Product: Rock Solid Battery Powered Power amp
Manufacturer: Audio Consulting - Switzerland
Cost: 7000 € approx
Reviewer: Geoff Husband - TNT France
Reviewed: November, 2003

Introduction

Let's go back in time to the dark days before silicone - go pre-transistor and you have puny valve amps where 15 watts is seen as meaty. Then along comes the transistor. In the space of a decade we go from single figure outputs to the-sky's-the-limit. Want 100 watts - of course sir. 200? 1000? No problem. And of course with such outputs speaker design can be radically altered. After all with a few hundred watts to play with who needs light cones? Now the designer has to build drivers capable of coping with the power, ferrofluid cooled tweeters, big gaps between coil and magnets, heavy stiff cones, multiple arrays of drivers in parallel, electrostatic panels dipping to 1 ohm. Which of course all need more power to drive and control them :-)

Move on to the late 80's and 90's and we see a polarization between "watts are good - more watt's are better" and the "the first watt is the only one that counts brigade". In one camp the monster transistor amp and inefficient speakers, the other valves - often single ended and high efficiency.

But in Audio Consulting (AC) we have a company that bridges the two. Makers of some staggeringly expensive valve amps, they have now turned to make something more affordable and to do it using transistors. Heresy of course, but there is logic to the move. AC have found mains quality to be absolutely critical in the sound of their SE amps to the extreme of building a 400 kgs (no misprint) mains conditioner. In the Rock solid they've neatly side-stepped the problem by cutting out the mains entirely - the thing uses batteries, this is not an option with power hungry valves. This seems blindingly obvious but it's not been done very often with power amps because of the amount of power needed, cost (batteries cost more than a cheap torroid) and the fact that batteries rarely seem to fulfill their potential - see the Naim website for a good article by Julian Verika for possible reasons. Certainly AC found they resulted in squashed dynamics amongst other nasties. Their solution was rather than take an amp and replace the power supply with a battery, to design a transistor amp from the ground up with battery power in mind.

Construction

The result is the Rock Solid (RS). Read the spec and you'd think it was a valve amp. Only 30 watts per channel, easing the load on the battery, silver wired input transformer, hard wired with silver wire, paper-in-oil bypass caps, wooden cabinet etc. In a small unassuming box, it looks more like a piece of medical equipment in it's grey 'granito' finish. Certainly it isn't going to impress the neighbours and personally the Piano black finish would look a lot classier, but in a world of amps with 10 mm thick alloy front panels, or massive valves, it'll be one to hide away. This too will be no problem as it runs very cool.

The amp is a true hand-built, custom affair, you can have it in various finishes, with on-board battery, off-board battery or dual mono, off-board supply (in one box). You can have output transformers matched to your speakers - you can even choose the knobs...

The review amp came with the top-of-the-range twin battery supply. This powers the amp by an umbilical, and the batteries are charged all the time by twin chargers - 4 boxes in all! If you want you can disconnect the amp entirely from the mains for ultimate performance with the turn of a knob, but to be honest I couldn't reliably identify the difference between the amp being trickle charged or running in isolation so I kept it "live".

The rear sports banana sockets that look cheap and plastic for an amp of this price - but they are chosen because of their sound quality. There is now a well argued school-of-thought that all connections should be low-mass, and those massive gold-plated brass connectors, beloved of hi-fi jewellery salesmen everywhere, ruin the sound quality. It is for this reason the cheap looking sockets are used and the philosophy extends to internal wiring and the supplied interconnect which use fine, single-strand, silver wire.

As for technical specs, the Audio Consulting website is coy, 30 watts per channel is about all you get, plus a list of the sexy internals. I'd guess it's no current powerhouse, but then I didn't try to make it drive Isobariks. But that 30 watts is significant. If we assume that the RS is primarily designed as a sound-quality-before-all-else amplifier, in the manner of some valve amps (e.g. SE's), then the RS produces enough watts to drive any reasonably efficient speaker in the average domestic environment. This takes it out of the 300b crowd and in this respect at least, puts it up against PP valve amps using EL34's for example, and of course the equally anachronistic Lab 47 Gaincard - the 25 watt transistor amp I had here 18 months ago.

Sound

Two pre-amps were used, My M3 and AC's own passive pre. The latter was so unusual it too deserves a review so I'll not comment further than to say both worked brilliantly.

I used two sets of speakers for this. The main ones were my Polaris Horns, with 104 dbl efficiency likely to test the first watt only. The second were my old IPL S3MTL transmission lines, which at 87 dbl efficiency were going to be at the limit of the RS's power output. It also co-incided with three 300b single-ended amps (AudioNote, Wavac and Audion). Regular readers will know that I bought the AudioNotes, but at the time of the test I still had my old Audion EL34 ETPP 30 watt amps to hand. This was a formidable line up of valves, and the RS also had to cope with the fact that for several years my system has become increasingly orientated towards valves - perhaps that makes me a typical potential RS customer? - I don't know.

Reviewing can be a hard job (fade in gypsy violin), because when we start everything is so new - it's easy to find appropriate hyperbole, to say - "never heard that before" or give some flowery description of the nuances of some performance, previously unnoticed, that component 'A' has dragged from a source. Note that descriptions like this are best done with some obscure piece of music your audience have no experience of - gosh! am I cynical today :-)

But in reality, as our experience of many different pieces of equipment increases, this easy option becomes rarer, and to rely on it either smacks of over indulgence to a manufacturer, or the belief that readers won't be trawling back-copies for the same praise lavished on another piece of equipment... But what this experience does bring is a sense of balance, a realisation that every component is a set of compromises and that really good equipment manages either to do one thing brilliantly or everything well. In this occasional series of low-powered amp reviews you'll see that the stand-out so far was the Audionote/M3/Quest Silvers because of their competence everywhere and brilliance in the area of mid-range transparency. I bought them... The Rock Solid is another amp deserving of praise, but in a very different way.

