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PostPosted: Thu Jul 16, 2020 12:15 pm 
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duhvoodooman wrote:
Yeah, I wouldn't put much stock in those numbers, given the questionable state of your meter. Let's see what the new one shows.



New multimeter:

Pin 1: 0.1
Pin 2: 1.0
Pin 3: 1.4
Pin 4: 0.0
Pin 5: 0.1
Pin 6: 4.5
Pin 7: 7.2
Pin 8: 0.0


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PostPosted: Thu Jul 16, 2020 3:00 pm 
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OK, you have definite voltage problems there. On my fully functional Sprocket, these are the pin voltages. Pins 1, 5 and 8 are not used on this single op amp implementation, so that's why they aren't reported. All readings are in VDC; my power source is 9.95V:

2: 4.94
3: 4.84
4: 0 (ground)
6: 4.97
7: 9.55

Your only two values that look correct are pins 4 & 6. Either the op amp is bad or you have voltage losses somewhere on the PCB. Please get the following voltage readings:

  • Your power source (this can be taken right at the DC Jack tab that connects to the PCB + eyelet farthest to the right).
  • Pull the op amp out of the socket and take voltage readings at those same five pin slots in the socket.

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PostPosted: Thu Jul 16, 2020 5:23 pm 
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duhvoodooman wrote:

Your only two values that look correct are pins 4 & 6. Either the op amp is bad or you have voltage losses somewhere on the PCB. Please get the following voltage readings:

  • Your power source (this can be taken right at the DC Jack tab that connects to the PCB + eyelet farthest to the right).
  • Pull the op amp out of the socket and take voltage readings at those same five pin slots in the socket.


Hi DVM,


Thanks for your quick reply, and thanks again for your patience helping me with this.


Power source: 9.1

Pin 1: 0.0
2: 0.0
3: 1.4
4: 0.0
5: 0.0
6: 0.0
7: 9.1
8: 0.0

What do you think this might mean? I have other tl071 ICs that I can try out, fwiw.


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PostPosted: Thu Jul 16, 2020 6:17 pm 
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No, the problem doesn't appear to be with the op amp, it's somewhere else on the PCB. The socket for pin 3 should be measuring just about one-half of your power source voltage (i.e. 1/2V). Looks like you're losing voltage somewhere. And pin 7 shouldn't be dropping almost 2 volts when the IC is inserted.

That 1/2V should be generated at the 50/50 voltage divider formed by R25 and R26. Take voltage readings at the top and the bottom leg of R25. What values do you see there?

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PostPosted: Thu Jul 16, 2020 6:47 pm 
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So, the reading at the top of R25 is 9.1

And at the bottom, it's 4.1


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PostPosted: Thu Jul 16, 2020 7:06 pm 
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That's pretty close to what you'd expect there, certainly much closer than the op amp voltages would indicate.

Check the voltage on both sides of R16, the 220K resistor right below the sensitivity pot.

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PostPosted: Thu Jul 16, 2020 7:18 pm 
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duhvoodooman wrote:
EDIT: HOLD ON, DON'T DO THIS YET--


I AM NOT DOING ANYTHING, I SWEAR!!


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PostPosted: Thu Jul 16, 2020 7:20 pm 
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duhvoodooman wrote:
That's pretty close to what you'd expect there, certainly much closer than the op amp voltages would indicate.

Check the voltage on both sides of R16, the 220K resistor right below the sensitivity pot.


left side: 4.2
right side: 1.4


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PostPosted: Thu Jul 16, 2020 7:24 pm 
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:lol: :lol: :lol:

Sorry, didn't mean to freak you out there. :oops:

OK, we're getting close! No way that voltage should drop that much across R16. Mine only drops from 4.94 to 4.84. Lemme think about this....

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PostPosted: Thu Jul 16, 2020 7:26 pm 
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duhvoodooman wrote:
OK, we're getting close! No way that voltage should drop that much across R16. Mine only drops from 4.94 to 4.84. Lemme think about this....


Awesome, thanks much.


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PostPosted: Thu Jul 16, 2020 7:30 pm 
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What EXACTLY is printed on that C9 ceramic cap?

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PostPosted: Thu Jul 16, 2020 7:37 pm 
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duhvoodooman wrote:
What EXACTLY is printed on that C9 ceramic cap?


223.


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PostPosted: Thu Jul 16, 2020 7:48 pm 
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With the Sensitivity pot all the way up (full CW), do you read any voltage on the middle lug of that pot?

