I measured between where R12 inside lead (as opposed to the lead near the edge of the board) amd R11 at the lead closest to P1.
I get 1v7 but turning the pot makes no difference in the value.
I get 1v7 but turning the pot makes no difference in the value.
I read it twenty times but you must remember I do not know enough to know what you mean.
Where do I measure these voltages?
Where do I measure these voltages?
So I measuring from ground (source pin on SIT) to the lead of R5 cklosest to the edge of the board I get -1.71 volts all the way through the range of P2.
Did I do this correctly?
I will have to take amp apart to measure the pot's wiper to either end.
If I take the trimpot out I might as well replace it.
Did I do this correctly?
I will have to take amp apart to measure the pot's wiper to either end.
If I take the trimpot out I might as well replace it.
OK
presume that you did put back R11 and R12 to original values
with violet wire disconnected, power amp On
connect black probe to GND
red probe connect to Gate of SIT - G pad on SIT pcb
rotate P2 all the way clockwise - write down voltage
rotate P2 all the way anticlockwise - write down voltage
power Off , gimme those voltages here, do nothing until I reply
presume that you did put back R11 and R12 to original values
with violet wire disconnected, power amp On
connect black probe to GND
red probe connect to Gate of SIT - G pad on SIT pcb
rotate P2 all the way clockwise - write down voltage
rotate P2 all the way anticlockwise - write down voltage
power Off , gimme those voltages here, do nothing until I reply
Removed trimpot - seems to have been fine. I put a new one in just ot be safe since I had one.
Now will re-assemble and see if anything has changed.
Just saw your message - nothing other than the trimpot replacement will have been done.
Will take me about 15 minutes to get it back together.
Now will re-assemble and see if anything has changed.
Just saw your message - nothing other than the trimpot replacement will have been done.
Will take me about 15 minutes to get it back together.
I used the source pin for ground and got -1,41 all the way from fully counterclockwise to fully clockwise.
That point is obscured by my large heatisink for 510 - I connected it to the SIT post.
I will see if I can get to it.
I will see if I can get to it.
It is time for audio demigods to get some sleep. When you reach divine status this will no longer be necessary but until then I will respect you are still human. We will continue this tomorrow though I will post what I find from trying the above.
well, you can use "GATE" pad on pcb, or you can clip on GATE (tinier) pin on SIT, or you can clip on any side of R5, or on side of R12 which is not showing constant -12V
I'm all Divine, all over my Beautiful Body ....... and Soul, above that
I'm all Divine, all over my Beautiful Body ....... and Soul, above that
Could there be a problem with that zener?
I will leave your body assessment to your own good judgement but I would quickly and vociferously vouch for your SOUL.
I will leave your body assessment to your own good judgement but I would quickly and vociferously vouch for your SOUL.
replace zener
everything from 5V6 to 10V will do
desolder SIT gate wire too
then repeat test described in #685
everything from 5V6 to 10V will do
desolder SIT gate wire too
then repeat test described in #685
Will take something from the SISSY SIT kit of parts. Probably the same.
That kit comes in handy! I stole the 510 from there, also. Making a list of what has been removed, of course.
When I look at the schematic that zener seems to be the only thing that could make the voltage NEVER change. I hope my dilettante's instinct is correct. Of course, I have no idea what a zener does when it fails ...
Take care,
That kit comes in handy! I stole the 510 from there, also. Making a list of what has been removed, of course.
When I look at the schematic that zener seems to be the only thing that could make the voltage NEVER change. I hope my dilettante's instinct is correct. Of course, I have no idea what a zener does when it fails ...
Take care,
Well, I have discovered why my bias voltage would not change and it is because of another stupid assumption and that was that resistors 10 and 11 joined where it looks like they would and they do not.
Figuring I would need to try different values I placed an extension wire in the center most hole for R10 and the hole closest to R11 and thought I could change the values that way - I had R10 and R11 connected together.
I should have looked at the PCB xray first.
SO now I have corrected that error and the bias voltage changes as it should - tyhe voltages I get are in the range you specified,.
Mea mea culpa for wasting your time. AGAIN.
So now to help a plonker understand: does changing the values of R12, R11 and R10 change the range of the voltage or, as I suspect, like a voltage divider for a heater supply, change where these same values occur above ground?
