This design has a strong op amp flavour because since university I consider differential amplifier the only right way to introduce negative feedback. I used filter design procedure described in TI's AN-346. R3 value may require some adjustment to compensate tubes' non-linear frequency response (still uncompensated by NFB). The maximum gain at 1kHz is about 30dB. Trying to get more I get worse response curve due to finite open loop gain.
For testing I use reference forward RIAA network described in Jim Hagerman's paper.
In this schematic input coupling circuit and output buffer (it is definitely required) are omitted.
Here you can see about ±0.3dB of deviation from flat response.
For testing I use reference forward RIAA network described in Jim Hagerman's paper.
In this schematic input coupling circuit and output buffer (it is definitely required) are omitted.
Here you can see about ±0.3dB of deviation from flat response.
It could be argued that a differential amp is the most popular wrong way to introduce negative feedback! The inverting configuration has the advantage that the feedback and the input arrive at the same circuit node, so (unlike the differential amp) no risk of common-mode distortioneasphyx said:
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