NVA AP70 INTEGRATED AMPLIFIER

The AP70 forms the next to top of the range integrated amplifier. The case includes two power supplies, one driving each channel.

AP70 Specifications

Inputs Six line level

Outputs 4mm speaker sockets.Tape out.

Power supply 2 x 160 VA

Power Output 70 W

Dimensions 430mm x 90mm x 320mm (whd)

AP70 Integrated Amplifier

An internal phono stage is available for this amplifier. For turntable use you must use that or an external phono stage like the NVA Phono 1, Phono 2 or equivalent. All 6 inputs are identical and hardwired to the selector switch using silver alloy cable with PTFE cover. The output of the switch is routed to the potentiometer and tape socket again with the silver alloy cable. The potentiometer is a very high quality. The signal is then routed to the amplifier PCB again with silver alloy cable. The pre-amp stage is entirely passive. The input to the power amp stage has minimum capacitive and inductive coupling and has been designed to operate correctly with the variable impedance output of a passive pre-amp stage. A current mirror operates at the pre-driver stage to ensure that the voltage rails track each other correctly. The driver stage has both current and voltage amplification using devices that could be used as output transistors. The output devices are 12 amp darlingtons and there are two per channel.

The power supply is based around two 160va transformers, one per channel. A two way smoothing stage is incorporated in each supply. There is no protection circuitry or filtering on the output of this amplifier so care must taken in its usage.

Do not short circuit the output. Do not use bi or tri wire (unless nva LS1 or LS3) or high capacitance or litz type loudspeaker cables as these will damage the amplifier as they create a virtual short circuit at very high frequencies which will create instability in the amplifier. As a rule of thumb avoid cables with a capacitance higher than 200pF per meter. Simple solid core or low capacitance stranded cables are cost effective but high quality silver or silver alloy cables such as NVA LS1 or LS3 are best. Avoid loudspeakers with an average of below 4 ohms load impedance or loudspeakers using high frequency notch filters in their crossovers. This amplifier has minimum capacitors, no inductors, and is a low negative feedback class AB circuit design that is unique. The amplifier has an output of 70W per channel. The case design has been created for sonic reasons and is glued and insulated to stop induced circulating currents and static charge problems associated with normal case designs. Due to the multi power supply nature of the design of this amplifier do not expect it to reach the design sonic performance until used for at least one week from new. It is recommended that the amplifier is left on at all times. Loudspeaker cables can be disconnected but do this at the amplifier end to avoid short circuits.

HI-FI NEWS

Hair-shirt styling and a minimalist interior yet, in the right system, the AP70 integrated gives a five-star performance

The styling of NVA's AP70 integrated amplifier is hair-shirt: featureless black with just two large control knobs on the fascia, one for input selection and the other for volume. The inside is minimalistic too. No phono circuitry, a passive pre-amplifier, as few active devices as possible, with hardly any capacitors in the signal path and certainly no inductors. No protection circuitry, and of course no speaker switching or tone controls.

On the other hand, the audio signal is positively mollycoddled. All signal routes are via silver alloy cable with PTFE sleeving. The input selection switch feeds the signal direct to a cermet volume potentiometer of 100K ohms linear law for high precision and channel balance. This is bypassed by 10K ohm metal film resistors to simulate log law characteristics for smoother volume adjustment. A combination of aluminum, perspex and wood for the case, with glue rather than screws connecting the metalwork together, is claimed to isolate the circuitry from magnetic eddy currents and static charge problems. Speaker output sockets suit only 4mm plugs, and neither the amplifier inputs nor its general circuitry are isolated from outside sources of interference. Not that this amplifier is aimed at those users who are likely to be blasé about these aspects - in fact you should make sure that accompanying equipment is well matched.

There is no lack of power, however. This is not one of those weedy 25W integrateds, but a strong 70W per channel is available from two 12A Darlington devices per channel, and dual mono construction is completed by two 160VA power transformers. Because of the lack of output inductors, solid core speaker cable is recommended for optimum stability, not bi-wired and ideally less than 5m in length.

