Preamplifiers

Lamm LL1 Signature Stereo Tube Preamplifier - An Audiophile's Dream

ARTICLE INDEX

Introduction

Vladimir Lamm has been designing tube-based audio components most of his life. Part of that career was in the (then) Soviet Union, and continued when he moved to the USA. The company, Lamm Industries, is based in New York.

Lamm Industries does not come out with new models every year like many companies do. The reason is simple. Each product has so much effort put into the design, testing the effect of changing the value of small parts here and there, the result is a product that cannot be improved upon. So, if you look at the product list on their website, the models originate over the years and are still available. Each one is hand built, but they don't have a warehouse with boxes of the preamps and power amps sitting around waiting to be sold. They have a non-interruptible production cycle based on statistical sales data over the years. After building a product, it is burned in for several days, and the consumer is urged to burn it in additionally when it is installed.

Not all of the Lamm products are really expensive compared to other high end components from various companies, but none of them are "entry level" either. Every product is the best it can be, within the cost constraints of that product.

Specifications

  • Design: Pure Class A Single-Ended Triode Preamplifier, Each Channel Contained within Two Chassis
  • Tube Compliment for Each Channel: Four 6H30 Dual Triodes, Two 6X4 Rectifiers
  • Maximum Output: 50 Volts RMS Each Channel
  • MFR: 20 Hz - 20 kHz, -0.1 dB
  • THD+N: 0.03% at 1 Volt Output
  • S/N: 87 dB at 2 Volts Output
  • Input Impedance: 16.5 kOhms
  • Output Impedance: 200 Ohms
  • Inputs: RCA
  • Outputs: XLR (Pin 3 Not Connected) and RCA
  • Dimensions (Each Chassis): 4.5" H x 19" W x 14.2" D (Including Front Handles)
  • Weight: 35.8 Pounds (Each Preamplifier Control Chassis), 21.2 Pounds (Each Power Supply Chassis)
  • MSRP: $42,690 USA
  • Lamm Industries

We have reviewed several Lamm units over the years, including the M2.2 Monoblock Power Amplifier, which is hybrid in design (tube used as the second stage, solid state input and output stage), the L2 Reference Stereo Preamplifier, which is also hybrid. Most recently, we reviewed the LL2.1 Stereo Preamplifier. It is an all-tube (including the rectifier) Pure Class A, single-ended, single-chassis preamp.

The LL1 is also an all-tube, Pure Class A, single-ended preamplifier. It does not use any negative feedback. However, it is like nothing ever seen before in the preamp arena. It is comprised of four chassis, with each channel having its own power supply chassis and control chassis, with a combined weight of 114 pounds. That's heavier than most power amplifiers.


The Design

First, let's talk about "rectifiers". Incoming AC to your wall socket cannot be used directly to create the music signal. Initially, it passes through a rectifier, which converts the AC (60 Hz in US, 50 Hz in Europe) to DC. The rectifier can be either half-wave or full-wave. A half-wave rectifier (first photo, below) chops off the negative portion of the AC's 60 Hz sine wave. The current is now flowing in only one direction, but half the power is lost.

half-wave-rectifier-tube-diode

With full-wave rectification (photo below), the negative portion of the AC is converted to positive. All of the power from the wall AC is conserved this way.

full-wave-rectifier-tube-diode

There are two 6X4 rectifier tubes in the LL1 power supply, and the circuit is a full-wave rectifier. There are two anodes (plates) in each 6X4 tube instead of just one. Here is a pin-out schematic of the 6X4:

6X4-schematic-pin-out

Following rectification, however, the voltage is pulsating at 120 Hz, going from 0 volts to 120 volts (or whatever voltage the secondary on the transformer is producing) and back to 0 again. So, the power still needs some work to make it usable. This is where power supply capacitors and chokes (called LC-filters) come in. The output of the rectifier is connected to the LC-filters, and power is stored there. The voltage and current needed for preamplification is drawn from the stored power, and it is very smooth DC. It's not perfect - as exemplified by the presence of "ripple" peaks in the output - but it is as close to being perfectly smooth as it can get.

