Fader + trafo buffer

[Matt Syson]

Reverting to the original sketch, 220 uF as an output cap will give a significant 'bass boost' which can be 'corrected' by the resistor splitting as mentioned or making the capacitor value much larger, at least 1000uF. Having some resistive or preferably a 'zobel' network on the secondary (the output connections) is also helpful to flatten the high frequency response, assuming you want flat!
Getting transformers to 'behave' when you have the possibilities of a few metres or a couple of hundred metres of twin screened wire on it takes a bit of work. Most 'simple' circuits work well enough on a bench but making then predictable, stable and reliable in the real world takes a bit more effort.

 

[JAY X]

Hi Matt! Thanks for your reply!.

I try to make work the single opamp (one section of an NE5532) transformer driver of the attached drawing, driving a 1:1 600:600, sowter 8403 trafo that i had around, and it did not work properly. I got sound, but also a sort of thump/latch up/saturation/oscillation, with half of the waveform disappeared.... But the dual opamp driver version from the lundahl 2811 spec sheet worked fine.

Jay x

 

[abbey road d enfer]

Hi Matt! Thanks for your reply!.

I try to make work the single opamp (one section of an NE5532) transformer driver of the attached drawing, driving a 1:1 600:600, sowter 8403 trafo that i had around, and it did not work properly. I got sound, but also a sort of thump/latch up/saturation/oscillation, with half of the waveform disappeared.... But the dual opamp driver version from the lundahl 2811 spec sheet worked fine.

Jay x

The value of the 45r resistor must be adjusted to the DCR of the xfmr you use. The Sowter probably has a lower DCR than the LL.

 

[JAY X]

Hi!

I know this thread is a bit old, but i don't want to open a new thread for just a new question on the same subject.

I changed my mind, and in order to save parts, I thought to go for a zero impedance driver for the Lundahl LL2811 output transformer wired as 1:1. The 45R resistor is to match the transformer primary winding resistance. I also don't need a fader with 10db gain, just an attenuator, a 10k potentiometer. I also could use this zero impedance configuration as a balanced line driver, instead of using a THAT 1646. ¿what do you think?

 

[abbey road d enfer]

I changed my mind, and in order to save parts, I thought to go for a zero impedance driver for the Lundahl LL2811 output transformer wired as 1:1. The 45R resistor is to match the transformer primary winding resistance. I also don't need a fader with 10db gain, just an attenuator, a 10k potentiometer. I also could use this zero impedance configuration as a balanced line driver, instead of using a THAT 1646. ¿what do you think?

Why do you want to do it differently than the app note?
The way you suggest, the 45r resistor in the bottom stage does not do anything, and the upper one needs to be 90r anyway.
You don't need two coupling capacitors, either. One is enough, make it bigger.
The 47k at the output of the opamps are useless.

 

[JAY X]

Hi Abbey!

Ok!. I understand, it is a bad idea!.
I'll stick to the original driver.

Even as a cheaper balanced line driver, (without the transformer), is it worth? Vs a THAT 1646?

 

[abbey road d enfer]

Even as a cheaper balanced line driver, (without the transformer), is it worth? Vs a THAT 1646?

Bad idea. Negative impedance becomes unstable. No benefit in terms of distortion. CMRR=0.