April 2015

SiebeNCore DIY Stereo Amplifier
In short, yep, it's a rave.
Review By Jeff Poth

  Ah, my readers, my partners in crime, my justifications for having gear everywhere and soldering in the middle of the living room- this one is a treat. An amp project so large you need both hands to count the number of chassis, and 4 digits to describe the output power. That's right, the SiebeNCore project! Seven monoblocks, each capable of 200W into 8 Ohms, 400 into 4 Ohms, and up to 560 into even more difficult loads. True balanced instrumentation grade discrete input circuits, an extremely precise class D feedback and modulation scheme, and specs that have to be seen to be believed (and have been replicated by independent dIY’ers). I'm not one for focusing solely on specs, though I am far from a pure subjectivist, however, when an amp has distortion measured in the ten-thousandths of a percent, PSRR of 85dB, noise residuals measured in microVolts, and is engineered by Bruno Putzeys, one takes notice.

Of Class D And Ncore Of Lore
"But wait, you've already written on NCore!!" some will cry... and they are correct. I have previously done a build for a friend in a stereo chassis, and the results were nothing to sneeze at. That said, I didn't have much time to evaluate as he was anxious to bring home his prize and enjoy on his own rig, fair enough. He's very happy with his stereo NCore amp as reviewed here. In this instance, I was to build quite a bit more amp, as seven monoblocks is not a small project for any man, even when the boards are pre-assembled. Alas, they are not all to remain with me, so completion of the build is bittersweet and shall go to a friend who commissioned the project for use in his home theater. I shall have to make do with a pair of world-class monoblock amplifiers. Such a burden, but someone has to bear it.

Using a single SMPS600 (the intended mating PS from Hypex) for each NC400 module, the monoblocks have a couple advantages over the stereo layout. First and foremost, wiring harnesses are already assembled from Hypex, and are of high quality for the interconnection of the SMPS and Ncore modules. This greatly simplified some aspects of the build, and allowed for a cleaner layout in some respects. The input wire and speaker outputs could be shorter, and closer to the connectors, meaning less need for all the wire fastening efforts. The chassis had a little more room, and the monoblock format is always a treat.

The Bits
The NCore 400 and SMPS600 are sourced from Hypex, with the chassis is from Ghent Audio and includes all connectors (of very good though not super-premium quality). The Hypex components are excellent, including the PSU/NCore 12 pin cable. The input wire is of very good quality, and is pre-terminated for the NCore input, and the power input cable is passable, comprised of 18 AWG copper in PVC. I chose to upgrade this to a twisted quad of 16 AWG copper wire, for lower resistance and a smaller loop area for less radiated noise, but as Hypex has met its specs with their 18 AWG input cable, it may be unnecessary. If you choose to do so, replacement pins for the header connector are JST Sales America Inc SVH-41T-P1.1 and the mechanically savvy person who would undertake this effort can figure out how to release the stock pins from the connector (there's a locking tang to depress). You will need to supply speaker cable for the binding posts, a bare minimum of 14 AWG is recommended, and twisting the leadouts is mandatory for best noise performance. Hypex describes this in their application notes, or you can see any number of builds on the web.

The Ghent chassis has some cool features- a low-key profiled aluminum faceplate, thick extruded aluminum clam-shell top and bottom, a nice connector set and pretty good machining/finish quality. Also notable is the adjustable blue LED indicator light- it can be off, dim, or bright switched externally from the bottom of the chassis, and is supplied from the SMPS600, J1 output terminals, pin 3 is +V (red wire to the LED board) and pin 5 is ground (grey wire to the LED board). I did have to fiddle with the boards a bit to get the mounting to allow full switch motion (and thus all three positions to be available). I actually had to drill out some mounting holes and adjust things on one unit. A wider cutout for the switch on the bottom of the chassis would alleviate this (which will supposedly be incorporated in the next batch of cases), and Ghent was good about providing a replacement switch for one with a too-short pin, as well as a mis-drilled bottom panel, and a problematic set screw. While these several problems were not optimal, overall quality is very good and Ghent did a good job of working to resolve my issues.

Da Build
Most of the build is self-explanatory, but there were a few things I changed up. First, and most important- the anodized aluminum is not conductive on the surface. Accordingly, you'll need to sand everywhere a mechanical connection is utilized for electrical conductivity, and probably should use lock-washers to ensure good continuity. I sure did. This means that the four corners of each chassis plate should be sanded around the screw holes, as well as at the XLR input, and the footer screw next to the IEC, where safety ground may (or may not be, depending upon your preference and familiarity with class II construction techniques) be attached.

