Bottlehead Forum
General Category => Technical topics => Topic started by: Mikey on January 19, 2010, 09:12:41 AM
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Forgive me....part of this verbage was stolen from a post over at the SET asylum:
Caucasian Blackplate wrote:
"For a tweeter amp, I believe parallel feed is absolutely the best way to go, especially if have or are planning to have active crossovers. By reducing the value of the parafeed capacitor, you can keep the hum of the DHT from playing through your delicate tweeters. A series feed amp will not allow you to do this. In fact, if you were quite clever, you could size both the coupling cap and parallel feed cap in your 2 stage amp to create a 2nd order high pass crossover... "
What caught my eye was the part about reducing the hum through the tweeters...
Exactly, how is this done?
I can provide system specifics if necessary,
Mike
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The parallel feed cap and the primary of the output transformer create a highpass filter, so any 60hz hum can be well reduced by this filter. The C-R filter between the driver and output tube does not have this effect though.
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As I have pointed out elsewhere, with this arrangement the driver must handle the full range of signals, the output tube gets a 6dB/octave reduction of the low frequencies, and the tweeter gets 12dB/octave. Unless the crossover is quite low (less than 500Hz?), or there is a further filter before the amplifier, the driver will overload long before the output tube is stressed.