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Nord Three SE 1ET400A Dual Mono Stereo Amp Review

March Audio

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Should have CE or FCC marking.

Hypex and Purifi modules are already CE approved, so whilst that doesn't automatically indicate a product made from them is also approved I think it unlikely that an implementation would be able to screw things up significantly to cause any problems
 

peng

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Yes, a Denon is waiting for review.

Thank you, if it happens to be one capable of processing 11.1 such as the AVR-X4400H or newer/higher model, please go to amp assign and select 11.1 (they might have called it 11.2) and pre out for FL and FR so that the FL/FR power amps would be disconnected (via relay iir..), before doing any continuous Voltage output vs frequency sweeps. This is so you won't get into issues when doing your test with you 2 V standard. No need to do so obviously for the 1 kHz test. The same should apply to corresponding Marantz models.

Note: After you made that 11.1 layout selection you can go back to speaker setup and select "none" to any channels not used.
 

mocenigo

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I wonder if ATI will start building amps using Purifi modules with a linear power supply?

When you think about it, why wouldn't anyone currently using Hypex modules start using Purifi instead? Bruno was pretty much the brains behind the products. I would expect him to take a lot of the business with him when he left Hypex. Evidently, he didn't sign a non-compete agreement.

In most european countries non-compete agreements are either illegal or very expensive for the employer.
 

phoenixdogfan

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I see Purifi is offering its own eval kit. Does that include a buffer board like the NC 400 or is it necessary to use something like a SPARKOS op amp.

It looks like it might be possible to just connect this kit to a Hypex A1200 PSU. If so, what plug (s) would I need on the Hypex end.
 

Matias

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Shadders

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Hi,
Sorry about this - but i have not searched the site thoroughly, but for this amplifier (and others), how do you calculate the S/N ?.

That is, what are the reference input and outputs for the S/N calculation ?

I can see that S/N=105dB for 5watts into 4ohms, and hence 305watts into 4 ohms is 18dB more - hence S/N=123dB, but it is the measurement points used, and the signals used, that i am interested in.

Thanks and regards,
Shadders.
 

ehabheikal

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This is a review and detailed measurements of the Nord Three SE 1ET400A Dual Mono Stereo Amp with the optional Sonic Imagery 990Enh gain stage. With that option, the cost is £1,979.00 excluding VAT. This translates into US $2,554. The unit was purchased new and drop shipped to me by a kind member. I had previously measured the reference design from Purifi so will be good to see how this version rates with a different input stage.

The Nord dual monoblock comes in a very attractive enclosure (most of which is not visible in this image):


Efficiency of class D amplifiers and switchmode power supply enables such slim case to be used. There are two rows of heatsinks on the sides but they are decorative for the most part. I will do a teardown separately. For now, the amplifiers dissipate heat into the bottom of the chassis and dual power supplies have their own heatsinks inside the box.

The back panel shows seriously beefy and nice feeling speaker connectors:


When I received the unit, it immediately shut down. The reason was a blown fuse. I replaced it with a spare that comes in the IEC holder. That worked for all but my last test which is the strenuous power vs frequency. I have let Colin know that I think the fuse amperage needs to be increased given our low operating voltage in US. Note that with music you are not going to hit this easily so it is more of an issue of lab/stress testing. I don't have a higher amp fuse to try with it until a batch arrives on Monday. The fuse is the smaller 5x25mm which I only have a few of in low amperage (usually are used in multimeters and such).

Edit: turns out the fuse that was sent for was for 240 volt countries. A "slo-blow" 10 amp replacement fuse was sent and worked fine.

Other than this, the amplifier was solid in its performance never shutting down or complaining. The enclosure didn't even get warmer than room temperature. Inclusion of two power supplies here relieves my worry of a the power supply being the weak link, not the amplifier.

Amplifier Audio Measurements
As usual we start with our dashboard of 5 watts into 4 Ohm at 1 kHz:

View attachment 39064

This is right on the money as far as THD+N and hence SINAD:
View attachment 39065

Which is great news of course.

Noise performance also matched the Purifi reference design:

View attachment 39066

We have a very low distortion and very low noise floor. This is all that you would want to ask an amplifier. That, and power so let's see how it does there:

View attachment 39067

Dual power supplies don't give you more power as we are essentially matching the reference design with one power supply.

I was surprised to see a rise in distortion with one channel worse than the other. Is this the Sonic Imagery 990Enh gain stage in play or were we given better evaluation samples at announcement? We won't know until we test another amp that uses Purifi gain stage.

