommended minimum ohm is important. For example, your 4 ohm speakers are seen as 2 ohms to each channel.

The amp amp does not change the resistance of speakers because the amp is bridged, it will still represent a 4 ohm load; however your amp determines how it reacts to the load - i.e. Splits it between channels.

Essentially, your issue is the amp is not stable, when bridged, below 8 ohm. Its recommendation is really one amp for each speaker, assuming load is 8 ohm each speaker.


Understand. My comment was simplified and perhaps in doing so, details were lost. But thanks for the clarification.


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PostPosted: Wed Dec 13, 2017 3:05 pm 
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I totally rocked a pair of 5 ohm Martin Logans with bridged 2200s.
I repaired one of the amps twice. It sounded great, but was getting expensive. :lol:

Speakers can dip below the published impedance rating and that's where the trouble begins. The Logans can dip down to 2 point something and when halved, ouch.
Check how low your Thiels can go.

This was the exact reason I found CAM. Looking for answers to this. Guess who finally got it through my head?


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PostPosted: Wed Dec 13, 2017 4:14 pm 
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sthomas1049...,
No issues, we are speaking the same language! Don't know if my explanation helped the OP or not anyways.


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PostPosted: Wed Dec 13, 2017 4:54 pm 
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I run a pair of C272's in bridged mode and they do very well with my PSB Goldi's that dip into the 3 ohm range occasionally.
Hifi Engine https://www.hifiengine.com/manual_library/nad/c272.shtml has all the info you need to set-up your C272's.
NAD does rate them down to 4 ohms in bridged mode and 2 ohms in stereo.

Good Luck and Happy Listening
John


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PostPosted: Wed Dec 13, 2017 5:18 pm 
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The manual I read for the C 272 clearly states 8 ohms or higher while bridged. The quote within my original post is from the manual. The manual also states a nominal 4ohm speaker is the minimum for stereo mode. Now if the C 272 has changed specifications during it’s life span then the OP will need to confirm he is reading the correct manual.

There is a difference between an amplifier that can handle a low impedance at a specific frequency for a short burst vs one that can handle the same low impedance across the majority of the frequency range as with the Thiel (which I will add has to be one of the flattest impedance plots I’ve seen…Excellent engineering!)


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PostPosted: Wed Dec 13, 2017 5:50 pm 
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Location: Saint-Augustin-de-Desmaures, QC, CA
I asked NAD this week about bridging a 272 and 372 to drive a pair of Magnepan 1.6 (4 ohms) and they said no. Moreover, rear of the amp says one 8 ohm or two 16ohm

http://img.canuckaudiomart.com/uploads/ ... lifier.jpg

My $0.02

-- 13 Dec 2017 20:51 --

I asked NAD this week about bridging a 272 and 372 to drive a pair of Magnepan 1.6 (4 ohms) and they said no. Moreover, rear of the amp says one 8 ohm or two 16ohm

http://img.canuckaudiomart.com/uploads/ ... lifier.jpg

My $0.02

_________________
I like gear and good sound but in the end it’s all about music.


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PostPosted: Wed Dec 13, 2017 10:46 pm 
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Well, this is only my experience.
I run a pair of C272's in bridged mode and they do very well with my PSB Goldi's that dip into the 3 ohm range occasionally.
Been running this combination for several years without any issues.
The NAD 272 brochure at this link:
https://www.hifiengine.com/manual_library/nad/c272.shtml
does rate them down to 4 ohms in bridged mode and 2 ohms in stereo.
I'm a single guy living in the country and my music does get a little loud from time to time.
Works for me!

Good Luck and Happy Listening
John


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PostPosted: Thu Dec 14, 2017 5:42 am 
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Hi Gang...... sorry for the late reply but Im working some long and strange hours these days.
This is the info I got from the Thiel CS2.2 speakers I run.

Crossover frequencies: 800Hz, 3kHz.
Crossover slopes: first-order, 6dB/octave acoustic.
Frequency response: 33Hz–27kHz ±3dB, 35Hz–20kHz ±2dB.
Phase response: minimum ±5°.
Time response: 150µs, –20dB.
Sensitivity: 86dB/W/m (2.83V).
Nominal impedance: 4 ohms (minimum 3 ohms).
Amplifier requirements: 50–250W

To be honest, I'm not fluent in technical terms or electronic wizardry.
So, as I summarize everyones input here, I CANNOT run the C272 amps in bridge mode if running the Thiel speakers (as they are 4 ohm) OR I can run them in bridge mode if I change to 8 ohm speaker, BUT some have run these amps in bridge mode with 4 ohm speakers and they haven't had any problems?
What is worse case senario, if I do try to run these speakers with bridge mode C272's?
Can I possible burn something out or do permanent damage to the equipment?
** Note...... I don't turn the volume up past 2 - 2.5 on the dial as I sit 10 feet away from these speakers and at this point output is over 80-85 db and I often find that I have uncontrolled ringing in my ears the next day. :?

Many thanks for everyones input.


Last edited by Neon on Thu Dec 14, 2017 6:09 am, edited 1 time in total.

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PostPosted: Thu Dec 14, 2017 6:01 am 
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Good day Johnnyj – You had me question the manual I read so had a look at the one you posted from Hi Fi Engine and it is the same. While Bridged, speakers rated under 8 ohms (nominal) are not recommended.

The brochure goes into detail to what the amplifier can handle at continuous power and IHF Dynamic Power. IHF Dynamic Power are just short bursts of power, and although it doesn’t state a duration, this is usually only around 20ms (+/- a few ms). So although the specifications do state IHF Dynamic Power 2ohms = 520 watts in Stereo Mode and IHF Dynamic Power 4ohms = 1132 watts in Bridge Mode, this does not mean the amplifier can handle those loads for long durations.

Neon - Despite both the PSB Gold and the Thiel 2.2 share the same nominal impedance of 4ohms their plots are vastly different. The PSB dips to around 3-4ohms between 70 and 400hz. This is only a short(ish) duration. The rest of the plot is well above 6 ohms. As per johnnyj this seems to be safe. The Thiels however, are almost ruler flat at 4 ohms between 50 and 50khz. This is nearly the entire operating frequency - not what I would call a safe load for C272 while bridged.

The standard for nominal impedance ratings (should the speaker manufacture follow such standards), is that the nominal impedance should be no greater than 1.25x the minimal impedance of said speaker.

Hopefully this clarifies and apologise for any errors – it’s early and I am still muscling through my first coffee.

-- Thu Dec 14, 2017 9:12 am --

Neon - Would also like to add…IMO the Thiels are an engineering wonder. What Jim Thiel (RIP) was able to pull off with Time Alignment, 1st order crossovers and nearly ruler flat Phase and Impedance Plots is an extremely difficult task. If you feel your NAD amplifiers are not sufficient, personally I’d sell both amps to fund something with more power. That’s just my opinion. But do not get rid of the speakers – if you do, drop me a line :wink:


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PostPosted: Thu Dec 14, 2017 6:24 am 
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Thanks sthomas! I do appreciate it. (--> put "thumbs up" here <--)
I just have one problem.......
Can you put your response to my dilemma in more laymen terms?
I'm just not up on the technical electronic end of things and although you sound very knowledgable in this area, it's as clear as mud to me as far as understanding your feedback. :oops:


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