Signal transformer question

[sreten]

Hi,

Sticking to the original question and its scope would help far more
than bigging up the 150ohm mic input transformers on a studio mixer.

rgds, /sreten.

 

[Steve Eddy]

Most of my CDP's have output impedances around 1k, so that's what I work with.

My passive pre is a shunt type, with a 100k pot and 10k series resistance. With the primary impedance of 14.7k, reflected from the 367k secondary load, the CDP will see impedances from 10k to 22.8k, satisfying the 1:10 ratio at all times.

Forget it.

It's not just what the CDP will see, but what the CMMI-5C will see driving its primary.

You don't want to feed the CMMI-5C with a 1k source impedance, let alone 11k which would be the best case scenario with your shunt attenuator.

I wouldn't recommend driving the CMMI-5C with more than a few HUNDRED ohms.

So unless you can add an active buffer between the output of your passive pre and the CMMI-5C, I'd find something else to use them for.

se

 

[IG81]

Forget it.

It's not just what the CDP will see, but what the CMMI-5C will see driving its primary.

You don't want to feed the CMMI-5C with a 1k source impedance, let alone 11k which would be the best case scenario with your shunt attenuator.

I wouldn't recommend driving the CMMI-5C with more than a few HUNDRED ohms.

So unless you can add an active buffer between the output of your passive pre and the CMMI-5C, I'd find something else to use them for.

se

I was simply explaining that from the CDP's point of view, everything's just dandy.

But I did not look that what the transfo "wants" to see at it's input correctly. The series resistance in the passive pre should be eliminated and the source's output R and C checked for LF roll-off. R could be diminished to ~220ohm and C augmented enough for a LF -3dB point sub-20Hz. I should check what is the lowest impedance the output op-amp in the source can safely drive and set that as R I suppose, as I will now be shorting the output to ground when volume is fully turned down.

IG