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PostPosted: Thu Jul 16, 2020 7:52 pm 
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duhvoodooman wrote:
With the Sensitivity pot all the way up (full CW), do you read any voltage on the middle lug of that pot?


Wow, not getting any voltage whatsoever with pot rolled either way.


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PostPosted: Thu Jul 16, 2020 8:00 pm 
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Good--you shouldn't. But where the heck is that almost 3V going to???

I'll ask the Boss (Keith, not Springsteen :mrgreen: ) to take a look tomorrow at where we are and see if he has any ideas.

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PostPosted: Thu Jul 16, 2020 8:06 pm 
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duhvoodooman wrote:
Good--you shouldn't. But where the heck is that almost 3V going to???

I'll ask the Boss (Keith, not Springsteen :mrgreen: ) to take a look tomorrow at where we are and see if he has any ideas.


Thanks, man. I'm learning a lot just by going through the circuit with your assistance. Have a pleasant evening.


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PostPosted: Fri Jul 17, 2020 8:46 am 
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WEIRD DEVELOPMENT!

I swapped out the curious ceramic 223 and 333 caps and replaced them with poly caps, and presto! The signal is no longer faint...but there's no envelope effect, despite trying to set the trimpot per the instructions.

The signal is definitely going through the circuit; kill the power and the signal goes silent when the effect is engaged. With power, the wet signal is identical to the dry in terms of volume, timbre, all that.

I reran the signal test, and here are the results:

Q1 base: clean signal, unity vol
VR1 lug 3: clean signal, unity vol
op amp pin 3: clean signal, unity vol
op amp pin 6: distorted, very loud
Q5 collector: distorted but not very loud, roughly unity with dry signal
Q6 collector: distorted but not very loud, roughly unity with dry signal
Q3 base: clean signal, unity vol
3PDT lug 7: clean signal, unity vol


voltages with new multimeter:

Pin 1: 0.1
Pin 2: 1.0
Pin 3: 1.3
Pin 4: 0.0
Pin 5: 0.1
Pin 6: 4.3
Pin 7: 7.3
Pin 8: 0.0

power source: 9.1

w/o op amp:

Pin 1: 0.1
Pin 2: 0.0
Pin 3: 1.4
Pin 4: 0.0
Pin 5: 0.0
Pin 6: 0.0
Pin 7: 9.1
Pin 8: 0.0

top of R25: 9
bottom of R25: 4.1

left of R16: 4.2
right of R16: 1.4

100K pot, lug 2: 0.0

Sorry to throw you a curveball! Is this progress?


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PostPosted: Fri Jul 17, 2020 9:39 am 
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When you day envelope, do you mean volume swell?


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PostPosted: Fri Jul 17, 2020 10:07 am 
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jimilee wrote:
When you day envelope, do you mean volume swell?


Sent from my iPhone using Tapatalk


Yes, the clean signal doesn't swell.


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PostPosted: Fri Jul 17, 2020 10:33 am 
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Interesting what the change to the poly film caps did. It'll take someone with a whole lot more theoretical knowledge than me to explain that, but I'm quite certain that the low voltages on pins 2 & 3 of the op amp are still the big issue here. You're just not getting the output from the swell-generation part of the circuit to generate an audible wet signal up at Q3. So we still need to figure out where that missing 2.8V across R16 is going.

Here's a couple more things to try:

  1. Remove the op amp again, disconnect the power source, and use your multimeter to check for continuity between the pin 3 socket and any of the other sockets. None of these sockets should show continuity. Then switch to the meter's resistance mode and check the resistance between the pin 3 socket and each of the other sockets. Only pin sockets 4 and 7 should show readable resistance values, both around 235 Kohms or so. What we're looking for here is some kind of circuit path in the socket itself where the missing voltage is being lost.
  2. Let's also check the function of the Zener diode, D1. Hook your power back up and check the voltage level on the left side of D1. I see 5.37V there on mine.

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PostPosted: Fri Jul 17, 2020 12:08 pm 
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duhvoodooman wrote:
Interesting what the change to the poly film caps did. It'll take someone with a whole lot more theoretical knowledge than me to explain that, but I'm quite certain that the low voltages on pins 2 & 3 of the op amp are still the big issue here. You're just not getting the output from the swell-generation part of the circuit to generate an audible wet signal up at Q3. So we still need to figure out where that missing 2.8V across R16 is going.