There is also a custom wound transformer, and capacitors and resistors so esoteric, I have never heard of the brands. You can see two analog voltage regulators in the middle. These are for keeping the filament heater voltage steady. They are not in the signal path. The reason I am describing the LL1 power supply in such detail, is that single-ended designs tend to suffer from AC hum, a problem that is attenuated in balanced designs. So, Lamm has gone to great length to build a power supply that will not allow hum to contaminate the music that you are listening to.

lamm-ll1-preamplifier-inside-power-supply-chassis

Inside the main control chassis, shown below, you can see four 6H30's (sometimes called the "Supertube") on the right. Each one is a low impedance (800 ohms) dual triode, so basically here, you have eight triodes driving the signal. Because of so much power, the preamplifier has only one gain stage (that's all it needs), and therefore, the output signal is inverted. So, you will probably need to reverse the connections on your speaker binding posts if your power amplifier is non-inverting.

lamm-ll1-preamplifier-inside-control-chassis

The photo below shows a close-up of the four 6H30 tubes in the control chassis. They have silicone rings around them to limit microphonics (vibrations that cause electrical noise). Notice also that the tube sockets are mounted on small posts rather than being flat against the circuit board (see inset for detail).

lamm-ll1-preamplifier-closeup-of-tubes

Here is a schematic of the 6H30 dual triode. Cathodes 1 and 2 are indirectly heated by a heater filament. The two grids are situated between the two plates (anodes). There is a screen that separates the two triodes from each other.

6H30-schematic

The front of the LL1 has plenty of toggle switches, and that is only on one of the channels ! ! !

The main chassis is on top and the power supply is on the bottom. In use, you would want to separate the two chassis by at least 4", to keep power supply electromagnetic radiation from interfering with the control circuits in the main chassis, but also for ventilation.

On the top, from left to right, are toggles for Output 1/Output 2, Mute/Operate, Normal/-12 dB (use this when you want more movement in the volume control), Line/Direct (Direct takes the signal from the corresponding input straight to the volume control, thus bypassing the rest of the switches), and Line1/Line 2 (input selection). On the bottom (power supply) are toggles for Power On/Off, Accessory Outlets On/Off (you can plug a CD player or other low wattage component here), and Remote 1/Remote 2 (remote control triggers for turning on other Lamm components, such as their power amplifiers).

lamm-ll1-preamplifier-front-600-pixels

On the rear panel are the RCA and XLR inputs and outputs. There are two sets of outputs, switchable from the front panel. There is also a tape loop. You can see the six-pin connector sockets that connect the power supply to the main control chassis via the supplied cable. On the bottom (power supply) you can see the accessory outlets, remote control trigger sockets 1 and 2, a grounding terminal, and the detachable grounded AC cord socket.

lamm-ll1-preamplifier-rear-600-pixels

To give you an idea of the size of this product - keeping in mind it is a stereo preamplifier - look at this photo of the shipping boxes as they arrived on my deck. Each chassis is housed in a wooden crate, with dozens of long screws. It took me half an hour just to get the screws out of the top of the four boxes.

lamm-ll1-preamplifier-in-shipping-boxes

I had to place them on the floor in front of the rack that has my sources and one of the power amplifiers. To move ahead on the story a bit, I loved the sound of the LL1 and have purchased the review units as my new preamplifier reference. An AnthroCart, custom built just for the LL1 to sit on four shelves, and an SACD/CD player to sit on the middle shelf, is on the way.

lamm-ll1-preamplifier-chassis-on-floor-no-connections


In Use

I burned in the LL1 a full week before I sat down for critical listening (it is burned in for 2 days at the factory).

I was awestruck at the sound. It was as pure and sweet as I have ever heard. The music was incredibly easy to listen to, with absolutely no fatigue. Detail was all there, but it never pushed itself. It was just present.

I had an unusual experience. One evening, I just kept listening, playing some great jazz from Miles Davis. I don't normally listen to music late at night because it keeps me from falling asleep quickly. But this time, I slept like I wish I could sleep every night. Deep, restful slumber. I didn't think much of it at the time, but a few nights later, the listening ran late into the evening again, and I slept that same deep, beautiful way I did that evening earlier. There is something about the sound with the LL1 that was doing this, and I don't really know what it is. However, as a neuroscientist, I am a believer in the power of music on the nervous system, perhaps something to do with synchronizing activity in the brain.

