ZEN question inputImpedance Trimpot etc - diyAudio
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Old 3rd April 2003, 12:24 PM   #1
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Location: Germany, Cologne
Default ZEN question inputImpedance Trimpot etc

Hi everybody,

i have already used the searchfunction but however i didnt find any usable information.
So here are my questions:

What about the inputimpedance of the ZEN? Should it be 4k75 or 47k5 ?

What is the trimpot for?
Do i have to adjust the voltage at the drains to be half the operating voltage?

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Old 3rd April 2003, 12:42 PM   #2
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Location: Southern Tier NY
The input impedance on mine is 47k5.

In regards to the bias trim pot, it should be adjusted so that the voltage at the drain of Q1 is Regulated voltage / 2 + 2. On my amp my regulated voltage is 41.2 Volts so I set the bias to achieve a voltage ov 22.5 volts once the amp is warm.

When you look across R0 you will find that the voltage will be very close to 0.66V.

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Old 3rd April 2003, 02:49 PM   #3
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Which Zen? If it's ZV4, then the input resistor is 47K.

The trimpot is used to set the DC operating point of the
output stage. We adjust it for symmetrical clipping if we
have test equipment, and for 1/2 the supply if we only have
a voltmeter.
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Old 3rd April 2003, 03:08 PM   #4
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I mean THE ZEN, the first 10W. There is some confusion, both values 47k5 and 4k75 are mentioned, i think it is a missprint, is it?
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Old 3rd April 2003, 05:03 PM   #5
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The confusion (input imp. of first ZEN) is based on the fact that there is a resistor of 47k5 from input to ground, but input impedance of this circuit is determined by 4k75 reistor in series with gate, as this is an inverting circuit with common source electrode. The input impedance will be varying and wil be a bit lesser than 4k75, ask Nelson for precise value.
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Old 4th April 2003, 02:09 AM   #6
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Location: Houston
Default Is half the the B+ plus 2 volts correct for V4?

Is the V4's proper operating points half the regulated voltage plus 2 volts? Where does the two volts come from?
I am adjusting mine to that because that is what the manual said. Is the 1/2 B+ better to keep the swing in the power supply envelope?

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