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發表於 2020-6-13 21:07:15
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Time flies, I have been using the U1 mini over 1 1/2 year. Everything is fine and improving upon each firmware update. The mini is sensitive to accessories, eg., power cables and footings. It's fun to play with.
Few days ago, Firmware V13 is released. I try it without delay. Leedh Processing Volume Control is newly added.
After a few trials on the new settings, I realize that Leedh Processing is effective in my system. The whole range is more clean and transparent.
I set my preamp to unity gain to suit Leedh Processing. There is info found on internet about unity gain which is very helpful to me. I would like to share it here:
With test equipment:
Disconnect the power amp from the output of the preamp, you don't need it for this adjustment.
Using a True RMS digital voltmeter (an AC meter that is accurate at frequencies other than just 50 or 60 Hz, the standard line voltage frequencies), you would feed a signal from a sine wave audio generator into a line input on the C34V, connected with a Y-cord so the meter can read the input voltage to the preamp. The input voltage from the generator is not critical-- say about 0.5 to 1 volt RMS at 400 Hz to 1 KHz. Just note what it is.
Once you've set the input voltage, disconnect the meter from the Y-cord and connect it to one of the preamp main outputs. Adjust the volume control (with all tone/loudness controls at the neutral detents or otherwise switched out of the circuit, same for the compander or any other signal path modifiers) until the output voltage equals the input-- 0.5 volt = 0.5 v, 1 volt = 1 volt, etc. Mentally note the exact position of the volume control pointer or mark it with a tiny piece of a post-it note or somesuch.
Without test equipment (takes a bit more effort):
You will need the power amp for this, or more specifically, its meters. Your MC7270 has input level controls. Turn them both the whole way down.
Connect an FM tuner directly to the power amp. (You don't need an antenna).
Disable the tuner's muting and tune between stations so you have pink noise playing out of the speakers when you raise the level controls on the 7270. Set the level controls so the meters read around 0.5 to 1 watt depending on how sensitive your speakers are (It doesn't need to be extremely loud, you just need something that gets the meter needles at least a third to half of the way up.)
Switch off the power amp, don't move its level controls. Connect it back to the main outs on the C34V. Connect the tuner (also without changing anything on the tuner) to a line input on the C34. Switch on the C34, switch on the power amp. Select the (LISTEN) input you have the tuner connected to. Advance the C34's volume control until the meters on the power amp read exactly the same as they did with the tuner connected directly to the power amp. This is the unity gain position.
Note or mark the volume control position as in the previous procedure.
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