So, here is a small list of the discs, and my accompanying comments. The other components were a Classé CDP-10 CD player, McIntosh MCD500 SACD/CD player, OPPO BDP-83SE-NuForce Edition universal player, Balanced Audio Technology VK-75SE power amplifier, Bryston 14B SST2 power amplifier, McIntosh MC1201 monoblock power amplifiers, Lamm M2.2 monoblock power amplifiers, Magnepan MG1.6 planar speakers, and Carver Amazing Mark IV ribbon speakers. Cables were Emotiva, Slinkylinks, and Legenburg.

Comparing power amplifiers, the Bryston 14B SST2 had the dryest sound quality (it has the least amount of distortion of all the power amplifiers). So this combination would probably appeal to the purist who wants the least change to the signal. The McIntosh MC1201 was a bit warmer, and it also has a little more distortion (hundredths of a percent instead of thousandths of a percent). The Lamm M2.2 was warmer sounding than the McIntosh, and this is because it is a hybrid amplifier, with a triode in the second stage. The Balanced Audio Technology VK-75SE combination was the warmest of all the pairings. The VK-75SE is an all triode, pure Class A amplifier, so this is no surprise. In fact, it uses two 6H30 triodes (one for each channel). However, it is limited to 75 watts output per channel, and that is really not enough power for symphonic recordings at reasonably loud levels. I would need something like a VTL or Manley to get the kind of SPL's that I like with full orchestra symphonies and have it be an all-tube power amplifier, driving low efficiency planar speakers. In any case, my favorite combination is a pure Class A triode preamplifier and large solid state monoblock power amplifiers. I recommend that you listen to this kind of setup if you get the chance.

Music played through the LL1 gave me an incredible feeling of inner peace. It was neutral to the extent that it did not emphasize any part of the audible spectrum more than any other, but it certainly was different than other preamps I have reviewed in the extent of its warmth, due to having almost exclusively 2nd order harmonics. There was absolutely no harshness to any part of its sound. Flutes were crisp, yet fluid and mellifluous. Pianos had depth and fullness, without congestion. Violins were clean and detailed, arpeggios from the harp raised the hairs on the back of my neck. Voices communicated with clarity and emotion. Transient attacks were lightning fast, but always stayed connected to the flow of the notes that followed.

The LL1 stimulates much more than the cerebral cortex. The music that passes through the LL1 trickles down to the limbic system, where emotions are processed. It was the same feeling I get when I have my weekly massage therapy, with soft music in the background. And yet, the LL1 was also like a cobra, lurking, waiting for the chance to spring its power onto the soundstage when musical passages demanded it. There seemed to be no limit to its abilities there. CDs are not all recorded at the same loudness, and when the music seemed too intense, I merely flicked that little - 12 dB toggle, and the volume settled down to perfection without my having to fiddle with the two volume controls. And, if the next disc had music that I wanted the neighbors to enjoy along with me, I flicked the toggle in the other direction. Regardless, I never had to turn the volume controls past their straight up, 12 o'clock, position, which was only half of the dial's turn. It was obvious that the LL1 had to prove nothing. Its mere physical presence tells you what is to come. It is comfort food for those with a big appetite for pleasure.

At $42,690 for the LL1 pair of preamplifier monoblocks, most will scoff. But, the LL1 is a masterpiece. It is not simply paint on a canvas. It is Renoir, Monet, Degas, Cézanne, maybe da Vinci too. The price of genius. The sound of angels. An audiophile's dream.

lamm-ll1-preamplifier-music-albums-column


On the Bench

For distortion measurements, I used an 80 kHz bandwidth, and the volume control set half way (12 'o clock, straight up).

With a 1 kHz sine wave test signal, distortion never went above 0.1% at 100 kOhms or 600 ohms load, 2 volts or 5 volts output. This pretty much covers the range of output voltages you are likely to encounter, and far below any input impedance combination you are likely to have with your downstream components. Notice that in all cases, the 2nd order harmonic predominated. In the first graph, the 2nd order harmonic is 70 dB below the fundamental, and the 3rd harmonic is 44 dB below the 2nd harmonic (so the 3rd harmonic is less than 1/100th of the level of the 2nd harmonic). This is what gives the LL1 such an incredibly sweet, delectable (I am writing this just before dinner, so I am using food adjectives) sound quality. It does not make itself known. It is just there, wafting on the background of the music, and adds a richness that is absent with most solid state products. Purists will say that is not high fidelity.

