Hi Group,
Doing an output stage with rather limited anode voltage (+120V), I run two cathode followers in differential/push-pull mode coupled to each side of output transformer - see attached .jpg
There's always a resonance bump where coupling capacitor meets transformer primary inductance, which can be tamed by adding series resistance-with-capacitor-in-parallel, raising output impedance in sub-low frequency range.
In order to get this sorted in the best way my intuition tells me to get rid of the coupling capacitor. I really do like to minimize parts in signal path.
Both ends of output transformer sees approximately +32VDC (+/-10%, depending on tube) so there is a net DC voltage difference of a couple of volts at max. - but this gets evened out when omitting the coupling capacitor (by the rather low winding resistance of the transformer, some 30 Ohms).
Measures fine. Both frequency response (gets rid of a 6dB bump at 11Hz) and MOL/50Hz (1% @ +18dBu both with and without coupling capacitor)
The questions are:
Am I getting this wrong - I can't get to wrap my head around implications for DC working conditions in CF stage?
Any other potential problems that I should consider?
Jakob E.
Doing an output stage with rather limited anode voltage (+120V), I run two cathode followers in differential/push-pull mode coupled to each side of output transformer - see attached .jpg
There's always a resonance bump where coupling capacitor meets transformer primary inductance, which can be tamed by adding series resistance-with-capacitor-in-parallel, raising output impedance in sub-low frequency range.
In order to get this sorted in the best way my intuition tells me to get rid of the coupling capacitor. I really do like to minimize parts in signal path.
Both ends of output transformer sees approximately +32VDC (+/-10%, depending on tube) so there is a net DC voltage difference of a couple of volts at max. - but this gets evened out when omitting the coupling capacitor (by the rather low winding resistance of the transformer, some 30 Ohms).
Measures fine. Both frequency response (gets rid of a 6dB bump at 11Hz) and MOL/50Hz (1% @ +18dBu both with and without coupling capacitor)
The questions are:
Am I getting this wrong - I can't get to wrap my head around implications for DC working conditions in CF stage?
Any other potential problems that I should consider?
Jakob E.