Hi all. I recently bought a Tisbury Audio passive pre to use with my Quad 306. I'm really liking it so far, but I have a quick question if anyone can help me out.
The specs on the website state that the output impedance at full volume is 0 ohms. The unit has fixed attenuations switches on the bottom to reduce the signal by a fixed -10 dB or -20 dB.
So, my question is, if I set the switches to either -10 dB or -20dB, at full volume will the output impedance still be 0 ohms? Or is the output impedance affected by the fixed attenuation?
Thanks!
The specs on the website state that the output impedance at full volume is 0 ohms. The unit has fixed attenuations switches on the bottom to reduce the signal by a fixed -10 dB or -20 dB.
So, my question is, if I set the switches to either -10 dB or -20dB, at full volume will the output impedance still be 0 ohms? Or is the output impedance affected by the fixed attenuation?
Thanks!
No, the output impedance not be 0Ω when attenuators are switched in, & yes, the output impedance will be affected by the fixed attenuation.
In fact even without the attenuator switched in, at full volume the output impedance of the passive Tisbury passive preamp will not be zero, but will be the output impedance of the connected source. At useable settings other than maximum or minimum volume, the output impedance will be significantly higher than the output impedance of the connected source.
Reading their FAQ, Tisbury seem to think they have an exemption from the laws of physics; they don't!
In fact even without the attenuator switched in, at full volume the output impedance of the passive Tisbury passive preamp will not be zero, but will be the output impedance of the connected source. At useable settings other than maximum or minimum volume, the output impedance will be significantly higher than the output impedance of the connected source.
Reading their FAQ, Tisbury seem to think they have an exemption from the laws of physics; they don't!
Ah, ok thanks for explaining that. Does flicking the attenuation switches increase or decrease the output impedance?
Fortunately, I don't have any issues with it, just curious about how it works. I was just wondering because the input impedance of my power amp is fairly low (10k), so I was guessing I'd probably want the impedance as low as possible on the passive pre.
Fortunately, I don't have any issues with it, just curious about how it works. I was just wondering because the input impedance of my power amp is fairly low (10k), so I was guessing I'd probably want the impedance as low as possible on the passive pre.
Anything under around 2k is fine for Rout, but they do not specify the maximum Rout for the
worst case attenuator setting (which is likely to be the -10dB setting). You could ask them.
worst case attenuator setting (which is likely to be the -10dB setting). You could ask them.
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None of this matters. The power amplifier doesn't draw significant current from the source. The source impedance is an irrelevance other than its effect on interconnecting cable length.
Increasing source impedance can lower the turnover frequency of any RF trap on the input of the power amp. I don't know what (if any) kind of trap it has.
They seem to teach marketing majors how to do this. They don't teach physics majors though. I feel cheated.
They seem to teach marketing majors how to do this. They don't teach physics majors though. I feel cheated.
True. The Quad 306 has an input impedance resistor of 22K shunted by 330pF, so any source impedance above say 5K is going to cut into the audio band.