A20x experience

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A20x experience

Unread post by eagwok33 » Sun May 27, 2018 9:28 pm

Finally, here are some impressions of my new A20x amp. The A20x was at first supposed to replace the A30 according to the Doc’s info. In the meantime the Doc changed his mind as the A20x was apparently not an improvement over the A30 and the A20x will not be produced anymore. Anyway, as it is the first NVA amp I own, I will let you know what it did musically in my system.

Well, it is a neat looking little amp for only £326 (incl. shipping). One could judge the amp by size and price, but this would be a big mistake! Why? Because, this little amp performs surprisingly well, when connected to my high efficient (98dB) and easy to drive Haigner horn loudspeaker-system. (My experience with higher gain amps – various chip amps for example - on my horn system has not been so great so far).

I started my listening sessions with the A20x after about 24 hours of having the amp just powered on in my system. Paired with my DIY passive pre amp the A20x was fun from the start, with a lively and energetic way to play music. As the gain of this little amp is quite high, I could use just the 6 to 9 o’clock range of the volume pots of my preamp. Beyond that range the music played became so loud via my horns that I feared my nice neighbors, who live in the apartment above us, would no longer be our friends. ;)

I’d like to state that lately I changed the Alps Blue stereo potentiometer to Nick’s (lurcher300B) recommendation of the mono version of the Tocos Cosmos carbon track potentiometers. This has been a clear improvement to my ears and results in more foot tapping during listening sessions. :) So, a big thanks to Nick for his tip! :clap: (I use a pair of 20K log type ones for my DIY passive pre).

During the first two weeks in operation (I left the amp continuously on), the performance of the A20x improved noticeably. At the beginning, the sound of the amp was closed-in in the mid-range, especially when listening loud and the amp sounded more forward and in your face, in comparison to the amps I normally use in my system.

Just to let you know, where I’m coming from:
I listen mainly in the near field of these full-range horns, i.e. the distance is about 2.7m. I always have loved the sound of low-powered SET amps connected to my horns as there is a magic in the mids and treble of such amp designs to my ears, and an openness, speed and fluidity in the reproduction of music, which I truly love and admire. One can get easily addicted to that... 8-)

Transistor amps can be superb but are different in this area to my ears and normally not as magical. But as always, there is a trade off with most low-powered SET amps in my experience and this is the bass slam and the overall dynamic impact of the music, also when mated with efficient speakers. For example, when I'm listening to a great rock band – let’s say Led Zeppelin - at very loud levels with my 2A3 SET monos in my system, the slam and dynamic impact of the lower registers is kind of missing.
I have heard some low-powered SETs with massive output transformers and well executed low impedance power supplies made from experienced tube amp builders, which can deliver the slam in the lower registers and the overall dynamic of music, but such amps are rare and, honestly, at this stage, I’m not experienced enough to build them.

This said, my current reference amp is the M2 clone amp, a DIY project I have done with a friend of mine, who suggested building two of these amps, one for each of us. This M2 clone is based on a First Watt = Nelson Pass design and is a class-A transistor amp, with an auto-former as voltage gain stage and a push pull Mosfet output stage. This amp is rather low in gain (14dB) and fits well to high efficient speakers. My M2 clone amp is very fluid, balanced and musically pleasing (connects you well to all kind of music played). It is dynamic, has bass slam (no wonder, it has 2x 320VA transformers in the ps) and is very quiet in operation when connected to my horns. My SE tube amps still have the edge in sheer treble magic, but listening to music through my M2 clone with my NVA phono3 / BBPSU is so much fun, that I don’t care about the tube magic the M2 can’t do. :dance:

Back to the A20x – as the review is about this amp :)
Regarding musicality, drive and dynamic shadings of reproduced music, this little amp is a real positive surprise after it is run in. :) It is more forward and rough sounding than the M2 clone, but with its lively and fluid reproduction of music the A20x is a fantastic bargain for the money! On many recordings, instruments are reproduced with energy and verve and make me smile. The A20x has a more energetic way of reproducing music fed from vinyl or CD than the M2. And for this entry level amp, the bass performance is astounding! Of course, the M2 has more weight, authority and slam but the liveliness of the NVA amp’s sound results in a well tuned bass for sure. :)

If the recording is on the hotter side - as some of the brass sections on Blue Note Jazz records - this liveliness and energetic performance can be too much, though and the music reproduced over my horn ls-system in the near-field then becomes a bit too nervous and forward sounding, which makes it harder to follow the message of such music.

