Tubes Asylum: REVIEW: Paul Speltz zero auto transformer Other by Marc Bratton

Model:	zero auto transformer
Category:	Other
Suggested Retail Price:	$???.??
Description:	auto transformer
Manufacturer URL:	Paul Speltz
Manufacturer URL:	Paul Speltz

Review by Marc Bratton ( A ) on January 20, 2003 at 10:47:15
IP Address: 63.184.72.124

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for the zero auto transformer

Paul Speltz is an audiophile who also happens to be an electrical engineer. Having built his own speakers, a 4.7 ohm design with which he was quite content, he started investigating amplifiers. He really liked the Atmasphere OTL amplifiers, which with a 4.7 ohm speaker design, obviously presented a problem. The 4 ohm speaker is hard to drive for any tube amp, but especially an OTL design. That was when he started investigating having a custom autoformer made to his specifications. The DIY Zero autoformer is the result of his investigation. To quote from his excellent documentation: "An auto-transformer" or "autoformer" is the simplest type of transformer. An autoformer has only one winding with multiple taps available. The impedance conversion is achieved by bringing the audio signal out on a different set of taps than the audio signal came in on." In short, an autoformer is a device that you can use to raise the impedance that your amplifier is having to deal with, in order to bring it into the range where its optimal power transfer characteristics are. The effect of doing so is not trivial, I can assure you...but I'm getting ahead of myself.
So, what you get is a pair of massive toroid transformers, that remind me of what you'd see as power trannies in a 250 wpc solid state bruiser. These have a biwired pair of black and white 14 gauge silver plated copper leads for your speaker connection, and on the other end you have have 4 wires, color coded gray, yellow, blue, and brown. These are your multiple impedance taps. Depending on what combination of wires you use, you can multiple the speaker impedance 2x, 3x, or 4 times.
Again, quoting from Paul's white paper: "Typical reported improvements from people who have used the ZEROS to increase their speaker's impedance are: A)Lower distortion (B)Firmer bass (C)Higher resolution (D)More extended and better focussed high frequency (E)More natural, effortless, and organic sound." I would have to say an embarrassingly simple "YES!" to ALL of the above.
The guys over at the Planar asylum have been telling me I really, really need to get something bigger than my little Music Reference RM10 amp to drive my MMG's with, which is probably huffing and puffing to even get 30wpc into the 4 ohm taps off to the MMGs. I wanted a 100wpc RM9, but it wasn't in the cards. So, I started looking into optimizing what I have, which is why the ZEROS appealed. Indeed, Roger Modjeski concurs that the RM10 does a LOT better into a 16 ohm load, light loaded on the 8 ohm taps. In fact, he'd voiced the amp using 16 ohm Quad ESL 63's. So, I ordered the DIY ZERO's, prepped the cables, and hooked them up on the 4x taps, moving my amp end speaker cables to the 8 ohm taps.
The difference was not subtle, I assure you. The bass became a LOT more taut, deeper, and quicker. In that regard, it sounded like I'd dropped in a solid state power house to replace the little RM10. No, it didn't turn the RM10 into a 200wpc powerhouse, but the quality of the bass was right there. After a 10 hour or so break in, I noticed ALL the improvements ennumerated above. I was startled to find that with string quartet recordings, the cello and viola were brought out of the background, and were more fully present in the room. Even the high registers of the violin sounded a lot more focussed, and fully present. They actually got sharper and brighter, but this was not a "high fi" kind of brightness. This was the kind of piercing REALITY you hear when you listen to a live string quartet. Harmonics now were propelled at me from the sound stage at warp speed, and just took another step towards what I hear at live unamplified concerts. Paradoxically, the sound is also more relaxed, and easier to listen to (not that it wasn't before). Vocals are more inflected and nuanced; the soundstage is also deeper, wider, and more fleshed out. Depending on the recording, the intensity of the effect ranges from subtle to startling. Kick drums in particular are now more of a treat. In summary, the RM10 still is a 35 wpc amp, but now sounds like a much more capable one, across the board. With a 16 ohm load, its sound is so much better that I don't feel any need to try any other setting. I did try the 12 ohm setting briefly, and feel it lost some of the qualities ennumerated above. I think Roger ought to just sell these with his RM10 as a package deal, and be done with it. The intensity of the effect is closer to an amp upgrade than a speaker cable upgrade.
So, while it may be a bit counterintuitive to think that adding more copper and iron in the signal chain is going to help things, I can assure you this thing delivers. Its benefits WAY outweigh any theoretical insertion loss. And, the beauty of it is, it doesn't matter HOW big your tube amp is, it'll probably sound better driving a 12 or 16 ohm load. So, if you have 4 or even 8 ohm speakers, I think these things are a stone cold bargain, and I recommend them highly.

Product Weakness: None that I can hear.
Product Strengths: As above.

Associated Equipment for this Review:
Amplifier:	Music Reference RM10
Preamplifier (or None if Integrated):	FT Audio LW-1 passive/EAR 834P
Sources (CDP/Turntable):	Teres/Morch UP4/Virtuoso
Speakers:	Magnepan MMG's
Cables/Interconnects:	DH Labs T14
Music Used (Genre/Selections):	all types
Room Size (LxWxH):	as x in x
Room Comments/Treatments:	my system (listed)
Time Period/Length of Audition:	2 weeks
Other (Power Conditioner etc.):	Brickwall/Monster
Type of Audition/Review:	Product Owner

Product Weakness:	None that I can hear.
Product Strengths:	As above.