Loading Jensen Transformer Properly

[jrasia]

I purchased a Jensen 1:1 line input and 1:1 mic input transformer to evaluate in my Soundcraft K3 console.
These are 'optional' transformers for this console series, though Jensen may not be the original brand sold by Soundcraft at the time.  Nevertheless these transformers are the proper turn ratio and impedance for this circuit.

Can someone clarify if and how to properly 'load' these particular Jensen transformers in the K3 circuit?  I believe the damping network Soundcraft suggests in their schematics is not properly loading to Jensen's recommendation for optimal frequency response etc.  My schematic understanding is not strong enough.

The Jensen Line input is JT-11p-1 - Jensen schematic is in the link below
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-11p-1.pdf

Soundcraft suggest installing a 3.3K for R1 and 470pf and 3300pf cap  for C1/C2-
Jensen wants to see at least 10k?

The Jensen Mic input is JT-MB-CA - Jensen schematic is in the link below
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-mb-ca.pdf

Soundcraft suggest installing a 1.8K for R6 and 4700pf cap for C5
Jensen wants to see a 3K load?

Sorry for the noob question.  Just want to make sure I'm getting an accurate frequency response from these transformers

Much appreciated!!!

Jason

 

[DaveP]

All you need to know is on the first page of this old thread.

https://groupdiy.com/index.php?topic=32441.0

Completely curing transformer ringing, cuts the top end.

Probably the best advice is that of PRR, just to load it with the correct nominal resistor to damp the oscillation if you must

The components in your circuit are called Zobel networks, they are custom made for individual transformers so you need to change these components when swapping transformers.

Jensen make some of the best transformers in the business so you may not need any correction at all, especially for 1:1 ratios.

DaveP

 

[Bo Deadly]

The resistor capacitor filter is called a "zobel network" and is used to dampen peaking at the upper edge of the frequency response. RL is the load. So the circuit is probably fine for those transformers. The line input almost certainly is. If it's not, you're talking about maybe a little bump or dip at 20kHz that isn't going to really matter. At least it's not likely that you will be able to calculate what the exact zobel network values need to be for critical dampening (meaning so that it rolls off without any bump or dip like shown in the Jensen datasheet). If I where doing this I would just drop it in and do a hires spectral plot to see if there's anything really funny going on at the high-end. The mic input is probably ok (R7 is the load resistor which is very close to the load in the Jensen schematic) but it is more sensitive to impedance matching. Specifically the transistors have an optimal source impedance for which they will yield the lowest noise. How to figure out exactly what that is and how well the transformer matches those parameters requires studying datasheets and reasoning about transistors and base currents and such things that I am not knowledgeable enough in to comment on.

 

[PRR]

> I believe....

Doesn't matter what you believe. MEASURE.

 

[JohnRoberts]

> I believe....

Doesn't matter what you believe. MEASURE.

+1


Measure twice cut once....

JR