Orange Squeezer Popping and weird voltages

[welcomb]

Hi, I built an orange squeezer using Tonepad's layout v2: http://www.tonepad.com/getFileInfo.asp?id=88

Actually I built 2 cos the first one I used a pref board and it had some problems so I etched the layout and built another.

The squeezer "seems" to be working but I'm getting pops whenever it's toggled on. I checked the output with my multimeter and there's a 2 to 3 mV DC there. I thought since there is an volume pot that should act as a pull-down resistor no?

I used all stock components, Motorola's 2N5457, and I can't find a JRC4558 but I got a CHN4558C instead. Used 1N34a cos can't find a 1N100. Other than that everything is as stated.

I adjusted the trim pot until I get values close the the GGG's instruction (https://www.generalguitargadgets.com/pdf/ggg_osq_instruct.pdf?phpMyAdmin=4a28f86a515b7883e7bc35a68d4e7b6d) and I took some the readings with both the input and output hooked together:

Q1 (Q2 in GGG's layout)
G = 0.007 (0.6)
S = 2.71 (2.6)
D = 2.13 (2.1 to 2.6)

Q2 (Q1 in GGG)
G = 2.71 (2.4)
S = 4.15 (4.0)
D = 8.79 (8.

1N34a
0.002 both ends

IC 4558 (This tonepad layout uses the other opamp of the IC)
1 = 8.18
2 = 8.18
3 = 0
4 = 0
5 = 3.95  (0 pin 3 in GGG)
6 = 0.35  (8.3 pin 2 in GGG)
7 = 8.13  (8.3 pin 1 in GGG)
8 = 8.79

As you can see, the values for the IC is way off. A puzzling thing is that isn't the non-inverting input of the opamp tied to a voltage divider between the 390k and 470k resistors? In which case why does the voltage show 0 in GGG's instruction?

Also why is there a DC voltage when bypassed, even though the volume pot is pulling it down? Or is 3mV not that significant?

[welcomb]

Ok I realized that GGG also used the opamp on pins 5-7, but my IC values are still waaaay off!

Q1 (Q2 in GGG's layout)
G = 0.007 (0.6)
S = 2.71 (2.6)
D = 2.13 (2.1 to 2.6)

Q2 (Q1 in GGG)
G = 2.71 (2.4)
S = 4.15 (4.0)
D = 8.79 (8.

1N34a
0.002 both ends

IC 4558
1 = 8.18 (8.3)
2 = 8.18 (8.3)
3 = 0 (0)
4 = 0 (0)
5 = 3.95  (4.7)
6 = 0.35  (4.
7 = 8.13  (4.
8 = 8.79

I have a very weird problem with my circuit. I removed the transistors and opamp (since I socketed them) and then turned on the power and took reading of the bias voltage at pin 5. The value I got is as above: 3.95V with 8.8V at V+.

I measured the resistor divider with my multimeter from the power and from ground and it is 390k and 470k ohms as stated in the schematics. If that's the case then shouldn't I be getting 4.8V instead of 3.95V? I measured the voltage from the +V to pin5 bias and it was 3.3V. Now 3.95 + 3.3 = 7.25V! How come my circuit violates Kircchoff Law when measuring across both resistors is 8.8V?!

Since I removed the IC, there's only a 0.047 capacitor in the path, which should be blocking the DC. What's with my weird value? Anyone can help me pls?

[aziltz]

Ok I realized that GGG also used the opamp on pins 5-7, but my IC values are still waaaay off!

Q1 (Q2 in GGG's layout)
G = 0.007 (0.6)
S = 2.71 (2.6)
D = 2.13 (2.1 to 2.6)

Q2 (Q1 in GGG)
G = 2.71 (2.4)
S = 4.15 (4.0)
D = 8.79 (8.

1N34a
0.002 both ends

IC 4558
1 = 8.18 (8.3)
2 = 8.18 (8.3)
3 = 0 (0)
4 = 0 (0)
5 = 3.95  (4.7)
6 = 0.35  (4.
7 = 8.13  (4.
8 = 8.79

I have a very weird problem with my circuit. I removed the transistors and opamp (since I socketed them) and then turned on the power and took reading of the bias voltage at pin 5. The value I got is as above: 3.95V with 8.8V at V+.

