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PostPosted: Fri Apr 28, 2023 7:47 pm 
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Yep, those voltages look good.

Now please do the same thing on the other two IC's and report them here.

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PostPosted: Sat Apr 29, 2023 11:47 am 
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Starting with the 4558 IC closest to the power connection

1. 0.9 to 1.3V, rapidly changing with no obvious pattern
2. 0V
3. 0V
4. -8.78V
5. 0.001V
6. 0.001V
7. -0.001V
8. 9.2V

4558 IC closest to the 4/5 pads

1. 0.002V
2. 0.002V
3. 0.002V
4. -8.78V
5. 0.001V
6. 0.001V
7. 0.02 to -0.12V constantly changing
8. 9.2V

This all looks odd to me, but again, I have no idea what right is, and my track record isn’t great. Looking at the data sheet it looks like there is a problem on Pin 1 of the first chip. Am I drawing the right conclusion here?

B/c I’m testing silicon I checked the voltage on the transistor 2SK246 and checked the data sheet to make sure I was labeling things correctly

3. 4.67V Drain
2. 2.42V Gate
1. 9.2V Source


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PostPosted: Sat Apr 29, 2023 12:35 pm 
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Yeah, I'd agree that the upper op amp IC is suspect based upon that pin 1 result. The way dual op amps like the 4558 generally work is that you want to see source voltage (V+) on pin 8, ground voltage (V-) on pin 4, and a voltage that's halfway between the two on pins 1 - 3 and 5 - 7. Because the circuit voltages are being provided by the charge pump, your V+ is nominally +9V and V- is nominally -9V, though the actuals always deviate a bit from that (your +9.2 and -8.8 values are pretty typical). So halfway between the two is ~0V, which is what you see everywhere else....except pin 1 of that upper op amp. So we need to check if that discrepancy is arising from the op amp itself or if there's a problem with the voltages coming into the socket. Next step is to pull that op amp out (Carefully! Lift straight up to avoid bending the legs, which are quite delicate) and take another set of voltage readings on the 8 pin sockets.

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PostPosted: Sat Apr 29, 2023 7:10 pm 
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Measured the sockets after taking the 4558 out

1. 0V
2. 0V
3. 0V
4. -9.08V
5. 0V
6. 0V
7. 0V
8. 9.26V

When I pulled the IC out there was a thread of metal shavings in the socket with it, don’t know if that could be the cause, so I re-installed the IC and took readings again:

And discovered the same readings s I got the first time around. Pin 1 is still wonky, bum IC perhaps?


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PostPosted: Sat Apr 29, 2023 7:37 pm 
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The socket readings are spot-on. Yeah, I'd replace that IC and see where you're at then.

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PostPosted: Mon May 01, 2023 3:28 pm 
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Slotted in a new 4558 today, same readings

Put the original problem chip in the other socket and the readings are dead level.

Put the chip that was fine in the problem socket, pin 1 is still having voltage problems.

No voltage problems in the socket, only when the pin is plugged in.

What the hell is going on?


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PostPosted: Mon May 01, 2023 3:34 pm 
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Is it possible there is a problem with something in the gain stages that is feeding through pin 1?

Perhaps I cooked a diode? Which doesn’t make any sense b/c the switch is currently set to neither led or asym


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PostPosted: Tue May 02, 2023 4:53 am 
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On Friday you reflowed the ends of R19 and reported that you now have signal through, but with new fuzzy feedback noises or something. Have you since that time gone through the circuit with your signal tester / audio probe again? You might try setting the controls for a fairly vanilla state (toggle switches in middle positions, TONE near the middle, DRIVE fairly low [mostly CCW rather than CW], LEVEL somewhere that makes testing and description easy) so that if/when/where dirt shows up along the signal chain you'll know you're near a problem rather than getting the "effect" that you are supposed to be getting. As for the ICs, use whichever combination seems to be behaving the best, regarding measured voltages. It may be sufficient, for starters, to check some places that are easy to get to, such as the pins of the two 4558's, the input and output jack TIP lugs, the footswitch lugs, and even the pot lugs. I would also suggest the Q1 gate and source, which are perhaps most easily accessed by finding the non-boring ends of R2 and R3.


