Voltage drop in a power supply
- Thread starter ward
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Help Support GroupDIY Audio Forum:
> 3-4 V ripple floating on a 50V swing isnt a big deal. Not to my ears at least.
It is a 21dB signal-to-buzz ratio. No, it is not horrible, but it is a long way from the 50+dB signal/buzz we try for in un-overloaded operation, and it adds a distinct flavor to the clipping.
(And the way I was counting: 20V peak-peak B+ ripple is "normal" for some small-cap amps, on a 250V peak audio plate swing is 22dB signal/buzz ratio.)
To clarify the effect: try a small push-pull amp (one that you can drive into overload without going deaf) with just 5uFd of main cap in a single rectifier-cap filter. If the driver and preamp supplies are additionally filtered, and the output tubes are fairly well matched, the idle and low-level buzz may be tolerable. But when you do your Neil Young tribute, one of his kill-the-amplifier solos, you get the local power company playing backup, embellishing your loud notes.
And I must say: it could be different in Sweden. In the US, I grew up with so much 60Hz hum/buzz that it is part of the music and my soul. I think that is true for much US-made early rock-n-roll music. 50Hz has a different position on the musical harmony.
Hmmmmm..... and it also depends on loading. If a pentode's load-line hits at or below the knee, swing is limited by supply voltage. But if it hits above the knee for the applied G2 voltage, it is current limited and that current depends on G2 voltage, which may or may not be filtered better than the plate. And that interacts with the wild swings of speaker impedance in the 50Hz-300Hz range.
It is a 21dB signal-to-buzz ratio. No, it is not horrible, but it is a long way from the 50+dB signal/buzz we try for in un-overloaded operation, and it adds a distinct flavor to the clipping.
(And the way I was counting: 20V peak-peak B+ ripple is "normal" for some small-cap amps, on a 250V peak audio plate swing is 22dB signal/buzz ratio.)
To clarify the effect: try a small push-pull amp (one that you can drive into overload without going deaf) with just 5uFd of main cap in a single rectifier-cap filter. If the driver and preamp supplies are additionally filtered, and the output tubes are fairly well matched, the idle and low-level buzz may be tolerable. But when you do your Neil Young tribute, one of his kill-the-amplifier solos, you get the local power company playing backup, embellishing your loud notes.
And I must say: it could be different in Sweden. In the US, I grew up with so much 60Hz hum/buzz that it is part of the music and my soul. I think that is true for much US-made early rock-n-roll music. 50Hz has a different position on the musical harmony.
Hmmmmm..... and it also depends on loading. If a pentode's load-line hits at or below the knee, swing is limited by supply voltage. But if it hits above the knee for the applied G2 voltage, it is current limited and that current depends on G2 voltage, which may or may not be filtered better than the plate. And that interacts with the wild swings of speaker impedance in the 50Hz-300Hz range.
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