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Review and Measurements of NAD C 320BEE PWR Amplifier

sajunky

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Nice to see such review, but it is unfair to compare 1:1 measurements of old amps. The heat inside cause solder joints to erode, capacitors get out of specs (if stored for years in a high humudity area) and the amp can lose stability without load. I had some old Pioneer amp and wanted do renovation, but number cold joints with visible cracks was covering 80% of the power board. In addition it was unstable hum (a sign of more problems on the board, preamp or in PSU and a bias current was getting complete out of hands in both channels. I spent already couple of hours on cold joints in the one channel and it didn't help. So I gave up, but if it were NAD, I wouldn't. :)
 

JohnBooty

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These are burst power measurements. Let me know if you like them and I will run them in future reviews. I think there is some merit to measuring this way as music is not continuous sine wave.

Absolutely love them, thanks!

I think they are almost (almost, not quite) more valuable than continuous power. The peak measurements are so much more representative of how they perform for real music, as you said.

Continuous power measurements are valuable because they show us how robust a design is, and a torture test like that can tell you how a unit will perform under the worst possible conditions. But as you say, this is not really related to actual musical performance.

Personally, I think 67 watts is not enough for home listening.

I find that many of my amps in the 30-80 watt range get plenty loud for a lot of situations. Maybe not for a main system in a large room but generally they can be very enjoyable.

After all the difference between 67W and 100W is less than 3dB.

67W gets you about 101.5db continuous from 85db/W efficient speakers at 8'. So you can listen at 80dB average and still have 20db of headroom. And of course we get another few dB on top of that thanks to those dynamic peaks.

Today's speakers have become smaller in size and shrunk in efficiency, needing fair bit of power to get them to produce proper dynamics.

That's the problem with small speakers, right? You can't just dump power into them to get high SPL. Most of them can't handle much more than 100W.

Bottom line IMO is that if you want some real SPL and satisfying dynamic peaks generally the way to get there is efficient speakers (possibly coupled with powered subs). With small speakers you can't get there with any number of watts.

Even a high-power 100W or 150W continuous amp will only get those tiny bookshelves 3dB louder. Most small bookshelves will be distorting by that point anyway.
 
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rwortman

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My NAD power amp is rated for the same 150 watts into 4 or 8 ohms. NAD switches the voltage on the power supply rails depending on load. They call it Powerdrive. They describe like it’s a positive feature. Basically it has the current drive for 150 watts into 4 ohms. If you have enough voltage on the power supply rails to make 150 watts into 8 ohms and connect a 4 ohm load the output stage can’t handle it so they drop down to a lower voltage. They say it increases the voltage for the 8 ohm load. I say it wimps out on the 4 ohm load. I think the power button on your example is broken. We have a small NAD integrated in a small living room system. It will turn on from either the power button or pressing an input select button.
 

restorer-john

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In testing, without undue stress, the unit went into protection and would not reset until I cooled it off with a fan and left it off for a few minutes. Most amps survive my testing without going into protection mode since I only push them to max power for seconds.

Also, in the process of changing my setup for 4 to 8 ohm, the unit went into oscillation, producing 107 watts on its own with no signal. So there is some instability in the design. This happened when I changed my load impedance to 8 ohm so perhaps you won't see it if you don't mess with speaker output while the unit is on.

The 320BEE NAD unit is full of over zealous protection circuitry. Twin PTCs, over voltage/over current, DC, AC, input stage muting/limiting and the SCR controlled switched HV/LV main amplifier rails. It's quite possible in certain situations to cause the amplifier to oscillate between rails- that's probably what happened with your load switching.

The soft clipping is really simple in concept. Based on the sagging of the supply rails under load, it simply shunts input signal. McIntosh used a similar design way back.

1566003484706.png


Basic Specs:

1566003603605.png
 

invaderzim

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There is definitely risk in buying old amplifiers. This one measures as if new so not a problem here.

It is great testing older equipment like this that still has quite a good reputation because so often I see people recommending buying things like this to save money and it is hard to tell how well some of them age.

I have two 50W integrated amps, one in the bedroom other in the living room and i never pass half the volume. One system is a denon with kef speakers, the other a marantz with monitor audio speakers. My father has a 100W yamaha with b&w speakers in his living room and maybe sometimes we go to 5/12, but it's normally on 4/12 of the volume. So i don't get the lack of power. The 3 systems are older than 10 years.

I guess it really depends on how loud one likes their music if it needs that much power to keep the dynamics up. I'm not typically one to crank it to where I can feel it and even with my 8 watt or so tube amp I rarely go past 1/3 on the volume. But for me while the little guy in my picture at the left really enjoys music he doesn't like it that loud. And I also have a subwoofer. But it does clearly struggle with keeping up the dynamics on the few occasions when I do really crank it but for once or twice a year I'm fine with it. At 200 watts and cranked up I'm sure more sound than I'd want would be making it outside the house and I don't like imposing my music on others.
 

restorer-john

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I have the Technics C-700 integrated (75 watts) and have not been able to find any speakers that produce compelling sound through it. Would you say the wattage is a limiting factor?

