Now have both channels at 55ma across R10...still no offset across R12. The circuit is not responding to P2 at all.
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
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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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?
Channel 2: Q2 drain to ground is 23.8V, Q1 drain to ground is -21.6
The exact same?
take a break , proceed tomorrow
or , maybe it's just me - I can't follow and find any logic , if trusting in #26
or , maybe it's just me - I can't follow and find any logic , if trusting in #26
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.
Zeroed offset with both meters connected. When I removed the meter from R10 offset jumped to 4 volts?
cool of
proceed tomorrow , post schematic with voltages at important nodes
be sure that DMM isn't with probes in current measuring position
proceed tomorrow , post schematic with voltages at important nodes
be sure that DMM isn't with probes in current measuring position
Alrighty. After a few days off, and new batteries for the meters here's what I have:
Right channel:
Q1: D to Ground = 21.6V, S to Ground = 68.1 mV
Q2: D to Ground = -21.2V, S to Ground = -60.1mV
R10: Current = 55 mA, voltage = .50
Offset at the output is bouncing around between 0 and 10 mV. Never stops moving.
Left channel:
Q1: D to Ground = 21.7V, S to Ground = 68.6 mV
Q2: D to Ground = -21.7V, S to Ground = -57.6mV
R10: Current = 54.8 mA, voltage = .50
Offset at the output is bouncing around between 0 and 10 mV. Never stops moving.
Right channel:
Q1: D to Ground = 21.6V, S to Ground = 68.1 mV
Q2: D to Ground = -21.2V, S to Ground = -60.1mV
R10: Current = 55 mA, voltage = .50
Offset at the output is bouncing around between 0 and 10 mV. Never stops moving.
Left channel:
Q1: D to Ground = 21.7V, S to Ground = 68.6 mV
Q2: D to Ground = -21.7V, S to Ground = -57.6mV
R10: Current = 54.8 mA, voltage = .50
Offset at the output is bouncing around between 0 and 10 mV. Never stops moving.
I had a similar problem, then found the center ground or 0v at the power supply was incorrectly connected. I inadvertantly connected to the stand off holes.
That's interesting. Those pictures show where I took the ground off the board with the green wire to the thermistor. I'll try adding another connection to the thermistor and see if that settles the offset.
That seems to have narrowed the range and slowed it down, but its still moving. Thank you 😉. Is it safe to hook up and test?
Alos, offset is very high when it first starts up ( over a volt ). It takes about 30 seconds to settle towards zero. Should this be a concern?
