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In Reply to: RE: DHT 01a tube preamp posted by mwhouston on February 15, 2025 at 15:20:48
You do need the cable hooked up and the amplifier hooked up.It is the shunt capacitance (in combination with the output impedance of the preamp) that will cause the highs to be attenuated.
The cable has shunt capacitance and the amplifier has shunt capacitance (that is called Miller capacitance). The capacitance from those two add together.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/15/25
Capacitance of my cables is 175pF (0.175nF). Quite low.
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With an output impedance of 330K playing into 175pf the -3db point of the low pass filter will be 2756Hz. The -1db point will be at 1378Hz.That is a massive lose of high frequencies and it is only going to get worse when you add in the Miller capacitance of the first stage of your power amp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/15/25
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Correction, with the 100k resistor in parallel with the 330k ohm resistor the output impedance is 76744 ohms so the -3db point of the low pass filter is 11850Hz. Better but still a lot of high frequencies lost in the audio band.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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