I should have noticed that this too clever by one million foolishness caused my problems. It should have been obvious but not to a plonker. I simply thought I had damaged something which I am good at.
Nonetheless I have gained a much greater understanding of how the amplifier works.
So now to begin again.
Obviously there was nothing wrong with the zener though I did remove it.
I think I will place it at the SIT just because that will be easier than trying to get it back in the PCB again.
M apologies, ZM
Figuring I would need to try different values I placed an extension wire in the center most hole for R10 and the hole closest to R11 and thought I could change the values that way - I had R10 and R11 connected together.
I should have looked at the PCB xray first.
SO now I have corrected that error and the bias voltage changes as it should - tyhe voltages I get are in the range you specified,.
Mea mea culpa for wasting your time. AGAIN.
So now to help a plonker understand: does changing the values of R12, R11 and R10 change the range of the voltage or, as I suspect, like a voltage divider for a heater supply, change where these same values occur above ground?
I should have noticed that this too clever by one million foolishness caused my problems. It should have been obvious but not to a plonker. I simply thought I had damaged something which I am good at.
Nonetheless I have gained a much greater understanding of how the amplifier works.
So now to begin again.
Obviously there was nothing wrong with the zener though I did remove it.
I think I will place it at the SIT just because that will be easier than trying to get it back in the PCB again.
M apologies, ZM
I wouldn’t consider that time wasted. I always learn something when ZM walks us through a logic or design, so I’d consider this good educational content 🙂
till now, you owe me ton of beer
let invest your energy in following my lead, try understanding circuit later ............... much later
now, set bias voltage (GATE) of SIT most negative, power off
assemble all wires , as for functional amplifier
do not touch trimpot at mos board
power on, measure Iq and output node voltage, write down what Iq, output node voltage and what SIT Ugs is, write here
try to set output node voltage to prescribed value; if you can't - write here
inform
let invest your energy in following my lead, try understanding circuit later ............... much later
now, set bias voltage (GATE) of SIT most negative, power off
assemble all wires , as for functional amplifier
do not touch trimpot at mos board
power on, measure Iq and output node voltage, write down what Iq, output node voltage and what SIT Ugs is, write here
try to set output node voltage to prescribed value; if you can't - write here
inform
I do owe you a ton of something, that is without doubt.
I am just now seeing your note.
Here is where I am: with R10 removed but Rs12 and 11 as specified on the schematic I get 34.5 Vds - 3.6 Vgs Iq 455 mV.
I re-inserted R10 - Vgs goes down to 21.5 and Iq went to 476 mV. I did not bother to measure Vgs. I did not touch the trimpots since I know there is no way that is going to work. Turning the mosfet trimpot would reduce the Iq but would not raise Vgs anywhere close to where I was without R10.
So I figure there is no question R10 is not needed with this SIT.
Since it is time to listen to some music and drink Rye whiskey I will return to more experimentation tomorrow.
I must listen to music or my day is ruined.
Thanks, Cody, for your commiseration.
I do hope my stupidity does help others in some way.
I think I am close.
Now I have to hope His Grace will give me a clue as to what to change - R12 or R11?
As always, my heartfelt thanks for your patience, wisdom and general wonderfulness, ZM.
And to all a good night!
I am just now seeing your note.
Here is where I am: with R10 removed but Rs12 and 11 as specified on the schematic I get 34.5 Vds - 3.6 Vgs Iq 455 mV.
I re-inserted R10 - Vgs goes down to 21.5 and Iq went to 476 mV. I did not bother to measure Vgs. I did not touch the trimpots since I know there is no way that is going to work. Turning the mosfet trimpot would reduce the Iq but would not raise Vgs anywhere close to where I was without R10.
So I figure there is no question R10 is not needed with this SIT.
Since it is time to listen to some music and drink Rye whiskey I will return to more experimentation tomorrow.
I must listen to music or my day is ruined.
Thanks, Cody, for your commiseration.
I do hope my stupidity does help others in some way.
I think I am close.
Now I have to hope His Grace will give me a clue as to what to change - R12 or R11?
As always, my heartfelt thanks for your patience, wisdom and general wonderfulness, ZM.
And to all a good night!