VACUUM TUBE VALLEY's SE TRANSFORMER TEST
Many of you may not know about these different brands and designs of single-ended output transformers, and many of you may not have the technical interest in the test procedure, so here is my suggestion: think of these output transformers as different baseball teams. There are large fan groups for each. You will note in America that Gordon Rankin roots for MagneQuest, while others will claim that the Tango iron is champ. Herb Recihert will swear by AudioNote, but I know he also loves Tango. I personally use MagneQuest transformers and I also love the sound of Tamura iron...choices, choices, choices.
The only important point is that I am fairly confident in saying that all of these transformers are made at a higher level of quality than the ones that are now appearing in our store bought amplifiers, and, as we demand more, soon these objet dart will be available...as they are in Japan.
Now for my VTV pitch...the more you know, the more you will enjoy your tube electronics. This is a really cool magazine and you should subscribe because these west coast thermionic techno-shamans are exploring tubes circuits in a completely unique way.
VTV LISTENS TO SE TRANSFORMERS
[Reprinted with the kind permission of Vacuum Tube Valley.]
Our policy at VTV is to audition audio products using multiple listeners in several sessions. By doing this, we are able to get a wide variety of opinions and reduce the potential for audio hallucinations and product biases. A total of 10 different listeners gathered for three different listening sessions of the single-ended iron.
In this series of listening impressions, we obtained most of the popular, premium single-ended transformers being offered by US, Japanese, British and Italian transformer designers.
The listening set-up consisted of an all-tube single-ended power amplifier using a 300B, driven by an octal dual-triode 6EM7 and rectified by a 5U4G. This is the same test amplifier described in Erics 300B article. We listened to different output tubes: the Shuguang 300B, the Cetron 300B, the WE300B (old version) and the VAIC VV30B and VV52.
The pre-amplifier was Dave Wolzes custom built all-octal line stage using 6SN7s, a loctal 7F8 and all tube regulation and rectification. The CD player was an Elite Electronics-modified Philips 960 or a prototype of the Dynaco CDV-Pro (tube output with HDCD). The speakers used were either the highly efficient horn-type Klipsch Chorus IIs or B & W DM 110s. Program material used included some GRP recordings (Fourplay, etc.), a few classical piano CDs and the Stereophile test CD. The listening room was located in our offices in Sunnyvale.
For all of our listening sessions, we are using a SOLID line conditioner by Power Science Industries, Palo Alto, California. Our offices are located in Silicon Valley where there are thousands of noisy digital computer power supplies lousing up the line voltage. The SOLID takes care of all the line hash and really cleans up the sound.
The following is a summary of the transformers reviewed.
We sampled two AudioNote UK transformers, the 2.5K (US$140) and the 3.0K (US$160) units. Both of the transformers are of the "open frame" construction. The 2.5K was tested with a single 300B set at 60 ma. This unit presented a balanced sound with a solid bass and low uppermidrange distortion. Midrange seemed just right" and the highs were not too bright, but actually sweet. A very nice transformer.
The 3.0K AudioNote unit was actually a bit better sounding with a single 300B, offering the balanced presentation with more solid bass. Overall, the AudioNotes performed quite well and were easy to listen to. Most reviewers felt the AudioNotes were the "best sound for the money."
These attractive transformers are hand-wound in Italy by G. Bartolucci and feature double C-core construction. They all have 4/8/16 secondaries, solid brass hookup terminals, and are beautifully potted in black, squared, all-steel cans. They are reminiscent of MC225 output transformers. The two Bartolucci units reviewed were the 2.5K Model 16/A/B ($215) rated at 90 ma for 2A3, 300B, 6B4G, etc, and the 3.0K Model 16/A/Y ($225) rated at 90 ma for a "91 " style 300B amp design.
With a 300B set at 60 ma, the 2.5K unit had clean, balanced mid-range and crisp highs on the bright side. We did note a hump in the upper-bass range. With the VAIC VV30B set at 80 ma, the 2.5K unit displayed bright highs and what sounded like intermodulation distortion in the upper-mids. The bass was strong and tight, but sounded a bit like solid state.
The 3.0K Bartolucci sounded more balanced in amp and the highs were less tizzy compared to the 2.5K unit. With a single 300B, the 3.0K might be the way to go.
We listened to the VT2-KB ElectraPrint ($249) which is a 2.7K unit that can handle up to 160 ma. It easily won the "biggest iron" contest, weighing in at fourteen pounds. First, we tried it with the 300B and were impressed by the very balanced presentation throughout the listening range. The bass was beefy and well damped. The mids were 3D and very lifelike. The highs were clear and extended. This transformer had an effortless sound quality.
