Adding an "EQ" to a micpre

[mkiijam]

If you were going to add a passive EQ filter circuit to a transformer / opamp / transformer micpre design, where would you take the filter IO?

 

[gyraf]

I wouldn't.

You'll need 1) low and predictable source impedance, this is only available after the micpre opamp - and 2) predictable load impedance, so it can't be before the output driving the transformer, finally 3) some gain (usually 20dB) to make up for the loss in the filter

What you need is the input stepup trafo, then mic pre opamp with selectable gains, then the passive filter, then an output stage set to the e.g. 20dB of needed makeupgain and giving low output impedance for driving the output transformer. If you want trim gain, this output stage is also where to implement it

/Jakob E.

 

[mkiijam]

Okay makes sense.

My plan is then just to build both "devices" into one box. I'll make a relay that will send the output of the pre directly into the input of the EQ, much like you would do with patching or an XLR cable or something. The only thing weird in my head is the output transformer of the pre driving the input transformer of the EQ (pultec)

 

[ruffrecords]

Okay makes sense.

My plan is then just to build both "devices" into one box. I'll make a relay that will send the output of the pre directly into the input of the EQ, much like you would do with patching or an XLR cable or something. The only thing weird in my head is the output transformer of the pre driving the input transformer of the EQ (pultec)

The output of the original op am that would have driven the output transformer, now drives the input to the EQ directly - no transformers required. The output of the EQ goes into the new output stage/opamp which drives the original output transformer.

Cheers

Ian