Well, if your desire is to absolutely reproduce the recording, it isn't going to happen. No system can do that without at least a bit of distortion. The issue is what you are willing to put up with. Good solid state preamplifiers and power amplifiers have very low distortion, so low, it is inaudible, and therefore, it does not matter whether it is mostly even-order or odd-order. With a preamp like the LL1, that little touch of 2nd order harmonic is like having your hot chocolate with whipped cream on top. It does not change the flavor of the chocolate, but it gives you an extra sensory experience, one which makes up for the fact that no hi-fi system can really make it sound like the orchestra is playing in your living room.

In the graphs below, you can also see some noise peaks. The coaxial interconnect is picking this up as electromagnetic interference, and is one of the drawbacks of a single-ended design. With a balanced design (also called differential), the interconnect is called XLR, which has three conductors, one positive, one negative, and one ground. The positive and negative conductor signals are complete waveforms, and are mirror images of one another (i.e., inverted phase - 1800 out of phase with respect to each other). The two signals are combined in the output stage by inverting one of them, and this eliminates the electrical interference noise picked up in the cable, as well as in the amplifier before inversion and combining the two signals, by common mode rejection ratio (CMRR). The process also increases the gain, because the two signals are added together.

The disadvantage of a balanced circuit is that the output stages are partially connected in a loop, resulting in the possibility of self-oscillation, which would show up as "ringing" in the output. Also, the input stage of a balanced amplifier tends to have more 3rd order harmonic distortion, while the input stage of a single-ended amplifier tends to have more 2nd order distortion. The pro industries, such as recording studios as well as musical groups performing on-stage, pretty much use balanced equipment throughout, because of its common mode rejection. This is very important when microphone cables and interconnects are long.

However, as you can see below, the noise in the LL1 is all below 100 dBv, which is inaudible. Hum from the AC supply (60 Hz) is also a problem in single-ended designs vs. balanced designs, and that is why the power supply in the LL1 is very sophisticated.

Another design that is different from the single-ended amplifier is the "Push-Pull" amplifier, where, again, there are two circuits side by side, passing the signal. At the input, the signal is passed through a splitter/inverter so that there are two paths, with each path having a complete signal, 1800 out of phase with respect to the other. At the output, the phase of the bottom signal (the red sine wave) is re-inverted by connecting the anodes of each signal path to the ends of an output transformer that is center tapped, with the center tap connected to a DC high voltage supply. (In the case of a solid state amplifier with no output transformer, the two signals are handled by PNP transistors on one side and NPN transistors on the other. The emitters are connected together and to a DC voltage supply.) During the process of combination with the top signal (the black sine wave), each signal is allowed to be "on" for just a bit more than half the waveform, so that one does not turn off just at the point the second one is turning on. Otherwise, crossover distortion would occur. The advantage of a push-pull circuit is that you get more power, and much of the harmonic distortion is cancelled out. However, it is the even-order harmonics that are diminished, while the odd-order harmonics remain. This makes the amplifier a bit harsher sounding, because even-order harmonics are euphonic, while odd-order harmonics are unpleasant. But, if the leftover odd order harmonic distortion is very low, it will be inaudible.

Before the first LL1 graph results are diagrams of a sine wave signal passing through a single-ended, balanced, and push-pull amplifier. The waveforms on the left are what passes through the amplifier, and the waveform to the right of the blue arrow is the output. For a balanced circuit, notice that the amplitude of the output represents the amplitude of the two input signals added together after one of them is inverted, and thus, twice the amplitude of each of the two input signals. For push-pull, you can see there is overlap between the positive and negative portions of the waveform (light blue line) when the signal is passing through the amplifier, in order to prevent crossover distortion. In general, preamps are single-ended and can be bridged to make them balanced. They are usually operated in Class A for part or all of the signal path. Some are push-pull. The LL1 is single-ended.

Power amplifiers can be single-ended, push-pull, balanced (either with single-ended or push-pull output stages), and can be set to operate in Class A or Class AB (and variations of AB). This is controlled by the amount of voltage, called the bias, on the tube's grid. Class A means that enough current to power the music at full level is flowing in the circuit even at idle (no music playing), and when a music signal passes through, the current is delivered to the output. The current that is not being used to drive the music signal is dissipated as heat. Class AB is where there is enough current flowing all the time to deliver a portion of the preamplifier's (or power amplifier's) output capability, and when that current demand is exceeded, the transistors or tubes then have to be turned on to a higher state so that the additional current can be delivered, rather than simply diverting current to the output that was already flowing. This turning on/turning off condition of Class B operation causes distortion.

