NX150 listening impressions

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Before I bought the NX150, I searched around to find some reviews and listening impressions and came up with virtually nil as it's only new, so I thought it would be a good idea to start a thread for NX150 builders to pass on their thoughts.

I noticed destroyerX has some listening impressions and like Carlos I'm a huge fan of AKSA and the 55N+ has remained my reference for a few years and will continue to do so as it suits my listening. Also like Carlos I like to build and try different amps but I've only built about 0.01% of what he has. :xeye:

The NX150 was tested in a system which uses a Sony CDP990, AudioSector NOS DAC, AKSA GK-1 SS section (no tubes), floor standing speakers using Scan Speak 18W/8531G00 & S2905/970000 drivers.

The first impression is one of overall smoothness without a hint of harshness. Female vocals do not have any edginess and remain controlled at all times as do other instruments in the Mid’s. Top end has a nice quality but misses that last amount of shimmer.... only a very small amount but noticeable.

The stereo image is very good and there is depth appearing in the sound stage . The vocals or instruments are well defined.

The bass has good tonal quality and is very powerful and maybe too much so for my system, but I did extend the speaker ports as an experiment and the bass became neutral and tonally balanced so it is just a matter of retuning the speaker to suit.

Overall, I'd say the sound is very accurate but I miss that extra charm, induced by H2 harmonics. The NX150 would kick a lot of commercial amps out of the way easily such as a Rotel I recently had.

I could easily live with the NX150, it is a Fine Amplifier.

The instructions are adequate for an experienced builder but maybe might need a few extra bits that we take for granted for the non experienced, such as heat sink mounting with Mica washers, checking for shorts onto the heat sink etc.

I'm looking at this amp in a very critical view considering the equipment that is out there and has to compete with plus I've had over 35 years in this game and have my own listening idiosyncrasies.

Anthony Holton was very swift to supply support and help during construction and has added this review :blush: to his web site plus some pics for those who are interested.
http://www.aussieamplifiers.com/nx150.htm

I'm not affiliated with Aussie Amps but I've added this thread as it's good for those interested in a DIY amp to get an idea of the sound. There are several other amps on this forum where I have also added listening and other comments from my experiences.
 

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NX150 inside and tweak

I thought I'd be smart and try a couple of tweaks by changing the input caps to Mundorf MKP's and C6 & C7 to Elna Cerafines. As usual with my limited amp design knowledge I bombed and the amp sounded best with the original components as supplied. If any builder does find some worthwhile enhancements, they can be posted so others can benefit.

I've add a pic of the inside and this 3U size case is an Altronics H5039 (Australia) which gave me plenty of room. It was mostly chosen as it has vent holes top and bottom where the heatsink is located plus has an easy internal mounting system so the amp can be worked on with the top and bottom covers removed. The pic has the tweak components shown before it was returned to original. This amp uses the PSU-Two power supply that is also supplied from Aussie Amps.
 

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Peter,

Nice review, and beautifully made amp!

Anthony has discussed his amp with me and he feels it's a corker - your experience bears this out. My congratulations to Anthony for his new product!

You may be right about the H2, but there's enough anecdotal evidence around to suggest that tuning an amp for best sound goes beyond the H2 and extends to the entire distortion spectrum. It's complicated!!

Your speaker skills were invaluable - nice trick with retuning!

Cheers,

Hugh
 
Hi Everyone

I did some Distortion tests on the NX150 and my up and coming NX400 amp today.

Into a 8 Ohm load @ 1khz it was down in the noise floor 0.005%
It only rose to just below 0.01% @ 10khz
Which is not far of the Max resolution of my HP Meter.

This would give you some idea of the Precision of this design.
and hopefully the quality of its sound quality.
 
Thanks Hugh.

I bet tuning an amp for the best sonics is complicated and gives me a head ache just thinking about it.... best left to guys like yourself and Anthony. I'm only an amp builder and my amp tweaking ability sux.

Tuning speakers to an amp or other components is important and it would be easy to dismiss a fine amp if not done. I've designed and built plenty of speakers and are tweaked to suit a particluar amp, system or application and when used with another amp, can have quite different sonics. There is however, one amp that has handled them all.... you know the one. ;)

The NX150 handled the workshop and the main system with ease but I didn't have my speakers from hell here that normally sorts out amp low impedance capabilities..... only one amp has handled those and no prizes for guessing which amp.
 
Tune the speakers plays a good goal in the sound quality direction

Not only adjusting the speakers, using passive filter, trying to reach the most possible flat response.

This match would create some problems to the amplifier, as it do not like those RLC there....this will create a need of the amplifier matching with the whole system.... speaker plus passive crossover network.

The result of the match is great, reason why i think that we must buy amplifiers and speakers from the same factory...as they are matched and will sound the best possible.