But hey, the amp has cost £300 (plus shipping) and has been designed as an entry level NVA amp. This said, the performance of the A20x is a bit of a miracle to me. :clap:

The only downside is a slight hum the amp produces connected to my high efficient horns, which you can hear from the listening seat in quiet passages of classical music for example or when no music is playing. (The hum increases somewhat with turning the volume up). It is not transformer buzzing as these small transformers are dead quiet in operation. It is a hum the amp produces also when connected to the speakers alone (but then lower in level), i.e. without the preamp (amp inputs shorted with cinch plugs). I assume this hum is audible, due to the amp being connected to high efficient speakers. In comparison to the A20x, my M2 clone amp is a lot quieter connected to the horn ls-system.

Taking into account, how much I invested in parts and chassis alone for my M2 clone amp - I would say roughly 3 times more than the price for the A20x – the money / performance return is by far smaller than the price difference! Ok, the M2 is the quieter, more musical and natural sounding amp plus has more heft in the bass department, but the A20x with its lively and energetic reproduction of music comes very close to this. The price / performance ratio of the A20x is definitely superb and a real challenge to beat!

A20x and P50sa:
Paired with the P50sa I bought recently from Derek (Klimangelis) all I said before about the A20x remains valid. On top of that, you get slightly more musicality as the synergy of the NVA combination comes through fully. :-) Richard choose the resistor values on the stepped attenuator of the P50sa very well as the high gain of the amp on my horns is a lot better under control with the stepped volume attenuator, than with my DIY passive pre with log potentiometers. What I mean, is the range of volume I listen with the P50sa is wider (from 6 to 12 o'clock in my system compared to 6 to 9 o'clock with my DIY passive pre). So, it is easier to set the volume for lower levels of music replay.

Still, the gain of the amp remains too high connected to my horn speaker-system. This means, the steps beyond 12 o'clock are for my taste too big to really enjoy the amp fully. One or max. two further volume steps result in most cases in a too loud music replay! :( So, beyond 12 o’clock, more and smaller resistor steps would be ideal for the A20x given my listening environment with high efficiency on the loudspeaker side. I’m sure for not so efficient speakers the gain of the A20x will be exactly right.

To sum up the musical performance of the A20x / P50sa combination:
The pre / amp combo shines in the mids and with its sweet treble reproduction. So, well recorded classical music and especially string music is a joy to listen too. :-) For example, some of the wonderful ASMF / Marriner / Argo recordings are a delight with this pairing. The liveliness and vividness of the reproduced music is a strong point of the A20x as it connects you well to most of the music played through the amp. On hotter recorded records, some Blue Note Jazz records as explained above or not so great recordings (for example Norah Jones – Broken from the LP “Not too Late”), the tendency to reproduce music a bit too nervous and forward sounding remains also true for the combination of P50sa /A20x (compared with P50sa / M2 clone).

So, what is my conclusion regarding the NVA A20x:

I learned that
• an amp doesn't have to be Class A to sound great 8-) This is good news especially for hot summer
days as the produced heat of Class A amps in summer is not so pleasant!
• never judge an amp’s performance by its size
• a minimalist design and expert knowledge of the designer plus his love for music are key
ingredients for a superb sounding amp :clap: and finally
• an amp doesn't have to cost a lot to connect you with your music 8-)

Enjoy your music,

Tubes and Vinyl rule, Music rocks! :icon-wink:

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Dr Bunsen Honeydew
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Re: A20x experience

Unread post by Dr Bunsen Honeydew » Sun May 27, 2018 9:48 pm

There should be no hum. You have a earth problem / incompatibility in the system. I suggest you get a piece of wire and connect between the earth terminal on the Phono2 or the outer of a spare phono socket on the P50 to the earth in a local mains plug and plug it in, it *should* solve the problem.

I would say the A20x is better suited to what you want than the new A30, it happens to be circumstance that suit it, where as with normal speakers the A30 will be better.

You can get a stepped attenuator with many more steps and better resistors if you wish, contact hi-fi collective, Nick (another one) will decide with you the best resistor layout. I will then tell you how to get in the pre and replace. If you are unsure and want me to do it then you have to send it back.

https://www.hificollective.co.uk/compon ... ators.html


Re: A20x experience

Unread post by Karnevil9 » Sun May 27, 2018 10:37 pm

Those Tocos pots are good & perfect for vintage amps.. I ended up going for the Noble pot in my Headphone amp..

Posts: 61
Joined: Wed Nov 01, 2017 9:18 pm

Re: A20x experience

Unread post by eagwok33 » Mon May 28, 2018 8:07 pm

Thank you Richard for the advice regarding the hum. I will look into it.

Thanks also for the link to hificollective and the mentioning of Nick there. I normally buy parts at his place. They are very customer friendly and know about their stuff. When there is more time to DIY again, I will look into your recommendation of a stepped attenuator with more steps and maybe also better resistors. :)

Tubes and Vinyl rule, Music rocks! :icon-wink:

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