Output line stage transformer for a line stage
« on: January 03, 2021, 03:18:23 AM »
Hello guys I am working on a very low output impedance line stage but would like to add
a transformer to the output to be able to use it also balanced.
So the output impedance will be 80-100R and the load 10K-45K
I had a 1:1 600R line stage transformer from jensen in mind but would like to add more opinions and solutions if
available....
The problem with 600R transformers usually when loaded high is elevated high frequency area on some of the transformers not
a good thing! Any thoughts?

Thanks.


dbelousov

Re: Output line stage transformer for a line stage
« Reply #1 on: January 03, 2021, 06:36:25 AM »
What's wrong with the "classic" quasi-floating balanced output?
Dmitry

abbey road d enfer

Re: Output line stage transformer for a line stage
« Reply #2 on: January 03, 2021, 07:03:36 AM »
Hello guys I am working on a very low output impedance line stage but would like to add
a transformer to the output to be able to use it also balanced.
So the output impedance will be 80-100R and the load 10K-45K
I had a 1:1 600R line stage transformer from jensen in mind but would like to add more opinions and solutions if
available....
The problem with 600R transformers usually when loaded high is elevated high frequency area on some of the transformers not
a good thing! Any thoughts?

Thanks.
Are you driving the primary from a 80-100r source? That is not good for LF response and THD.
You should drive it with near-zero impedance, at least. Better, drive it with a negative-impedance source.
https://www.lundahltransformers.com/wp-content/uploads/datasheets/feedbck.pdf
In particular, driving a transformer from the output of a dedicated line driver (THAT1646, SSM2142, DRV135) is not a very good idea since the output Z is not very small.
HF resonance on a 600:600 Jensen is typically in the Megahertz range. If that worries you, it could be tamed with a simple Zobel circuit at the output, but it's generally deemed unnecessary. One of the reason  is that audio generators and drive circuits do not go that high, so your typical audio bench would completely ignore it.  :)
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: Output line stage transformer for a line stage
« Reply #3 on: January 03, 2021, 09:05:21 AM »
Are you driving the primary from a 80-100r source? That is not good for LF response and THD.
You should drive it with near-zero impedance, at least. Better, drive it with a negative-impedance source.
https://www.lundahltransformers.com/wp-content/uploads/datasheets/feedbck.pdf
In particular, driving a transformer from the output of a dedicated line driver (THAT1646, SSM2142, DRV135) is not a very good idea since the output Z is not very small.
HF resonance on a 600:600 Jensen is typically in the Megahertz range. If that worries you, it could be tamed with a simple Zobel circuit at the output, but it's generally deemed unnecessary. One of the reason  is that audio generators and drive circuits do not go that high, so your typical audio bench would completely ignore it.  :)

If I understand you correct It would be good to use a 600R line stage transformer but ideal would be 0 ohms source. Maybe you know the aprox. primary inductance of the JT- series of jensens?

Re: Output line stage transformer for a line stage
« Reply #4 on: January 03, 2021, 10:51:37 PM »
If I understand you correct It would be good to use a 600R line stage transformer but ideal would be 0 ohms source. Maybe you know the aprox. primary inductance of the JT- series of jensens?

The higher the source resistance, the higher the THD of the transformer which is why abbey suggested using a negative impedance converter to "cancel" out the DC resistance of the transformer's primary and thus reduce distortion.

The primary inductance also forms a hi pass filter with the source resistance, so higher source resistance, higher cut-off frequency, Jensen does not state the primary inductance in their data sheet, however, if it is stated as 600:600 it will definitely work with lower source impedances and higher load impedances. Jensen gives you recommended values for Zobel networks to provide a Bessel response.

If I were to choose, a 10K:10K transformer placed at the input of the recieving equipment is better than a 600:600 output transformer at the output of the emmiting equipment.

Re: Output line stage transformer for a line stage
« Reply #5 on: January 03, 2021, 11:48:10 PM »
The higher the source resistance, the higher the THD of the transformer which is why abbey suggested using a negative impedance converter to "cancel" out the DC resistance of the transformer's primary and thus reduce distortion.

The primary inductance also forms a hi pass filter with the source resistance, so higher source resistance, higher cut-off frequency, Jensen does not state the primary inductance in their data sheet, however, if it is stated as 600:600 it will definitely work with lower source impedances and higher load impedances. Jensen gives you recommended values for Zobel networks to provide a Bessel response.

If I were to choose, a 10K:10K transformer placed at the input of the recieving equipment is better than a 600:600 output transformer at the output of the emmiting equipment.

I understand! Thank you!


 

Related Topics

  Subject / Started by Replies Last post
3 Replies
3170 Views
Last post February 26, 2006, 07:05:38 PM
by PRR
0 Replies
1456 Views
Last post May 30, 2018, 10:40:48 AM
by eternal slang
4 Replies
265 Views
Last post January 04, 2021, 09:53:24 AM
by Space2World
1 Replies
86 Views
Last post January 08, 2021, 10:25:58 PM
by radardoug