something with LM4702 and Power FET

[SY]

I have on hand Cinemag, Jensen, Ampeg, and Peerless-Altec input transformers. Magnequests have also passed through here. All were in the 2 ounce range, and all worked exceptionally well.

 

[troystg]

I think he might be confused as to "low level input" transformers and "output load matching" transformers..

Major weight differences between the two.. But different applications also.

 

[FastEddy]

Steve_Eddy: " ... A line level input transformer that weighs 5 pounds isn't an input transformer but someone using large power transformers and calling them "input transformers. ... The combined weight of input and output transformers for two channels wouldn't even weigh a pound! ..."

I refer the gentleman to the answers I gave some moments ago ...

And this: " ... It is very close to Wiliamson schematic. Ulta Linear, push-pull, 70 Watts. Tubes KT88 for output, 6H6 Driver, 12AX7 for phase splitter and preamp. All transformers toroidal and self constructed. ..." http://www.diyaudio.com/forums/attachment.php?s=&postid=251454&stamp=1066390830 ... " ... About transformers: all them (3) are toroidal. Power 16 cm2, output 8cm. Power range on 60watts 20Hz-20kHz without feedback ..." ... and you are welcome to ask igormac how much these transformers weigh ... http://www.diyaudio.com/forums/showthread.php?postid=251489#post251489

These are typical of tube DIY and not the really big, heavy stuff:

http://www.diyaudio.com/forums/attachment.php?s=&postid=276065&stamp=1070553779

http://www.diyaudio.com/forums/attachment.php?s=&postid=276070&stamp=1070553993 ... impedence matching at rear, bigger power transormer in front ...

http://www.diyaudio.com/forums/attachment.php?s=&postid=295307&stamp=1073247929

http://www.diyaudio.com/forums/attachment.php?s=&postid=295357&stamp=1073251632 ... power in the middle, impedence matching left and right ...

http://www.diyaudio.com/forums/attachment.php?s=&postid=303527&stamp=1074176700 ... power torrid in middle, impedence left and right ...

http://www.diyaudio.com/forums/attachment.php?s=&postid=310586&stamp=1075035372 ... dual setup ...

http://www.diyaudio.com/forums/attachment.php?s=&postid=336945&stamp=1077995496 ... power transformer(s) in a seperate box = mostly cause the chassis won't take the weight of all transformers ...

http://www.diyaudio.com/forums/attachment.php?s=&postid=340438&stamp=1078385106 ... big custom torrids for power ... ( http://www.diyaudio.com/forums/attachment.php?s=&postid=340919&stamp=1078428810 )

http://www.diyaudio.com/forums/attachment.php?s=&postid=340599&stamp=1078404960 ... this whole rack weighs more than 100 pounds = 'cause of the transformer weight ...

http://www.diyaudio.com/forums/attachment.php?s=&postid=343361&stamp=1078690585 ... medium input transformers, heavy output transformers and heavy torridal for power ... best guess for total weight ~= 45 pounds

... need I keep going ??

 

[troystg]

I did not see any mention of an "INPUT SIGNAL TRANSFORMER" as significantly heavy in those posts. Admittedly I did not look at all of them.

I still state that I think there is some confusion between input, power and output transformers.

Not criticizing and I hope it is not read that way.

Most (98%) of input transformers are going to be very small and "relatively" light weight.. ~2 ounces..

Power and speaker output impedance matching transformers will be significantly heavier. >2 pounds.

 

[SY]

... need I keep going ??

Nope, no need, you've already convinced me that you don't know what an input transformer is.

Here's a datasheet for a very commonly used one:

http://www.jensentransformers.com/datashts/11p1.pdf

 

[Steve Eddy]

... need I keep going ??

No, because what you've gone on and on and on with so far has been completely irrelevant.

You said you wanted balanced inputs.

I suggested transformers.

You said they were too heavy.

I said that one of the best input transformers on the planet weighs in at less than 2 ounces.

You claimed that input transformers can weigh upwards of 5 pounds.

You provided a bunch of links, yet I didn't see a single 5 pound input transformer in any of them.

But that's beside the point.

The fact remains that one of the best input transformers on the planet, which will provide you with the balanced inputs that you're saying you're wanting, and provide you with better common-mode rejection than an active balanced input as well as providing you with ground isolation that an active balanced input simply can't, comes in a can about 1 inch in diameter and 1 inch tall and weighs just a couple of ounces.

If you don't want to use them, that's fine. But don't not use them because you somehow believe that input transformers weigh upwards of 5 pounds.

se

 

[Steve Eddy]

Most (98%) of input transformers are going to be very small and "relatively" light weight.. ~2 ounces..

Right. Here's a photo of one "in the nude."

Dimensions (excluding PC pins) are 1" wide, 3/4" tall, and 7/8" deep. Weight is 1.2 ounces. Potted in a MuMetal can, the weight will come up to a couple ounces.

