What is the effects of different transformer types...

[Schu]

I have seen a few different transformer types being used as I search for an amplifier... I'd like to know what the effects of using different types of transformers are?

 

some folks claim they specify their own, some folks use toroidal, and so on...

[mike stehr]

Are you asking about different types of output transformers?

[WMcD]

I'm a bit hazy on this.  But.

 

In a tube circuit the output transformer has a gap in the structure of the laminated core.  This makes it less effective but prevents the magnetic core from saturating with magnetic fields. 

 

This arises from the fact that all the d.c. plate current though the tube is going through the primary of the transformer with the a.c. music increasing and decreasing the magnetic field.  Of course the change in the magnetic field creates current in the output windings and we hear music on that end. 

 

So, the power supply is pushing d.c. through the anode to cathode connection of the tube, say 10 mA with no input to the tube. But the input to the tube on the grid, is making the tube act like a "valve" an conduct more or less current in time to the music.  The tube and primary winding is seeing 10 mA with peaks and valleys of the sine wave input (music) driving current between 9 mA and 11 mA.  There is a corresponding change in the magnetic field in the core of the output transformer. 

 

Saturation means that the iron in the core has a top limit on the intensity of the magnetic field and will just stop growing at that level even if the primary windings are increasing current due to the music signal.  So we need the gap to dummy down the effectiveness of the core so it doesn't saturate at say, 10 mA.  It if did, the top half of the sine wave would no longer move up the magnetic field to what it would otherwise be at 11 mA.

 

Aside: I suspect that the autotransformers used by Klipsch do not have a gap.  However, they are fed through a capacitor and so there is no d.c. though them and no saturation from d.c.

 

Toroid transformers don't have that gap and are more efficient in some ways but can saturate more easily.  I think they are not used as output transformers for that reason.

 

OTOH, toroids  are used as power supply transformers where they are handling just a.c. from the mains.  Rectification through diodes really means that the bank of capacitors are fed with just the top of the a.c. wave from the mains (aka pulsating d.c.)   The caps are charged up and the result is pure d.c.  more or less.

 

You could think of this like having a car battery and a charger.  The battery is charged up to 12 volts and then because you drain it with headlights, it sags to 11.5 volts.  Then you connect the charger and battery voltage goes to 12 volts.  So you disconnect the charger.  Eventually the battery voltage sags again and you connect the charger . . on and on.  Here we have the charger input to the battery as a square wave but the output is almost constant voltage with some ripple. 

 

This all means that the effect of the battery / capacitor doesn't know about whether the input comes from a toroid based input or anything else. 

 

WMcD

 

 

 

[Schu]

Does all this have effect on sound quality? Is there a preference for builders/designers?

Ive often heard that much of the "magic" comes from a good transformer... why is that and why would a designer take one type over another? 

[WMcD]

I was hoping that someone who is very conversant would jump in here. 

 

For now I'll say, "It is far too complicated to explain in a short way."  This is my code for "I don't understand it either."  (Stolen from AC Clarke -- but a lot of teachers use this.)

 

Here is a rather involved explanation:

 

http://education.lenardaudio.com/en/14_valve_amps_5.html

 

Contrary to what I thought, it is possible to use a toroid as a tube output transformer.  It must be larger than a laminate type though.  The saturation issue.

 

The article sets out a lot of technical detail about the many difficulties in making a very good transformer which works over a wide range of frequencies.  All seem to get back to cost.  The bigger the better and other improvements come at the cost of complexity of windings.

 

You can look it up yourself but Nelson Pass designed a transistor amp which used them to have no voltage gain but will produce current gain (push current into a speaker load).  The input stage, to amplify voltage, is an autotransformer.  He found the amp sounds like a tube amp and he thought that maybe the magical sound of a tube / transformer amp is in the transformer rather than the tube.  OTOH, he makes transistor amps without transformers (except for the power transformer) which reportedly sound like tube amps perhaps because the type of transistor (field effect transistors). 

 

In another article he mentions that a buyer should judge amplifiers by weight.  He generally doesn't build amps with output transformers and so this means the power supply transformer should be big (and therefore, expensive).

 

WMcD

 

 

 

 

 

 

[derrickdj1]

My simplistic take on all this is that some transformers cost more and may be better built than another.  But, even a less cost on that is operating in it's range and matched with the appropiate amp, should pretty much sound the same as a more expensive transformer.

[mike stehr]

On ‎11‎/‎1‎/‎2016 at 1:07 PM, derrickdj1 said:

But, even a less cost on that is operating in it's range and matched with the appropiate amp, should pretty much sound the same as a more expensive transformer.

That may be true to a point...

 

Here's the rub...winding a excellent output transformer is just as much art as science. Some are wound on machines, and some are hand wound. This reflects the price.

If that is what we are actually conversing about...output transformers with regard to tube amplifiers.

 

How deep is your wallet? What type of output xformers? Single ended? Push-Pull? What type of output tubes for these particular types of output transformers?

You can buy output transformers wound with silver along with exotic cores like cobalt, it just depends how deep your wallet is. Do they sound better than a cheaper output xformer that has the same specifications/wattage/primary impedance? Probably...only one way to find out and I know I can't afford it.

 

The Guy Mike Lafavre from Magnequest. He has all the rights to all the old Peerless audio transformers, along with the paperwork and whatever else necessary to wind them.

He does excellent work. Along with that, and the rights to Peerless iron a customer is going to pay for it.

 

Some may say the Chinese wind lame output transformers. Yet again, this just depends how deep the wallet is. The Chinese can wind excellent OPTs for big money, or you can get one made from recycled car doors and scrap copper...

 

That being mentioned, there is excellent OPTs out there for reasonable prices.

And also some seriously awesome iron out there for big bucks.

 

[Marvel]

"The Guy Mike Lafavre from Magnequest. He has all the rights to all the old Peerless audio transformers, along with the paperwork and whatever else necessary to wind them.

He does excellent work. Along with that, and the rights to Peerless iron a customer is going to pay for it."

 

My Moondog 2A3 amps have Magnequest iron on them.

 

Schu, output transformers are also made with differing primary values to match up with specific output tubes and amplifier topologies, i.e., PP, SET...

 

Bruce

[Schu]

Thanks... I can see that specifications are the primary requirement, but I wondered  why a designer/builder would choose one style over another... and more over, why they would choose one manufacturer over another within a given format.

On top of that, a few builders are specifying there own hand wound over off the shelf units...

[NOSValves]

On 11/3/2016 at 9:35 PM, Marvel said:

"The Guy Mike Lafavre from Magnequest. He has all the rights to all the old Peerless audio transformers, along with the paperwork and whatever else necessary to wind them.

He does excellent work. Along with that, and the rights to Peerless iron a customer is going to pay for it."

 

My Moondog 2A3 amps have Magnequest iron on them.

 

Schu, output transformers are also made with differing primary values to match up with specific output tubes and amplifier topologies, i.e., PP, SET...

 

Bruce

True quality and cheap never go together.  Mike Lafavre from Magnequest  a true Artisan