For those who demand the sweet sound of single ended operation, here we have it. This amplifier is the culmination of two and one half years of experiments and tests to achieve the best posssible sound from single ended operation and consumer oriented components. As with our other amplifers, the MAG-1515 and 1515i, circuit deployment rather than high dollar components are the key to the sonic quality of this amplifier.
For the sake of keeping the amplifier vintage, I have designed it with the use of the 6SL7 and the 6L6, tubes which are concurrent in the history of tubes. I chose the Sovtek 6SL7 for its quality and availability. The tube is very linear, and at first has a hard sound. When it breaks in after four days the sound warms up and images pop out. The 6L6 of choice is the Sovtek 6L6GC (the cheaper Russian no name brand is shown). It is very good sounding and sweet right from the start. One can choose the JJ/Tesla's also for more midrange detail. The rectifier though is the 5Y3. As with the MAG series I use metal film resistors and orange drop capacitors. I also have separate legs after the 330 µF for the preamp/driver section to minimize crosstalk. The same is true for the screen grid of the tetrodes. I also bypass the main filter for extended filtering and minimal crosstalk to 20K. The sockets are Amphenol phenolic for high quality and long life.
The audio tubes are both octal and very linear. I chose of all the different combinations of circuits to use the cathode follower, direct coupled to the voltage amplifier tube for lowest pre-NFB distortion. I have also chosen to make tetrode or ultralinear connection builder selectable. The tetrode operation gives a bit more power, while UL operation has the best of both triode for linearity and tetrode for power. I prefer not to offer the amplifier in triode operation for my own personal preference of power versus the "sweetness" that triode output tubes seem to offer. Yet it can be a selectable option in the kit.
One listen to this amplifier, however, and one can hardly miss the sound of triodes. The reason is that the output transformers are the Hammond 1628SE 5000 ohm primary impedance 25 watt. The result of this transformer is a wave that has the characteristic of 2 to 3% even order harmonic distortion at full power. This distortion is present from 20 to 20 kHz at 8 watts even with NFB. This makes for a pleasant sound due to the fact that it is exactly the way our ear operates. Due to the pressure difference between the inside of our eardrum and the outside, fluid being on one side and air being on the other side, our ears naturally distort a sine wave with even order harmonics. Yet the response itself is flat and the amplifier's distortion itself (pre-transformer) is very low. So all one hears is sonic purity with the silky smootheness of the transformer (that was my impression when I first heard them). Also, since I am using less than half of this transformers output power capabilities, there is no chance of core saturation. And since the amplifier idles at about 170 milliamps total, the power supply, capable of providing up to 250 milliamp, will remain rock solid. As a matter of fact, SE amplifiers have the tendency to draw less current at full output, so voltage increases slightly, giving the impression of increased dynamic range. The result is a sonic purity signature equivalent to the MAG-1515 with the silky quality of single ended operation.
Bass is deep and tight due to two things: tetrode or UL operation and a current negative feedback. The feeedback signal goes through a voltage divider and uses the current signal of audio rather than the voltage signal. This is what I believe extends the frequency response audibly on both ends of the spectrum. UL operation keeps distortion low. The result is a sonic character that is our philosophy: Sonic purity.
All kits come with hardware premounted.
8 watts RMS per channel @ < 5% THD
FREQUENCY RESPONSE 20-20 kHz @8 watts
10-40kHz@ 1 watt
OUTPUT IMPEDANCE 8 Ohms
INPUT IMPEDANCE 100K
INPUT SENSITIVITY 1.5 volts for full output
(2) Sovtek 6SL7
(2) Sovtek 6L6GC (Matched Pair)
(1) Sovtek 5Y3
JAN Phillips 6SL7; Tesla/JJ 6L6GC; One Electron Output Transformers
JAN Phillips 6SL7
Tesla/JJ 6L6GC add $35
One Electron OPT no extra charge. However, there is no UL connection.
William S. Granger
I received the amp today and decided to use the cheaper tubes
to start. I chose the Natalie Cole/Unforgettable CD.
It had more detail than my A75 even after the A75 warms
up. The bass is
even taughter. Well I swapped tubes and the midrange smoothed out a
Can you tell I like it? I tried some harder rock and found
that I had to turn
it down a little bit. Guitars sound right: I use to play through a 50 watt Marshall
and a 30 watt Hiwatt and they just sound right again. How did we ever let this
technology fall by the wayside? The edges are smooth not harsh, not sterile. WOW!
The highs could be a little more pronounced but that's
not the amp (Mr. Granger retracts this statement later).
That is the transmission lines I use. They do that to everything.
Thanks Gabe, I can now get rid of my A75 roomheater and
build some more tube gear.
Well I'd love to tell you how great it is for a few more paragraphs but I got to get back to my Stereo. You
And an hour later
Email your request and I will reply with postal address.
Money orders, checks, or PayPal accepted.
Please allow ten days for shipping. Tubes are quality
control checked and broken in (not used!) for kits. Built units are tested
for four days for quality control and break-in.