I´m designing a passive 600 Ohm constant K filter ( High-pass T filter).
I usually use typical balanced line drivers (such as THAT 1646 line driver) and receivers for interfacing my designs with other circuits but I would like this filter to be 100% passive.
So, I would like to use input and output transformers to interface my filter with my audio mixer aux sends.  This will be my first transformer based project so my knowledge on this field is quite scarce. Maybe they´re not even necessary?
Checking my mixer specs the Aux send is 150Ohm impedance and the line input is 10KOhm.

So, the transformers main primary/secondary impedance ideal characteristics should be:

Input transformer: 150 Ohm primary - 600 Ohm secondary
Output transformer: 600 Ohm primary - 10 KOhm secondary

I would like to know this is correct and if other important characteristics are needed in order to select an appropiate one for each stage (input and output).
« Last Edit: March 31, 2018, 01:22:05 PM by LazyTurtle »


ruffrecords

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #1 on: March 31, 2018, 04:05:48 PM »
You constant K filter works best if the source impedance is 600 ohms and the load is 600 ohms.

For the source you could simply pad out the 150ohm source by adding 450/2 ohms in each of the hot and cold inputs.

Since you are feeding it into a 10K line input, the simplest way to load it with 600 ohms is to place a 600 ohm resistor across the output. You might wish to increase it a little so it and the 10K in parallel equal 600 ohms but it is probably not necessary.

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'

mjrippe

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #2 on: April 01, 2018, 11:38:19 AM »
Since you are feeding it into a 10K line input, the simplest way to load it with 600 ohms is to place a 600 ohm resistor across the output. You might wish to increase it a little so it and the 10K in parallel equal 600 ohms but it is probably not necessary.

10k || 600R = 566R

10k || 620R =583.8R

620R is a standard value and brings it a bit closer, but either one will be "close enough for rock & roll". 

abbey road d enfer

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #3 on: April 01, 2018, 11:51:02 AM »
So, I would like to use input and output transformers to interface my filter with my audio mixer aux sends.  . Maybe they´re not even necessary?
Probably not, unless you want galavanic isolation


Quote
Checking my mixer specs the Aux send is 150Ohm impedance
It does not mean it is capable of driving satisfactorily a 150 ohms load.

 
Quote
Input transformer: 150 Ohm primary - 600 Ohm secondary 
  In addition to the fact the insert send would have difficulties driving such a low load, that would elevate the level by 6dB, which may not be desirable.


 
Quote
Output transformer: 600 Ohm primary - 10 KOhm secondary 
  That would elevate the level by another 12dB.

If you really want xfmrs, use a 600:600 at the input of the filter, with additional series resistors at the secondary to adjust to 600 ohms, and a 10k:10k at the output, with a 620r resistor across the primary.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
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Re: Line input & output transformers for 600 Ohm passive filter
« Reply #4 on: April 02, 2018, 09:59:23 AM »
Why are you designing a constant K filter when there are much better options out there that dont use  the image method, instead they use network synthesis, such as the Butterworth, Chebyshev, Bessel, etc...?

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #5 on: April 03, 2018, 01:52:13 AM »
Probably not, unless you want galavanic isolation

I will firstly try the transformerless design and see if it works.
I really don´t need galvanic isolation for any special reason right now, and it will cost more expensive.

It does not mean it is capable of driving satisfactorily a 150 ohms load.
Absolutely agree. In fact, the ideal would be to use a very high impedance connected to the Aux send...


In addition to the fact the insert send would have difficulties driving such a low load, that would elevate the level by 6dB, which may not be desirable.
 That would elevate the level by another 12dB.
If you really want xfmrs, use a 600:600 at the input of the filter, with additional series resistors at the secondary to adjust to 600 ohms, and a 10k:10k at the output, with a 620r resistor across the primary.

Yes, I wouldn´t want to add any extra dBs to the input signal so the way to go (in case I decide to use transformers) is the configuration you have told me.

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #6 on: April 03, 2018, 01:54:24 AM »
Why are you designing a constant K filter when there are much better options out there that dont use  the image method, instead they use network synthesis, such as the Butterworth, Chebyshev, Bessel, etc...?
Well, it´s just because I want to bring some specific sonic print to my set. And just stuff around with this type of filter...

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #7 on: April 03, 2018, 02:00:06 AM »
Thank you all for your answers!  I will hopefully start this project soon and will report how it is going.

