LKV Research Phono 2-SB MM/MC Phono Preamplifier: Affordable Excellence
In the name department it kind of reminds me of Andrew Jones’s Pioneer SP-BS22-LR loudspeakers. Forget the name. If, like the Pioneer speakers, the LKV Research Phono 2-SB was an overachiever and a ridiculously great value for the money, you wouldn’t care about the name, even if you had to look it up every time you recommended it to someone, as I did yet again to reference here those ridiculously good and cheap speakers.
Like the SP-BS22-LR, which saves a boatload of money with an extruded plastic enclosure, the LKV Phono 2-SB eschews a heavy, machined aluminum chassis and thick faceplate for one of modest gauge (some might call that a euphemism), black powder coated aluminum damped internally top and bottom with a mass loaded polymer sheet.
The exterior savings allow Hutchins to concentrate on a premium, quality parts packed interior and a feature set as well as specifications rare, if not unheard of at its $2500 price point—not that there isn’t some stiff competition at this price point. Yes, it looks like just a pair of circuit boards stuck in a box, but what were you expecting?
When I saw at T.H.E. Show Newport Beach 2013 the innards of this superbly engineered and constructed phono preamp and heard the “factory direct” price, I hoped it sounded as good as it looked inside.
The basics include a robustly designed outboard power supply housed in a box similar to the signal processing one to which it is connected via an umbilical. The ultra-low optimally biased circuit features cascoded JFETs and bipolar transistors in a differential balanced configuration with zero looped feedback and Class A operation, polypropylene, low dialectric absorption signal path capacitors, dual mono four layer circuit boards for shorter signal paths and improved grounding and something few phono preamps feature: three grounding options to minimize noise and avoid ground loop hum.
Unusual, especially at this price point, is that every unit gets a sonic audition and you are supplied with a spec sheet showing the performance of your particular unit.
The back panel features both single-ended RCA and balanced XLR inputs and outputs. Other than the three ground positions selectable via a power supply chassis mounted switch, that’s all that’s available outside.
Before purchasing an LKV Phono 2-SB (from herein out referred to as the LKV) you need to make your needs known to the manufacturer as there are two no extra cost +3 or +6dB additional gain options. The standard LKV offers three gain settings of 59dB, 50dB and 40dB in balanced output and -6dB for each setting in single-ended output. Add +3 or +6dB to each number if you choose either option.
In other words if you have a particularly low output MC cartridge like an Ortofon A90 or Anna with but .2mV output you may find useful the +6dB option. Even with that option you can get a standard MM gain output of 40dB using the lo gain and single ended output or 46dB balanced output.
How much gain you actually need is not as simple as it may at first seem. Page 10 of the instruction manual offers some valuable set-up tips in that regard.
Setting the gain and loading requires you to remove the top cover, which is easily done by unscrewing four machine screws. Inside, on each of the identical circuit boards you will find two banks of three rocker switches. Gain depends upon how they are (identically) configured. If you are spatially challenged you may at first be faced with some confusion especially since the photo shows but a partial section of the circuit board, but you’ll figure it out.
Loading is set via a series of tiny jumpers not intended for use by the fumble-fingered. I managed but if you are not adept at this sport, consider a miniature needle nose plier set from Radio Shack or Home Despot. Don’t use a big clunky pair. Also, be sure to carefully insert so that the jumper captures both pins. Remember that if you switch from single-ended to balanced operation you will need to re-configure the jumpers.
A word of caution: when I removed the jumpers, one at a time, to configure for the Ortofon Anna, the metal insert in one jumper fell out and disappeared. I shook the chassis a bit to be sure it hadn’t landed on the circuit board and it was no where to be found. Fortunately, I had in-house an old Audio Alchemy VAC In the box phono preamp that uses similar jumpers so I was quickly back in business. Perhaps the LKV should come with a spare jumper or two? Or maybe mine was just a case of reviewer’s bad luck.
The configuration chart, which looks like an insane game of Tic-Tac-Toe, presents greater confusion for the spatially challenged, so just take your time before replacing the cover to make sure you’ve set it as desired and consistently between the two channels.
The loading options in balanced operation are 100, 206, 300, 666, 1k, 2k and 47.5k ohms. They say “the devil is in the details”, and there he is in the fourth balanced loading option so watch out!
