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A guide to building the Pass F4 amplifier.
A guide to building the Pass F4 amplifier.
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Old 11th September 2018, 06:23 PM   #1071
albertli is online now albertli  Canada
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yup

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Old 12th September 2018, 03:42 PM   #1072
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A guide to building the Pass F4 amplifier.
To put this in perspective, Fets seem to measure Vgs somewhere in the neighborhood of low 4.x volts. Let's call it 4.20 for argument sake. 4.20v vs 4.17v represents somewhere near 0.7% matching tolerance. Generally, matching within 1% is considered excellent and matching within 10% still works great. I have some memory of Nelson stating that Pass Labs matches devices to within 10% tolerance.
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Old 12th September 2018, 05:51 PM   #1073
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A guide to building the Pass F4 amplifier.
10mV , I believe , was statement
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Old 12th September 2018, 06:04 PM   #1074
Eric is offline Eric  United States
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A guide to building the Pass F4 amplifier.
Ah, I was on the right track with "10"... 10mV is much tighter tolerance than 10% - thanks for the clarification.
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Old 12th September 2018, 06:12 PM   #1075
Zen Mod is offline Zen Mod  Serbia
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A guide to building the Pass F4 amplifier.
don't fret

what's few % between friends

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Old 13th September 2018, 08:44 PM   #1076
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Wood base is done and 18v 400vA trany is in place. Will go on stuffing the boards tomorrow.
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Old 15th September 2018, 05:08 AM   #1077
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All board have been stuffed but found short of 2 p1 5k. Will send order tomorrow.
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Old 15th September 2018, 08:04 PM   #1078
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Have the 5k pots installed and have the boards check without the mosfet connected. I put +/- 22v from the bench supply and have the following numbers.

R3/4 10 ohm
R9 4.7K
R8 22k
P2 at middle of 250 ohm
R23 changed to 15k, for the reason that I don't want the LED too bright.

mA meter series with positive
Board 1). 86.5 mA
Board 2). 86 mA

The voltage at R3/4
Board 1). 73.8mV 74.5mV
Board 2). 73.1mV 74.3mV

240 gate reference to ground
P1 at max 1). 6.49v 2). 6.81v
P1 at min 1). 4.26v 2). 4.94v

9240 gate refence to ground
P1 at max 1). 6.18v 2). 6.60v
P1 at min 1). 4.02 2). 4.45v

Do all the above numbers look right?
Thanks
Albert

Last edited by albertli; 15th September 2018 at 08:07 PM.
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Old 16th September 2018, 04:00 PM   #1079
albertli is online now albertli  Canada
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Quote:
Originally Posted by albertli View Post
Have the 5k pots installed and have the boards check without the mosfet connected. I put +/- 22v from the bench supply and have the following numbers.

R3/4 10 ohm
R9 4.7K
R8 22k
P2 at middle of 250 ohm
R23 changed to 15k, for the reason that I don't want the LED too bright.

mA meter series with positive
Board 1). 86.5 mA
Board 2). 86 mA

The voltage at R3/4
Board 1). 73.8mV 74.5mV
Board 2). 73.1mV 74.3mV

240 gate reference to ground
P1 at max 1). 6.49v 2). 6.81v
P1 at min 1). 4.26v 2). 4.94v

9240 gate refence to ground
P1 at max 1). 6.18v 2). 6.60v
P1 at min 1). 4.02 2). 4.45v

Do all the above numbers look right?
Thanks
Albert
Jim, Choky,
I can't remember what I did for my amp some 10 years ago and can't find the notes for it. I remember I need 8-9v on those gates to operate , is it? What should I check so to up the voltages to target? The total current for the front part should be around 10mA but I only have 8.6mA on each. R3/4 is working fine with around 73mA on each.
Thanks
Albert
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Old 17th September 2018, 01:27 AM   #1080
albertli is online now albertli  Canada
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I check all the pages including the F4 thread for anything talking about adjustment and tuning of the amp. I finally find out I made a big mistake on checking the gate voltages by referencing the ground. I should check across the gate to gate. 😄
I have them firing up and breaking in. I set both channels at 130mv to start and it drifting up to 166 after about 40 minutes. I thought it is normal. MOSFET at 36c and heatsink 30c. See how it goes.
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