Same issue exists at 8 ohm although not as exaggerated:

View attachment 39068

This makes me think the issue may be in the amplifier.

Note that this is not an audible concern so don't jump off the cliff please. :)

We see an exaggerated version of the same in intermodulation distortion relative to input level:

View attachment 39069

Frequency response is flat and similar to reference design:
View attachment 39070

Sweeps of power versus frequency gives us varying curves (ideal = all curves on top of each other):

View attachment 39071

We see that at 20 Hz where we need most power, we have least amount of it. This is typical of amplifiers since 20 Hz tone changes slowly not giving a chance for power supply capacitors to recharge between cycles.

Finally here is the 19+20 kHz at the same 5 watt power of Purifi reference design:

View attachment 39073

The pair around the main tone are identical to reference design. Noise floor is a hair higher but that is probably run to run variation.

Conclusions
The Nord Three SE 1ET400A Dual Mono Stereo Amp is an attractive build of the Purifi class D amplifier technology. The dual mono configuration raises the price fair but but my belief is that it will last a lot longer than the single power supply version. Measured performance is just a bit worse than Purifi reference design as power increases beyond 25 watts or so. Not an audible difference but would be good to figure out where this is coming from. I can't detect any improvement from Sonic Imagery discrete 990enh opamps. So personally I would go with the stock gain stage and save enough money for a night out alone.

I am happy to recommend the Nord Three SE 1ET400A Dual Mono Stereo Amplifier. It builds on state-of-the-art Purifi amplifier modules and delivers it in nice packaging.

--------
As always, questions, comments, corrections, etc. are welcome.

The Pink Panthers are making up their Christmas list and I can tell you it is going to be a long, long list. The have become sophisticated enough to create their lists on Amazon! One has been daring enough ot put in Caviar for heaven's sake! I am going to need money and lots of it. So please donate generously using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/




Thanx it is as good as you described and measured. Zero buyers remorse, actually negative buyers remorse :) with soncoz as source, also on recomendation from your work, and feeding ls50 meta.. Thanx Amir and if you ever come to visit Egypt give me a heads up before coming so i can make sure i can show what Egyptian gratitude is like.
 

gsp1971

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These amps using Purifi or Hypex modules seem to have a gain of between 25-27dB and produce around 130-150W @ 8Ω and around 250W at 4Ω. Doing the necessary calculations, I find that they need an input signal of 2.4V (RCA) and 4.8V (XLR) to be driven to full power.
Can they be driven directly from a source and skip the need (and cost) for a preamp? My source is an Oppo BDP105D.

And if a preamp is needed, are we talking about an active preamp that outputs something greater than the standard 2V (RCA) of a digital source, correct?

Thanks in advance to anyone who can help out.
 
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ehabheikal

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I have one purifi and it is working fine without preamp.it is connected directly to the dac from soncoz
 

boXem

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These amps using Purifi or Hypex modules seem to have a gain of between 25-27dB and produce around 130-150W @ 8Ω and around 250W at 4Ω. Doing the necessary calculations, I find that they need an input signal of 2.4V (RCA) and 4.8V (XLR) to be driven to full power.
Can they be driven directly from a source and skip the need (and cost) for a preamp? My source is an Oppo BDP105D.

And if a preamp is needed, are we talking about an active preamp that outputs something greater than the standard 2V (RCA) of a digital source, correct?

Thanks in advance to anyone who can help out.
There seem to be an issue with your calculation.
Vin = SQRT(power*load) / 10^(gain/20)
150 W 8 Ohm 27 dB => SQRT(150*8) / 10^(27/20) = 1.55 V
RCA or XLR is same value.
And these amps output a lot more power at 1% distortion.
 

JimB

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There seem to be an issue with your calculation.
Vin = SQRT(power*load) / 10^(gain/20)
150 W 8 Ohm 27 dB => SQRT(150*8) / 10^(27/20) = 1.55 V
RCA or XLR is same value.
And these amps output a lot more power at 1% distortion.
I confirm that, too. Given an input stage with 26 dB gain (=20x, and is midway between the posed 25 and 27), one needs a nominal 2.0V input to achieve rated output of 200W into 8 ohms, and 400W into 4 ohms. It takes less than 2.0V input to get to the power limit at lower impedance loads.
 

hapnermw

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I can confirm that a Topping D90 does not drive this amp to full output - adding an A90 resolved this. Setting the A90 at max volume and using the D90 digital volume works well.

