Mislead on transformer specs ??

ya, SINEWAVE

Here's a picture of measurements I made. I can't make sense of it.

Hi Mike, I think you need to view the _ratio_ of impedances (turns ratio squared) when matching. The absolute impedances of the windings are much less important at low power levels.

I'm not sure what I can do with that info. I bought it as a 1.5 meg ohm to 100 ohm transformer or 122 to 1 turns ratio. So I'd like to put a 64 ohm set of earbuds on it and see 960,000 ohms. I don't see how that's going to happen. MikeK

So load the sec. with 64 ohms, and measure the pri. impedance.

It may be specifying the impedances of the generator and loads needed to maintain the specified performance, rather than the matched impedance ratio of the transformer (I'm reaching, here).

I'd pop a sine wave onto pins 1 and 3, and measure the amplitude of the wave out on pins 6 & 7, or 4 & 5. Then I'd do it going the other way. That should tell you the turns ratio, independent of any design impedances. An output impedance of 1.5x10^6 ohms seems pretty big -- a

What instrument are you using to measure impedances? Is there a chance that your audio impedance measurements are off?

Yes; 100 ohm 1-3; refer to filament transformer citation standards or protocol. It is extremely reasonable that the "M" stands for "thousands". If you were over-driving the transformer, you would see peak clipping, and if you monitored input current, you would see exponential-like rise near the peak. Best ou could do is drive 50 ohms 1-2 and put secondaries in series for 3K Z.

..at least you did not lose a lot of money on it.

p://i395.photobucket.com/albums/pp37/Qmavam/TransformerData2.jpg

Start with the basics and give us the dc resistances. On your page of figures there just isnt enough info on there to make sense of them.

NT

amdx Inscribed thus:

That could be the audio phasing transformer for a sideband rig.

I measured the DC resistance of the windings, that was enough to convince me that I didn't get the transformer that I wanted.or that the company specified. Pin 1 to 3 = 75 ohms Pin 1 to 2 = 37 ohms Pin 2 to 3 = 37 oihms. Pin 4 to 5 =130 ohms Pin 6 to 7= 130 ohms.

Oddities All measurements at 2 khz, phase shift is near zero Open circuit, 1 volt into Pin 1 and 3----- I get 1 volt out on Pin 6 and 7.

If I put 1.5 meg ohm between pins 6 and 7, looking into Pins 1 and 3, I see

100 ohm load Pin 1 to 3---looking into Pin 6 and 7 = 325 ohms ( 0.38 volts ) ( 1 volt )

Then reversed hookup.

I still don't know what this transformer is supposed to transform, but I do know it is not 1.5 meg ohm to 100 ohm. Feedback appreciated. MikeK

"amdx"

Some makers in the past use the letter " M " for thousand - derived from Roman the number system.

A good rule is to multiply the winding resistance by 10 to estimate the rated load resistance for most audio transformers.

..... Phil

How are you measuring impedances? Describe your method.

If the specs on the transformer mean 1500 ohms at pins 4-5 and 6-7, and you have

I will but you need to pay attention :-)

I copied a circuit that I used years ago to measure transducer impedances. I built this circuit;

I have only recently built the board and I had my own questions about it measuring properly. So, several times through this transformer measuring, I would get an impedance, (say 680 ohms) and just as a check I would put a 680 ohm resistor in as the DUT and verify that the scope had the same amplitudes showing on the scope as the orignal DUT. Also the phase can be checked, the phase was always near zero during these tests. The board probably isn't real important at 2 khz but at 500 khz or 1 Mhz you want to tighten up so parasitics don't interfere. Here's the schematic of the board, it might help in understanding.

If I didn't make this understandable, please let me know where I failed and I will try to make it clear. At this point I have requested an RA from the company I ordered the transformer from. It is not as advertised and I hope they will change there webpage. Thanks, MikeK

I agree "Something's wrong"

From the data you posted, it looks like the windings 1-3 to 6-7 have a 1:1 ratio. I don't usually see Zs and ZL printed on transformers, my guess is that for the correct operation of the transformer, it wants a source impedance of 100 ohms, and load impedances of 1.5 megohms on the two secondaries, i.e., wants very little loading. One way to check is to put a load of 1.5megohm on pins 6-7, and see if the reflected load on the primary is 1.5megohms. Most audio transformers would give you lower impedances because of stray capacitances and insufficient magnetizing inductance. This looks like a chopper transformer, where a rapidly switched DC voltage is connected to the transformer primary. An AC voltage at the switching frequency appears on the two secondaries, it is amplified and synchronously switched again, to provide an amplified DC voltage. I've worked on old chart recorders and DC amps that used such circuits. The transformers tend to be pretty small. The electrostatic shield is consistent with use as a low-level chopper. The frequency range is "off" for audio (300-3000Hz for communication), but would be reasonable for 1khz chopping in order to preserve the square wave for phase detection. Notice the low power levels... 1.33uw! The transformer is probably specially designed with high magnetizing inductance and low capacitance to minimize loading from the primary circuit.

Just a guess.... but it has specs on it that you don't usually see on audio stuff.

Paul G.

"Paul Gormless Git."

Piss off idiot.

This is the same method you posted over on The Radio Board, isn't it?

Have you tried the method of measuring the image impedances of a transformer that was described there?

Measure the impedance at pins 1-3 with pins 6-7 shorted; call this Zis. Measure the impedance at pins 1-3 with pins 6-7 (and all others) open; call this Zio.

Calculate SQRT(Zis*Zio). This is the image impedance at pins 1-3. This will be the impedance to which the transformer will be best matched at pins 1-3.

Do the same thing in the other direction to find the image impedance at pins 6-7 (measure at 6-7 with 1-3 successively shorted and open).

Yes it is. When I saw the spec's for this transformer and series connection of 3 megohms, I thought even with the 1-8khz, + or - 0.2db specification, It might still work decently for a crystal radio. It is not to be.

I have not tried it. Just the DC resistance measurements alone have me convinced this is not a 1.5 meg transformer. I just hope to get a return authorization. If I get any time, it will be Thursday, I will try it then. Thanks. MikeK

Measure the impedance at pins 6-7 with pins 1-3 shorted; call this Zis.

Measure the impedance at pins 6-7 with pins 1-3 open; call this Zio.

Calculate SQRT(Zis*Zio). This is the image impedance at pins 6-7. This will be the impedance to which the transformer will be best matched at pins 6-7.

And as a last test, I put 100 ohms on pins 1-3 and the impedance seen at 6-7 is 330 ohms.

None of it makes sense to me. Anyone see what's going on? Thanks, Mike