Listening Tests on my Amplifiers:
I was invited by an associate to come see and hear his audio system. I knew that he has some serious tube equipment (including one of my early P-P amps) but I had never seen it.
Jose's Sound Room:
I took my Lexan Tubelab SE, a (still unfinished) Simple SE, and a box full of tubes, and headed North. When I arrived, I grabbed an amp in each hand, and went inside. As I carried my equipment up the stairs, I could hear someone playing the sax in the room. No, this sound was coming from speakers. The music was playing from a SACD player through a 27 based line stage into a Korneff 45 amplifier.
There were several tube amplifiers in the room. All of them were SE amps. The previously mentioned Korneff (center - grey) and a Moth 2A3 (left - black) would be listened to today. Jose, told me that he did not need any more than 1 or 2 watts. His speakers were 106 db efficient. I understand the math (2 watts through 106db speakers sounds like 20 watts through 96db speakers, and 200 watts through 86 db speakers), but It is hard for me to realize how anyone could be happy with 1 watt. Nevertheless, I brought my Tubelab SE with the NX-483 tubes. It makes about 1.5 to 2 watts (right - clear). I also brought a Simple SE (front - powered up) with a wide selection of tubes. There are a pair of Cary 805's in the rear, but they are currently tubeless. They could be deadly through these speakers.
I can not now remember the brand name on the speakers but they were giant horns with Lowther drivers and powered subwoofers.
Vinyl? Of course. I thought I was set with my 30
year old Technics direct drive turntable. It was cool with my Pioneer
receiver in the 1970's and it sounded awesome with my Phase Linear / Carver
setup in the 90's. I never even knew that turntable setups like this
The phono stage or the CD player fed this 27 based line stage. It drove long cables to the amplifier.
Another picture of the amps.
The Tubelab SE with NX-483 tubes. Compare this picture with the one on my home page. The power transformer has been rotated 90 degrees to reduce hum. Not visible is the choke that I added, it is under the right hand OPT. The twisted pair of white wires running across the top of the PC board go to the choke. I have been recommending the choke to customers with efficient speakers, now I finally added it to my amp. I also added a surplus 20uF 400V polyprop cap under the left OPT. Another recommended addition.
The listening session:
When I was
invited to bring a couple of amps to Jose's house, I got my Tubelab SE out of
the closet where it has been hiding. I remembered its last visit to some
high efficiency speakers, where it went HUMMMMMMM. I had fixed this by
rotating the power transformer 90 degrees, but these were 106db speakers. I
decided that my CRC power supply was going to become a CLC power supply. I
found a power choke of unknown specifications, but 150 ohm DCR, so I wired
it in place of the 150 ohm resistor in the power supply. I tested the amp,
removed the tubes for transport, and put the amp in the trunk of my car. I
also unhooked my Simple SE, gathered up about 15 pairs of tubes, and headed
The Tubelab SE could hold its own against the other 2 amps and sounded very similar to the Korneff 45 amp. The Simple SE with no feedback, KT88's in triode mode sounded almost as good. I would have liked to hear some of the other tubes and a few different transformers. That will happen another day.
It was noticed
by Jose, that the "bass didn't sound quite right" through his speakers.
Neither of the other listeners noticed it. It did not stop us from listening
to it for most of the afternoon. We
believe that this may be due to the massive size of the OPT's and the fact
that they (due to their size) have the most loss of all the transformers
that I bench tested a while back. The iron losses tend to be nonlinear due
to magnetic hysteresis and other factors. Some of the hysteresis related
factors tend to be constant. My normal listening levels are in the 5 to 10
watt range (86db speakers) where the constant effects would be a small
percentage of the sound power. The average listening level at Jose's house
was probably far less than 1 watt.