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Multi-Way Conventional loudspeakers with crossovers

Placing autotransformer in crossover
Placing autotransformer in crossover
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Old 7th December 2018, 10:50 PM   #21
EarlK is offline EarlK  Canada
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Here's a good example of how JBL used to use autoformers ( back in the day ).

Placing autotransformer in crossover-autoformer_example_in-network_-png

The point is that an autoformer is also an inductor and some of the more clever designers will just build it into the overall network ( when they can ).

Notice the switched conjugate resistors ( source side of the autoformer ) working to present a consistent impedance to the preceeding capacitor.

I'm a bit surprised the OP didn't see the "reflected" impedance issue crop-up since those pics seem to be snaps of XSim ( which has an excellent impedance window ).

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Old 7th December 2018, 11:47 PM   #22
EarlK is offline EarlK  Canada
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Quote:
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FWIW here's an ancient Altec two way autoformer schematic: http://digilander.libero.it/stevevis...N800schema.jpg

GM
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Placing autotransformer in crossover-n800d_schema-jpg


Must be a case of dimming eyes, but that's no autoformer, instead that's Altec's ( clever ) kludge-up in how-to-make a multiple-fixed attenuation LPad ( using resistors ).

Multiple taps on a single Ohmite variable 25W?? wirewound resistor are implemented.

Click the image to open in full size.

Here's a thread ( over at AK ) that details the N800E ( using resistors )..

Worth noting is that the posted schematic is incomplete ( in the posted schematic the HF section wasn't referenced to ground ).

Still, it's good info if one uses it carefully.

The exposed N800E will look something like this;

Click the image to open in full size.

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File Type: jpg N800D_schema.jpg (60.5 KB, 51 views)

Last edited by EarlK; 8th December 2018 at 12:16 AM.
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Old 8th December 2018, 12:35 AM   #23
GM is offline GM  United States
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The original 800D [among others] had an auto-former and that's the correct diagram AFAIK, but I can't find any pre LTV docs on-line, so not surprised that this apparently was yet another example of their extreme cost cutting demands that ultimately destroyed them.

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Old 8th December 2018, 01:10 AM   #24
Xoc1 is offline Xoc1  United Kingdom
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I have a pair of Tannoy Monitor Golds with autotransformers in the crossovers.
The Tannoys have 5 taps
The Tannoys have a single 50 ohm resistor connected to the autotransformer which is switched in the opposing direction to the tweeter.
When the HF is in the highest position the 50 R is disconnected.
I understand what the following parts of the HF circuit do but I am unclear on how the 50R effects the circuit
Copy of schematic attached, the only difference from what I have is the LF inductor is nearer to 3mH.
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Old 8th December 2018, 01:35 AM   #25
EarlK is offline EarlK  Canada
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Quote:
Originally Posted by Xoc1 View Post
I have a pair of Tannoy Monitor Golds with autotransformers in the crossovers.
The Tannoys have 5 taps
The Tannoys have a single 50 ohm resistor connected to the autotransformer which is switched in the opposing direction to the tweeter.
When the HF is in the highest position the 50 R is disconnected.
I understand what the following parts of the HF circuit do but I am unclear on how the 50R effects the circuit
Copy of schematic attached, the only difference from what I have is the LF inductor is nearer to 3mH.
When switched in, the 50 ohm resistor lowers the circuit resistance as seen by the 6.8uF cap.

It doesn't matter if it's placed in front or behind the autoformer > the 50R resistor still lowers the circuit impedance.

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