I feel very good to see that others could perceive this, and use to do this matching.

regards,

Carlos
 
SamL said:
Hi rabbitz,

Interesting review. I notice that Carlos is running his NX150 around 55Watt. How much are you running yours at?

TIA,
Sam

Mine's running 59V rails without a load so would do a tad better than the 56V rail 146W into 8R and 230W into 4R. I think if I remember correctly, Carlos is going to do a full power version as well.
 
I am giving up related to construct the full power version.

The speakers i have are already hitting the bottom of the excursion with my lowered power version..... i can imagine problems with the full power version.

At least, i will have to buy more speakers and disturb my neighboors (more!)...as i live in a building.

The small power version sounds good enougth.... also i will have 2 pairs free to check more schematics...as i am maniac to construct and listen....a maniac!

regards,

Carlos
 
Carlos

I didn't notice that you only used 1 pair on the output :bigeyes: .... I'm an idiot and need to use my glasses more.

Maybe Anthony can chime in and advice builders that might want a lower powered amp and explain the changes that have to be done plus any sonic benefits or advantages if any.
 
Life teached me that the ones are humble to say "I am an idiot" ...are never an idiot

And i could learn that several that say that are not...many times can be.

But i never could find someone that were humble enougth to say that....and was really an idiot.

I do not believe....you have just not took attention in some detail, or i have expressed myself bad in your language.....join the group man...the 50 up club...we use to forget details....well...almost all the time, a detail is not more than a simple detail....but when is not...booooom!....and this is fun too!

By the way...i live in a building...of appartments...an appartment building....as building is everything we build with bricks...hehe...learning.

The reduction of power, related to Holton Amplifier was because i have many units with this Voltage.... many Aksas, including last model, Symassym(last model), Gem and LM3875...all them powered using 37 volts.

This was the practical reason...the other, more important, is to feel those amplifiers without be fooled by the power, also i avoid to listen them in stereo when testing...as sound stage can fool me too.

I think that is not fair to compare, to my own knowledge and pleasure, units with different power ratios...and also i dislike to check sound stage, as many times it is aided by the use of separated supplies, one supply to left and other to rigth channel.

This was the reason i made it to work in lower power.

The input is controled by zener diodes...so, the reduction of voltage did not made nothing related biasing...the bias control could compensate adequatelly without the substitution of limiting resistors, and i had not the need to change the Voltage amplifier current.

The resistance, in series with the stabilizing zeners where changed to make it work with the same current used by Mr. Holton.

The only advantage i had was that two output pairs was not needed anymore....and my speakers is here lasting long, because i have some care with them

The amplifier is strong enougth, and power peaks are reproduced undistorted and very loud....sligthly better than Symassym, in dinamic headroom, the NX worked fine.

I imagine that the hability to reproduce peaks are very dependable of the supply regulation....if it is stable, and how stable it is

Using the same supply and same speakers i can compare things in a more fair way...supply goes "on" all time long, feeding both amplifiers... when A is in the resistive load (33 ohms not to drain too much curren) B is under testing connected to speaker.

Input goes plugged....but the source signal can be adjusted monitoring the output power...to allow the same power in the output, because of sensitivity differences

regards,

Carlos
 

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Just had a look at aussie amplifiers site looks great!

Their amplifier kit seem to be very well designed...
and the reviews seem to show that the amps sound quality is
awesome.
Is there anyone else who has built this amplifier?
It would be good to here from them...



Opamp
 
Re: Life teached me that the ones are humble to say "I am an idiot" ...are never an idiot

destroyer X said:
.....join the group man...the 50 up club...we use to forget details....well...almost all the time, a detail is not more than a simple detail....but when is not...booooom!....and this is fun too!


Like yourself and Hugh, 1951 was the year I arrived ;)
 
destroyer X said:
very clear

Gee Carlos,

that NX150 picture is so clear, i can even read the numbers on a zener, nothing much left to guess.

If you posted such sharp pictures of your appartment building we could see you sitting behind a window after enlargement. :clown:
(looks like the comedy capers building, you 50 ups should be familiar with the flat bus from that silent movie episode)
 
If you choose to run the NX150 in Class A.
several modifcations would be required, a more heavy duty transformer than would normally be required for a 50 watt Class AB amplifier.

The general rule of thumb is 2.5x. So if a 100VA transformer is
required for Class AB amplifer of 50 Watts into 8 Ohms.
Then 250VA would be required for a 50 Watt Class A amplifier.
This provides a very comfortable margin and ensures that the
transformer is not over stressed.
So for a stereo amplfier 500VA would be the requirement.

A bias setting of 2.5 Amps would set the NX150 into Class A
for a maximum power out of 50 watts RMS into 8 Ohms.

Some extra filtering in the power supply would also be helpful
40,000uf per voltage rail would be a nice start.

And much larger heat sinks also:hot:
 
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