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Model: | zero auto transformer |
Category: | Other |
Suggested Retail Price: | $???.?? |
Description: | auto transformer |
Manufacturer URL: | Paul Speltz |
Review by Marc Bratton (A) on January 20, 2003 at 10:47:15 IP Address: 63.184.72.124 | Add Your Review 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 |
Follow Ups:
So if you are going to spend $500 (or so) on an autoformer, why not get a valve amp with a decent output transformer - you'd save a load of money 'cause OTL designs can be really expensive. I agree to a point that it may be better to use the autoformer even on a decent valve amp, but i would point out that the autoformer is a torroid and not a great deal of valve amps use torroids as output transformers because of problems with DC imbalance etc; those that do use them are reputed to sound better over ones that use E/I or C cores.You are right that valve amps like higher impedance because they have a higher output impedance than a solid state version. This is particuarly true of feedback-free designs (since feedback lowers output impedance amongst other things).
Still if it works, then dont knock it i guess....
...which would explain why ESLs always sound better being driven by valve amps - because the impedance is better matched....
...so why dont they make higher impedance coil speakers any more?
Why DONT "they" make high impedance speakers anymore? Paul goes into some detail about this in his white paper. Basically, the 4 ohm speakers suck more current from the solid state amps in the dealer's show room, so "sound" more "efficient". They're not. They require 2 or 4 watts to get that 2.83 volt signal which is the standard, instead of 1 watt like a higher impedance speaker. This is why 'efficiency' was quietly dropped as a way of rating speakers, and 'sensitivity' was put in its place. It's a red herring, and a cynical trick done by the speaker manufacturers, much like making a slightly rising top end to make 'em "stand out". Far as toroids saturating easier with DC, it's a nonissue with an autoformer, which is "dry", meaning it is not "soaked" with DC bias current in the 1st place. And I'm willing to bet that even a big tube amp with a really butch output trannie will STILL sound better with these things giving it a true 16 ohm load, than they'll sound straight off their 4 ohm taps, trying to drive a 4 ohm load. I'd LOVE to put this to the test, if anyone would like to loan me their high powered tube amp. But I do agree with you that, the smaller the amp's power supply and output trannies, the bigger the improvement is likely to be.
thanks for the response marc, the DC imbalace/torroid comment was mainly in explanation of why tube manufacturers dont use torroids for output transformers. I have a really decent tube amp design which i am planning on marketing soon. I will try torroidal output transformers in the final prototype (am currently using 4-section C-core). I will be interested to see if theres an improvement.
I agree with the virtue of the auto former, I have use the seocndary of my output trans out of phase to the cathod of the output tubes and it sounded much better too. but if a tube amp have a properly design output trans that can handle low output impedence, it should be equivelent to having the seperate output trans and the auto former combined right? i hv use a few SS McIntosh with autoformer before and always wanted to get one to try.... where can we get it and for how much.. tks
Paul Speltz goes into some detail in his website as to why even tube
amps with really big output transformers still benefit from driving a 16 ohm load. To oversimplify, even the best output transformers are by their nature somewhat compromised, and if you shift the load upwards, you're more in their optimal power transfer curve.
The DIY ZERO is $433.00 shipping included in the continental US.
He also has a model wherein the cables are already prepped for more money, and one really nice one that comes in its own custom made box.
The DIY is by far the biggest bargain. If you click where it says
"Paul Speltz" under "Manufacturer's URL", that'll take you right to his website.
Very interesting review.FWIW, I rewired my home brew MTM speakers so that the Mid/Woofs were in series for 16 Ohms rather than the original parallel for 4 ohms.
On the same 8-ohm tap of my 300B SET amp, the difference was striking.
Tube amps seem to like high impedance loads.
Nice review Marc. You mentioned it was like dropping in a solid state powerhouse. Are you implying your tube amp sounded more like a solid state amp? Do you still hear the positive characteristics of your tube amp then? Did you notice any increase in volume at the same preamp setting? Did you notice that your amp "runs out of gas" at a higher volume level now?
Thanks,
steve
...the bass was quicker, tauter, deeper to at least in part to the higher damper factor. The RM10 retained (indeed, increased) its tube
midrange magic and treble sweetness...otherwise, what would be the point? I've tried bigger solid state amps with my Maggies, and while some things such as dynamics and bass were indeed better, the all-important midrange was not. Most affordable solid state amps I've heard with my MMG's sound competent, but not inspiring. The RM10 inspires, especially now that the ZEROs allow me light load it. I might add, I've tried light loading before...I had 8 ohm Epos ES11's that I ran off the 4 ohm taps. The effect with the ZERO's & MMG's is a whole 'nother league.
I think what's really going on here is that the ZERO's allow the amp to act more a voltage source, less as a current source. ANY amp likes that better. Theoretically, I should be experiencing a slight drop in volume. Maybe I do...if I do, the salutary effects of the Zeros are such that I'm not noticing it.
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