Half those numbers and you have the single ended loading options, other than 47.5K, which is available in either configuration. These ranges should be sufficient for all but the seriously anally retentive. The rest of us surely fall into the humorously anally retentive, or we’d just play CDs and be done with it.
The three grounding choices allow you to connect the ground planes on both circuit boards to the AC plug’s ground prong (“Bldg Grd”), or to each other (“Float”) or to the power supply chassis’ binding post (not the same as the one on the main chassis to which you may or may not connect the tone arm cable’s ground wire). That one is useful if your system is “star grounded” to a single ground reference.
Useful Claimed Specifications
LKV Research claims for its Phono 2-SB greater than 60dB signal to noise ratio at High Gain referenced to .5mV input and greater than 80dB s/n at lo gain referenced to 5mV input (moving magnet).
Total Harmonic Distortion balanced out is an impressively low > 0.008% at 2.0V output. Single ended out is the same but at 1.0V output. RIAA equalization error is claimed to be less than +/-0.1% from 20Hz to 50kHz. Crosstalk is better than -90dB with a 5mV inputat 10kHz, one channel driven, either balanced or single-ended, right to left and left to right. These are very respectable specs, especially the signal to noise ratios, particularly considering the $2500 asking price, which would be far higher were this not sold factory-direct.
Balanced Versus Unbalanced
Are cartridges “balanced” devices? Yes, in the sense that they are not referenced to ground, though depending upon the tone arm wiring arrangement yours may or may be referenced to ground. The cartridge itself is “balanced”: that is, the red and white pins send the positive phase of the right and left channel’s signal and the green and blue ones the negative phase for each channel.
If your tone arm wire preserves this arrangement, the RCA plug’s pin carries the positive half and its ring carries the negative. A separate ground wire (or a pair) allows the option of tying the negative phase to ground or not.
When the tone arm wire terminates with RCA plugs and the phono preamp jacks are RCA, the negative connects to ground in the phono preamplifier. The voltage on the ground side is an unvarying 0. The voltage on the plus side is the tiny cartridge voltage to be amplified and of course it varies with the musical signal. The phono preamplifier amplifies the difference between the varying voltage and ground.
This works fine under most circumstances but the tiny voltage is susceptible to outside interference from RFI/EMI, ground loops, etc. usually heard as hum and/or noise, though sometimes it can be more insidious: only audible when it is not present. Sometimes it can be particularly gross, as in the time I lived down the block from a hospital and heard really loud, garbled ambulance calls along with my Steely Dan. When the phono preamp amplifies the difference between the cartridge signal and the noise or EMT calls and ground, it has no way of rejecting the unwanted noise.
The balanced connection via a three-pin XLR plug into a balanced phono preamp carries both the positive and negative wave halves and a separate ground. Very simply put, if both the positive and negative halves pick up the same interference and the amplifier is amplifying the signal not referenced to unvarying ground, but rather to the difference between the two conductors, since the noise is essentially the same on both conductors the amplifier rejects the signal that’s identical on both conductors, thus cancelling out the noise.
Much high performance audio gear isn’t “dual differential” balanced because of the added cost. Essentially you need two of everything. It is impressive that LKV manages dual differential balanced operation at such a reasonable price. When you connect via RCA plugs you lose the balanced advantage though once the signal enters the unit it I is differentially amplified.
If you are not using the balanced “out” XLR jacks to connect to a balanced line preamplifier, using RCA to XLR adapters produces no advantages. However, if you are connecting to a balanced line preamplifier and your turntable’s cables don’t internally tie the negative side to ground and terminate in RCA plugs, it is to your advantage to at least try RCA to XLR adapters with the LKV or other balanced phono preamps. You will gain the noise cancelling advantages as well as 6dB of additional gain, which you may or may not need. However, before doing so check to see if your tone arm wire or turntable floats ground or connects it to the plug’s outer ring. Rega for one, does it that way. So if you have a Rega TT and wish to use the LKV in balanced mode, you will need to have it re-wired, breaking the ground connection to the RCA plug.
If you don’t currently have noise issues, all of this is more or less moot, though some argue that if you’ve got it use it. All you have to lose is noise and interference. All you have to gain is +6dB (which is a doubling of the voltage).