I measured the resistor divider with my multimeter from the power and from ground and it is 390k and 470k ohms as stated in the schematics. If that's the case then shouldn't I be getting 4.8V instead of 3.95V? I measured the voltage from the +V to pin5 bias and it was 3.3V. Now 3.95 + 3.3 = 7.25V! How come my circuit violates Kircchoff Law when measuring across both resistors is 8.8V?!

Since I removed the IC, there's only a 0.047 capacitor in the path, which should be blocking the DC. What's with my weird value? Anyone can help me pls?

Hi,

Just chiming in because I built one on bread board this weekend without any problems using the GGG circuit.  Is this soldered up? What kind of power supply are you using? 

I did a some quick math, and if the 470 and 390 were reversed, you would get 3.9 instead of 4.8 from an 8.8 power supply.  I'm sorry I don't have more to suggest.

Good Luck,

- Austin

[welcomb]

Thanks for your reply Austin.

I used the Tonepad layout v2 but I verified it with the GGG layout and it seems identical. I checked the resistors again and they are not reversed, but even if they were, it wouldn't explain the 3.3V.

I build 2 circuits, 1 point-to-point on pref board and when that didn't work, I built the second one on an self-etched pcb. So yah they're both soldered, but the one on the pcb is easier to remove. I removed the 0.047uF capacitor connected to the divider but still have the same readings.

Currently I'm powering it with a 9v battery, which has about 8.8V measured with my DMM.

Any experts here have any insight to me perplexing situation?

[aziltz]

Thanks for your reply Austin.

I used the Tonepad layout v2 but I verified it with the GGG layout and it seems identical. I checked the resistors again and they are not reversed, but even if they were, it wouldn't explain the 3.3V.

I build 2 circuits, 1 point-to-point on pref board and when that didn't work, I built the second one on an self-etched pcb. So yah they're both soldered, but the one on the pcb is easier to remove. I removed the 0.047uF capacitor connected to the divider but still have the same readings.

Currently I'm powering it with a 9v battery, which has about 8.8V measured with my DMM.

Any experts here have any insight to me perplexing situation?

sorry I'm no expert at debugging, i just didn't want to see you go unanswered.  if BOTH pcb and perfboard aren't working in the SAME way, my first hunch would either be the circuit, the power or the op-amp (if you used the same one in both).  But seeing as how you've tried to figure out the DC Bias without op-amp, I'm truly puzzled.  Perhaps a picture might help someone else see a construction issue?  I'm really just guessing here.

again, sorry I can't be of more help. 

[CynicalMan]

That's weird. Did you measure your battery loaded or unloaded?

[welcomb]

Thanks all who replied.

I unsoldered the 2 resistors and made a simple voltage divider on my breadboard, and get the same results. Maybe my DMM is busted though it was just bought recently. I'll have to borrow one from a friend and try again. gah

[R O Tiree]

Some low-end  (and some not so low-end) DMMs just do not have a high enough impedance to be used with much confidence for measuring voltages across components in the hundreds of k-ohms ranges and above . When you are measuring voltage, the impedance of the meter is in parallel with the item under test, so what it's actually measuring is some other new voltage in your circuit which is now reacting to the presence of the voltmeter as a new component in the circuit.

It is obeying Kirchoff's Laws... it's obeying the letter of them, not the spirit, as it were.

[welcomb]

Hmm... I did consider that but I didn't think the effect would be that great. I tried my friend's DMM (his cost about $20) and it has the same readings. Voltage across the 390k and 470k divider is 3.3V and 3.9V respectively with 8.8 across both resistors.

I did some calculations and you're right! If the DMMs have a 1M resistance across, then they will parallel with the resistor being measured and the readings match!

I found some info on building a simple circuit to test such high resistor networks: http://home.cogeco.ca/~rpaisley4/xHiZmeter.html. I just bread boarded a TL072 which I happen have lying around and use it as a buffer, and the bias voltage was 4.7V! I probably go build a more permanent buffer for my DMM.

Fancy that, even DMM need buffers. 

[R.G.]

It's funny - it's almost like Mother Nature doesn't care what we think.