The primary impedance is (say) 5k only when the secondary is loaded. That load is impedance-transformed to the primary and causes the impedance that the amp sees.
Take away the secondary load and the impedance the amp sees shoots up. If the amp is still driven, Ohm's Law says that the same anode current in a much higher impedance will generate a much higher voltage.
Jan
Take away the secondary load and the impedance the amp sees shoots up. If the amp is still driven, Ohm's Law says that the same anode current in a much higher impedance will generate a much higher voltage.
Jan
you can connect coupling caps of proper size to the plates of your pp amp, and on to another set of OPT whose secondary you connect to the speakers...leaving your original OPT to act like a choke....bass is better this way it seems since inductance is not influenced by dc currents your second OPT...
of course you added complexity to your build, but hey, this is DIY, we are allowed to get crazy as long as we do not electrocute ourselves..
of course you added complexity to your build, but hey, this is DIY, we are allowed to get crazy as long as we do not electrocute ourselves..
impedance matching is based on a resistor load of fixed ohms to reflect that resistance to the primary based on the square of the turns ratio....
but real world speakers are anything but a resistor, so no need to worry a lot...
That's an interesting idea Tony. So you basically use separate transformers for the DC and AC current paths. You could probably save money by replacing the 'DC xformer' by a pair of chokes, no?
Jan
There is ideally no net DC in the "DC transformer", even when it is the only transformer.
The choke-coupled-cap-transformer trick works good in single-ended (no DC cancellation). While that is rare in large audio amps, pre-war radio modulators could be the big exception. Even though the audio side was usually push-pull, the RF amplifier side never was. So the RF amp's DC current was socking the core. There are ways to do it SE but the reduced efficiency was hard to bear.
The choke-coupled-cap-transformer trick works good in single-ended (no DC cancellation). While that is rare in large audio amps, pre-war radio modulators could be the big exception. Even though the audio side was usually push-pull, the RF amplifier side never was. So the RF amp's DC current was socking the core. There are ways to do it SE but the reduced efficiency was hard to bear.
Tony's suggestion in post #25 introduces additional coupling networks and resonances, so this may not be easy for an amp with global feedback. For example, at low frequency the effective output resistance (output stage Ra and reflected load RL) interacts with a modified shunt L from the original OPT and the added new OPT. And the new coupling cap resonates with the new OPT primary inductance, making for a large value cap (especially if phase shift in the audio band is a concern) with similarly large voltage rating. These are the typical issues faced by anode choke/parafeed amp afficiando's.
The difference between a power transformer and an output transformer is that the former is fed by a voltage source, whereas the latter is fed by a current source).
Disconnect the secondary, and the transformer behaves as a high-value inductor. So you're comparing an inductor connected to a current source, with one connected to a voltage source. The former results in large voltages, the latter results in small currents.
Disconnect the secondary, and the transformer behaves as a high-value inductor. So you're comparing an inductor connected to a current source, with one connected to a voltage source. The former results in large voltages, the latter results in small currents.