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The BA-3 as preamp build guide
The BA-3 as preamp build guide
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Old 27th July 2014, 07:25 PM   #21
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The BA-3 as preamp build guide
"across" , pretty important part of the puzzle
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Old 27th July 2014, 07:29 PM   #22
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Now have both channels at 55ma across R10...still no offset across R12. The circuit is not responding to P2 at all.
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Old 27th July 2014, 07:41 PM   #23
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The BA-3 as preamp build guide
offset is not same as voltage

so , you're looking for voltages at some nodes (ref. to gnd) or voltages across some parts ......... but offset is ( by consensus) usually voltage at output , ref to gnd

gimme voltages at both Jfet drains , ref to gnd , same as voltages at both JFet sources ...... P3 in mid position
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Last edited by Zen Mod; 27th July 2014 at 07:44 PM.
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Old 27th July 2014, 07:54 PM   #24
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Channel 1: Q2 drain to ground is 23.8V, Q1 drain to ground is -21.6

Channel 2: Q2 drain to ground is 23.8V, Q1 drain to ground is -21.6

The exact same?
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Old 27th July 2014, 07:56 PM   #25
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The BA-3 as preamp build guide
sources ?
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Old 27th July 2014, 08:08 PM   #26
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Channel 1: Q2 source to ground is 60.1V, Q1 source to ground is -68.8V

Channel 2: Q2 source to ground is 61.4V, Q1 source to ground is -68.0V

Offset on channel 1 at the RCA output is bouncing around 0 - 20 mV

Offset on channel 2 at the RCA output is bouncing around 0 - 20 mV
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Old 27th July 2014, 08:22 PM   #27
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60V ?????

something's very fishy there !

you didn't mixed PSU rails ?
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Old 27th July 2014, 08:23 PM   #28
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Starting over measuring offset in volts at output
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Old 27th July 2014, 08:25 PM   #29
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take a break , proceed tomorrow

or , maybe it's just me - I can't follow and find any logic , if trusting in #26
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Old 27th July 2014, 08:47 PM   #30
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Im thinking you had it in #23. I was looking to measure offset in the wrong place, increased the bias without decreasing offset, and may have zapped my jfets. Now measuring 0 at the source.
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