letterbeacon

Testing frequency response of a transformer
« on: May 28, 2019, 06:00:02 AM »
I have a few 600:600 input transformers and I'd like to check their frequency response.

Is it as simple as connecting my interface with the terminals on the primary and secondary of the transformer and running something like REW through them?


5v333

Re: Testing frequency response of a transformer
« Reply #1 on: May 28, 2019, 11:46:13 AM »
I would suggest
Hook up your transformers with the intended circuit and load.
Have a look on scope while injecting the circuit with a signal generator.
What does a squarewave at 5khz look like?
Is it free from overshooting and ringing? Then do a sweep.
See if the response is flat and at what point you have -3db.
Also if the output is balanced, check symmetry between the ends of the secondary.

If something looks strange, try to treat it with resistive loads and/or capacative loads like zobel nets.
And then measure freq response once again.

Hope that helps.

Re: Testing frequency response of a transformer
« Reply #2 on: May 28, 2019, 01:10:28 PM »

Hook up your transformers with the intended circuit and load.


But what if the transformer is used to balance the output of a signal gen?  In that case we don't know the intended circuit and load.
« Last Edit: May 28, 2019, 03:26:12 PM by warpie »

john12ax7

Re: Testing frequency response of a transformer
« Reply #3 on: May 28, 2019, 02:45:40 PM »
For a basic test just using REW in a loop is fine.  In addition it's also a good idea to hook up a few different loads to see how it will behave in the real world.  For example 10k, 600 ohm,  and also some capacitance to simulate a long cable run.

5v333

Re: Testing frequency response of a transformer
« Reply #4 on: May 28, 2019, 05:01:44 PM »
But what if the transformer is used to balance the output of a signal gen?  In that case we don't know the intended circuit and load.

well you just have to find out what the generators output Z is then and what load the transformer will be hooked up with!

5v333

Re: Testing frequency response of a transformer
« Reply #5 on: May 28, 2019, 05:06:01 PM »
the bandwidth between an ext source and the transfomer coupled input could be around 100khz-1mhz.

its been some time i used REW now but isnt it restricted to 44.1 and 48khz FR?
you wil only see what happends up to nykvist (22.05khz and 24khz)

ruffrecords

Re: Testing frequency response of a transformer
« Reply #6 on: May 28, 2019, 05:46:52 PM »
But what if the transformer is used to balance the output of a signal gen?  In that case we don't know the intended circuit and load.

The OP was asking about testing input transformers in which case you presumably do know the load.

If you want to test an output transformer then you need to know the driving source as a minimum.

In both cases you also need some idea of the likely maximum level the transformer will be expected to handle and then test it at that level.

As a rule, you need to make some choice as to driving and load impedances as well as operating level but using REW to make measurements is very instructive. You can easily see the harmonic dostortion structure as you approach saturation.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Testing frequency response of a transformer
« Reply #7 on: June 02, 2019, 04:42:00 PM »
REW works away fine at 96khz for me , as long as your interface can do 96k  REW can too.

EmRR

Re: Testing frequency response of a transformer
« Reply #8 on: June 02, 2019, 04:52:38 PM »
A set of variable series and shunt resistances to modify input and load Z are useful with unknown transformers, or to determine how far away from nominal is acceptable.  Test with the highest bandwidth available. 

You will probably find not much significant response deviation with 600:600 types, with level handling capabilities and phase response at the edges being more responsible for sonic differences. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

abbey road d enfer

Re: Testing frequency response of a transformer
« Reply #9 on: June 04, 2019, 05:30:22 AM »
But what if the transformer is used to balance the output of a signal gen?  In that case we don't know the intended circuit and load.
Most xfmrs have a response that varies significantly dependant on the source and load impedances; that's why some manufacturers recommend a specific load impedance or provide for a switchable internal termination.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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