measuring and treating audio transformers

[5v333]

Found it!

Cheers!

http://vintagewindings.com/products/TransDesign1.html

 

[abbey road d enfer]

attached is a pic of how i measure without any termination except for the impedance set resistor. this is wrong?!

Definitely...

  you mean i should measure right off the generator output?

As I wrote, the frequency response of a xfmr depends on the source and termination impedance. If you want a significant measurement, it must be done in the same conditions as the ones you're going to use it.

i forgot to check which way the phase curve went of course when i did the sweeping!!!!

If you used REW, you could save all the measurements.

 

[5v333]

to place the transformer in test, in a similar enviorment as the actual circuit (thats what the resistor was trying to mimic ) is nothing new for me but not measuring across the pri directly was new stuff for me...

maybe we should put it together with the rest of the circuit infront of it. attached is the equivalent of the eq when filters are flat.

if i inject a signal at the very begining of the first transformer via a 100R resistor. were should i put my probes when measuring the phasesplitter?

 

[trobbins]

Is their no secondary winding termination resistance (ie. only a valve grid) ?

What is your probe loading resistance and capacitance?

What is your scope bandwidth for X and Y channels, and are you using OEM probes and are they compensated?

OP wouldn't be using  REW I'd expect  for these particular tests, and would have to have a good soundcard and probes  in a good setup to look at output HF response.

 

[5v333]

not really, my plan was to find a good RC termination for resonance free response, good squarewave looks and symmetry. but... if im hooking up my scope in the wrong way i guess im with out a clue over what actually should be sitting on the secondary windings.

my scope is a fluke pm3084. one probe is unknown the other is a testec something. both have x1/x10 and screws for calibrating a flat square.

 

[abbey road d enfer]

to place the transformer in test, in a similar enviorment as the actual circuit (thats what the resistor was trying to mimic ) is nothing new for me but not measuring across the pri directly was new stuff for me...

maybe we should put it together with the rest of the circuit infront of it. attached is the equivalent of the eq when filters are flat.

if i inject a signal at the very begining of the first transformer via a 100R resistor. were should i put my probes when measuring the phasesplitter?

You're interested in evaluating the response from the source to the secondary; that's how it will perform in practice.  So the input probe should be at the output of the generator and the output probe at the grid(s). In fact the output probe should be a differential one across the whole secondary. Note that the impedance of the probing circuit will alter the response somewhat.
Now if you want to evaluete just the phase-splitter transformer individually, you should drive it with the equivalent impedance of the preceding circuit (about 380 ohms), and again measure the input signal at the generator, not at the primary.
Measuring a transformer from primary to secondary (i.e. putting the input probe at the primary) gives an indication of what the tranformer is capable of when driven by a zero-impedance.

 

[abbey road d enfer]

OP wouldn't be using  REW I'd expect  for these particular tests, and would have to have a good soundcard and probes  in a good setup to look at output HF response.

Using REW limits the frequency range to 24kHz, so not useful for evaluationg ultrasonic resonances anyway. In addition, the typical low-ish (10-20kohm//several hundred pF) impedance of soundcards disqualifies them.

 

[5v333]

thanks for not giving up on me!!

well i havnt got a diff probe so i guess i have to do with regular probes for now..

so if i wanna evaluate the response of the phasesplitter when in actual circuit, do i measure right at the priamary and secondary then?

 

[abbey road d enfer]

thanks for not giving up on me!!

well i havnt got a diff probe so i guess i have to do with regular probes for now..

Ther are no such things as differential probes; it's a shortcut to describing the use of standard probes  connected to two inputs that are set in difference mode.

so if i wanna evaluate the response of the phasesplitter when in actual circuit, do i measure right at the priamary and secondary then?

No, you measure the input at the generator, before the 380r resistor.

 

[5v333]

there is no 380R in the actual circuit..!

im talking about measure the phasesplitter together with the 3 resistor pad and the input transformer in front of all that. fed by a 150Z  signal.

 

[abbey road d enfer]

there is no 380R in the actual circuit..!

im talking about measure the phasesplitter together with the 3 resistor pad and the input transformer in front of all that. fed by a 150Z  signal.

If you do that, you measure both teh input xfmr and the phase-splitter xfmr.
If you want to measure the phase-splitter xfmr on its own, you must drive it either from teh pad or from an equivalent 380r resistor. The pad you have drawn ahs an equivalent source impedance of ca. 380 ohms.

 

[5v333]

and how to go about if i would like to check the phasesplitter - in circuit.

ive been trying to have ref probe just after the input transformer and the other probe just after the phasesplitter. phase response looks more sane this way.
signal injected att the input transformer primary via 100R.

 

[abbey road d enfer]

ive been trying to have ref probe just after the input transformer and the other probe just after the phasesplitter. phase response looks more sane this way.

This is correct, you will evaluate the phase-splitter xfmr, with its working source impedance ant its working load.
Caution: it's true as long as the probe load is negligible.
In order to verify that, you would need to check that loading the secondary with an additional probe (or the equivalent impedance) does not significantly alters the measurement. I would think your probes, in conjunction with the scope, show an impedance of 1Meg//100pF, and on the x10 position 10Meg//10pF. You may make the measurement in the x10 position. There should be enough signal amplitude to produce readable results.

 

[5v333]

hurray!!!

yeah i mostly do theese kind of checks in x10 mode.

this is great. its like i got a new tool today!

its fairly basic actually but still i cant find about theese stuff on the internet... i encurige you or someone else to write some small text about measuring and working with transformers when designing circuits.


so for a last question while we are on the subject!

attached is another simplified circuit.

if we want to evaluate the OT in the circuit, should we hang a ref probe at the phasesplitter sec and the other probe on the output of the OT?

have a great evening!

 

[abbey road d enfer]

its fairly basic actually but still i cant find about theese stuff on the internet... i encurige you or someone else to write some small text about measuring and working with transformers when designing circuits.

Metrology and measurement techniques is a vast subject; I'm too old to start a book. 
You should be able to find reference books; googling "electronic measurement book" gives several hits that look adequate. After that you need 3 or 4 decades of expertise. ;D

if we want to evaluate the OT in the circuit, should we hang a ref probe at the phasesplitter sec and the other probe on the output of the OT?

Yes; that would be correct in describing the actual operation; however the tube characteristics are an important parameter here.
I would suggest driving the primary via a resistor equivalent to 2x the plate resistance of the tube. The measurement would be more "intrinsic" so to speak.

 

[CJ]

all you need is ears, 

 

[ruffrecords]

Using REW limits the frequency range to 24kHz, so not useful for evaluationg ultrasonic resonances anyway. In addition, the typical low-ish (10-20kohm//several hundred pF) impedance of soundcards disqualifies them.

The latest version of REW  supports sample rates up to 192KHz.

Cheers

Ian

 

[trobbins]

The latest version of REW  supports sample rates up to 192KHz.

Yes it works well using an asio driver with my emu 0404, which provides a 1 megohm input to allow 10:1 and 100:1 scope probes for simple amplifier testing with a 96kHz bandwidth.

 

[5v333]

all you need is ears, 

i think you´re on to something!

 

[5v333]

i thought, all you need was cheese!