Velleman K4000. Valve Power Amplifier Kit

The iron hand in the stainless steel glove

by André Jute

The Belgian Velleman K4000 Valve Power Amplifier, from the world's largest and most reputable manufacturers of kits of all kinds, is probably the best-selling kit tube-amplifier in the world. It produces 95Wrms per channel in Class B, enough to drive a large disco into hearing impairment, and 15Wrms per channel in Class A, which is what the hi-fi purist really wants to know. It costs around $700-800 (e-mail or call Velleman Export Sales in Belgium on +329-384-3611 to discover your nearest source) which is less than you will pay for a really good 95W transistor amp. Operated from a CD with a volume control, the K4000 requires no pre-amp, which is a saving; on the other hand, I measured input sensitivity at 765mV for full output, so those whose CD player puts out the "standard" 300mV will extract a "mere" 40W or so from the K4000 unless they splash out for a pre-amp. If you want a full-service pre-amp, Velleman sells a good one in kit-form with all-digital controls for under $300 but soldering it is trickier than building the tube amp with its big, widely spaced parts.

To build the K4000 you need wire cutters and strippers, an adjustable spanner, needle nose pliers, an allen key, and a soldering iron. Adjusting the fixed bias requires a well-calibrated digital multimeter which you can, if you are keen, also build yourself from Velleman's K7100 kit (note added 4 October 1996: K7100 no longer available as a kit).

You need one more thing: respect for high tension electricity. Tube amps carry lethal voltages. For your own safety you must follow the clear instructions.

The kit comes well packed in a large, sturdy box. The instructions are occasionally written in Belgish but we had no problem following their careful logic once we worked out that "cinch connectors" are phono sockets. "Valves" are tubes.

Parts quality is, by general electronics kit standards, first class. The toroidal output transformers sound much better than comments from within the audiophile community in Britain and the US ('doughnuts belong on the breakfast table') had led me to believe they could. However, by audiophile standards the minor parts quality is barely passable, one ceramic cap (horrors!) even finding its way into the signal path. But working on this amp is so easy you are almost invited to experiment with trick caps and resistors. We earthed ours to a better standard than is common in either Europe or the US (by linking the power input earth to the chassis) and were not blasted with the hum the manual warns will punish those disregarding its warnings about earth loops. In standard form hum measures 1.2mV, with our earthing mods 2.0mV; either way no hum was audible in a very quiet room in the country.

The soldering points on the three boards are well spaced so untidy soldering hardly matters. When the kit is assembled, even with the top cover off the soldering is hidden. Everything possible has been done to make construction as painless as possible. All except one of the resistors are bandoliered in order of use. The fuses are so arranged that the testing sequence can be done without damaging later parts if you make a mistake in the earlier part of the circuit.

One of the holes on the board was not drilled and we knocked it through with a nail. The output terminals to the speakers are so close to the special and expensive toroidal output transformers that one must choose between risking burning the most expensive parts in the amp with the soldering iron or leaving the leads longer than necessary so that the output transformers can be bolted in after the soldering is done. We chose to leave the leads long. If we ever build another K4000, we will tag and bolt the wires to the output terminals and forget about soldering. More seriously, the cutout for the clip-in on/off switch is too big and the switch must be glued in place; glue it from the back to avoid messing glue onto the beautifully finished front panel. Seasoned kit builders will hardly notice these solecisms but audiophiles building the K4000 as their first and probably only kit may consider they are entitled to more care.

The design, except for the unusual fixed bias (which is responsible for the exceptional bass), is standard parallel push pull ultra-linear feedback though, as we shall see, the sound it makes, once output rises above 15W, is very different from a standard push pull tube sound. It is built on four boards, one for power smoothing, one as a buffer and pre-gain stage (Velleman calls this a "pre-amp") outside the feedback loop, and one per channel containing the voltage gain/phase-splitting and power tube stages.

The complete amp took about twenty hours to build at snail's pace, checking everything three times. If you mess anything up, you can send the boards back to Velleman to fix. Experts may allow four or five hours.

Once assembled, the K4000 looks absolutely stunning with its eight EL34 parallel push-pull valves plus two 12AX7 phase splitter/driver valves sitting out in the open on acres of gorgeously polished stainless steel. The single 12AU7 that serves both channels as a buffer/pre-gain tube is hidden under thecasework. The amp gleams like the chandelier at City Hall but sounds better.

The Velleman K4000 worked first time we switched it on, sounding right after only the briefest warming-up period. I repeat, first time, no messing, no fiddling. This is where all that Velleman kit experience pays off.

The sound improves over the first hundred hours or so as the parts settle in and one rebiases the valves to perfection. The soundstage is wide, high and deep. A 95W power band with a half-power (-3dB) point as low as 10Hz will surely vibrate any house--you can't hear below 16Hz but you can feel-in which you are careless enough to turn the volume up on a good bass subwoofer. There is comfortable oomph to handle any sudden transients of kettle drums, snares and other instruments of sonic torture.