Class A is very inefficient, and the power supplies have to be large (and expensive). Most power amplifiers are Class AB, and are biased into Class A for part of their power output. High end amplifiers will have a higher percentage of the total power capability biased into Class A. Mass market receivers tend to have only a very few watts biased into Class A. The LL1 preamplifier is biased as Pure Class A, meaning that its total output current capability is flowing all the time. It gets very warm because of this, and needs good ventilation. The power supplies also have to be large, and the combined weight of just the two power supplies for the LL1's two channels is more than 40 pounds.

single-ended-signal-diagram

balanced-signal-diagram

push-pull-signal-diagram-showing-splitter

lamm-ll1-preamplifier-1-khz-2-volts-100-kohms

lamm-ll1-preamplifier-1-khz-2-volts-600-ohms

lamm-ll1-preamplifier-1-khz-5-volts-100-kohms

lamm-ll1-preamplifier-1-khz-5-volts-600-ohms

At 10 kHz, the following graphs. Notice again, that even at the tortuous 600 ohm load, which you will never encounter in a real setup, it was still the 2nd order harmonic that predominated.

lamm-ll1-preamplifier-10-khz-2-volts-100-kohms

lamm-ll1-preamplifier-10-khz-2-volts-600-ohms

lamm-ll1-preamplifier-10-khz-5-volts-100-kohms

lamm-ll1-preamplifier-10-khz-5-volts-600-ohms

Here are graphs using a combination of 19 kHz and 20 kHz sine waves as the input signal. The 1 kHz B-A peak was about 60 dB below the fundamentals in all cases.

lamm-ll1-preamplifier-19-khz-20-khz-2-volts-100-kohms

lamm-ll1-preamplifier-19-khz-20-khz-2-volts-600-ohms

lamm-ll1-preamplifier-19-khz-20-khz-5-volts-100-kohms

lamm-ll1-preamplifier-19-khz-20-khz-5-volts-600-ohms

IMD stayed below 1% for all combinations of output voltage and load impedance.

lamm-ll1-preamplifier-imd-2-volts-100-kohms

lamm-ll1-preamplifier-imd-2-volts-600-ohms

lamm-ll1-preamplifier-imd-5-volts-100-kohms

lamm-ll1-preamplifier-imd-5-volts-600-ohms

THD+N vs. Frequency indicated that distortion remained constant with a 100 kOhm load, and had more distortion at the low end with the 600 ohm load. In general, the LL1 sounded very neutral.

lamm-ll1-preamplifier-thd-plus-n-vs-fr

THD+N vs. Output Voltage showed that, even at 600 ohms, the LL1 was not straining. I set the volume control all the way up for this test. For both impedances, clipping (1% THD+N) occurred at 50 volts output. However, you will never need more than 10 volts, even for transient peaks.

lamm-ll1-preamplifier-thd-plus-n-vs-output-voltage

The measured frequency response was 20 Hz - 20 kHz, - 0.1 dB at 2 volts and 5 volts into 100 kOhms. At 600 ohms, there was rolloff below 100 Hz, but again, you will never encounter this level of downstream impedance. The LL1 wasn't designed to work with a 600 ohm load, and that's why the cut-off frequency in the bass region is much higher than it has to be (this has to do with the limited µF value of the output coupling capacitors, which were not designed to work with a load of 600 ohms; this low impedance, in turn, leads to the limitation in reproducing the full spectrum of low frequencies). In the LL1, when working with a 600 ohm load, the lower cut-off frequency is within the 66-70 Hz region. When working, for example, with a 10 kOhm load, the lower cut-off frequency is around 4 Hz. We show the 600 ohm spectrum here simply to illustrate the real potential of this incredible product.

lamm-ll1-preamplifier-fr


Conclusions

I am not sure how to impart my true feelings about this product. It is difficult to do this with words on a website page. I usually have some adjectives in my mind when I finish up a review of a great component. But this time, I will use a noun: Magic. I have never heard anything like it before, and I suspect I won't encounter it again. That is why the review unit is being readied for my reference lab. Enter an heirloom.