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Old 5th January 2011, 01:50 PM   #1
T101 is offline T101  Bulgaria
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Default L here, L there, L Everywhere *-*

This thread is about a circuit used in those speakers: Audiophile Tube Amps and Tube Gear from DECWARE
Discussed in that thread: http://www.diyaudio.com/forums/full-...r-decware.html

It is something new to me and I am curious. How does it work?

It seems to me that it has something in common with the T-Bass cirquit found here: 'T'-bass drive for OB LF drivers. and attached below

Both alter the conductivity of an inductance through current/voltage applied to it's middle point or through magnetic inductance induced by coul - the last is the case that I'm interested in... and probably not only me...

Apart from the pure theoretical explanation it is also interesting for me whether it is necessary the two inductances to interact with the driver's permanent magnet or it can be another permanent magnet or a core or two air cored transformers.

I understand it might be naive, but if it is something useful and relatively easy to understand and DIY why not get into it's knowledge.

Best Regards!
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File Type: jpg FRXinside.jpg (24.2 KB, 626 views)
File Type: jpg t-bass circuit for ob..jpg (42.8 KB, 623 views)
File Type: jpg circuit.JPG (40.0 KB, 623 views)
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Old 5th January 2011, 04:21 PM   #2
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i havent had time enough to look at the links you provided (im just off tv shopping) but i believe you are asking about mutual coupling between coils, and the use of a trannie as a mutually coupled inductor.

i dont usually use trannies in this way, so i cannot really say much about the subject, other than i only know of this technique being used for a very large inductance value, for a sub passive filter for example. im sure it will work in your application, if you design correctly; other than that i dont see/know what possible benefits it would have in a 'non subwoofer' application.

many some others would contribute, and fill in the blanks, as there are plenty with similar and greater experience than i.

BUMP!
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Old 5th January 2011, 04:47 PM   #3
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I am interested in how this works. My take is that we are looking at the top circuit in your 3rd attachment

dave
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Old 5th January 2011, 05:24 PM   #4
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That's two of us. If not that, I suspect that it'll be something v. close.
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Old 5th January 2011, 06:44 PM   #5
T101 is offline T101  Bulgaria
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It definitely has lots to do with core saturation. As we know inductances with saturated core become conductors.
Bigger load on the secondary winding means leser current draw from the primary and vice versa.
The current draw is altered through load (resistance) that means that the load exhibited by the secondary winding alters the resistance of the primary.

In that case the amount of current drawn by the loading resistance in paralel with the secontady winding is proportional to the current fed to the primary.

The bigger the frequency the more saturation of the core the bigger the current fed to the loading resistor, the bigger the current demand to the primary winding the lesser is it's resistance...
But all this in the last paragraph happens in some curved shape (impedance graph) related not so much to the initial inductance of the L's, but to the core characteristics and the loading resistor value.

It's some kind of controllable/shapable low pass circuit.

Edit: What about a L and R in series instead of only R for the load of the secondary winding? Or even RLC or every frequency dependant circuit that can ultimately shape the impedance curve of the primary winding...

Last edited by T101; 5th January 2011 at 06:50 PM.
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Old 6th January 2011, 04:39 PM   #6
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aha i get it now. instead of seeing the inherent capacitance between windings as a problem (and trying to minimise this, as most trannie designers do), and creating a bad (in the conventional sense) transformer....but with some extra additions of components

getting me thinking now......... ........couldnt you just do this with an air cored trannie too? less saturation to deal with, but a bigger capacitance to add to circuit?(flatter hysteresis also?)

I like the thinking
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Old 7th January 2011, 09:24 AM   #7
T101 is offline T101  Bulgaria
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Lag (hysteresis) with the initial imp curve of the primary winding won't be any different than if there were no secondary windings.
But I wonder what it would be with several secondary windings, each with a band pass or high pass filter attached to it.

Seems an inviting design if it is possible a 20mh low DC resistance inductance is being controlled by several secondary windings connected to small value, smal tolerance filter components.

Question: is the following statement a valid one: "in order to achieve small component values in the controlling(loading) circuits, the secondary winding should have bigger dc resistance"

And another question: what it takes to draw bigger current through higher resistance?

Now I see a controversy - bigger load makes one components values smaller and others greater.
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Old 23rd March 2011, 08:45 PM   #8
T101 is offline T101  Bulgaria
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I did some thinking, I made some simulations and decided to use this "system" as a Continiously Variable Midrange Level Selector in my ongoing project.
It's symply a BSC with adjustable depth and I can't think of a proper name for it.
The maximum depth is adjustable by the R in paralel with the L (primary winding) of the BSC.

Now the transformes are ordered (laminated E-type Iron cores) and I will report when I have some practical results.

I have topic in Bulgarian language in my forum: ????????? BSC ??? Continious Correction Midrange

I apply two screenshots of two simulations, one with 128 ohms of loading load and one with 0.1 ohms loading load.

Additionally a selector for different additional capacitors can be added in order to maintain one an the same either acoustical or electrical crossover frequency.

Best regards!

P.S. Only a slight correction for the above statements. Core saturation is not the case here. Only ordinary transformer qualities. Bigger current draw=less impedance for the primary. So far no negative side effects predicted. I will have the system electrically measured for added distortion and what so ever once it is ready. - hope that is soon!
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File Type: jpg seriesAbsc2.jpg (70.1 KB, 409 views)

Last edited by T101; 23rd March 2011 at 08:53 PM.
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Old 24th March 2011, 08:28 AM   #9
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Quote:
Originally Posted by T101 View Post
It definitely has lots to do with core saturation.
I don't think saturation or current draw has anything to do with it. Drawing more current through a transformer by increasing the load does not effect the flux density, it only effects the losses. If one has a particularly lossy transformer, then increased current draw could have a noticeable effect as frequency increases but I suspect this is not the main mechanism at work in the concept.

dave
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Old 24th March 2011, 08:17 PM   #10
T101 is offline T101  Bulgaria
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Dave, look at the "p.s." part of my last post, I have made the same notice.

Meanwhile I found out yet another thing.

If we have a normal inductance and a transformer with primary and secondary winding with equal properties to the normal inductance and do the following:

a. Connect the single inductance in parallel with a 4 ohm resistor, and

b. Connect the primary winding of the transformer in parallel with a 8 ohm resistor and the secondary winding again with a 8 ohm resistor;

Then we get exactly the same curves.

Only one difference though the single resistor carries more load than the two resistors together.

The two resistors both carry signal at maximum of -9 db, which is about -4.5 db roughly and the single resistor is at -3 db peak level.

So the transformer and two resistors version will dissipate less heat through resistors and more through the transformer core.

At a ratio of 0.65:1 for the loading resistor of the secondary winding versus a single resistor in a BSC this means less demand for power capacity of the loading element as part of the job is done by the transformer core.
And this is only for transformers with efficiency of 99-100% which do not exist.
Probably the loading element will have to be no more than 0.5 times the power capacity of the R in a RL.

The price of the transformer itself may be too big to justify the savings from smaller resistor.

It may seem that the loading resistor is not in the signal path, but it actually is exactly there.

With those transformers I ordered I may end with just a 3.25, 7.5 and 15 mh low DCR iron cored inductances... which is not that bad...

WAIT!

Circuits are not equivalent! I was mislead by sims with my intended crossover!

They are different (see attached screenshots) and it is now obvious that someone who is qualified enough must speak. - Because obviously I am not such person.
I almost mislead myself.
And in the transformer version the loading resistor and the bypass one do not get equal loading. They are equal to one point after which the loading one gets less current and the bypass gets more.

More thinking needed!
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