So how does the RS sound? Well my immediate impression was that this, though coming from a manufacturer of single-ended valve amps, doesn't sound like one. I'm not sure if it's possible to get that "hear-through" transparency in the midrange using anything other than a single-ended triode, but certainly I've yet to hear a convincing alternative. Here the RS is very good by any other standard, it's from the top draw and does it in a way that really reminds me of my old EL34 Audions.
It doesn't sound like a transistor amp, it's totally devoid of grain and very smooth. It also, like my old Audions has a big meaty sound belying it's paucity of power. In this respect it outdoes even the Audions by underpinning everything with powerful clean bass. It's not as crisp and fast as the Korato KTA100 but not far behind. Driving it hard into the Ipl's it eventually begins to sound a bit loose 'down-below' before clipping discretely. Of course the Loth-x horns would perforate your eardrums if fed with 30 watts, and so the idea of clipping was a long way from reality. The RS punched out basslines with speed and impact that had me checking to see if I had the sub (a REL Stentor) fired up - I hadn't. In this respect it was well ahead of the Audions.

In the midband there was a sweetness and warmth that the EL34's had, giving a lovely feel to female vocal, real curling-up-in-front-of-the-fire stuff. The big punchy sound was equally good when it came to bringing out the menace of 'Mars' or the impact of Nirvana.

At the top end it was a creamy as you could wish without sounding rolled-off, hard-struck cymbal being big and shiny without setting your teeth on edge.

The soundstage was 'Rock-Solid', big bold images in a believable acoustic, but without the 'holographic' effect of the Quest Silvers at their best.

And this brings me to the thing the Rock Solid does best - consistency. Most of my serious listening is done in the evening, this applies to reviewing too. During those times I thought the Quest Silvers, for the most part, had a significant edge in the critical midband - enough to keep me very happy in my recent purchase :-) True, the RS gave a deeper bass performance and were certainly much quieter (silent) in operation.

BUT at almost any other time of day the lead the AudioNote's had evaporated. Listen at 11.00am and the Silver Quests sounded small, constricted and flat whilst the SR continued to fire-on-all-cylinders. And in this respect alone the Silver Rock trampled any other amplifier to have crossed my portal.

The effect of mains supply had been well documented over the years, voltage variations, frequency variations, spikes, drop-outs and an increasingly large amount of RF hash pollute our juice. The situation will inevitably get worse with the multiplication of radio waves, and the privatisation of electricity supplies, suppliers constantly cutting the supply as fine as they can. The RS does away with all this - at a stroke you are free of the local farmers milking machine, the local Aluminium smelter, your own washing machine and the penny-pinching electricity company. Here I have a 16 amp supply (on a good day). The lights dim when I switch on a heater - One test amp switched itself off when we used the washing machine, another buzzed so badly it was unusable. When we go over to cheap electricity at 10.30 pm every mains transformer buzzes like a hive of angry bees. So OK, I'm in a poor area, but sure as hell it isn't the worse (California anyone?).

The fact is that for much of every day the RS was the best sounding amplifier I had here.

Conclusion

For the same money you could buy a nice pair of 300b monoblocks, but you'd have to be prepared to put up with the set of compromises they offer - noisier, very low power and higher running costs, not to mention their susceptability to mains interferance. Compared to more conventional amplifiers, valve or solid-state, the Rock Solid makes a convincing case for its inclusion in a series of high-end amplifier tests. It didn't shine in any one area above all comers, but provided a high-class and balanced view of events without any weaknesses. In fact I preferred it to the Lab 47 Gaincard and my Audions. It's powerful enough to drive most speakers, and its very simplicity should aid reliability - no revalving here. Personally I didn't like the looks but then that's personal, apart from that the criticism ends. But what you might think of as a niche attribute, its use of battery power, is in fact of general interest to many of us, and if you live in an area of particularly bad power supply it may be the answer to all your prayers.

In a world of "me too!" products the Rock Solid is certainly worth giving a try...

Manufacturer's comment

What a nice review! Thank you very much.

There is some news from the never ending story of R&D. The batteries seem to be much more critical in the final result than we even thought. We have compared many types and only one or two brands are really doing the RS justice. One is the Sonnenschein/Dryfit, the other the Swiss brand Leclanché. We will not guarantee any sonic perfromance in the future without those two types of batteries. Unfortunately the RS reviewed was still having other batteries, which we consider to be good, but we came across much better ones in the meantime.

We also finalised the output transformer (which is a auto OPT in fact) during the last two weeks. Huge improvements here, even in the 1/1 mode. Speaker efficiency seems to be less a problem for the RS than impedance, and he really is most happy with impedances of 8 ohms or higher. A good transformer does miracles when used at a good SS amplifier. We did first studies with class A Kaneda type of amplifiers some 15 years back.

We observed that the Dulcet speaker from Mantra Sound which is over 8 ohms average, worked significantly better when reflected in a 2/1 mode, which is 16 ohms at the RS' output. We did not include the OPT in the RS on purpuse as this keeps costs for the amplifier at a reasonable level. The OPT is a substantial upgrade even in the 1/1 mode, and allows the RS to drive any speaker regardless of impedance and even efficiency. Low efficiency is less a concern to the RS than impedances lower than 8 ohms. This became clear with 83dB/w/m speakers from Spendor which have a regular impedance curve around 8 ohms. Perfect match.

The OPT comes in the same cabinet as the RS itself (see attached picture) and is available in copper of silver. Prices are:

Copper/Granito cabinet versions version will be CHF 2360.00/stereo. Silver/Granito cabinet version CHF 3360.00/stereo.