SOUND QUALITY

Musical detail is maintained at such a level that, in my view, this amplifier easily attains audiophile levels.

With the NVA on a RATA Torlyte stand, and fed from AVI and TEAC CD players using silver alloy, PTFE coated interconnects, an astonishing musical performance was brought forth once the amplifier had been warmed up for a few days. (NVA recommends it is powered constantly.) Output was anything but thin, instead imbued with a satisfying amount of body that ensured the warmth of orchestral instruments and vocals was achieved with highly natural results. And yet this has been managed without any suggestion of coloration, the sonic delivery crystal-clear.

This is one of those products whose performance is so coherent that it is almost impossible to talk about the characteristics of bass, midband and treble; it is much easier to concentrate on the musical detail which is maintained at such a level that, in my view, this amplifier easily attains audiophile levels.

There is no rounding, or falling away, of detail at the frequency extremes. Cymbals and maracas exhibit excellent transient qualities while sparkling with clarity. Bass guitar and percussion hold firm and fast with every note carefully crafted.

These characteristics are maintained with a wide range of speakers and at all listening levels. While there is a volume level for each disc at which the output sounds its most natural, you can turn the level down without losing the enjoyment of the music.

Musically the amplifier is a revelation on just about every disc you can find. It has the capability of raising the hairs on the back of your neck with discs that might otherwise appear mundane - I even found myself playing Karl Jenkins's Adiemus, Songs of Sanctuary right through from beginning to end!

What you must do to achieve these levels of performance from the NVA is get everything else about your system absolutely right. Cabling is highly important; source distortion components must be free from distortion artifacts and as accurate as possible. The speakers must be nominal 8 ohms and not have nasty crossover impedance effects from notch filters and the like. Not that you have to worry about driving ability otherwise. Get the system right and this amplifier responds with five-star performance.

WE ARE SO CONFIDENT IN THE QUALITY OF OUR PRODUCTS AND DESIGNS WE OFFER 30 DAY NO QUIBBLE RETURNS POLICY

Available in 120v or 240v please stipulate on purchase

NVA's Overall Philosophy

Generally, we have never been keen on producing conventional literature, because it's usually just glossy expensive paper full of pretty meaningless specifications which have little bearing on how good the sound of audio equipment is when playing music. If you buy hi-fi equipment on the basis of what a manufacturer says about himself (including us!) you really do deserve what you get.

As an alternative, one of our dealers suggested that we try to explain good design and how to recognize it. People probably won't believe this, but really the basics are very straightforward. A famous British amplifier designer is supposed to have said, "Good amplifier design is not the things that you do right, but the things you don't do wrong". I really wish I had said it first, because it's amplifier design in a nutshell. You can come up with all the new circuit configurations under the sun such as feed forward, low feedback, class A to Z, but ignore the common sense ground rules, and you will have a sonic bag-of-nails capable of being blown away by a couple of EL34's in a 1950 Williamson tube circuit. I am afraid 80% of the amplifiers built today fall into this category. The thing that never stops amazing me is that so many audiophiles keep falling for it. There is nothing like a good story to have people hocking the next three years' spare income on the latest all-singing, all-dancing creation. Not only that, a good story sells magazines as well, which just exacerbates the problem.

Here are my ground rules:

1. There is only one thing better than the best component money can buy, and that is no component at all.

2. Never use two components when you can do the job with one.

3. Screw up your earth (ground) paths at your peril.

4. Always use the largest transformer (toroid if possible) you can cost in.

5. If your ears and your test equipment tell you two different things, trust your ears.

6. If you have a fault in your source material or elsewhere in the equipment chain, you cannot correct it by creating an inverse fault in the amplifier with tone, balance, and filter controls. Two wrongs do not make a right.

