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1970s Design Indulgence

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Sylvain View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2021 at 5:09pm
Thank you for a more readable, digestible posting..Yes Indeed Audio amplifiers Manufacturers mention their new design ''in house'' transformer production. The ''Novelty'' of their amended/upgraded/reconfigured Transformers are but declared in the achievement claimed. IN House protect design and production technique patent rights. 


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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 20 hours 9 minutes ago at 8:43am
I will admit that my ability to think what is happening on the end of the charge pulse conduction angle, isn't good.

insufficient magnetising current or magnetic flux

At such times it is best to go back to the basics:

"energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another"

We're in the business of transferring energy into speaker cone movement and the by-product, heat.

The energy at the end of the reservoir capacitor conduction angle should equal zero. It should start at zero and end at zero.

Where it starts is in the ripple voltage trough - the minima of the ripple voltage.

Current is drawn until the peak voltage waveform reaches its maxima, including the bridge rectifier voltage drop (which defines that maxima).

We can only look through the window of transformer primary current. We must imagine the voltage waveform, but we know (or should, by now), that the current transition in the centre of the 'scope display is also the voltage zero. The half cycle (at 50Hz) lasts 10mS, and the 'scope display calibration is 2.5mS per major division.

Therefore, voltage maxima is 2 divisions to the left (5mS) of centre, and is where charge current drops to its minima.

The peak energy in watts, is the voltage maxima times the current minima.

If the end of the conduction angle is at zero current, then the answer is zero, because x * 0 = 0.

If the end of the conduction angle is positive, then there is excess energy because x * y = something. Where does that excess go? Heat.

If the end of the conduction angle is negative, then there is energy loss because x * -y = minus something.

If there is energy loss in the capacitor's charge, it stores less energy.

This would be indicated as a deeper ripple voltage trough, except without making the 'scope chassis be mains neutral, we cannot display it (there are things I won't do).

The transformer magnetic flux strength needs to be such that the conduction angle ends at zero, otherwise we have energy loss, because it wasn't there in the first place.

Which frequencies suffer the most due to this energy loss? Bass!

The treble frequencies also suffer by having "their ends chopped off".

The audible result is harshness, which is distortion, which is not shown on the audio analyser - exept for the maximum output test, which is less.

Which transformers work at higher magnetising current? Laminated types.

So don't go looking into mad assumptions of why old laminated transformed amplifiers do better bass, as you just learned how.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 8 hours 6 minutes ago at 8:46pm
I've been asked about R-core and C-core transformers regarding this design.

Like toroids the cores are strip wound round a mandrel, but then cut in two (miraculously, without springing apart) to allow the bobbin(s) to be slid into place, before being joined up again.

They feature a flux gap like a conventional EI. A toroidal doesn't feature a flux gap. The flux gap allows a more linear magnetising current, which is useful in audio matching transformers.

The problem is that R-core and C-cores are made of thin high grade steel and so cannot handle as much flux as an EI, which tends to use thicker laminations.

This project needs a transformer somewhere in the region of 60 to 80 mA magnetising current, and the grade of steel determines how much it will buzz. We don't want it to buzz, and I will guess it requires low grade GOSS laminations. R and C cores tend to be HG or SHG (high or super-high grade).

The main problem is the mains voltage which isn't constant, so, with a toroidal which may be OK at 240V, it will saturate and buzz like crazy at 250V. Unless, that is, it's run at low magnetising current to start with. However, the low magnetising current is the problem.

Whereas an EI might do 56mA at 230V and 78mA at 250V, a toroidal might be 16mA at 230V and 90mA at 250V - the exponential curve is more pronounced. If it were 60mA at 230V, it would probably burn at 250V after making loud buzzing noises.

An R or C core is designed to operate just as "linearly" as an EI but at much lower magnetising current, and so is unsuitable.

Maintaining the magnetising current is so important that primary voltage taps are a must, and making sure the right one for the supply voltage is an even bigger must.

Just consider trying to obtain a range of 60 - 80 mA over the fictitious 230V range - from 207V to 253V - it's impossible. However, there are manufacturers who try that impossible to comply with the idiot EU ruling. Some use very tall toroidal transformers and some multiple cores for the transformer not to saturate. There are also toroid core coatings to try and even things out.

If an EI transformer can be made to do the job (the RS 504111 can, but is too low on VA), then if you can put up with a little hum that's only audible at very close quarters, then the amplifier will do the perfect job we're after.
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