For some reason the MD-421 - Canford step up - EF183 - started sounding bass heavy.
This may be to bad resistive, capacitive contact cleaning itself.
Or the grid of the EF183 may had been blocked and unblocked it self?, Today and previous day sound started off fine and withing 3 minutes of tube operation bass heaviness suddenly came to play without apparently touching anything.
Trying to compensate for bass a few Pleiades filters were added. (200Hz and higher up to 800Hz) But when the deep bass was cut remaining treble was too high.
So it was decided to remain at the 419mH Canford primary inductance and add a second low cut pole adjusting the coupling capacitor from the EF183 anode to the disco mixer mic input.
22nF made the sound clear as it had been before.
This indicates that 2 different low cut filters need to be used.
Same principle seems to apply to the Grampian ribbon mic. Of course much lower primary inductance will be needed.
Further experiments need to be made including connecting an EMI RS106A which is a 12dB per octave Low Cut and High Cut filter.
This may be to bad resistive, capacitive contact cleaning itself.
Or the grid of the EF183 may had been blocked and unblocked it self?, Today and previous day sound started off fine and withing 3 minutes of tube operation bass heaviness suddenly came to play without apparently touching anything.
Trying to compensate for bass a few Pleiades filters were added. (200Hz and higher up to 800Hz) But when the deep bass was cut remaining treble was too high.
So it was decided to remain at the 419mH Canford primary inductance and add a second low cut pole adjusting the coupling capacitor from the EF183 anode to the disco mixer mic input.
22nF made the sound clear as it had been before.
This indicates that 2 different low cut filters need to be used.
Same principle seems to apply to the Grampian ribbon mic. Of course much lower primary inductance will be needed.
Further experiments need to be made including connecting an EMI RS106A which is a 12dB per octave Low Cut and High Cut filter.
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