Can a series inductor be placed in the power supply of a class A/B amp?

Pass showed such a circuit, with a large shunt cap on either side, to
reduce ripple (hum) in his ZEN amp. But, of course, this is a class A
amp that presents a mostly constant load to the PS.

Will the energy storage/release of the inductor cause problems in
supplying power to a class A/B output stage? Or, is it not worth the
expense and labor to install such devices at this location?

Thanks......

wrote in message


Can a series inductor be placed in the power supply of a class A/B
amp?

It's been done often with tube circuits.

Pass showed such a circuit, with a large shunt cap on either side, to
reduce ripple (hum) in his ZEN amp. But, of course, this is a class A
amp that presents a mostly constant load to the PS.


Will the energy storage/release of the inductor cause problems in
supplying power to a class A/B output stage?

Don't think of it in terms of transients, think of it as a LC low-pass
filter.

I think that the major detractor for inductive filtering in 50-60 Hz power
supplies is the relatively low cost of active regulators and the ease of
building output stages with lots of power supply rejection at low
frequencies.

Or, is it not worth the
expense and labor to install such devices at this location?

Power supply inductors typically have to pass large DC currents which make
them more even more costly because you have to take steps to avoid
saturation.

wrote in message


Can a series inductor be placed in the power supply of a class A/B
amp?

It's been done often with tube circuits.

Pass showed such a circuit, with a large shunt cap on either side, to
reduce ripple (hum) in his ZEN amp. But, of course, this is a class A
amp that presents a mostly constant load to the PS.


Will the energy storage/release of the inductor cause problems in
supplying power to a class A/B output stage?

Don't think of it in terms of transients, think of it as a LC low-pass
filter.

I think that the major detractor for inductive filtering in 50-60 Hz power
supplies is the relatively low cost of active regulators and the ease of
building output stages with lots of power supply rejection at low
frequencies.

Or, is it not worth the
expense and labor to install such devices at this location?

Power supply inductors typically have to pass large DC currents which make
them more even more costly because you have to take steps to avoid
saturation.

"Arny Krueger" wrote in message ...
wrote in message


Or, is it not worth the
expense and labor to install such devices at this location?

Power supply inductors typically have to pass large DC currents which make
them more even more costly because you have to take steps to avoid
saturation.

More to the point, again: look at it as part of a low-pass filter.
You DON'T want the transients to get through because most amplifiers
have poorer power supply noise rejection at higher frequencies.

Now, considering that an inductor, along with the power supply
caps, are part of a 2nd order low-pass filter, we can start to
see what sort of values we need. Let's assume we want a 10 Hz
cutoff frequency, so that it's down 40 dB or so by the time we
reach the 100/120 Hz ripple frequency.

For a tube amplifier, the power supply is loaded with the effective
plate load, maybe 5000 ohms, say. A maximally flat 2nd order low-
pass filter for a 5000 ohm load at 10 Hz requires an 110 henry (that's
110,000 millihenry) inductor and about a 2.5 uF capacitor. Well,
110,000 millihenry inductors are a little hard to come by, so we get
a compromise of maybe 100 uF and 10-20 henries.

FOr a solid state amplifier, the load is essentially that of the
speaker, so assume 8 ohms. A maximally flat 10 Hz filter would require
about 1500 uF and about 200 mH.

Now, that solid state amplifier might draw 5 amps from the power supply.
Go out and price 200 mH inductors that can pass 5 amps without saturation.
(hint: it's going to take a LOT of copper and a LOT of iron: second
hint: aluminum and silicon are a LOT cheaper).

"Arny Krueger" wrote in message ...
wrote in message


Or, is it not worth the
expense and labor to install such devices at this location?

Power supply inductors typically have to pass large DC currents which make
them more even more costly because you have to take steps to avoid
saturation.

More to the point, again: look at it as part of a low-pass filter.
You DON'T want the transients to get through because most amplifiers
have poorer power supply noise rejection at higher frequencies.

Now, considering that an inductor, along with the power supply
caps, are part of a 2nd order low-pass filter, we can start to
see what sort of values we need. Let's assume we want a 10 Hz
cutoff frequency, so that it's down 40 dB or so by the time we
reach the 100/120 Hz ripple frequency.

For a tube amplifier, the power supply is loaded with the effective
plate load, maybe 5000 ohms, say. A maximally flat 2nd order low-
pass filter for a 5000 ohm load at 10 Hz requires an 110 henry (that's
110,000 millihenry) inductor and about a 2.5 uF capacitor. Well,
110,000 millihenry inductors are a little hard to come by, so we get
a compromise of maybe 100 uF and 10-20 henries.

FOr a solid state amplifier, the load is essentially that of the
speaker, so assume 8 ohms. A maximally flat 10 Hz filter would require
about 1500 uF and about 200 mH.

Now, that solid state amplifier might draw 5 amps from the power supply.
Go out and price 200 mH inductors that can pass 5 amps without saturation.
(hint: it's going to take a LOT of copper and a LOT of iron: second
hint: aluminum and silicon are a LOT cheaper).