Audio Research LS28 Triode Stereo Preamplifier
- Wonderful build high quality
- Wealthy, heat sound
- A great deal of options
- Undoubtedly spouse-friendly
- Good value
Audio Research as an organization is half a century previous, based in 1970 by William Johnson. They’re one of many pioneers in hi-fi gear design.
Lots has changed over the many years, but one factor has not: Excessive Quality.
The LS28 preamplifier, which is the topic of this assessment, is testimony to that statement. It is a stereo tube element, utilizing four 6H30P twin triodes, biased into Pure Class A.
This preamplifier is way from what existed again within the day. It has the power to name inputs, show the variety of hours the tubes have been used, invert the signal, change to mono, and other options.
The 6H30P is a (comparatively) current tube, having been imported from Russia. It is a very powerful dual triode, and the LS28 has 4 of them.
AUDIO RESEARCH LS28 PREAMPLIFIER SPECIFICATIONS
Stereo Tube Preamplifier
Four 6H30P Dual Triodes
+0 – 3 dB, 0.four Hz – 200 kHz (Balanced, 200 kOhms Load)
Less than 0.007% at 2 Volts RMS Output
18.5 dB at Balanced Output, 12.5 dB at Single-Ended Output
100 kOhms Balanced, 50 kOhms Single-Ended
600 Ohms Balanced, 300 Ohms Single-Ended
2 Volts RMS Balanced, 1 Volt RMS Single-Ended
103 Step Rotary Quantity, Rotary Input Selector, On/Off Energy Change, Menu, Enter, Mono, Invert, Mute
120 Volts, 240 Volts, 60 Hz AC
19” (48 cm) W x 6.5” (13.7 cm) H x 13.7” (34.8 cm) D
15.9 Kilos (7.2 kg)
Audio Research, Audio Research Preamplifier, Preamplifiers, LS28 Preamplifier, Preamplifier Review 2019
The LS28 uses 4 6H30P dual triodes for sign achieve. That’s four triodes for each channel. There is just one achieve stage, nevertheless. It’s all in Pure Class A bias and with no unfavourable feedback. All of that is to the sign’s benefit.
“Installing” the LS28 includes eradicating the duvet and inserting the four tubes. They arrive packed in foam (see under).
Every tube is marked with one of the following labels: V1, V2, V3, or V4. The tubes are assigned a selected socket that’s indicated within the consumer’s guide.
It’s worthwhile to be careful when inserting the tubes into the sockets. Line up the 2 pins which are separated by probably the most area as seen within the photograph above. Then push the tube down into the socket firmly however gently.
The rubber rings (photograph under) that surround the highest of the tubes are referred to as “dampers”. Tubes have microphonic characteristics, so are delicate to sound vibrations. When sound within the listening room reaches the tubes, vibrations of the glass envelope reach the filaments, causing them to also vibrate. This vibration is converted into electrical signal. So, by putting the rubber dampers across the glass envelopes, the vibrations are lowered significantly.
There are four inputs, obtainable as both balanced XLR (the 4 sets of inputs on the left aspect – see photograph under) or single-ended RCA (the four sets of RCA jacks to the fitting of the balanced inputs). Apart from two sets of XLR and RCA outputs (the jacks to the fitting of the RCA inputs), there is a set of XLR and RCA Document-Out jacks. The Document-Out is at full voltage (no quantity control). There are also some connectors, similar to RS232, for external management system use.
When powering on the LS28, it is muted and goes via a warm-up (“Start-Up”) period to heat the tubes. After that time, you should push the Mute button on the entrance panel to enter normal operation. The nice and cozy-up takes about 45 seconds.
The left-hand rotary knob selects the input, while the right-hand knob adjusts the quantity.
By pressing the Menu button, you’ll be able to access the varied features, comparable to stability between the two channels, show brightness, mono operation, inverting the sign, and determining the variety of hours the tubes have been in use. The 6H30P tubes will final approximately 4,000 hours, after which they should be replaced.
You’ll be able to change the names of the inputs if you want and in addition set one of the inputs to unity achieve if you want to pass-through the signal to a encompass sound processor.
A really good remote control is included. It seems to have been routed out of a single piece of aluminum, and It can be used to entry all the options of the LS28.
I examined the LS28 utilizing an OPPO BDP-105 Universal Player, Balanced Audio Know-how VK-500 Stereo Energy Amplifier, and Magnepan 20.7 Planar Magnetic Full-Range Speakers. Cables have been Mogami, Wireworld, Morrow Audio, and Raven Audio.
I used one of many balanced XLR inputs and balanced XLR outputs.
I’m an enormous fan of Baroque classical music, and there’s no composer that characterizes this period than J. S. Bach. His Brandenburg Concertos are a superb instance, having been recorded numerous occasions by numerous orchestras and conductors. This specific one is with the Academy of St Martin-in-the-Fields, carried out by Neville Marriner (Philips B00005LKEJ).
Although Concerto No.1 in F, 1, Allegro may be probably the most recognizable, I like Concerto No. 3 in G, three, Allegro probably the most because of its quicker pace.
The album shouldn’t be demanding when it comes to dynamics, and perhaps that is one cause I like Baroque music a lot. It is nice for enjoyable. Nevertheless, clarity and detail are a unique matter, and the LS28 excels here. This can be a results of the Class A bias. To remind you what Class A is, it means the output is absolutely on at all times, and the actual voltage and current are delivered as wanted, with the remainder of the output being dissipated as warmth. It’s inefficient to make certain as a result of power is being wasted, but the resulting sound is value it.
