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Old 2nd January 2009, 10:59 AM   #181
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Location: Utrecht
Are there any HV direct drive amps for hybrid esl designs?
I guess it would be easier and cheaper to build one for the lower voltages instead of the very high voltage for full range esls.

Amplimo's are rather expensive and you could spent that amount of money for the direct drive amplifier.

In a recent article Menno vd Veen discussed about trannies (valve amplifiers) lacking the ability to resove micro-details because the core material doesn't respond lineair at very low level. I guess this problem might be in esltrannies as well.
A benefit of direct drive (as I heard it at a dutch meeting), is the ability to put a lot of power in the low bass, where ordinairy trannies have problems like core saturation.
drs M.J. Dijkstra
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Old 2nd January 2009, 02:05 PM   #182
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Naturally, I am cautious in disputing any point with Calvin. But I would say that there are atypical assumptions under which transformer coupling could be as good as direct high voltage, maybe. I am not sure I fully appreciate the value of throwing up a learned smoke-screen of "what if" possibilities instead of advancing the discussion as Calvin is so very capable of doing.

As for details fo my A-B test, I can't remember much except is was single blind. My own judgment was formed over a far longer period and abundantly clear to me the superiority of HV drive in the respects most central to ESLs (granted, DIY is always superior). Of course, I have since given up the HV amp, so that says something too.

There are many shortcomings to coupling transformers and more so when the compass of frequencies is wide. Like motorcycle mufflers, a world of compromise even with a lot of money to throw at the unit.

Moreover - and MAYBE this can be corrected just like with motional feedback - there's no feedback around the coupling transformer. But then with feedback, maybe not a lot simpler than just going HV in the first place. I think if tube amps had no feedback around their transformers, no one would buy a tube amp except output transformer less.

Building a HV amp is pretty complex and you are almost always on your own since you can never duplicate the components that, say, Sanders used. Not necessarily expensive... since the only transformer is in the power supply! The risk of shock may attract you or repel you (or both) depending on your personality.

Yes, there is a half-way concept using a mild step-up transformer instead of the familliar 10k-8ohm output transformer. It should have the benefits and half the drawbacks... back to you Calvin.
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio
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Old 2nd January 2009, 02:55 PM   #183
Calvin is offline Calvin  Germany
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Hi, cautious I bite ..budd I bup my deef out bebore
I donīt have any suspicions at all about the preferences of Yours in that test. Itīs just that there are so many factors influencing the result that a general Pro or Con might not be appropriate (hope this is the right word for it).

The core material shows some hysteresis, which might present a problem. On the other hand we see globally fed back amps driving a very complex load. So we need heavy compensation in such a amp. I donīt believe that this comes with no ill effect? At least my experience with such amps prooves different to me.
The best sound and highest resolution of details I hear is when my panels are driven via real good trannies (e.g the Amplimos) and KR Audio Kronzilla DMs (which even means two trannies in the signal-path). A DD-amp prototype (SE-triode wo feedback) featuring KR-Audios 845 tubes (running at 2kV) performs slightly less good. Other (high feedback) DD-amps performed much worse. So I donīt really see a īresolution problemī when using a first class tranny.
But I havenīt given up on the DD-amps yet. Maybe the new special made tubes (4kV-Triodes by KR) will lead to a breakthrough.

The rising impedance towards lower frequencies reduces the current - and hence power- need! This means that the panel becomes more and more īefficientī! If it wereīt for the rising current demand towards higher frequencies, even a small class-A DD-amp with just a few mA of Bias current would be sufficient (e.g. 2kV at 2mA is just 4W)! The problem arises with high frequencies where You need much greater currents (>25mA) if the amp shall have sufficient power bandwidth. So any amp designed to drive a panel to the upper bandwidth limit will be vastly overzised current-wise at lower frequencies. On the other hand a FR-Panel needs high transformation-factors (>100) which lead to large currents in the Ampere range in the primary winding of the transformer, not only at higher freqs, but already at low frequencies. This and the need for high inductance values asks for beefy cores and makes the construction overall more complicated. So while the DD-amp rather gets problems driving the panel at the upper bandwidth limit, the transformer gets problems at both ends. With a hybrid-ESL the demands the tranny faces are greatly reduced. It can then be constructed such that it easily achieves a sufficiently high bandwidth limit. It then can outperform most DD-amps.
So the lesson I learned is: "stay away from FR-ESLs"

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Old 9th January 2009, 02:08 AM   #184
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I'll start with a little gleeful story. I found an ancient Partidge output transformer in my junk box a few months ago. Well, actually their best ever. Turns out they sell for $500 or more. I'm waiting for the market to recover before flogging on eBay. Point of the story: tremendous subtlety, art, and sicence, in making good transformers (which happily for me, converts to price... I'm hoping).

With a direct HV Sanders amp, now I finally recall, the load isn't a transformer but is really a lot of non-reactive wire-wound resistors. That's as clean a load as you could want to drive. The ESLs just sort of hang off the load. They require very little power (we all know how loud one acoustic watt is when produced efficiently) and so the ESL characteristics have only modest influence on the amp... which is really just driving a well-behaved resistive load.
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio
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Old 12th February 2015, 05:08 PM   #185
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Default ESL direct drive

Dear Brian:
Iīm very impressed with your "enterprise" , coss is my dream to do drive do ESL quads.
I have one triple Stacked setup(panels from Wayne Pickett) and playing it with one OTL , wHich I done, but I have in mind built one Direct drive amplifier for the ESL57.
I will travel to USA, Orlando in april to catch refurbished Quad panels with Wayne, and like to know your system. Is possible.
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Old 14th February 2015, 02:13 AM   #186
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Location: Toronto and Delray Beach, FL
I'm glad to see this topic re-surface. Granted, I never did careful ABX comparison after carefully matching for loudness, freq response, etc, but I lived with a Sanders-like amp (B+ was 2300 VDC) for many years and I feel direct-drive can provide a large improvement in sound over transformers.

BTW, I sold the Partridge transformer mentioned in post #184 (Jan, 2009) for $1000 a year ago on eBay. Got $350 for a pair of Thordarsons this year. If you experiment with transformers, hold on to them for 35-45 years (if your spouse doesn't mind), you never know what they might be worth.

HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio
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