Orange Squeezer Trouble

[krister]

Should there be voltage after the output cap (on the minus side)? Right now there is 5.32v on the plus side and 0v on the minus side with 0v running all the way throught the circuit to the gate of Q2. Thanks.

[krister]

Pin 1 = 5.30v currently, is this too low?

No, it is now correct. The opamp is biased OK.

So the remaining problem is in the JFETs.
(1) Does the voltage on the gate of Q1 and the source and gate of Q2 change as you turn the 10K pot?
(2) have you checked your JFET pinouts? It is possible that Q2 is incorrectly inserted and is coducting from its "gate" through the 4.7K to ground.

(1) Does the voltage on the gate of Q1 and the source and gate of Q2 change as you turn the 10K pot?
The voltage does not change.

(2) have you checked your JFET pinouts? It is possible that Q2 is incorrectly inserted and is coducting from its "gate" through the 4.7K to ground.
I have checked the pin outs and they are correct.

[krister]

Last night I figured this out. The source of Q1 is half the voltage it needs to be. What controls this? I still can't figure it out. I even took an OS that works correctly and compared components and voltages. The components match but the voltages do not. I figure if I can get the voltage to double on the source of Q1 the rest will fall into line. Thank you for all of your suggestions.

Kris

[petemoore]

Should there be voltage after the output cap ... if it's an output cap, it is a DC blocking cap, and 0V should be there, on the outside the DC circuit.
  not sure how much 2k2 Vs. 2k4 would matter, but since it's right there on the source, it's probably worth it to build a resistor of closer to the shown value and try that there.

[R.G.]

(1) Does the voltage on the gate of Q1 and the source and gate of Q2 change as you turn the 10K pot?
The voltage does not change.
(2) have you checked your JFET pinouts? It is possible that Q2 is incorrectly inserted and is coducting from its "gate" through the 4.7K to ground.
I have checked the pin outs and they are correct.

Here is why question 1 matters: The way this thing works is that Q1 is a constant current source hooked up to feed that 10K trimmer. The voltage at the gate of Q1 and the source of Q2 is supposed to change as you turn that trimmer. The trimmer is there to adjust out the differences in JFETs for Q2 to act as a variable resistor. What is happening in your circuit is that the Q2 JFET has its gate clamped to ground. The voltage at its source is slightly higher, and you are using J201's which have a very low Vgs voltage. So Q2 is always turned on, and it shunts all of the signal away from the signal path.

Here is what will tell you what is wrong.
(1) Open Q2's source from the circuit. Read the voltage across the 10K resistor. Does it now move from 0V up to perhaps 4-5V as you turn the trimmer? If not, this circuit is faulty and must be fixed. If it's faulty, measure the value of the 10K resistor with a meter. Does it actually go from 0 ohms up to nearly 10K? Or is it perhaps a 1K pot, or shorted? If it is really 0-10K, then there is a problem with Q1, the 2.4K resistor, or the 4.7uF cap. The circuit will not work properly until you can dial in an appropriate voltage from 0V up to 4 or 5V with the 10K trimmer.

(2) presumably the Q1/10K circuit now gives you the correct voltages. Remove the 470K resistor leading from the diode to the gate of Q2. Clip your voltmeter across the 100K resistor which remains connected from the diode's cathode to ground. Play a few notes. Does the voltmeter show a voltage of up to a couple of volts as you hit notes? If not, then the circuit composed of the 1.5K resistor, 100K resistor, diode, and 4.7uF cap is faulty and must be corrected. Inspect and fix until you get that correct.

(3) When both other circuits are working correctly, reconnect Q2. Let us know if it does not now work.

The J201 is a poor choice for this circuit. If you have MPF102s, use them.

[krister]

(1) Does the voltage on the gate of Q1 and the source and gate of Q2 change as you turn the 10K pot?
The voltage does not change.
(2) have you checked your JFET pinouts? It is possible that Q2 is incorrectly inserted and is coducting from its "gate" through the 4.7K to ground.
I have checked the pin outs and they are correct.

Here is why question 1 matters: The way this thing works is that Q1 is a constant current source hooked up to feed that 10K trimmer. The voltage at the gate of Q1 and the source of Q2 is supposed to change as you turn that trimmer. The trimmer is there to adjust out the differences in JFETs for Q2 to act as a variable resistor. What is happening in your circuit is that the Q2 JFET has its gate clamped to ground. The voltage at its source is slightly higher, and you are using J201's which have a very low Vgs voltage. So Q2 is always turned on, and it shunts all of the signal away from the signal path.

Here is what will tell you what is wrong.
(1) Open Q2's source from the circuit. Read the voltage across the 10K resistor. Does it now move from 0V up to perhaps 4-5V as you turn the trimmer? If not, this circuit is faulty and must be fixed. If it's faulty, measure the value of the 10K resistor with a meter. Does it actually go from 0 ohms up to nearly 10K? Or is it perhaps a 1K pot, or shorted? If it is really 0-10K, then there is a problem with Q1, the 2.4K resistor, or the 4.7uF cap. The circuit will not work properly until you can dial in an appropriate voltage from 0V up to 4 or 5V with the 10K trimmer.

