[T]he integrated amp, in its various guises, offers a solution for almost every user. Other than those with very large rooms, power-hungry speakers, or a combination of the two, most audiophiles can find an integrated amp that offers their preferred combination of sound quality, inputs, power and price. The integrated amp, then, is the audio equivalent of the hamburger. From a .99¢ fast food burger, to the $5,000 “FleurBurger 5000”, from flame-broiled (vacuum tubes) to fried (transistors), the burger and the integrated amp can be for the rich, or the poor, a single serving solution. By the way, as a hamburger loving Texan, I like both fried and grilled burgers. It just depends on the rest of the burger, and your mood.
I’m covering old territory, but it’s important to repeat certain concepts for new buyers. The strengths of the ideal integrated amplifier are many: lower cost than two/three separate, but similarly capable components; complete control by the designer to optimize impedances, the single biggest problem when designing tube equipment; elimination of 2 sets of RCA jacks and a set of interconnects; reduced susceptibility of the system to induced hum because of fewer transformers, fewer chassis, fewer power cables, fewer wall jacks, and less volume where two components could interact adversely; increased “wife acceptance factor”; fewer pieces of metal, plastic and individual parts to rattle and resonate; improved reliability (two or three components will be more likely to have a malfunction in a given time, than one component); ease of selling/trading (there are more buyers for integrated amps than separates); and other more obscure factors.
Certain extremes come to mind: NAD integrated amps of the ‘80s and ‘90s, which were everywhere; the mighty Ongaku by Kondo; the Dynaco SCA35. Though the Kondo is head and shoulders above the other two, you can’t fault the budget pieces for being made to a price–the middle class deserves good sound. Into very crowded company, with stiff competition from companies that are long defunct (Dynaco, Scott, Fisher), along with the plethora of current choices, comes a promising product from a relatively new company. This new integrated amp from Raven Audio, the Raven Reflection, is as different from these integrated amps, as they were different from each other.
Tubes, Topologies and Build Quality
Korean designer SE Han has drafted a moderately complex circuit for an integrated amp. Many integrated amps feature a passive preamp section, which is nothing more than a power amp with selector switch and volume control. The Raven is a preamp and an amp, on the same chassis. It truly is an integrated amp. The input is SRPP (Series Regulated Push-Pull), feeding a cathode follower, driving the power amp first gain stage, followed by the phase splitter/driver stage, then output tubes.
Front to back, the tubes are:
12AT7: preamp tube amplification
12AU7 (5963): Current source of 12AT7 (1st and 2nd tubes form an SRPP)
6922 (6Dj8): Preamp output tube (cathode follower)
12AT7: Power amp first stage
12AU7: Phase inverter and driver
As supplied, I liked the sound, but there were problems. There was too much glare and graininess, mostly caused by some of the 9-pin Russian tubes, which are pretty bad compared to the most mundane RCA from the ‘60s. After talking to Mr. Han, and contemplating the function of the various tubes and how their parameters would affect the circuit, I started tube rolling. The tube that most affects the sound is the tube that should have the least affect, the 6922 (6dj8), which is used for a cathode follower. A cathode follower is a 100% feedback circuit, but the feedback is all local (rather than loop feedback around multiple tubes, which doesn’t really work, local feedback does work).
Wanting to see how similar tubes would sound in the cathode follower position, I tried several tubes that were similar, and that might work in the circuit: the 6cg7 (a 9 pin version of the 6sn7); the 6gu7 (a 6 volt version of the 12bh7, and similar to the 5687); and the Russian 6N6p (it’s halfway between a 6dj8 and 6h30p, but sounds better than both, in my opinion). Mr. Han said that the extra heater current of the 6n6p would be safe, and it proved to be a better sounding tube. The gain of the 6n6p is lower (22 versus 33) and plate resistance is lower. The sound was very similar, but with less granularity, and better transparency. The 6cg7 and 6gu7 both were “romantic” sounding. Though the circuit is not optimized for either tube, I did enjoy the results. Both 6cg7 and 6gu7 imbue the amp with a romanticism I associate with golden age tube products. I did all my listening with either Russian military surplus 6N6p (considered to be an excellent tube, though no longer in production) and used (almost worn out) RCA 6cg7. Though feedback would imply that the sound of the tube would be partially eliminated, tubes with different gains and different transconductance will change the behavior of the circuit. Where the feedback really helps is to increase the lifespan of some tubes that would otherwise be too noisy, or too weak. The old RCA 6cg7 were just an afterthought, but they sounded great. The cathode follower is a handy tool, and not evil, as has been implied by various audio “gurus.”
Some of the tubes supplied were NOS, some were new Russian tubes. I alternated the supplied NOS Sylvania 12at7 with my own NOS Brimar 33A 101k; the Russian 12au7 was replaced with Sylvania 5963; the Russian 6922 was replaced with either RCA 6cg7 or Russian military surplus 6N6p; the Russian 12at7 was replaced with good used Mullard 12at7; and the supplied NOS 5963 drivers were kept. I never substituted the output tubes, but this amp did sound noticeably more refined at the Lone Star Audio Fest where Mr. Han was using NOS Tung Sol 6550. A marvelous tube.
There are so many possible combinations of tubes that I consider my tube rolling to be very casual and not at all exhaustive. It would take a lot of money and a lot of time to find the best combination. After changing tubes, the sound was cleaner, better detailed and frequency response was smoother.
The Raven is the heaviest integrated amp I have ever handled. It feels very solid. Machining and finish are excellent. The touch and feel of the controls are solid and reassuring. Internal wiring is a combination of copper and silver. Jacks and binding posts are high quality. There is one set of balanced inputs, and 4 single-ended, which are enough inputs. Provisions are made for 4 and 8 ohm loads, with 8 ohms being my preference with my 6 ohms, nominally rated speakers. The amp runs in self-bias, or cathode bias, which is my preference for consumer electronics. Many listeners will mess up with amps that require the user to adjust the current on a regular basis. It is rated at 50 watts per channel, a conservative number I believe, a remote control is included to control volume, and the price is $6,995.
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