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #8 on: January 08, 2019, 11:34:51 AM »
Probably not, unless you want galavanic isolation

 It does not mean it is capable of driving satisfactorily a 150 ohms load.

   In addition to the fact the insert send would have difficulties driving such a low load, that would elevate the level by 6dB, which may not be desirable.


   That would elevate the level by another 12dB.

If you really want xfmrs, use a 600:600 at the input of the filter, with additional series resistors at the secondary to adjust to 600 ohms, and a 10k:10k at the output, with a 620r resistor across the primary.

Hi, just to confirm, shouldn´t the 600:600 transformer be used at the output and the 10k:10k as the input?

ruffrecords

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #9 on: January 09, 2019, 07:04:47 AM »
Hi, just to confirm, shouldn´t the 600:600 transformer be used at the output and the 10k:10k as the input?

No, the 600:600 should be at the input because the filter wants to see a driving impedance of 600 ohms. The output wants a load of 600 ohms which is made up of a terminating resistor in parallel with the whatever it is feeding (assumed to be a 10K input impedance). This is why the output transformer should be 10K:10K

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: Line input & output transformers for 600 Ohm passive filter
« Reply #10 on: January 10, 2019, 11:32:14 AM »
No, the 600:600 should be at the input because the filter wants to see a driving impedance of 600 ohms. The output wants a load of 600 ohms which is made up of a terminating resistor in parallel with the whatever it is feeding (assumed to be a 10K input impedance). This is why the output transformer should be 10K:10K

Cheers

Ian

Hi Ian,

But, wouldn't using a 10k:10k at the input using a 620ohm resistor in parallel in the secondary do the work with an output transformer using a 600:600?

This way we keep a high input impedance and low output impedance

For sure I'm missing something here...

Could you please explain?

ruffrecords

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #11 on: January 10, 2019, 02:40:43 PM »
Hi Ian,

But, wouldn't using a 10k:10k at the input using a 620ohm resistor in parallel in the secondary do the work with an output transformer using a 600:600?

This way we keep a high input impedance and low output impedance

For sure I'm missing something here...

Could you please explain?

Unfortunately not because the 620 ohm is reflected to the primary so the input impedance still looks like 620 ohms.

Remember, transformers do what it says on the tin. They transform voltages, currents and impedances. You stick 620 ohms on the secondary of a 1:1 transformer and looked at from the primary it will be 620 ohms.

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: Line input & output transformers for 600 Ohm passive filter
« Reply #12 on: January 11, 2019, 01:40:27 AM »
Unfortunately not because the 620 ohm is reflected to the primary so the input impedance still looks like 620 ohms.

Remember, transformers do what it says on the tin. They transform voltages, currents and impedances. You stick 620 ohms on the secondary of a 1:1 transformer and looked at from the primary it will be 620 ohms.

Cheers

Ian

Dear Ian,

Thank you very much for your explanation.
Ok, so then using a 10k:10k at the output will make no sense neither as the output impedance seen as the secondary will be 620ohm, is this correct?
Maybe using two 600:600 Ohm transformers would be a better solution, right?

Thanks,

Julian

ruffrecords

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #13 on: January 11, 2019, 03:20:01 AM »
Dear Ian,

Thank you very much for your explanation.
Ok, so then using a 10k:10k at the output will make no sense neither as the output impedance seen as the secondary will be 620ohm, is this correct?
Maybe using two 600:600 Ohm transformers would be a better solution, right?

Thanks,

Julian
Except at the output you want to load the output 620 ohms as lightly as possible so the filter output always has the right load. The problem with using a 600:600 transformer here is that its inductance will be lower. Inductance defines the low frequency response of a transformer. If the transformer response is 3dB down at 5Hz for example that means  the reactance of its primary winding inductance equals 600 ohms at 5Hz. Even though this reactance will be 4 times higher at 20Hz (2400 ohms) it still represents a significant additional load and will upset the performance of the K filter. However, the reactance of a 10K:10K transformer at 20Hz should still be about 10K ohms.

So, to amplify what I said earlier, transformers do what they say on the tin, but within limits.

To add to what others have already said, if you use a 600:600 transformer at the input, the filter output is balanced and floating so you don't really need a transformer at all, just a 620 ohm resistor.

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'

CJ

Re: Line input & output transformers for 600 Ohm passive filter
« Reply #14 on: January 11, 2019, 07:53:15 PM »
have you looked at the passive eq by New York Dave?  lots of info on that at this forum,
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