Here's a couple more things to try:

  1. Remove the op amp again, disconnect the power source, and use your multimeter to check for continuity between the pin 3 socket and any of the other sockets. None of these sockets should show continuity. Then switch to the meter's resistance mode and check the resistance between the pin 3 socket and each of the other sockets. Only pin sockets 4 and 7 should show readable resistance values, both around 235 Kohms or so. What we're looking for here is some kind of circuit path in the socket itself where the missing voltage is being lost.
  2. Let's also check the function of the Zener diode, D1. Hook your power back up and check the voltage level on the left side of D1. I see 5.37V there on mine.


With no op amp, I’m getting resistance of about 250K-ish between 3 and both 4 and 7, as you predicted, but am also getting readings of 640k-ish between both 3 and 2, and between 3 and 6.

For the zener, I’m getting, about 5.2 and 5.4 volts


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PostPosted: Fri Jul 17, 2020 12:23 pm 
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OK, the Zener is fine.

Not sure what to make of that ~640K resistance between pins 3 and 2/6. Asked Keith to take a look at this thread, so hopefully he may have some ideas....

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PostPosted: Fri Jul 17, 2020 12:45 pm 
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duhvoodooman wrote:
OK, the Zener is fine.

Not sure what to make of that ~640K resistance between pins 3 and 2/6. Asked Keith to take a look at this thread, so hopefully he may have some ideas....


If you're measuring a resistance between pins 3 and 2/6 with the IC out of the socket, then you likely have something that is causing a semi-short. You should remove the IC socket.

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PostPosted: Fri Jul 17, 2020 3:59 pm 
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byoc wrote:
If you're measuring a resistance between pins 3 and 2/6 with the IC out of the socket, then you likely have something that is causing a semi-short. You should remove the IC socket.

Just some advice here: Removing components with three or more solder attachments to the PCB is tricky, because you can't pry it up from side to side while applying the heat, like you can with a 2-lead component like a resistor or capacitor. You want to be sure not to force it loose as this will often damage the solder pads and eyelet or break a trace on the board. Two things are key in desoldering and removing something like a socket: patience and the proper tools. I strongly recommend a solder sucker to remove most of the solder from each joint and then some high quality desoldering braid to remove the residual. When the solder has been thoroughly removed from all of the eyelets, the component should almost fall out of the PCB.

Here are a couple of links for these tools:

https://www.amazon.com/WEmake-WM-SP4-So ... 0002KRAAG/

https://www.amazon.com/gp/product/B008O9VLA2/

The MG Chemicals desoldering braid is the best I've ever used--it soaks of molten solder like a sponge. I doubt that I'll ever use another brand. Highly recommended!

The other thing you might consider if you don't plan to re-use the socket (personally, I would install a new one) is to gently cut it up with a pair of fine cutting dikes and remove it in smaller pieces. This is often much easier than getting it out in one piece.

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PostPosted: Fri Jul 17, 2020 7:35 pm 
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duhvoodooman wrote:
byoc wrote:
If you're measuring a resistance between pins 3 and 2/6 with the IC out of the socket, then you likely have something that is causing a semi-short. You should remove the IC socket.

Just some advice here: Removing components with three or more solder attachments to the PCB is tricky, because you can't pry it up from side to side while applying the heat, like you can with a 2-lead component like a resistor or capacitor. You want to be sure not to force it loose as this will often damage the solder pads and eyelet or break a trace on the board. Two things are key in desoldering and removing something like a socket: patience and the proper tools. I strongly recommend a solder sucker to remove most of the solder from each joint and then some high quality desoldering braid to remove the residual. When the solder has been thoroughly removed from all of the eyelets, the component should almost fall out of the PCB.

Here are a couple of links for these tools:

https://www.amazon.com/WEmake-WM-SP4-So ... 0002KRAAG/

https://www.amazon.com/gp/product/B008O9VLA2/

The MG Chemicals desoldering braid is the best I've ever used--it soaks of molten solder like a sponge. I doubt that I'll ever use another brand. Highly recommended!

The other thing you might consider if you don't plan to re-use the socket (personally, I would install a new one) is to gently cut it up with a pair of fine cutting dikes and remove it in smaller pieces. This is often much easier than getting it out in one piece.



Thanks for the good advice. I just removed the socket, and soldered the op amp straight in...and now it works! The ramp-up is a bit slower than I’d hoped but it does the faux steel guitar/Tomorrow Never Lnows sound perfectly!

Thanks DVM, your helps been invaluable. Off now to look into some mods to sweeten this thing up a tad. Love ya, BYOC!


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