With 2 x 95Wrms claimed (102Wrms measured @ IkHz with less than 1% distortion) and such bass capability, of course the Velleman K4000 will rock till you drop. What is more remarkable is its ability to present the vocals and small chamber pieces I like best with the requisite delicacy. Those 15 Class A watts walk tall. But while all that European breeding sings sweetly to any handy maidens, when the K4000 puts on its stainless steel knight's armour it smites a hefty blow against the transistor heathens from the East. It is as if someone commissioned Velleman to refine an overachieving American effort at an Hell`s Angel's heavy metal tube amp just far enough to get it through the front door at the rectory. And never mind that once inside it would stomp any twee little 10W 300Bs it discovered wearing glasses.

My reference setup is a Quad CD66 player, Quad 34 pre-amp, Quad 405 series 2 power amp, Quad ESL-63 electrostatic speakers (sensitivity 85dB). The room is 18ft long. With the K4000 installed in the amp position, up to painful volumes (say 15W) it sounds far better than any tube amp this cheap should. It sounds good too with my son's $160 Sony Discman and Bang & Olufsen S25 bookshelf speakers, so it isn't tiresomely finicky about partnering equipment like, alas, so many other tube amps. It certainly won't require specially sensitive, expensive speakers.

Over 15W the velvet gloves wear away right suddenly and the K4000 starts to sound more and more clinical. My tranny freak friends are all rushing out to buy one: it is the first tube amp which in their eyes returns respectability to glassware--and, amazingly, at a price that is cheap even by tranny amp standards. It is true that I have heard less incisive tranny amps in recording studios but then I do not object, as the tranny freaks do, to that warm good fellowship most other tube amps lay on the music. They love this amp because it beats tranny amps at their own game of power and unrelenting revelation. To them it is a high compliment that the K4000, played very loudly, can be seamlessly A/B-ed with my Bang & Olufsen setup. Since most of them don't believe that you can play an amp below 15W, they will never discover that the K4000 is schizo.

You can tailor the sound precisely to what you want by swopping parts. An octet of really well-matched EL34 Premium Valves from Chelmer Valve Company (+44-1245-35-5296) smoothed the sound out tremendously at all volumes. Maplin (+44-1702-55-6987), the British distributors, give away a low-hum RC earthing network with the K4000s they supply and they sell for a few bucks selected caps to replace the ceramics in the signal line which bring a reduction of "stereo graininess" (I heard it only when I placed the speakers very close together and very faintly at that).

Who will buy it? A good sounding off-the-shelf tube amp this versatile usually costs from three times as much up into the stratosphere, and few amps of any kind at any price deliver this much real clout. So: Multi-taste music lovers on a budget who want a versatile tube amp. The supercharged 440 hemi-head dragster krowd of hard core rockers who crave anti-social power. Musical vivisectionists, previously of the tranny faith, arriving hotfoot from Audiolab and Krell. Bass freaks with concrete transmission lines to the backs of their gardens. Disco operators with pretensions to culture. And comfortable tube afficionados multi-amping multi-driver speaker setups who fail to see why they should spend Ray Lumley money (or use tranny amps) to power the lowest bass frequencies less well than the Velleman will.

The K4000 offers something--ranging from damned competent to truly outstanding--for everyone: charm for the harmless lovers of Early Music, stops at all shades of opinion in between, all the way up to psychopathic power for those who regret they were born too late to heil at Nuremburg. Hell, it even goes well with Swedish furniture, which guarantees spouse appeal in the yuppie set. Whichever way you look at it, at twice the price the Velleman K4000 would still be an audio bargain.

E-mail or snailmail Velleman (Velleman Components NV, Industrieterrein 33, B-9890 Gavere, Belgium) or phone (+32 9 384 36 11) or fax (+32 9 384 67 03) to find out the name of your nearest stockist. In the USA contact Old Colony by snailmail (PO Box 243, Peterborough, NH 03458) or phone 603 924 6371 or fax 603 924 9467.

André Jute was educated in motivational psychology, economics and business management at universities in the United States, South Africa and Australia. He earns his living as a management consultant, graphic designer and novelist; he writes a syndicated weekly column on classical music. He holds patents in automobile suspensions, internal combustion and pipe-laying equipment. Before taking up valve amplifiers he rebuilt old Bentleys.

© 1996 Andre Jute

NEWSFLASH!

Velleman K4000 upgraded to K4040

Thoughful development leads to even neater casework, better capacitors and connectors, easier biasing

The K4000 is being "redesigned" and the new version will be available from April 1997. The K4000 will be replaced by the K4040. The K4040 in essence makes the Velleman kit, already a very acceptable piece of livingroom furniture, even prettier, and other changes are intended to make a good amp sound better by replacing those parts in the original specification which audiophiles in any event replaced. The cost of replacement was modest, but Velleman is presumably keen to avoid even the smallest irritation to customers of the best-selling kit amp in the world, and to give reviewers no chance to pick even the tiniest of nits.