I added a shield into the chassis, again attached with a lock-washer on a sanded location. The green jumper is because the aluminum pieces used for this were joined with JB-Weld epoxy, which is not conductive. Accordingly, the top piece needed to have a ground added. In retrospect, fasteners would have been easier. Was this extra effort necessary? Maybe not- but it certainly can only help, not hurt, by adding more shielding and heat-sinking ability to the chassis. I used blue thread-lock on the fasteners and throughout the build. I suggest you doing so as well, as it helps keep things nice and stable, yet don't squirt it all over like a super-soaker. Small amounts work just as well. The SMPS was mounted via its standoffs, one of which is metal and was coupled to the sanded portion of the chassis with a lock washer.

The NCore was mounted with the stock screws, into the tapped threads in the integral heat-sink/heat-spreader. It's highly recommended to use a thin layer of heat-sink compound between the two surfaces, to ensure maximal thermal coupling to the chassis, thus keeping the amp cool and improving product life and performance.

Also mounted via two screws is the LED module. You'll need to make a jumper cable to connect pin 3 (+V to red) and pin 5 (Ground to grey) on the board. Just twist the wires from pin 3 to the red wire supplied, solder, and heat-shrink for insulation, and repeat for pin 5 and the grey wire.

Now is a good time to mount the safety ground to chassis wiring, as well as a ground connection for the Nampon standby control logic. This runs to one side of the IEC-mount power switch, with the Nampon wire from the input cable mounted to the other.

Once these are all mounted, the rear panel can be added via the bottom two screws (with sanding and lock-washers!) and connectors can be soldered and attached. The supplied cable is a twisted pair with shield, and has an extra Nampon wire to control standby operation. Pin one is inherently connected to chassis in the Neutrik input connector supplied by Ghent, and the shield should also be connected to chassis. Theoretical best is to connect the input wire to the chassis separately from, but close to, the pin 1 chassis connection, but it's not a real-world issue so the shield is terminated to the combined pin 1/chassis connection in this build. The Hypex supplied cable has blue connection to pin 2, and white connection to pin 3, and should be kept as short as reasonable without kinking the cable, particularly near the connector to the NCore. Speaker cable leads are a pair of 16 AWG twisted pairs, soldered at the binding posts and run to the connectors on the NCore board. Take care to keep the twisting tight as close as possible to the board connectors, and don't use the side of the inner connector closest to the center of the board as that's the noisiest place for a leadout wire. Also take care that you solder these before mounting, as you'll melt the insulating/locking washers. Arrange the washers so that the tabs fit the notches in the plate, and tighten well, with more thread-lock once they're mounted (again, after soldering, so remove all plastic pieces before soldering)

The power input connections are made with a twisted quad of 16 AWG, to minimize radiated noise. These are soldered to L/N, while the safety ground connection is made with an insulated faston crimp connector, if one later decided to float the chassis relative to safety ground, they could open the chassis and remove the faston. The top two terminals are for the power switch, which in my build is a standby only switch. Unplug it if you want to save the ~12W idle per monoblock, but it's easiest on the PSU to leave it in standby rather than unplug, unless you're going to be out of town in which case unplug altogether for safety from lightning, etc. One side of the switch connects to chassis (same terminal as safety ground but any location works, so long as the chassis is grounded) and the other side to the Nampon wire from the input wire set. All soldered terminals are covered in heat-shrink for safety.

You'll note the braided PET sleeve on the power input wiring, as it's puffed out a bit to keep that noisy wire away from all other connections in the amp, but it's not strictly necessary. Since the PSU/NCore wiring harness routs over the aluminum shield, the sleeve is necessary on that bundle to provide some abrasion/pressure relief so that there's no risk of the edges of the aluminum (though dull) from damaging the wires. The wires on this connection should be twisted reasonably tightly, to keep the bundle of 12 wires from radiating or picking up noise.

Once you've got a good assembly together, with all connections properly made, you can plug it in yet please be careful as there is exposed voltage on the PSU in particular. If all the LEDs on the amp and the front LED light up, you're good for a "connected to speaker" test. Give it a whirl! I choose to leave the chassis open during initial testing for any troubleshooting- none was needed, these things are nearly impossible to screw up if you're paying attention.