The Technics is a Class D, 45w/ch@8ohms and 75/ch@4ohms.

It's a very unusual aesthetic design and looks like a classic late 70s/early 90s design turned up side down if you ask me.
 

rwortman

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Your comment re: 67 watts not being enough power for home listening is interesting. I have the Technics C-700 integrated (75 watts) and have not been able to find any speakers that produce compelling sound through it. Would you say the wattage is a limiting factor? If not, any thoughts on what speakers folks with these amps might check out?

What speakers have you tried and what didn't you like about them?
 

Blake Klondike

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What speakers have you tried and what didn't you like about them?
thanks for the response-- will see if i can remember:

cambridge audio aero 6 bookshelves were flat-sounding-- no depth to the sound stage
technics sb-c700 speakers were far too bright and the low end was boomy
castle warwicks were so bright that they hurt my ears
pioneer sp-b22-lr were flat-sounding with poor resolution

i honestly think that i am comparing them to things like harbeth p3s with 100w of amplification and everything is falling short. i don't know much, and would love to find some natural, even speakers with good imaging that this amp could drive well. my instinct is that 35w just isn't enough for that kind of performance, but would love to be proven wrong!
 
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amirm

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Here is the performance of the NAD C 320BEE Power amp alone (bypassing the pre-amp) as requested:

NAD C 320BEE Power Amplifier Audio Measurements.png


The noise floor drops a lot, revealing other spurious tones.

Here is the power curve into 4 ohm:

NAD C 320BEE Power Amplifier Power into 4 Ohm Audio Measurements.png


So you are definitely better off driving the power amp direct if you have a DAC with volume control.
 

msmucr

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Here is the performance of the NAD C 320BEE Power amp alone (bypassing the pre-amp) as requested:
...
The noise floor drops a lot, revealing other spurious tones.
...
So you are definitely better off driving the power amp direct if you have a DAC with volume control.

The pre-amp is the weaker link in both distortion and noise.

Amir, thank you very much for taking the time for additional measurement!
I was curious what that does, because I clearly preferred the bypass for nearfield desktop listening.

Not sure, if that applies also to their later evolution of this amp design, but guessing it's rather similar. Its current descendant 326BEE also features the same jumper bypass, so it might be worthwhile place for alternative setup, if someone use source with own output volume control.

All the best,

Michal
 

audimus

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NAD went through some struggles and transformations around that time as I remember. One of the business model changes was the introduction of some low end products which weren’t necessarily designed or built well. I had one of those horrors. Reading the poorer pre-amp quality of this unit above reminded me of this. I think NAD was best with its amplifier designs, not so much with the other stuff.

I had a DVD receiver model L53 where $600 was a low end price for NAD. It was a good fit for emerging “home theaters” at the time during the transition from analog to digital with optical inputs and SW pre-out for a 2.1 system to hook up the emerging HDTVs. It was very underpowered but the biggest disappointment was the DVD player itself which would wheeze and cough everytime you put a disk in and take about a minute or so to start playing with a picture quality that was mediocre. I used it only for a short while and put it away. When I opened the unit recently, I was totally shocked at what I found.

I took it out for a temporary hook up but there was intermittent sound out of the DVD and from the optical inputs. But analog inputs were fine. I decided to open it up to see if there were some corroded connectors or solder cracks.

It had an OEM DVD transport with its own DAC board from a company that made cheap Walmart sold DVD players (the name escapes me at the moment) and the receiver used this cheap DVD DAC for its external optical inputs as well! In a NAD branded unit! That explained the wheezing and coughing from the DVD player and much less than impressive sound from the receiver.

It wasn’t representative of NAD, for sure, but it was my first and last NAD.
 

GigaChunk

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Well, at least I know what the soft clipping switch actually does now!

Thanks for the review Amirm - I bought this amp second hand 4 years ago. Nice to know it's fairly competently designed, especially the power amp section. Preamp performance isn't a concern for me as I use a separate dac/preamp.
 

rwortman

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thanks for the response-- will see if i can remember:

cambridge audio aero 6 bookshelves were flat-sounding-- no depth to the sound stage
technics sb-c700 speakers were far too bright and the low end was boomy
castle warwicks were so bright that they hurt my ears
pioneer sp-b22-lr were flat-sounding with poor resolution

i honestly think that i am comparing them to things like harbeth p3s with 100w of amplification and everything is falling short. i don't know much, and would love to find some natural, even speakers with good imaging that this amp could drive well. my instinct is that 35w just isn't enough for that kind of performance, but would love to be proven wrong!

And did you try these same speakers with another amp and they sounded better? Maybe you just didn't like the speakers. Those don't necessarily sound like amplifier problems unless you were cranking the sound up to the point of clipping.
 
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