(2) presumably the Q1/10K circuit now gives you the correct voltages. Remove the 470K resistor leading from the diode to the gate of Q2. Clip your voltmeter across the 100K resistor which remains connected from the diode's cathode to ground. Play a few notes. Does the voltmeter show a voltage of up to a couple of volts as you hit notes? If not, then the circuit composed of the 1.5K resistor, 100K resistor, diode, and 4.7uF cap is faulty and must be corrected. Inspect and fix until you get that correct.

(3) When both other circuits are working correctly, reconnect Q2. Let us know if it does not now work.

The J201 is a poor choice for this circuit. If you have MPF102s, use them.

Thanks, R.G., I'll try these things out. I did switch MPF102s, right when you said J201s are not a good choice a while back in the thread. Thank you for your strategies, hopefully the issue will be resolved or I will find the faulty part. I've swapped around a good number of them. Sound likes the 10K trimmer may be the issue. We will see.

[krister]

(1) Does the voltage on the gate of Q1 and the source and gate of Q2 change as you turn the 10K pot?
The voltage does not change.
(2) have you checked your JFET pinouts? It is possible that Q2 is incorrectly inserted and is coducting from its "gate" through the 4.7K to ground.
I have checked the pin outs and they are correct.

Here is why question 1 matters: The way this thing works is that Q1 is a constant current source hooked up to feed that 10K trimmer. The voltage at the gate of Q1 and the source of Q2 is supposed to change as you turn that trimmer. The trimmer is there to adjust out the differences in JFETs for Q2 to act as a variable resistor. What is happening in your circuit is that the Q2 JFET has its gate clamped to ground. The voltage at its source is slightly higher, and you are using J201's which have a very low Vgs voltage. So Q2 is always turned on, and it shunts all of the signal away from the signal path.

Here is what will tell you what is wrong.
(1) Open Q2's source from the circuit. Read the voltage across the 10K resistor. Does it now move from 0V up to perhaps 4-5V as you turn the trimmer? If not, this circuit is faulty and must be fixed. If it's faulty, measure the value of the 10K resistor with a meter. Does it actually go from 0 ohms up to nearly 10K? Or is it perhaps a 1K pot, or shorted? If it is really 0-10K, then there is a problem with Q1, the 2.4K resistor, or the 4.7uF cap. The circuit will not work properly until you can dial in an appropriate voltage from 0V up to 4 or 5V with the 10K trimmer.

(2) presumably the Q1/10K circuit now gives you the correct voltages. Remove the 470K resistor leading from the diode to the gate of Q2. Clip your voltmeter across the 100K resistor which remains connected from the diode's cathode to ground. Play a few notes. Does the voltmeter show a voltage of up to a couple of volts as you hit notes? If not, then the circuit composed of the 1.5K resistor, 100K resistor, diode, and 4.7uF cap is faulty and must be corrected. Inspect and fix until you get that correct.

(3) When both other circuits are working correctly, reconnect Q2. Let us know if it does not now work.

The J201 is a poor choice for this circuit. If you have MPF102s, use them.

Thanks, R.G., I'll try these things out. I did switch MPF102s, right when you said J201s are not a good choice a while back in the thread. Thank you for your strategies, hopefully the issue will be resolved or I will find the faulty part. I've swapped around a good number of them. Sound likes the 10K trimmer may be the issue. We will see.

I'm sorry R.G. I must be a retard. I thought you meant the 10K audio pot for volume. Yes the voltage does change when I turn the 10K trimmer. There isn't enough voltage though at least half of what it should be to make this thing sing.

[R.G.]

Does the 10K resistor read 10K on the ohmmeter scale of your meter?

What voltages do you get when you turn the 10K?

Does it change smoothly for the whole rotation, or stop before you get to one end or the other?

Does opening up the Q2 Source have any effect on how this works?

[krister]

1) Open Q2's source from the circuit. Read the voltage across the 10K resistor. Does it now move from 0V up to perhaps 4-5V as you turn the trimmer? If not, this circuit is faulty and must be fixed. If it's faulty, measure the value of the 10K resistor with a meter. Does it actually go from 0 ohms up to nearly 10K? Or is it perhaps a 1K pot, or shorted? If it is really 0-10K, then there is a problem with Q1, the 2.4K resistor, or the 4.7uF cap. The circuit will not work properly until you can dial in an appropriate voltage from 0V up to 4 or 5V with the 10K trimmer.

OK, R.G., I found the problem and I feel so stupid for not checking, RS sold me a 1k timpot in a 10k package. The number is marked 102 instead of 103. I have to learn to check these things instead of chasing my tail for hours on end, which I did last night til 1 am. I'll change the pot and I expect it to work correctly after the change.

Thank you to everyone for your help and support. I would still be chasing my tail otherwise

[krister]

I changed the trimpot to a 10k and the circuit works as expected now. It sounds great!

Thanks, R.G. and Pete.

[R.G.]

Yahoo! You got it! Good work.