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A guide to building the Pass F4 amplifier.
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Old 22nd July 2021, 09:10 PM   #2781
Ben Mah is offline Ben Mah  Canada
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A guide to building the Pass F4 amplifier.
I would think resistance between input positive and ground would be very high, so something is wrong.

I suppose there could be a path to ground through JFET gate to source if shorted or gate to drain if shorted, or through D3 or D4 if they are shorted, or through R2 if shorted.

I don't have a meter like Chip's so I don't know what the readout means. I would set the meter to measure Resistance rather than Continuity to be sure of the measurement.
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Old 22nd July 2021, 09:29 PM   #2782
andynor is offline andynor  Norway
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Brainfart on my part, not unusual. Glad Ben stepped in! I have measured using the beep mode on a Fluke. If I am not mistaken, a beep means low resistance/good continuity. But I am not sure the R shown there is the actual R between the two, so excited to hear what the measurements are in resistance mode.
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Last edited by andynor; 22nd July 2021 at 09:42 PM.
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Old 22nd July 2021, 10:13 PM   #2783
Dennis Hui is offline Dennis Hui  Canada
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A guide to building the Pass F4 amplifier.
Chiptech,

Please confirm those measurements in resistance mode for both channels.

On post #2775
( A guide to building the Pass F4 amplifier. ) you stated the same (negative) values for both,
yet commented they are very different.
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Old 22nd July 2021, 10:17 PM   #2784
andynor is offline andynor  Norway
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Nice, this will lead to a solution I am sure. At least if the resistance mode shows something interesting.

Dennis: in post #2770 Chip posted readings of 7R3 for the left channel input, but prolly not in R mode. Anyways, divergence was around 32R.
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Old 22nd July 2021, 10:25 PM   #2785
Dennis Hui is offline Dennis Hui  Canada
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A guide to building the Pass F4 amplifier.
My mistake.

I would still suggest a re-measurement in resistance mode since it's not clear what a
negative resistance value means.

Anyway, I'll bow out for now.
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Old 22nd July 2021, 11:54 PM   #2786
ZUM911 is offline ZUM911  Australia
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There is something weird with the negative resistance. It indicates that there is current in the circuit. If the amp is off during the measurement there shouldn't be any current flow. Be sure any residual voltage in the supply caps is drained before making the measurements.
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Old Yesterday, 09:42 PM   #2787
Chiptech is offline Chiptech  United States
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A guide to building the Pass F4 amplifier.
Quote:
Originally Posted by thimios View Post
Are you sure that you haven't burn the input rca applying very hot airon for a long time?
I was on the road for past four days.

Today I checked continuity for left/right all RCA connects on input/output and got beeps across the board, including inside/outside of back panel.
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Old Today, 05:18 AM   #2788
Chiptech is offline Chiptech  United States
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A guide to building the Pass F4 amplifier.
I was out of town since Thursday. Today I went back and read thru all the posts since #2725.

And I came up with new measurements for both channels, with power on and with power and signal in from Pre-amp [I've tested the Pre-amp many times and it delivers a signal to the left channel].

Looking at the numbers - the left R5 has a lower value than the right with the signal in on 1.167 vs. 5.727, but not sure what that might indicate?
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Old Today, 10:12 PM   #2789
andynor is offline andynor  Norway
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It indicates less current than through the right channel equivalent resistor. You need help from bigger Boyz, but as far as I can tell it might affect / be caused by what’s happening at the drain of Q2. An obvious and possibly unnescessary question is: sure that R5 is 1k and R22 750R? And is the voltage at the negative input of the PCB the same as at the negative rail of the PSU?

Good luck! Hope the AC is working…

Regards,
Andy
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Old Today, 10:15 PM   #2790
andynor is offline andynor  Norway
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The left chan consistently has about 3 volts less than the right chan, at several measuring points. Strange… not only the R5 measurement is funny…
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