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how to measure unknown step up transformer?

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how to measure unknown step up transformer?

Postby vinylips » 05 Aug 2010 16:28

hello ! can anyone tell me how to measure an unknown step up transformer ? hunted one down for cheap . it is made for phono use only thing is I do not know its ratio .Im going to plug it in my denon 301 and take a listen but just wanted to know if there is a simple way to measure its output to conclude its ratio. from what I understand the 301 has .4mv.so If I measured 4.0 at the output I could conclude its a 1:10 ratio . read somewhere that measuring with a multi meter can damage the transformer . figure I would ask before I do anything other than listening. thankx
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Postby sreten » 05 Aug 2010 16:49

Hi,

Measuring small AC voltages with a multimeter is a tricky business.

The easiest method I'd say is fit a dual pot to the output (100K).
Then adjust the pot so there is no difference in apparent gain in
circuit or out of circuit.

Them measure the resistance ratio of the two sides of the pot,
it will be very near the actual gain, e.g. if its 10.5 then the
ratio will certainly be 10:1 or 20dB gain, ideal for the Denon.


8) /Sreten.
sreten
 

Postby analogous » 05 Aug 2010 17:36

Easiest way I know.

You need a multimeter.

Download a free tone generator.

Set the tone generator to, say, 1 kHz.

Use the multimeter to set signal level of the line out on your PC. You need a 3.5mm connector. Use the volume control of the PC to set the output to, say, 100mV.

If you worry that there might be DC on the output, use a small film capacitor. A standard type 0.1uF poly cap costs something like 10 cents.

You can connect it to the secondary just as well as the primary. if you measure 10mV on the primary, it means 1:10, or 20db.
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Postby 1200y3 » 05 Aug 2010 18:29

You will also need a load resistor on the secondary to get the reflected impedance on the primary. Without a secondary load the transformer and MC generator will not function.
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Postby Blue Angel » 05 Aug 2010 18:53

Hi

FWIW. I have a few of these devices (SUT's). On one, there's a warning to the effect 'never to use a conventional 'continuity tester' to measure as magnetisation of the transformer core will result. The SUT is Japanese and has a switch for balanced operation and the cores are 9 9's pure silver wire. I have often wondered about the 'continuity tester' bit. Could they mean a digital multimeter?

ba
"If you don't like my principles, I have others" - Groucho Marx
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Postby Cornelius900 » 05 Aug 2010 19:06

a continuity tester (an analog or digital multimeter on range ohms or diode test or continuity (beep trough)) applies DC power to the circuit which you want to test. The meter then checks if there is a current flow through the tested circuit.

As the current flows in one direction, the current magnetises the transformer core. (a little bit).

Cheers,

Kees
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Postby vinylips » 05 Aug 2010 19:23

analogous wrote:Easiest way I know.

You need a multimeter.

Download a free tone generator.

Set the tone generator to, say, 1 kHz.

Use the multimeter to set signal level of the line out on your PC. You need a 3.5mm connector. Use the volume control of the PC to set the output to, say, 100mV.

If you worry that there might be DC on the output, use a small film capacitor. A standard type 0.1uF poly cap costs something like 10 cents.

You can connect it to the secondary just as well as the primary. if you measure 10mV on the primary, it means 1:10, or 20db.


thankx for the tip.so, if you dont mind, let me run through this. I generate a test tone of 1k
plug a mini cable into my lap top (headphone out jack) crank volume up to 100mV (reading on my multi meter) then plug that test tone output into the step ups input .from what I understand, the output of the step up should be plugged into its source input.then measure the voltage at the step ups input . ?? hope this makes sense.again a big thankx.this method seems to be simplest to me as I have cables, a multi meter and even a mixing board with test tones on it .
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Postby sreten » 05 Aug 2010 21:23

Blue Angel wrote:Hi

FWIW. I have a few of these devices (SUT's). On one, there's a warning to the effect 'never to use a conventional 'continuity tester' to measure as magnetisation of the transformer core will result. The SUT is Japanese and has a switch for balanced operation and the cores are 9 9's pure silver wire. I have often wondered about the 'continuity tester' bit. Could they mean a digital multimeter?

ba


Hi,

A "continuity" tester needs enough voltage to turn on silicon diodes or
diode junctions of transistors which is around 0.6 to 0.7 volts. On cheap
multimeters this used to be simply the voltage produces by a penlight
cell battery, 1.0 to 1.3 Volts (with a thumbwheel zero adjustment).
1V dc is a lot for small low impedance low signal transformers.
(The actual current determined by the meters Kohm/Volt rating.)

FWIW whilst the windings may have been silver, the cores certainly
were not, high quality iron of some sort, the type of windings are
not relevant to the dc magnetisation of the core.

I'd say a digital multimeter will be far safer than an analogue
"conventional continuity tester" as it can and presumably does
incorporate "foldback current limiting" for continuity functions.
(Which means it only uses higher voltages when it has to, most
of the time it will use tiny voltages for the tiny currents it needs.)

8) / Sreten.
sreten
 

Postby Blue Angel » 05 Aug 2010 21:49

sreten wrote:
Blue Angel wrote:Hi

FWIW. I have a few of these devices (SUT's). On one, there's a warning to the effect 'never to use a conventional 'continuity tester' to measure as magnetisation of the transformer core will result. The SUT is Japanese and has a switch for balanced operation and the cores are 9 9's pure silver wire. I have often wondered about the 'continuity tester' bit. Could they mean a digital multimeter?

ba


Hi,

A "continuity" tester needs enough voltage to turn on silicon diodes or
diode junctions of transistors which is around 0.6 to 0.7 volts. On cheap
multimeters this used to be simply the voltage produces by a penlight
cell battery, 1.0 to 1.3 Volts (with a thumbwheel zero adjustment).
1V dc is a lot for small low impedance low signal transformers.
(The actual current determined by the meters Kohm/Volt rating.)