An externally hosted image should be here but it was not working when we last tested it.

se

 

[FastEddy]

Oh, well ... I guess these guys are just wasting their time: http://www.diyaudio.com/forums/attachment.php?s=&postid=340599&stamp=1078404960

Each of those impedence matching input and output transformers weighs more than 2 pounds. ...

... and maybe these guys are wasting their time as well: http://upload.wikimedia.org/wikiped...former02.jpg/616px-PoleMountTransformer02.jpg

 

[Steve Eddy]

Oh, well ... I guess these guys are just wasting their time: http://www.diyaudio.com/forums/attachment.php?s=&postid=340599&stamp=1078404960

Each of those impedence matching input and output transformers weighs more than 2 pounds. ...

There are no input transformers on that amp.

se

 

[FastEddy]

... if you say so ...

 

[troystg]

Oh, well ... I guess these guys are just wasting their time: http://www.diyaudio.com/forums/attachment.php?s=&postid=340599&stamp=1078404960

Each of those impedence matching input and output transformers weighs more than 2 pounds. ...

... and maybe these guys are wasting their time as well: http://upload.wikimedia.org/wikiped...former02.jpg/616px-PoleMountTransformer02.jpg

Please write the builder of those amps and ask them the weight of the input transformer only.

 

[Steve Eddy]

... if you say so ...

I say so. If you believe there is one, point to it. Or better still, let's see the schmatic.

Until then, you've convinced me as well that you don't know what an input transformer is.

se

 

[moamps]

FastEddy:

A picture is worth a thousand words, as they say, so here we go:

These little round thingies (fastened to the chassis with metal cross pieces) in front of the black input tubes are INPUT transformers.

At the back of the amp, you can see 2 toroid power supply transformers and 2 EI chokes.

OUTPUT transformers are these chrome cubes on the topside of the amp in the picture below.

Regards,
Milan

 

[pinkmouse]

And here's another. Cute little things, ain't they!

 

[Steve Eddy]

And here's another. Cute little things, ain't they!

They sure are!

What's that thing next to it with the wires coming out?

se

 

[ashok]

Hi Steve (Eddy),
Have you any idea where I can get those small laminations and the bobbin like the one in the picture you posted.
Thanks.
Ashok.

 

[FastEddy]

So as not to confuse the issue(s) to much:

One amp's input transformer can be a pre-amp's output transformer ... same, same if the transformer were located on the amp, it might be called "input", located on the pre-amp it might be called "output".

There are some sizable output transformers on tube pre-amps that connect to the inputs of power amps ... I suppose one could say that these are the "input" matching transformers of the line amp, being used in the pre-amp to match the input of the balanced line(s) and the amp.

It used to be quite common to see tube pre-amps with heavy, good sized output transformers, sometimes as large as the speaker drive output transformers on the downstream line amps ... this used to be common in stage performance equipment where the tube pre-amp(s) might be located at a control center, feeding an umbilical snake the size of your leg, several hundred feet to the line amps in the speaker columns on the stage ... the idea being to match the balanced snake line impedence ... which could get quite high in the resistance and capacitance quotient ... thus reducing cross talk and improving the response curve of the lines. These types of ideas carry over to high end tube systems where the pre-amp(s) may feed quite healthy balanced lines directly into the amps' input tube stage ... over there, on the other side of the listening room.

Bigger impedence matching transformers = broader and better response curves, less succeptability to outside EMF interference, broader matching with a variety of snakes, etc ...

(I used to be licensed in three states to install this stuff = seen 'em, messed with 'em, installed 'em ...)

 

[FastEddy]

Original thread continues ... " Transformers: Very easy to impliment and usually very good sounding ... But the weight penilty is too great a burden ... I would prefer alternates using passive or active parts. ..."

Anyway, too resume: A solid state balanced input suitable for the LM4702 (wieght of this part ~~ 0.1 Oz.) :

 

[SY]

Take a look at the SSM series from Analog Devices; they have that functionality on a single chip. They do not have the galvanic isolation of a good input transformer, but they have excellent balance and CMRR.

 

[Steve Eddy]

Take a look at the SSM series from Analog Devices; they have that functionality on a single chip. They do not have the galvanic isolation of a good input transformer, but they have excellent balance and CMRR.

It's my understanding that those excellent CMRR figures are had by shorting the inputs together and feeding it from a single source impedance, thereby assuring that there's no imbalance of the source impedance which can significantly degrade the CMRR performance of active balanced inputs.

In the realworld, source imbalances due to the resistance tolerance of buildout resistors and even manufacturing tolerances of drawing the wire can result in source impedance imbalances sufficient to significantly degrate the CMRR of active balanced inputs.

Some pro gear actually has trimmer resistors and capacitors on their outputs so that the source impedances can be precisely trimmed and be able to achieve something closer to the advertised CMRR.

Good quality input transformers on the other hand have such high common mode input impedances that they're pretty insensitive to source impedance imbalances which is why they can give you excellent CMRR when fed from unbalanced sources.

se