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Old 6th December 2010, 10:22 AM   #1
nige838 is offline nige838  United States
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Default Switching Amp? 25watts WITH OUT tubes or Transistors?!?

Why have I never heard of the third option? A true switching amplifier...



The Mag Amp—World?s First Switching Amp | Stereophile.com
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Old 6th December 2010, 10:58 AM   #2
Arnulf is offline Arnulf  Europe
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There is so much ******** in the post you linked to it's hard to decide where to begin:

Magamps are not switching amplifiers. AC amplifiers where envelope is recovered (think of AM detection).

Magamps were not designed in 1960s. Try decades earlier. Perhaps this particular one was which seems rather weird, considering that far superior alternatives were already avaliable at that time.

The price they charge is downright silly and I cannot possibly imagine magamp displaying superior performance in terms of sound quality than either of the "first two options", as you implicitly dubbed them, simply due to nature of magamp's operation.

Why haven't you ever heard about them ? I guess you don't have much interest in the obsolete technology, just like most people. Then again, who better to answer this question than yourself ?
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Old 6th December 2010, 01:18 PM   #3
Gilgy is offline Gilgy  United Kingdom
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I've had the idea at the back of my mind to look into using magnetic amps in a guitar amp. It's about #930 on my to-do list, technical info on the concept doesn't seem to exist on the internet though.
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Old 6th December 2010, 03:19 PM   #4
Pano is offline Pano  United States
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There have been other posts about mag amps on the forum. They are not switching amps.

I used lighting dimmers in London theatre that were tube driven mag amps. Big, but they worked.
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Old 6th December 2010, 04:53 PM   #5
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Quote:
Originally Posted by nige838 View Post
Why have I never heard of the third option? A true switching amplifier...



The Mag AmpóWorld?s First Switching Amp | Stereophile.com
Search around for "Carver magnetic amplifiers" he had them commercially avail. not very long after his "auto-correlator" sound processors and pre-amps were "the buzz" (in the general shake the purist wannabe audiophiles tree".
Indeed the concepts and practical applications are rooted in military electronics of at least the 1940's, and very probably somewhat earlier.
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Old 6th December 2010, 05:12 PM   #6
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Magnetic "amplifiers" were around way back, used mainly for motor speed control, power supply regulators and light dimmers. Slow, non-linear, heavy, noisy, but reasonably efficient at low carrier (60 Hz) frequencies. Not really an amplifier, but an AC modulator with diode envelope detection. Transformer saturation via a DC control winding is used to control inductive AC current passage thru it. Looking at the Lundahl patent, I see that two are used in P-P to improve distortion.

I see many problems with using mag amps for audio. A high frequency carrier would have to be generated, so probably plenty of power transistors and maybe an IC in there. The high frequency carrier (similar to class D amplifiers) would lead to very hot magnetics, since they have to run into saturation at the HF. This is a definite NO-NO for swithcing amps. This would be very inefficient, likely fans are needed to cool the box. The output has to be diode demodulated and then Low Pass filtered to remove the HF carrier. EMI considerations, regulatory approval/license issues. Almost certainly limited audio HF frequency response due to the magnetics HF carrier limitations.

The LP output filter makes for a high Z/poor damping factor output, just like for class D amps, so feedback around the whole thing is needed then. That drives the HF carrier freq. requirement up even higher, leading to near melt down of the magnetics. A vacuum tube front end is needed to provide the power to run the two xfmr control windings and provide excess gain for the feedback. Thats probably close to a VT power amp or two in there already. The distortion figures are likely quite poor due to limited feedback bandwidth available. I don't see any specs posted for the amp for distortion, power consumption, frequency response, or damping factor. At that price though, any buyers are probably a little light headed anyway.
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Old 6th December 2010, 06:55 PM   #7
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by tympani1d View Post
Indeed the concepts and practical applications are rooted in military electronics of at least the 1940's, and very probably somewhat earlier.
Actually I think they go way further back, to early 1900s, when Alexandersson alternator was invented. It was used in conjunction with mag-amps for AM audio broadcasting.
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Old 6th December 2010, 07:49 PM   #8
Pano is offline Pano  United States
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Whether good or practical or not, it's too bad no one here has built one just for fun. I've thought about it, but like Gilgy, it's way down the list.
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Old 7th December 2010, 12:03 AM   #9
Gilgy is offline Gilgy  United Kingdom
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ok, it may move up my to-do list after seeing this

Homemade Magnetic Audio Amplifier.

YouTube - Homemade magnetic amplifiers made from common materials.
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Old 7th December 2010, 12:59 AM   #10
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Hmm, Steiner's circuit is using pulsating DC in the Xfmr cores, which would be more efficient than the full swing AC that appears to be used in Lundahl's patent (#3,131,360 figure 2). (lower hysteresis losses with SE flux changes) The patent mentions saturable reactors and a power gain of 200. Steiner is getting a power gain of 2000 with the DC pulses. Maybe some hope for a practical design that way. But the carrier will have to be a lot higher freq. than 35 KHz for HiFi. (more bandwidth needed to linearize the gain with feedback)
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