After that it is all down to experience, and fine-tuning the design to your own taste. It is easier to get a half-way decent sounding amp using Vacuum State Logic (warm glass bottles) than Solid State Logic (hopefully cool lumps of plastic) because there is less to do wrong (Neanderthal Logic). That is why so many people have jumped on the valve bandwagon. All things being equal, bits of doped silicon encapsulated in metal or plastic (transistors) potentially are capable of doing more things with music, i.e. wider (frequency), larger (amplitude), cleaner (distortion and noise) for less cost. Remember though, the more you try to do, the exponentially easier it is to do it wrong.

If you can get most of it right, then think very carefully before you try to get the very last bit, because you may be too clever and ruin everything you've gained thus far.

This explanation is all very simplistic of course, and common sense and experience must apply as well. For example, a Class A circuit is a lot simpler that the equivalent Class B or AB. Ergo, applying my logic it should be better. Wrong, unless you spend a fortune on the power supply, which then makes the amplifier grotesquely expensive and heavy. The problems of current demand by the amplifier outweigh the simplicity. If I could buy 1000VA transformers not larger than 4" square, and weighing less than two pounds for £10, and if I could get good and consistent output transistors (i.e. not FETs) that could sink 20 amps, and either, not get hotter than 70 degrees C doing so, or stand 150 degrees C without going into self-destruct mode, I would produce Class A amplifiers. I will not produce them just because they have become some reviewers latest buzz word.

Every amplifier has its own sonic character, which is very much down to the musical parameters that are most important to the designer. The process is very much "lose on the swings, gain on the roundabouts". I once knew an amplifier designer, in fact I employed him back in Tresham Audio days to produce a professional FET power amplifier, who saw no necessity for listening to the amplifier at all. It was only after he left, and some ears were applied to the design that it started to sing, not as much as the best hi-fi amplifiers, but it went very loud and was virtually indestructible.

My greatest hang-up is information retrieval - musical information, especially dynamic separation. I will always go for information even at the expense of upsetting the "make everything bounce and swing with the tempo" brigade. My other priority, which seems to be out of favour at the moment, is neutrality, or as I prefer to call it, lack of the irritation factor.

Richard Dunn, Founder and Owner, NVA

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PLEASE NOTE ALL NVA PRODUCT IS BUILT TO ORDER SO THERE WILL BE A DELIVERY DELAY AS THE PRODUCTION AND TESTING IS SCHEDULED. AVERAGE DELIVERY TIME IS FIVE TO SEVEN DAYS BUT CAN ON OCCASION GO OUT TO FOURTEEN DAYS DEPENDING UPON ORDER PRESSURE

We offer a 100% trade in value on our products if you trade up within the nva range of like products within two years of your purchase date (only applicable to direct sales from us or through ebay). After that date we will still trade in your item but on a sliding scale as to age and condition. You must print out and keep your ebay receipt or invoice to verify your purchase date.

THIS SERVICE AND OFFER IS QUITE UNIQUE IN THE WORLD OF AUDIO AND HI-FI

NVA AND SPEAKER CABLE SAFETY

For best sound the amplifier should be left powered up. Electricity consumption is very low. It is for this reason that the power switch is located on the back panel, where it may not be easy to reach. Turn the amplifier off when you do not intend to listen to it for extended periods.

NVA amplifiers are unique, and one thing that makes them so is the minimal compensation for the output stage. It is very possible to send this amplifier into oscillation by connecting too large a capacitive load on the output, the usual culprit being unsuitable speaker cable such as Litz or Goertz type constructions. The amplifier normally runs cool, but if it is driven unstable the output transistors will become hot and the sound will distort and the amplifier could fail putting your loudspeaker coils in danger. You can check for this by placing your hand on the amplifier and feeling for hot spots. If you find the amplifier overheating switch off immediately and consider changing your cable.

Only NVA LS1, LS2, LS3, LS5 is recommended for use with this amplifier, other cables invalidate our guarantee. If you insist on using other cable please ensure it is no more than 200pf per metre and it should not be used in lengths over 10 metres. If you wish to Bi-Wire this can only be done with NVA cable and they can be made that way on order for small added cost.

For design performance only NVA Soundpipe Super Soundpipe or Soundcord  Interconnects should be used, but this is for sonic as opposed to safety reasons.