Just for kicks, we tried the VT2-KB with the new VAIC VV52 Super Power Triode set at 500 volts and 100 ma. The sound was awesome with a "Big Tone" quality like no other combination in this comparison. The Electra-Print and the VV52 are the ultimate set up for amp builders who can spend some bucks.
The FS-030 ($300) has been available since 1992 and is used in a lot of custom SE amps made in the US and elsewhere. We also obtained a sample of the limited production FS-030 that was wound with a special oxygen-free copper wire originally designed for cyclotron electro-magnets.
First, we tried the standard FS-030 with a single 300B. This transformer is limited to 60 ma plate current by design, so we set the current at that level using 300 volts on the plate. This transformer has a relaxed sound with nice midrange and sweet highs. However, the bass seemed under-damped and the overall sound was not as balanced as the AudioNote UK transformers.
Then we hooked the FS-030 up to a VAIC VV30B power triode set at 60 ma and 300 volts on the plate. With this combination, the bass was somewhat loose and the highs seemed slightly veiled. This is probably due to the circuit operating parameters not being optimized for the transformer.
We hooked up the limited production FS-030 with the oxygen-free copper wire and noticed a significant difference. The sound was more balanced and the bass was tighter than on the standard FS-030. We also noted that the air gap on this FS030 was wider than on the standard one.
This may have something to do with the sound quality because all of the other open frame SE transformers we reviewed appeared to have a wider air gap.
We have no doubt that when the standard FS-030 is "tuned" to a specific amp design and speaker system, it can perform well.
The UBT-1 ($95) is a 1.6K transformer that can be made a 3.2K unit by hooking an eight ohm load to the four ohm tap. In this configuration, the primary inductance is less than optimum, but this transformer has good bass response, so this is not a bad compromise. With a single 300B at 60 ma, this transformer had clear mids and highs and was very detailed, but not sibilant.
There was somewhat less bass than either the AudioNotes or the ElectraPrint. We also listened to this unit through the B & W DM-110 speaker and liked what we heard. This transformer seemed to work better with a non-horn type loudspeaker system. At $95., the UBT-1 is a "best buy" in its performance range.
The 4.8K UBT-2 ($118) we tested was a pre-production unit, but was checked for specification. Connected to a single 300B at 60 ma, this unit had clear mids, but the highs were somewhat peaky. The bass was a little mushy and there was not a lot of punch in the low frequency spectrum. This performance can be attributed to somewhat of a "mismatch" in impedances with this transformer (4.8K vs. approximately 3K in the others).
The Tamura 3.0K F-2007 ($600) is easily the most attractive transformer in the test. It is flawlessly finished and beautifully potted and has a gold band on the bottom with a metal and ceramic ID badge on top of the unit. This transformer is used in many of the "high end" amps made in Japan.
With a single 300B at 60 ma, the sound was smooth with balanced mids and highs. There was "extreme detail" in the upper mids, but the lower bass was somewhat distorted. This transformer would sound excellent through early Western Electric horn drivers or Altec 288 horn drivers.
Again, just for kicks, we tried the Tamura with the VAIC VV52 set at 500 volts/80 ma and were treated to "ultra detailed" sound with balanced mids and highs. The bass was not as full as the Electra-Print, however.
In the typical Japanese tradition, the Tango transformers were beautifully made and well potted with a hammertone metallic finish. The XE-60 ($450) we listened to was a 3.5K unit rated at 140 ma.
First we tried it with a single VAIC VV30B at 80 ma. The overall sound was balanced and sweet. Very nice to listen to. There was a nice presence and lots of musical information. The bass, however, was somewhat soft, especially when compared to the Electra-Print.
We hooked up a single 300B at 60 ma and the sound was a bit more recessed and laid back compared to the VV30B. The mids had good depth and presence and the highs remained sweet.
Lastly, we tried a single VAIC VV52 power triode at 80 ma with the XE-60. We noticed more bass, more detail and a bigger sound. The mids were "flatter" and had a bit less presence.
THE BOTTOM LINE
In a properly designed amplifier, any one of the transformers we evaluated in this article can sound excellent. However, our listening group came up with some "favorites":
For those on a budget using a single 300B, the AudioNote 2.5K or 3.0K were the clear winners, with a well-balanced sound and a realistic quality with low listener fatigue.
Users of a single 300B with horn speakers and a larger budget should consider the Tango XE-60 for its sweet and balanced sound that would complement many finicky horn speakers.
The audiophile who wants the ultimate in "Big Tone," regardless of price, should consider the Electra-Print VT2-KB with the VAIC VV52. This combination easily had the best balance, biggest bass and the best low and mid-bass clarity with our SE amp and speakers.
e-mail Dr. Harvey "Gizmo" Rosenberg: firstname.lastname@example.org
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