FWIW whilst the windings may have been silver, the cores certainly
were not, high quality iron of some sort, the type of windings are
not relevant to the dc magnetisation of the core.

I'd say a digital multimeter will be far safer than an analogue
"conventional continuity tester" as it can and presumably does
incorporate "foldback current limiting" for continuity functions.
(Which means it only uses higher voltages when it has to, most
of the time it will use tiny voltages for the tiny currents it needs.)

8) / Sreten.


Thanks, Kees C and sreten

I have a few digital multimeters. The two I use regularly (a Fluke 111 and an Isotech IDM-73) are both powered with 9V batteries. Because of the warning, I have never been tempted to measure this particular SUT which is a Nagatron Z-Coupler Ag 9200.

Regards

ba
"If you don't like my principles, I have others" - Groucho Marx
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Postby sreten » 05 Aug 2010 21:52

vinylips wrote:
analogous wrote:Easiest way I know.

You need a multimeter.

Download a free tone generator.

Set the tone generator to, say, 1 kHz.

Use the multimeter to set signal level of the line out on your PC. You need a 3.5mm connector. Use the volume control of the PC to set the output to, say, 100mV.

If you worry that there might be DC on the output, use a small film capacitor. A standard type 0.1uF poly cap costs something like 10 cents.

You can connect it to the secondary just as well as the primary. if you measure 10mV on the primary, it means 1:10, or 20db.


thankx for the tip.so, if you dont mind, let me run through this. I generate a test tone of 1k
plug a mini cable into my lap top (headphone out jack) crank volume up to 100mV (reading on my multi meter) then plug that test tone output into the step ups input .from what I understand, the output of the step up should be plugged into its source input.then measure the voltage at the step ups input . ?? hope this makes sense.again a big thankx.this method seems to be simplest to me as I have cables, a multi meter and even a mixing board with test tones on it .


Hi,

As I understand it VI (vinyl inches per second ?) is saying :

Get a 100mV reading from a 1KHz AC output of your laptop.

Connect that to the output side of your SUT.

Measure the voltage on the input side, 10mV = 20dB, 5mV = 26dB etc.
(Rechecking the output side of course.)

8) /Sreten.

FWIW there will be a capacitor already on nearly all laptop outputs.
sreten
 

Postby analogous » 05 Aug 2010 22:02

vinylips wrote:thankx for the tip.so, if you dont mind, let me run through this. I generate a test tone of 1k
plug a mini cable into my lap top (headphone out jack) crank volume up to 100mV (reading on my multi meter) then plug that test tone output into the step ups input .from what I understand, the output of the step up should be plugged into its source input.then measure the voltage at the step ups input . ?? hope this makes sense.again a big thankx.this method seems to be simplest to me as I have cables, a multi meter and even a mixing board with test tones on it .


The headphone jack is what supply the 100mV, or, perhaps better, 10mV. It is the source. Connect this to the transformer primary. Or use the mixing board instead.

Connect the multimeter to the secondary.

It does not matter what frequency you use, within reason. 20Hz risks saturating the core. 1kHz is standard in audio. It is a good frequency.

And just in case, check for DC on the output of the PC or mixing board. You do not want to fry the transformer. Capacitors block DC.
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Postby sreten » 06 Aug 2010 01:29

Hi,

Connecting to or measuring the primary or secondary does not matter.
Around 10mV 1KHz AC to the primary to measure the secondary.
Around 100mV 1KHz AC to the secondary to measure the primary.

8) /Sreten.
sreten
 

Postby vinylips » 06 Aug 2010 19:41

analogous wrote:
vinylips wrote:thankx for the tip.so, if you dont mind, let me run through this. I generate a test tone of 1k
plug a mini cable into my lap top (headphone out jack) crank volume up to 100mV (reading on my multi meter) then plug that test tone output into the step ups input .from what I understand, the output of the step up should be plugged into its source input.then measure the voltage at the step ups input . ?? hope this makes sense.again a big thankx.this method seems to be simplest to me as I have cables, a multi meter and even a mixing board with test tones on it .


The headphone jack is what supply the 100mV, or, perhaps better, 10mV. It is the source. Connect this to the transformer primary. Or use the mixing board instead.

Connect the multimeter to the secondary.

It does not matter what frequency you use, within reason. 20Hz risks saturating the core. 1kHz is standard in audio. It is a good frequency.

And just in case, check for DC on the output of the PC or mixing board. You do not want to fry the transformer. Capacitors block DC.

OK, here is what I got . I think it is to be a 1:15 step up . got the headphone out of the pc at .1v (200v scale), then at the secondary output I got 1.5 v(200 volt scale) .hopefully this is correct . I did listen to it and it does work.not a huge difference but a slight difference. just sounds a little different than the mc portion of the 640p .now from what I understand, a 1:15 step up would put me in the 200 ohms area of loading .still want more.so 1:10 is the way to go for the denon .just took a chance on the unkown. can always send it back .thankx again for everyones help and tips .hope I got it right !
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Postby Cornelius900 » 06 Aug 2010 20:01

I think you can get a more accurate result when you use the 2V range/scale.

That 0.1V can easily be 0.05V or 0.09V (or 0.145V)

Cheers,

Kees
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Postby vinylips » 06 Aug 2010 20:12

Cornelius900 wrote:I think you can get a more accurate result when you use the 2V range/scale.

That 0.1V can easily be 0.05V or 0.09V (or 0.145V)

Cheers,

Kees

VERY GOOD POINT .figures I dont have a tester of that sort . perhaps a trip to the store .thankx
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