The top panel connects just like the bottom with a bugle head screw and lock washer per-joint, between the clam-shell half and rear panel for certainty of conductivity. On the front, you'll have two supplied aluminum bars, again, lock-washers and screw in place. Once they're in place, sand the inside of the cutouts for the bars on the faceplate to hopefully allow some conductivity, then snap the front faceplate in place and fasten with the two set screws and provided Allen key.

Whoo bam, you've got yourself an amp, if nothing went south during your build. Now that I've written nearly 2000 words, shall I get on to the whole impetus of the article?

What Does It Sound Like Already?
As mentioned in my previous article, the sound is very similar in "personality" to the Herniator amp as reviewed here, a neutral, powerful amp that can drive just about anything you want. The NCore takes the neutrality to a new level, with improvements in every single metric I can think of. I can honestly say that it's the closest thing I've worked with to the "Straight wire with gain" ideal. I don't begrudge people their amps that sound best to them with a flavor that meets their needs- that's great, enjoy the hobby, build stuff with personality, if that's what you want. That's not, however, what Bruno and the Hypex crew want. They want the personality to come from the music, and the amp to be simply a means to that, and that philosophy is one that suits me quite nicely.

The NCore brought me closer to the music- there was a sense of stability, presence, and authority that made voices, instruments, and the soundstage that much more palpable and believable. Detail is shockingly good- not thrust in your face, but laid out for you to appreciate the texture or resonance of an instrument or voice. Some might find the bass overtight, but this DC coupled amplifier is flat all the way down, it just doesn't let the woofers be as resonant as some higher output impedance amps can, so that's a system-matching thing. This isn't a romantic amp and will not be ideal for all speakers or listeners. I found the clean and stable presentation to serve music, with distortion already in place, particularly well. Electric guitars gained that much more personality, as did synth-based/electronica. With classical guitar, a lush, full-bodied presentation was beguiling and appropriate to the recording, and with more standard pop fare, the singers just sounded a little more real and fleshed out, with better intelligibility and vocal inflection than with other amps I compared this to.

I didn't expose a flaw while listening to the NCore. They're neutral, powerful, quiet, clean, and are as romantic or aggressive or dynamic as the recording. They were a surprisingly good match to the Bottlehead Quickie (reviewed here) driving them, but when I brought the big dog TVCs back into the mix for true balanced operation, my front end really started to disappear (a very nice thing). The TVCs want a lower impedance load than the NCore offer, so it's fortunate that I have the Dayton SA1000 (reviewed here) to run as well- though I had to implement some Cinemag CMLI 15/15B input transformers on the input to the SA1000 to keep from creating an unbalanced load or ground loop between amps. Four signal transformers as a preamp- pretty elegant way to allow both single-ended and balanced outputs to be run, isolated, off the same TVC.

In short, yep, it's a rave. I try not to do that, as am always tempering my judgment and look for shortcomings. I am thrilled to have SiebeNCore's spectacular amps. They happen to match my amp stands quite nicely too, which is just the cherry on top. They're not too cheap, plus there are some really nice amp circuits that can be DIY'ed at the higher end of the DIY cost spectrum, so that's a point of consideration. Heck, one can assemble an entirely decent whole DIY system for the $1500 or so it takes to put a set of these together, so value is a tough metric to judge, despite their absolutely superb performance, and that's my only reservation. As a fan of Hypex's UCD technology, it's not surprising I'd enjoy these evolutions that much more, but as with anything, individuals need to make up their own minds and these won't be for everybody. I've left a little wiggle room on the top end of the ratings, but make no mistake- this is the finest amp I've used. Also note the separate value and fit/n/finish ratings for the Hypex bits and the Ghent bits. I have a pair of amps hooked up on nice stands right now, with the others blurred in the foreground below... I don't want to give them up, but must ship I suppose. Sigh.

Specifications
Type: Hypex NCore 400 Amplifier Kit
Output power 400W @ 4 Ohms
Characterized from open circuit down to 2 Ohm.
Lower load impedances are allowed, 24A current limit
SNR: Unweighted, min 124dB @ full power, 101dB @ 2.8Vrms 
Output Impedance: 0.7 milliOhms (corresponds to a DF of 11000) 
PSRR: Better than 85dB
Price: €325w

Manufacturer
Hypex Electronics B.V. 
Kattegat 8 
9723 JP Groningen 
Netherlands

Voice: +31-(0) 50-5264993
Website: www.Hypex.nl

Ghent Audio
Room 302, No. 535, Shengnan Road
Xinzhuang Industrial Park
Shanghai, 201108
China

E-mail: ghentxu@ghentaudio.com 
Website: www.GhentAudio.com