While having to use a preamp is less than ideal, the D90/A90 pair provides audio quality that was unattainable for 10X the price just a few years ago. Plus, you get a SOTA headphone amp for free.
 

JimB

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I can confirm that a Topping D90 does not drive this amp to full output - adding an A90 resolved this. Setting the A90 at max volume and using the D90 digital volume works well.

While having to use a preamp is less than ideal, the D90/A90 pair provides audio quality that was unattainable for 10X the price just a few years ago. Plus, you get a SOTA headphone amp for free.
What "amp" were you driving? Was it an unbuffered Purifi module, or an assemble amp from someone with an input buffer with ~26 dB gain?
 

gsp1971

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There seem to be an issue with your calculation.
Vin = SQRT(power*load) / 10^(gain/20)
150 W 8 Ohm 27 dB => SQRT(150*8) / 10^(27/20) = 1.55 V
RCA or XLR is same value.
And these amps output a lot more power at 1% distortion.

Thank you boxem and JimB. Your calculation is correct, it is the one I used as well, I just read somewhere that the result of the formula (i.e. the 1.55V) is the RMS input V, whereas if you want the peak V you do 1.55 V * SQRT(2) = 2.2V. May be that last part is not needed.

In any case, let's use the 1.55V. Even if I use the increased power rating at 1% distortion, say 250W @ 8Ω, it still gives me 2.0V Vin, which is the standard RCA output of most digital devices. So the question remains, can I use my Oppo 105 to drive them, skipping the preamp? Or would I be safer with an active preamp? (and I am not talking unbuffered Purifi modules, I am talking 25-27 dB gain, either Hypex, or buffered Purifi).

PS. @Boxem, just for my understanding / learning, why is the XLR Vin the same as the RCA? Isn't the XLR gain lower by 6 dB?

Thanks guys - the more I learn / understand, the more I love this game.
 
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JimB

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Thank you boxem and JimB. Your calculation is correct, it is the one I used as well, I just read somewhere that the result of the formula (i.e. the 1.55V) is the RMS input V, whereas if you want the peak V you do 1.55 V * SQRT(2) = 2.2V. May be that last part is not needed.

In any case, let's use the 1.55V. Even if I use the increased power rating at 1% distortion, say 250W @ 8Ω, it still gives me 2.0V Vin, which is the standard RCA output of most digital devices. So the question remains, can I use my Oppo 105 to drive them, skipping the preamp? Or would I be safer with an active preamp? (and I am not talking unbuffered Purifi modules, I am talking 25-27 dB gain, either Hypex, or buffered Purifi).

PS. @Boxem, just for my understanding / learning, why is the XLR Vin the same as the RCA? Isn't the XLR gain lower by 6 dB?

Thanks guys - the more I learn / understand, the more I love this game.
Until you are talking about power supply rail voltages, you use RMS. So, you are really asking about the characteristics of the OPPO 105 - volume control on its outputs? It does offer volume control of the analog outputs. The manual I have does not mention output levels as far as I can tell.
 
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ScofieldKid

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I'm driving a class A/B amp with an Oppo 105... Works for me... I wouldn't fault you for wanting a volume knob though...
 

boXem

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PS. @Boxem, just for my understanding / learning, why is the XLR Vin the same as the RCA? Isn't the XLR gain lower by 6 dB?
Because a voltage is the difference of potential between 2 points. Ground and tip for RCA, hot and cold for XLR.
The gain of an amplifier is the factor applied to the input voltage to obtain the output voltage. Not to the potentials.
If you need different voltages depending of the type of the input to obtain the same power at the output, then different gains are applied depending of the type of the input.
 

gsp1971

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I'm driving a class A/B amp with an Oppo 105... Works for me... I wouldn't fault you for wanting a volume knob though...

It's not that I want a volume knob. The Oppo does have a volume knob. Just trying to establish what I really need. I don't see the reason in forking out money on components I don't need. I'd rather spent the money in buying better quality components that I do need. Thx.
 

gsp1971

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Until you are talking about power supply rail voltages, you use RMS. So, you are really asking about the characteristics of the OPPO 105 - volume control on its outputs? It does offer volume control of the analog outputs. The manual I have does not mention output levels as far as I can tell.

amirm has measured the Oppo 205. 4.1V XLR output, 2.17V RCA output. I would not expect that Oppo 105 is massively different.
 
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