Guitar represents a superb check for transients because when a string is plucked, the vanguard of the sound could be very intense.
I completely loved listening to this album by Julian Bream entitled Baroque Guitar (Sony Classical B000003F1J). The assault at the vanguard of plucked notes was nearly as good because it gets. In fact, if just analyzed the sound, I might not benefit from the music, so after I decided the standard of copy, I sat back and listened. This is really an excellent album, and it paired properly with such a high-quality preamplifier.
This album, Buddy Wealthy, The New One (Pacific Jazz B009Z1W6L6) is considered one of his greatest. Particularly, the first monitor, “Away We Go”, is just unimaginable. No lack of dynamics right here. The truth is, it’s a large check of any audio element, from the trumpet solo to Buddy’s drum solo on the end. Explosive is an effective description. I feel my electric invoice took an enormous bounce, nevertheless it was value it. What a wonderful musician he was. The LS28 did an awesome job of reproducing all the jazz orchestra.
I moved the LS28 into certainly one of my different listening rooms the place there’s a turntable (VPI-HR-X with Sumiko Blackbird Cartridge), Move Labs Xs Phono Preamplifier, Cross Labs Xs 300 Energy Amplifiers, and MartinLogan CLX Full-range Electrostatic Audio system.
Jimmy Smith was a jazz organist back in the day. This album, Again at the Hen Shack (Blue Observe 4117, UPC 753088411779), is typical of his extraordinary talent. He performed a Hammond B3 with a Leslie speaker. The speaker drivers rotated, which delivered a tremendous vibrato sound that was really three-dimensional. The LS28 gave a sound that could be very wealthy with even-ordered harmonics, and this made for a particularly fulfilling listening experience.
Bach is about as removed from jazz as one can get, and yet, just as lovely. His Concerto in D Minor (Decca 028948322527) with Vladimir Ashkenazy at the keyboard and David Zinman conducting the London Symphony Orchestra is an ideal instance. Despite the fact that this music goes back almost 60 years, everybody will acknowledge this musician’s and conductor’s names. Turntable producers are telling me that gross sales of their merchandise have doubled within the final yr. Albums like this one are the rationale. Clarity and detail are essential, and the LS28 introduced them both with aplomb.
Invoice Evans was a well known jazz pianist. On this album, On the Montreux Jazz Pageant (Analog Productions – Verve 753088876219), he joins Eddie Gomez on bass and Jack DeJohnette on drums. It’s an exquisite album, and it gained the 1969 Grammy for Greatest Jazz Instrumental Album, Particular person or Group. The superb remastering from the unique analog tapes makes a distinction that may be heard with the LS28 within the signal path. Evans’ piano is superb, and Gomez’ bass on “Embraceable You” has the transients and wealthy tonality that only a preamplifier just like the LS28 may give.
On the Bench
With a 1 kHz enter check signal and a couple of volts output (exams have been made utilizing balanced XLR enter and output with a 100 kOhm load except the place famous), distortion was low at 0.zero08%. The second-ordered harmonic was the predominant distortion peak, and this gave a wealthy, heat character to the sound.
If the output is increased to 5 volts, the distortion rises to 0.026%, which continues to be respectable. Nearly all of the distortion consists of the second and third-ordered harmonics. A really small amount of IM (- 110 dBV) can also be current.
Using 19 kHz and 20 kHz sine waves at 2 volts output, we see IM peaks at 18 kHz and 21 kHz, in addition to a B-A peak at 1 kHz. There are additionally some peaks within the 37 kHz to 41 kHz vary.
Growing the output to 5 volts, the IM peaks additionally improve in quantity, however it’s still affordable. Most of the time, solely about zero.5 volt – 1 volt output can be wanted to drive your energy amplifier. Some high-powered amplifiers (e.g., 1,000 watts RMS) may require 5 volts to drive them to full output, however that might solely be for short transients.
IMD at 2 volts output was 0.032%.
At 5 volts output, it was 0.132%.
THD+N vs. Frequency yields the following graph. It all the time stays under 0.08%. The two channels are barely totally different, but that is simply the best way tubes behave. As a result of so much of a tube is mechanical (filament, plate), efficiency is slightly variable from tube to tube. It doesn’t affect the sound, nevertheless.
THD+N vs. Output is proven under, with a load of 100 kOhms and 600 Ohms. The quantity management was set to 55, which is about midway. You’ll be able to see that, with a 100 kOhm load, distortion stays under zero.04% by means of 5 volts output. A 600 Ohm load is only for a tutorial examination. It doesn’t have a practical value. We just need to see how the element performs beneath excessive stress, and the LS28 does fantastic.
Frequency response was down zero.2 dB at 20 kHz for a 2 Volt output, and down 0.9 dB for a 5 Volt output. The enter was 2 Volts, and the quantity management was at 41 and 68 for two Volts and 5 Volts output respectively.
The AUDIO RESEARCH LS28 PREAMPLIFIER is a high quality product. It is superbly constructed and has a heat, lush sound that tubes excel at. I have no reservations about recommending it extremely.
- Wonderful Build Quality
- Excellent Sound
- Absolutely Balanced, One Achieve Stage, No Unfavourable Feedback
- Giant Array of Inputs and Outputs
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