Did I lose HF response...?

I added the circled components trying to get closer to the original Yamaha design... Now it seems my HF response is muted? Can anyone explain why? or if these addition would affect that?

http://i907.photobucket.com/albums/ac273/jwhmca/700MICPRED.jpg

The 47K/1uF (R17/C9) are the components loading the transformer. They don't have an influence on the HF response.
1K/47 pF (R19/C11) form a zobel network, to damp the transformer resonance at high frequencies.
Try if the HF response improves if you remove C11. I don't expect you will notice any difference...
It seems the value of C4  (8,2 nF) is rather high. This might cause HF rolloff or even resonance with the secondary transformer winding.
My first attempt would be to remove this capacitor, and check the result.

I suspect the reason you lost HF is due to the way your pad is arranged, the instrument input is constantly loaded with 1350 ohms, which is way too low for most instruments.
What's more, in the mic positions, the xfmr input sees too high an output impedance from the pad.

You have TWO Zobel networks on the xfmr's secondary...but I bet none is correct. Anyway, one is enough; must be adjusted under test (unless the xfmr's manufacturer has very precise info).
The input cap (C10-10uF) is not needed. If you connect directly the secondary to the non-inverting imput of the opamp, you'll have better performance. YoR18 is not needed; just adds noise.

Thank you for the thoughts...

Can you offer any alternatives to the mic pad resistor values? I copied them from the original input matrix... maybe I got it wrong? How "low" do you think the instrument input should be?

jwhmca said:

Thank you for the thoughts...

Can you offer any alternatives to the mic pad resistor values?

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I believe the steps are 10dB...? It's almost impossible to design a 10dB pad for a xfmr-equipped mic pre. There is always a compromise of too low input Z and/or too high source Z seen by the iron. Detrimental to frequency response, distortion and noise. I reckon the pad should be 20dB minimum.

I copied them from the original input matrix...

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Mic preamps have never been Yam's forte...

  How "low" do you think the instrument input should be?

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The instrument input should be minimum 100k ohms driving a 200R, which would imply about 55dB attenuation in this configuration. It is not practical to do a DI input that way.

Is that why I see the other micpres with the instrument on the opamp side of the input transformer?