The modifications will be :

1. The housing:

Same stainless steel look as before but,

-Removable ground plate convenience in original assembly wiring and subsequent service

-Removable aluminium front panel for more convenient adjustment of bias current

-The bolts for the transformers will no longer go through the housing so they will be invisible at the rear panel

-Gold plated high quality speaker connectors replaces nickelplate items used before

-Input cinch (phonos) on a separate p.c. board to fit more neatly and for easier assembly into the back panel

-Some other minor changes.

2. Electrically:

Same set-up as before but,

-Universal power transformer (115V to 230VAC and choice of 300 or 285VAC output)

-Small 3 position power switch with stand-by function and LED indicator

-Use of polypropylene film capacitors

-Input short circuit during warm up

-LED indicator behind front panel for setting bias without DMM, a nice safety feature

Thus the alterations add up to what the keenest audiophiles already made to their K4000, plus a few construction-convenience and service tidying operations. In combination, and taking the popularity of the amp into consideration, they simply confirm that this amp was designed and packaged the right way from the start. It is nice to see the world's most trusted electronic kit maker does not rest on its laurels. This upgrade is proof that they develop their products continually to improve the convenience of customers, and that they listen to customers--even to the special needs of audiophiles!

If you want to put your name down for a K4040 before the gadarene rush, you can e-mail Velleman HQ by double-clicking on their name. They have distributors in just about every country I ever heard of, so if you are not in Europe, tell them where you are and ask the name of your local distributor. Or look it up on their kits netsite which also has information on their other kits.

© André Jute 1997

Upgrading the Velleman K4000

Mike Kontor shares his trade secrets for turning the K4000 into a killer audiophile amp

The Velleman K4000 valve amplifier is a wonderful sounding unit which I have been selling successfully here in Australia in two versions: the standard version and an "audiophile" version using premium valves and parts.

VALVES

You can experiment with output valve brands for a different, perhaps "better sound".

The input tube should be a 12AY7; this will give far better sound and also more gain. 12AU7's are terrible tubes, no matter who makes/made them -grainy, dead, liveless. Best 12AY7 I've tried is the Sylvania military (CV) version, but all the 12AY7's I tried trounced any 12AU7.

The two 12AX7's should be the superb Sovtek 12AX7WXT, the best of this type available, and a truly stunning tube.

POWER SUPPLY

You can double the capacitance by using 470uF caps, available from RS Components, stock number 127-767. It's a direct fit; you'll have to shorten thepower transformer bolt, though (or use a shorter bolt) as these caps are twice as high as the supplied ones.

CAPS

"Preamp" board:

C19L and C19R should be polystyrene instead of the ceramics supplied. C20L and C20R should be audiophile quality; I use the AXON cap which is excellent. Just let it stand up on its leads, there's plently of room for them both around the valve.

Amplifier board:

C13--use RS Components 821-043; solder one leg into the board, the other wraps around the pcb pin where the input wires join.

C15 - C18--use RS 821-037. These are film foil polypropelene from Arcotronicz, really superb caps.

MISCELLANEOUS

Instead of mounting four 30 ohm resistors per valve (for the cathode resistance), I mount PCB pins, 2 per valve, diagonally opposed (drill the holes out a little) and then solder a single half watt 10 ohm resistor across these pins. Why? Because if a valve blows and takes out the resistor, you can change the resistor without taking out the amplifier board (which is a pain!).

I use better speaker binding posts (Michell) and teflon insulated RCA input sockets.

I use better quality wiring from input sockets and between the boards: use a good "balanced" lead, ie. two signal wires plus a screen, and connect thescreen at both ends to the GND lead. Van den Hul 501 phono lead sounds very nice, is cheap and easy to work with.

I find it better to attach the transformer leads to the speaker terminals before mounting the transformers, this way you do not run the risk of melting the transformer insulation while soldering the leads to the terminals. I fit an earth post to the underside of the amp--you can use one of the left over-pcb studs and screws--scrape away some paint from the chassis first, and solder the earth pin of the mains socket to this.

You can also fit a volume control, two more inputs and a selector switch to turn this amp into a direct input amp, ("integrated amp"); it has enough gain for most speakers, and anyway this gain is much higher with the 12AY7 tube and further is adjustable at R58L/R.

There is an error in the instructions--Page ED4-30, line 14, should read: "Connect the red wires of the power supply transformer to the terminals marked red of the relay pcb." (It actually says "power supply" pcb. Figure 11 shows the wiring correctly.)

If anyone out there has had experience with this beautiful amp, let me know!

Happy listening.