Reviewing Manley Neo-Classic 300B Preamplifier RC
Kindly reprinted with permission from The Inner Ear Report - by Blair T. Rogers
Source: Manley Laboratories, Inc.
Price: $7,895.00 Cdn, $5,250.00 US,
Rating: 3'1/2 musical notes
Avid readers of this magazine will remember that a Manley Labs 300B Retro, push-pull/single-ended-on-the-fly convertible amplifier was reviewed not long ago (Vol. 12 #3).
David Manley is no longer associated with the company that bears his name but he is undeniably responsible for a share of the tube renaissance that has swept high-end audio in the past twenty years.
Once VTL became truly established, following the success of the 75/75 amplifier, an absolute cascade of amps and pre-amps poured onto the market with no apparent limit to configuration or power. Two hundred, three hundred, and even five hundred watt tube amplifiers were in production. These were, perhaps, the glory days of VTL. David Manley was able to develop original designs with the right tube for any purpose. He had a canny understanding of electronics, particularly thermionic devices, and how they could be used. Remember the Tiny Triodes? His innovative ideas always kept VTL on the leading edge.
It was 1989 when EveAnna Manley joined the company and began working her way through every function from testing to sales and finally, management. Luke Manley bought out the VTL name in 1993 and EveAnna and David founded Manley Laboratories Inc., to produce their own line of electronics. With EveAnna selling, the company experienced significant growth and moved into an 11,000 square foot building in Chino, California, thirty-five miles east of Los Angeles. Three years later, David left unexpectedly to pursue other interests in Paris, leaving EveAnna as de facto operating CEO of the company at less than 30 years of age. She collaborated with two other employees; Hutch Hutchinson and Baltazar Hernandez to develop significant, new hi-fi and professional pieces for the Manley Labs line and to attend to some badly needed fixes for older designs. Between 1996 and 1999, the company doubled its sales and workforce to 40 employees and increased its floor space two-fold by annexing the adjacent building. EveAnna Manley is now the official CEO of a multi-million dollar corporation with products distributed by over 100 dealers worldwide.
Those accustomed to the status quo in audio design may be a bit shocked or totally thrilled by this preamplifier. I believe that, chronologically, this is David Manley's final signature piece. Shortly before he left for Paris, he had an idea for a headphone amplifier that could also be used as a line driver. The design was intended to showcase a pair of 300B output tubes, probably for two reasons: a single 300B can provide superb drive capabilities for both headphones and a linestage; and no one had done it before. The word is that he left a couple of circuit boards with tube sockets bolted to them, a bunch of wires and a few resistors at the back of his workbench as a sort of sketch to be fleshed out later.
EveAnna recognized the potential in this bird's nest of wires and showed Baltazar how to do a layout of a printed circuit board one Saturday morning. On Monday, he returned with a working prototype, the genesis of the 300B linestage.
The finished unit weighs 28 pounds and measures 19 inches by 13 inches by 3 inches high. In keeping with the Manley Retro look, the tubes and transformers are exposed on the top deck and the substantial front panel is gold-plated, featuring an illuminated window on the right that displays the Manley signature logo and model designation. To the far right, the power switch is a no-nonsense affair built for a battleship. Two gold-plated control knobs are placed to the far left, fluted, fluid and massive to the touch. Just a selector and a volume control. Two headphone sockets grace the center of the panel.
Explicit instructions for the correct power-up and power-down procedures are silk-screened onto the center top of the chassis. All the tube numbers are there too, including the function of the tube (pre-amp and driver) and instructions for the correct pin orientation of the 300Bs. The immediate impression is that this unit was made to last as long as vacuum tubes will be available. Stock up now because your great-grandchildren will want them. The archeologists that discover one of these pre-amps thousands of years from now will certainly want them.
The case is supported by four legs that are slightly thicker and longer than usual.
The top deck sports three more of those battleship switches: two for selecting headphone impedance ranges or line-out muting and one that, surprisingly, allows output through a transformer or a large film capacitor.
Finally, the last items of retro chic: a lovely pair of octal socket, 0D3 cold-cathode regulator tubes glowing with an ethereal violet light, right next to a brace of GZ-34 rectifier tubes. And of course, those directly heated 300B triode power tubes are right out in front, where the convergence of the glass-blower's art and radio-age genius can be fully appreciated.
