Hi Group,
I see some strange behavior in some SSM2141- wonder if some of you can shed light on this.
Link to 2141 data sheet: http://www.analog.com/media/en/technical-documentation/data-sheets/SSM2141.pdf
This circuit (see attached) is a minimalist balanced-to-balanced circuit, picks up a differential signal on input, outputs a servo-balanced replica, gain trimmed by the 2K "p17"
C61-62 are 2u2 polyester (they are here because the 2-3mV DC input offset of the IC annoys the previous stuff) and with the internal 25K resistors in the 2141 (from data sheet above) this suggests a lower Ft of ca 2.9Hz - and all is as expected at +Input, Pin3..
However, across C62, at the inverting input, Pin2, I get a -3dB point at ca. 15Hz, pointing to ca 4K8 Ohms load instead of the expected 25K..??
I have a feeling that the load/cutoff here relates to the absolute "symmetry" of the input differential - it seems to behave best at precisely-ground-symmetric signals, but this should surely not be a requirement for an input like this?
Have I mucked around with transformers for so long that I've finally lost my solid-state realism?
I see some strange behavior in some SSM2141- wonder if some of you can shed light on this.
Link to 2141 data sheet: http://www.analog.com/media/en/technical-documentation/data-sheets/SSM2141.pdf
This circuit (see attached) is a minimalist balanced-to-balanced circuit, picks up a differential signal on input, outputs a servo-balanced replica, gain trimmed by the 2K "p17"
C61-62 are 2u2 polyester (they are here because the 2-3mV DC input offset of the IC annoys the previous stuff) and with the internal 25K resistors in the 2141 (from data sheet above) this suggests a lower Ft of ca 2.9Hz - and all is as expected at +Input, Pin3..
However, across C62, at the inverting input, Pin2, I get a -3dB point at ca. 15Hz, pointing to ca 4K8 Ohms load instead of the expected 25K..??
I have a feeling that the load/cutoff here relates to the absolute "symmetry" of the input differential - it seems to behave best at precisely-ground-symmetric signals, but this should surely not be a requirement for an input like this?
Have I mucked around with transformers for so long that I've finally lost my solid-state realism?