The jfets were purchased as 2 sets matched or matched quad, but then again, who knows for sure without testing first. They are B grade 8 to 12mA idss. I dont know the exact figure.
I turned it off for now on the bench.
Will come back later power it on.
If it stays at correct bias, I will then attach to the rest of the system.
I turned it off for now on the bench.
Will come back later power it on.
If it stays at correct bias, I will then attach to the rest of the system.
List of things you can do
1) use jfets with Idss of 7mA or lower
2) reduce the value of R6 and R7 to 5K
3) Increase R8 to 33k, leave R9 at 10K, Increase trimpot to 10k
4) Use TLVH431 (only requires around 100uA)
5) Use Mosfets with low Vgs threshold.
You don't need to implement all the changes just what ever gets the job done
1) use jfets with Idss of 7mA or lower
2) reduce the value of R6 and R7 to 5K
3) Increase R8 to 33k, leave R9 at 10K, Increase trimpot to 10k
4) Use TLVH431 (only requires around 100uA)
5) Use Mosfets with low Vgs threshold.
You don't need to implement all the changes just what ever gets the job done
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The brain wave from the 42nd dimension was correct.
42 really is significant.
Hitch hikers was right
Hahahaha
42 really is significant.
Hitch hikers was right
Hahahaha
Looks like TLVH431 will operate on 100uA in a through hole package
R8 will need to be about 50k since it has 1.24V reference
R8 will need to be about 50k since it has 1.24V reference
There is one other thing you can add to the list.
Use mosfets with the lowest Vgs threshold, that will lower the bias voltages required meaning a larger voltage drop ie more current through the 10 k resistors to feed the shunt
Use mosfets with the lowest Vgs threshold, that will lower the bias voltages required meaning a larger voltage drop ie more current through the 10 k resistors to feed the shunt
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Now that you have fixed that channel, there is a chance the other channel will go cold.
In which case change the resistor on that channel too.
In which case change the resistor on that channel too.
Unfortunately, the channel will not warming up now when hooked up to the system.
I don't want to deviate too far from the original part values.
If I replace the jfets and mosfets, will it be a good compromise?
I don't want to deviate too far from the original part values.
If I replace the jfets and mosfets, will it be a good compromise?
Use jfets with Idss around 7mA and low Vgs threshold mosfets or use TLVH431
If you're using the regular TL431 part you want to ensure that the voltage drop across R6 and R7 is greater than 15V at startup when cold. ie 1.5mA feeding into shunt.
If TL431 turns off you will then notice that voltage across R6 and R7 has changed from the start up values.
If you're using the regular TL431 part you want to ensure that the voltage drop across R6 and R7 is greater than 15V at startup when cold. ie 1.5mA feeding into shunt.
If TL431 turns off you will then notice that voltage across R6 and R7 has changed from the start up values.
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I may have had a bit of a brain fart.
I stayed up till 3am.
Kept thinking we need around 15V at the 10 k resistor cause we need around 10V across the shunt to bias the circuit, but the shunt is fed by both sides of the supply not just one.
Let me think more. My brain is temporarily melting down.
I stayed up till 3am.
Kept thinking we need around 15V at the 10 k resistor cause we need around 10V across the shunt to bias the circuit, but the shunt is fed by both sides of the supply not just one.
Let me think more. My brain is temporarily melting down.
It's ok man. I wanted to say- even if it's not fixed, you've done a very good job of troubleshooting.
I couldn't do it. I dont know enough to know where to make changes. So thank you!
I couldn't do it. I dont know enough to know where to make changes. So thank you!
didn't catch up with Pico's changes here, due to some personal burnouts these dayz (welcome to New Territories, Mighty ZM 
) , but here it is
ref. to Store schematic , https://cdn.shopify.com/s/files/1/1006/5046/files/P-F4-1V20-schematic.pdf
replace R9 to 5K1 or close to that
replace R6 and R7 to 7K5 or - maybe close but cigar - 8K2
replace R22,R5 with 680R
you'll not hear any difference vs. already happily operating F4
) , but here it isref. to Store schematic , https://cdn.shopify.com/s/files/1/1006/5046/files/P-F4-1V20-schematic.pdf
replace R9 to 5K1 or close to that
replace R6 and R7 to 7K5 or - maybe close but cigar - 8K2
replace R22,R5 with 680R
you'll not hear any difference vs. already happily operating F4
The only brain fart I had, was thinking I had a brain fart.
Everything I said earlier is absolutely accurate.
THIS IS THE SOLUTION TO YOUR PROBLEM
I can explain further so it is clear in your mind if you want.
Measure the voltage drop across R5
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didn't catch up with Pico's changes here, due to some personal burnouts these dayz (welcome to New Territories, Mighty ZM
ref. to Store schematic , https://cdn.shopify.com/s/files/1/1006/5046/files/P-F4-1V20-schematic.pdf
replace R22,R5 with 680R
you'll not hear any difference vs. already happily operating F4
I feel we should keep R5/R25 and (R22+P2)/R24 the same.
So if we make R22, R5 equal to 680 we should maybe also change R24 and R25 to 680.
Maybe not technically absolutely necessary, but I am thinking to keep the ratios the same might be a good idea
For the sake of friendly math we could go with 750 Ohms. Hahaha
There are quite a few ways to tackle the problem.
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didn't catch up with Pico's changes here, due to some personal burnouts these dayz (welcome to New Territories, Mighty ZM
ref. to Store schematic , https://cdn.shopify.com/s/files/1/1006/5046/files/P-F4-1V20-schematic.pdf
replace R9 to 5K1 or close to that
Rather than reducing R9 to 5K we could leave it at 10K and increase R8 to say 33K.
This will further reduce some of the current being taken from Ika of TL431