Anyone heard of autoformers?

[bowtie427ss]

So if it had many terminals, it could still be an inductor, that changes values, depending on how it's wired?

Best example i can give in a pinch it the Altec N-1285 network. It is a two-way network with selectable 500, 800, or 1200 hz crossover point.

Rather that using several multiple inductors, it uses laminated core inductors which are tapped at various points to provide the values necessary for the desired crossover points.

When i find a good pic i'll post it.

Obviously, a re-capped network. But, note the original inductors, and the number of leads connecting the large one to the original circuit board.

 

[JBL GUY]

Confusing

So if it had many terminals, it could still be an inductor, that changes values, depending on how it's wired?

That sounds neat.

Yes to your question.

All transformers are inductors, but not all inductors are transformers.

In simple terms, an inductor is just a coil of wire. Yes, for those that want to be very precise, even a straight piece of wire has some inductance.


See the first picture showing the magnetic field of the inductor. In simple terms, it is this magnetic field that has varying characteristics depending on the inductor and the frequency of the signal, that allows an inductor to help a speaker crossover manage the audio signals as they are sent to the various drivers.


See second picture.
A transformer is made up of two coils of wire in proximity of each other.
The magnetic field of the first coil is intercepted by the second coil and a voltage or signal is generated.

This is why it is recommended that the inductors in a speaker crossover are mounted at right angles to each other. It will help reduce any unwanted signal present in one inductor from appearing in the other inductor and being sent to the wrong speaker driver.


See third picture.
An autotransformer is a single coil of wire with multiple connections.
Each connection will have a specific characteristic, depending on the design of the autotransformer.

 

[bowtie427ss]

All transformers are inductors, but not all inductors are transformers.

Have actually seen a semi-local tube guy use the primary of a transformer as a smoothing choke/inductor in a power supply.

 

[twiiii]

There are transformer-less amps out there that are designed to drive low impedances with out breaking a sweat. Accuphase comes to mind. Crown reference amps, Threshold, McIntosh 7200, 7100, . Mac builds tube amps that will drive 2 ohms, 2301 for instance. If you like the older classic sound how about a pair of 3500's from Audio Classics. Bryston makes amps that will drive 2 ohms, so, 4 ohms is a walk in the park. A Mac 501 will meet specs driving a 4 ohm speaker from the 8 ohm tap, that's something other amps can't do. So imagine how well it performs with the 4 ohm tap.
My Old Crown P2sa would drive 2 ohms all day and meet specs. I would stay away from external autoformers unless you are using them to drive 70.7 or 100 volt distribution lines where the bandpass has been filtered first. If the company doesn't give band width, insertion loss, distortion frequency response figures walk away.

 

[Guest105]

Has anybody heard, or had experience with autoformers made by AntiCables? They are supposed to allow you to double or triple the your speaker's ohms, thus making it easier on your amplifier and reducing distortion. They're not cheap, so I wanted to see if other Akers had experience with them and if their design is based on sound engineering principles. Thanks in advance.

Perhaps we should proceed from the crossover detour and try to address the OP's questions. Will the AntiCable product reduce current demand on the OP's amplifier? Will it reduce distortion? Are these claims based on solid engineering principles?

What are the potential advantages and disadvantages of the use of autotransformers for the stated purpose? Anyone else used them?

I tried to address these questions in Post #8, but my technical knowledge is (obviously) limited.

 

[mhardy6647]

It's the transformerish-looking thing in the top lefthand corner of the picture. I had asked what it was in the past and someone said it was an autotransformer. I had always wondered how they could make a six-driver design work with such a simple crossover, but that thing must surely be an essential part of it.

looks like a tapped choke to me.

 

[Adda]

~bowtie427ss

Ah yes I see, it saves a lot of space compared to having separate inductors.

~JBL GUY

I know one and two, from crossovers and my ribbons have transformers, round wire inner windings, and flatwire outer windings, with metal layers as core.

The third one, looks similar to what you find i power supplies, different tabs could be used for different voltages, so the power supply can be used in different countries, just by moving a jumper.

 

[JBL GUY]

~bowtie427ss

Ah yes I see, it saves a lot of space compared to having separate inductors.

~JBL GUY

I know one and two, from crossovers and my ribbons have transformers, round wire inner windings, and flatwire outer windings, with metal layers as core.

The third one, looks similar to what you find i power supplies, different tabs could be used for different voltages, so the power supply can be used in different countries, just by moving a jumper.

Yes as part of the transformer as in my second picture.

The third one would be the configuration used in the devices in question, autoformers made by AntiCables.

I to would like to hear from from those that have used these.

I looked for some additional data, such as maximum power capability or square wave response, but did not find any information in my rather quick look.

 

[Adda]

I to would like to hear from from those that have used these.

I looked for some additional data, such as maximum power capability or square wave response, but did not find any information in my rather quick look.

Hmm, do you think they could be used with a long DIY ribbon? that might be interesting.

 

[Gang-Twanger]

Perhaps we should proceed from the crossover detour and try to address the OP's questions. Will the AntiCable product reduce current demand on the OP's amplifier? Will it reduce distortion? Are these claims based on solid engineering principles?

What are the potential advantages and disadvantages of the use of autotransformers for the stated purpose? Anyone else used them?

I tried to address these questions in Post #8, but my technical knowledge is (obviously) limited.

Thank you... I was going to suggest the same thing. My apologies to the OP for the detour. Didnt intend for it to spin off so far off course like thar. I had been totally-confused about an autoformer/autotransformer's use in a speaker system (as opposed to a choke), which is what we're talking about here.

Ya' know...I'm gonna' have to read through these posts a few hundred times. I'm more-confused than when I got here.

 

[gagelle]

Hello Adda,
My system runs very well and has the best sound of any system I've ever owned. I just wanted to know about the autoformers because they're supposedly in the circuit of some of the Macintosh models. I would never use the device without first contacting ModWright. (the designer of my amplifier.) I suspect that Mr. ModWright would give me the same advice that you did, so I thank you for your warning.

Transformers should not be in the signal path unless there is no other option, like with ESLs or ribbons, some amplifier designs and passive preamps.

If the amp can't handle the speakers, I think it would be better to find an amp or speaker so the system fits together.

 

[gagelle]

I thank everyone for their advice. I never expected responses from so many Akers with advanced knowledge of audio engineering, which goes to prove that AK is the best audio site.

 

[gagelle]

Than you for the links, mhardy. As I suspected, the engineering is more complex than I thought.

An autoformer is essentially a transformer with a physical (electrical) connection between the "primary" and "secondary" windings. Unlike a transformer, it provides no electrical isolation... which is not really an important factor except for power supply applications.

Please don't assume that autoformers or transformers in an audio circuit are a bad idea a priori. It's just not true! The important thing is quality and approriateness of the design... and quality in transformers (or autoformers) does not come cheap.

I have for the past few years used a passive autoformer volume control in lieu of an active preamp in my 'real' hifi - it sounds very, very good.

If you want to get an idea about quality "iron" of all , peruse Dave Slagle's Mike LeFevre's, John Atwood, or Jack Elliano's businesses' web sites, for a good starting point! These guys know their iron

http://www.intactaudio.com/
http://www.magnequest.com/home.htm
http://www.one-electron.com/
http://www.electra-print.com/index.php