No tube cage is provided for this preamplifier and this is consistent with Manley Lab's style. The few of us who appreciate tubes are no longer afraid of them or want to hide them away inside a box. We've grown to love them and want to admire them in their glowing, thermionic glory.
This line-stage preamplifier is machined out of a solid billet at Manley Labs. The output and power transformers are wound in their own magnetics department for this particular application. There are five selectable RCA input jacks and three outputs, including one for tape direct, on the back panel. Two front panel headphone jacks are provided and impedance can be optimized with switching for 30 to 400 Ohms or 300 to 4000 Ohms. Line outputs are muted when headphones are selected.
A twenty-four position, gold contact Grayhill selector switch with 1%, half watt metal film resistors is used for the volume control. Input selection is by a widely-spaced ceramic selector switch. Input impedance is 100K Ohm and output impedance is 100 Ohms.
The audio tube complement runs in class A and is comprised of a large octal-based 6SL7GT input driver and one 300B triode per channel. The B+ supply employs a pair of 5AR4 (GZ-34) rectifier tubes driving a proprietary ripple-reducing circuit to remove all remaining AC ripple. The plate supplied for the 6SN7GT's are regulated by the mercury vapour OD3 tubes. The power supply is very stiff, with plenty of capacity, very quiet (claimed signal-to-noise ratio 105 dB 20Hz to 20kHz) and totally free of vibration. I never experienced any radio frequency interference or grounding problems with this unit. Manley Labs claim to have developed special ripple rejection architecture and I believe this to be true as this is one of the quietest pre-amps I have ever encountered. I don't use headphones but this would be a significant consideration for those who do.
Gain is set at the factory at 18dB at maximum volume. Output power with 100 Ohm headphones is 1 watt or 10 volts RMS (28 volts peak-to-peak). With 600 Ohm headphones this increases to 25 volts RMS and 70 volts peak-to-peak. The amplification circuit does employ some feedback which can be adjusted internally, if necessary, from 8 to 12 dB. Frequency response is claimed to be ±1 dB from 5Hz to 50 kHz.
Although the power supply was designed to produce a rectified 500 volts DC, the plates of the 300Bs are run quite conservatively and the power tubes should see a long service life, perhaps exceeding 10,000 hours, especially when combined with the slow turn-on characteristic of the specified 5AR4 rectifiers.
I've given up trying to tell people how good the Manley Labs 300B linestage sounds. I think it's a combination of prejudice and ignorance on their parts. One designer I spoke to scoffed at the thought of a 300B being used as a line driver tube. "Rolled off and mushy," he said, without having heard it. Quite the opposite really.
The first night I plugged the unit in with my Quad 63s and listened to an LP of Ansermet conducting the Carmen Suite I raced upstairs and phoned my friends. "It's like... a ballerina," I said, over and over. "You got to hear this!"
Well, that was a year ago and I've discovered a few more things since then. First, I replaced the stock Sovtek 300Bs with Vaic C37 glass 300B tubes. This was a big improvement in sweetness and clarity.
This is a pre-amp that has a slightly dark midrange and a slightly soft deep bass but you will only notice that if you have speakers that really go deep. The mid-range is sweet... anything but forward... and the treble is as extended as it possibly can be without being unnaturally emphasized. Solo vocals like "They Can't Take That Away From Me" on Tuck and Patti's Love Warrior LP are completely relaxing and involving.
This number was recorded in a large studio... singer and solo electric guitar. The ambiance reproduced by the Manley 300B is deep and liquid: the way it should sound at a concert in a live, intimate hall... if everyone else would just go home!
Then of course, came the Amazon turntable and I discovered what this pre-amp could really do. It can rock the house with a pair of Quad 63s. You want bass? We've got plenty. I found myself digging out my 12 inch 45s: dance records by Yello... just incredible rhythm, drive and tight, deep bass that was visceral and thoroughly satisfying.
Keep the unit a good distance away from loudspeakers and amplifiers to avoid feeding energy into the 300Bs as they can pick up and amplify stray sound waves. The result would be "ringing" of the tubes. Also use resonance prohibiting shelving.
Synopsis & Commentary:
The Manley 300B preamplifier makes glorious music. Considering the single-ended design and the choice of output tube it is remarkably neutral. Yes, a little soft but never out of control. It is outstanding among other tube designs for several things: quality of materials and finish that imply longevity and value; a power supply with fortitude; a bit of retro whimsy that never betrays thoroughly modern performance; and more than a touch of valve glamour.