Excellent news. The right hand side of the stage (Q11 et al) is biased correctly.
Gate of Q4 not being close to 0 volt is strange. Can you check the joints of R13? or perhaps Q4 is toast. Re-test it.
What is the voltage -across- R6 ? Between 1 and 2 volts? Can you adjust it to be in that range with P1?
Changed Q4 Gate = 4.9 mV OSC
Across R6 = Approx 3.0 V .... No change when adjusting P1
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Q4 is good now. But your reading across R6 (and ineffectiveness of P1) shows that there is no current through Q5 meaning that both Q4 and Q5 were toast. Replace Q5, and remeasure across R6. Hope you read 1.5 volt. If you do, recheck and note voltages. Replace 2.2k by actual Q2. Compare voltages to those with 2.2k.
Once you have a running board, you will want matched Q4 and Q5. IMO matching is more important for these two than for the quad of jfets in the first stage. This can be taken care of later.
Pierre
Rich - When you adjust P1, does it change the voltage across R6?
You want the voltage across R6 to be in the order of 1.5 times the voltage across R28. This will indicate that Q4 and Q5 are both drawing enough current.
Seems in the ball park from my remembering, assuming 2,46 mA runs in the diff pair so slightly more than 1mA per se, seems fine
approx 1.5 v across R 28
that means 3 mA flowing. Slightly more than the measure on R6 but in an order of magnitude.
But if Vref of the led is 1,65V, you should find about 1V on this resistor ( 1?65 minus 0,65V drop between B and E )
So I suspect your led to have slightly greater Vref than 1,65. Mostly a 2V onecan you measure the direct voltage on led ?
I am suprised by the amount of heat at the 2.2k (Q2 )
Which is the reading on R29 ? That would tell us what current is flowing in here. It should be around 10 mA. Flowing through the 2K2 it means 0,22W. So if you use a 1/4W standard it means near max dissipation, or even on a 0,6W model it can be hot. if you use a Dale 1/10W, it will burn one day or another
In any case you should find very similar measures on both R28 & R29. About a volt.
If you can't get it, you can always keep the led you use actually and change R28 and R29 values. In your case, you could change R 28 for 750R and R 29 for 150R and it would be also fine
Best,
nAr
This means the differential pair is biased with 3 mA total. There are 2.5 mA flowing through Q4, leaving .5 mA for Q5. The split should be more even. Again, does the voltage across R6 changes when you adjust P1?
As nAr kindly pointed out, this is normal. It is dissipating about a quarter watt
. No worries.
Oopps, my bad, should have looked closer. Seems the diff. pair doesn't share the bottom current evenly
Rich -
I'm wondering if by any chance all is fine and what we observe is a side-effect of using 2.2k instead of real Q2.
You could try this now:
1) Remove 2.2k.
2) Install Q2.
3) Verify that there is a piece of wire (short-circuit) in lieu of R15.
4) Adjust P1 so you get close to 0 volt on R10.
5) Re-measure the voltages across R6, across R28, and across R29.
Good luck.
I'm wondering if by any chance all is fine and what we observe is a side-effect of using 2.2k instead of real Q2.
You could try this now:
1) Remove 2.2k.
2) Install Q2.
3) Verify that there is a piece of wire (short-circuit) in lieu of R15.
4) Adjust P1 so you get close to 0 volt on R10.
5) Re-measure the voltages across R6, across R28, and across R29.
Good luck
.
Checking P channel ZVP 3310a
I have - on C and I get OL on gate and .6V on E .... Yes , I'm being very careful not to short or touch leads with my fingers
I'm using the guide ZM was kind enough to supply , but would like to know if I'm understanding correctly just for confidence ...
Thanks All , Rich
I have - on C and I get OL on gate and .6V on E .... Yes , I'm being very careful not to short or touch leads with my fingers
I'm using the guide ZM was kind enough to supply , but would like to know if I'm understanding correctly just for confidence ...
Thanks All , Rich
Rich -
I'm wondering if by any chance all is fine and what we observe is a side-effect of using 2.2k instead of real Q2.
You could try this now:
1) Remove 2.2k.
2) Install Q2.
3) Verify that there is a piece of wire (short-circuit) in lieu of R15.
4) Adjust P1 so you get close to 0 volt on R10.
5) Re-measure the voltages across R6, across R28, and across R29.
Good luck
1) ZVP In
C=23.99 V
B=20.47V
E=-11.51
Bottom of R10 is solid 0V
R6 = -3.52v
R28= 1.34
R29=1.31
By E do you mean Drain pin ? The one who's connected to output cap. The Drain of Q3 should be near Ground level ... ???
If you refer to schematic, ZVP has voltage gain and output taken at the Drain (low point of Q2 in schematic.) If I assume C for you is Source, V+rail, 23,99V looks OK. If B is Gate, then you have 3,52V between Gate and Source. The mosfet is likely to start conducting or already doing it. If your E point refers to Drain of mosfet, then it stands way to low, should be at Ground level, and P1 should permit you to adjust Drain (out) close to zero volts.
Ok, it's well connected then
I assume those are direct resistor measurements, not against Ground. In that case, you run about 13 mA in ZVP3310, and 2,69 mA through the diff. pair. Your R6 direct measure indicates that you run about 2,34mA in Q4. It leaves only 2,69 - 2,34 = 0,35 mA only for Q5. There's likely a problem here. Diff pair currents should be equally shared.
P1 should be set midpoint again before firing up. Mostly to get the voltage drain of Q4 in a convenient place for driving ZVP gate. P1 permits finetuning of output close to zero.
Last thing, have you removed C7 ? I don't remember.
Best,
nAr
By E do you mean Drain pin ? The one who's connected to output cap. The Drain of Q3 should be near Ground level ... ???
If you refer to schematic, ZVP has voltage gain and output taken at the Drain (low point of Q2 in schematic.) If I assume C for you is Source, V+rail, 23,99V looks OK. If B is Gate, then you have 3,52V between Gate and Source. The mosfet is likely to start conducting or already doing it. If your E point refers to Drain of mosfet, then it stands way to low, should be at Ground level, and P1 should permit you to adjust Drain (out) close to zero volts.
Ok, it's well connected then
I assume those are direct resistor measurements, not against Ground. In that case, you run about 13 mA in ZVP3310, and 2,69 mA through the diff. pair. Your R6 direct measure indicates that you run about 2,34mA in Q4. It leaves only 2,69 - 2,34 = 0,35 mA only for Q5. There's likely a problem here. Diff pair currents should be equally shared.
P1 should be set midpoint again before firing up. Mostly to get the voltage drain of Q4 in a convenient place for driving ZVP gate. P1 permits finetuning of output close to zero.
Last thing, have you removed C7 ? I don't remember.
Best,
nAr
C7 not in the board
C=S
B=G
E=D
Sorry , Its a bit better than T,M,B
P1 pin =+/- 100 mV
Q5 Gate = 3.6 mV
Q4 Gate = 22.4 mV
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C7 not in the board
C=S
B=G
E=D
Sorry , Its a bit better than T,M,B
P1 pin =+/- 100 mV
Q5 Gate = 3.6 mV
Q4 Gate = 22.4 mV
If Q5 gate is at 3,6 mV, then you should have zero volt on the pin said where to set voltage to zero volt in Pearl II manual.
Is R16 in place and jumper on R15 ?
What do you pin by P1 pin ? is it a reading on one of P1 pins, or the point on the board where it says to set P1 for 0V ?
Best,
nAr
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