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PostPosted: Tue May 02, 2023 12:43 pm 
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another audio probe party and I got the same result. An accidental discovery was touching the tip of the output from my mixer to the housing caused the signal to output to my amplifier through the cable connected to the output jack of the pedal and the input of the amplifier. I don't have any real problems transmitting the signal

I recorded a couple of sound samples across the sweep of the drive knob and the volume knob, but the forums don't like my freaky M4A file format.

On the drive knob there is increasing feedback at both CCW and CW extremes that rises in volume and pitch as the limits of the sweep are approached. It is silent at the center

On the Volume knob it behaves similarly with not entirely screwed up sound at the beginning of the sweep and growing more distorted as it approaches the 60% area of the sweep where it fuzzes out entirely and transitions to feedback which gets louder and higher pitched as the pot approaches full CW rotation

So exciting


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PostPosted: Tue May 02, 2023 2:44 pm 
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It's a stumper all right.

(1) Re: the feedback: Do you have continuity between footswitch lugs 7 and 9, for either footswitch position? You shouldn't, but I'm just trying to see where a feedback path might be.

(2) I don't have my own Green Pony close at hand to try this myself, so this next one is purely theoretical from my reading the schematic, but I am curious what you can find with your audio probe / signal tester if you operate your pedal with IC1 removed. This may render the two switches less relevant and keep signal from appearing at the IC1 socket pin 7, but I think you should still get a signal at IC2 pin 1 / C12 / R16. How does DRIVE affect it? TONE? Is it fuzzy/feedbacky? Does LEVEL turned up still make it more so?


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PostPosted: Tue May 02, 2023 3:23 pm 
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Sorry for being MIA for the past couple of days--busy times for us right now as my daughter just gave birth to our first grandchild last week and we've been doing a lot of running back & forth (they live very close by, fortunately).

I'm a bit confused about exactly how/where you're signal probing, so let's take a step back and look at the schematic:

The "Drive" control is a misnomer--it's actually a blend control, as one half of it (VR1a) sends some portion of your incoming signal through the IC1a gain/clipping stage and the rest through a bypass path to the IC2b stage. As you turn it CW for more gain/distortion, it also increases the gain produced in IC1a by increasing the resistance of the other half (VR1b) of that dual-gang Drive pot located in the IC1a feedback loop. Since you've shown that (to my surprise) the IC wasn't causing the problem, we need to try to pin down where it's coming from. So I would suggest probing some points up in that first section of the effect circuit and see what we can learn.

I would suggest initially setting the Drive control all the way CCW so that the signal is going exclusively through the clean section of the circuit. The first thing we want to rule out is that the fuzzy feedback you're getting isn't arising from the JFET input buffer. So use your signal probe to confirm clean signal at the input of the effect circuit on the eyelet 5 solder joint just above the footswitch, where your signal enters the PCB circuit. Assuming that checks out, now probe the gate (middle leg) of the 2SK246 JFET, followed by the source (upper leg). You should hear the same clean signal at the same volume at both points that you heard on eyelet 5. If not, report back here with what you're hearing.

If the JFET checks out, please check the clean signal path next. Probe the bottom lead of resistor R9 (20k)--you should hear that same clean signal at the same or just slightly reduced volume. Now turn the Drive pot to full CW and probe the bottom of R9 again--the clean signal should be greatly reduced or even inaudible.

Now probe the top lead of resistor R11 (56K). You should hear a much louder and quite distorted signal there coming out of IC1a, but without that fuzzy feedback thing going on. Now turn the Drive control back to full CCW. Re-probe the top of R11 and you should have a fairly quiet clean signal, quieter than the input signal.

Please run these signal checks exactly as I've described and report back with your findings. See probe points circled on PCB diagram below.

Yeah, I know this stuff is tedious, but I don't know a better way to pin down the source of your problem, since we've eliminated the easy stuff. I do have my own GP right here to be able to cross-check your findings against a verified working unit.

Attachment:
GP_front_of_circuit_probe_points.jpg
GP_front_of_circuit_probe_points.jpg [ 128.3 KiB | Viewed 1376 times ]


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PostPosted: Thu May 04, 2023 9:50 am 
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I'm catching up with some regular life stuff, nothing like welcoming a grandchild, (congats!!!) but typical end of school year stuff for high school and college. I'll have time probably tomorrow to sit down and do this. I don't mind tedious, but given my total lack of knowledge on the subject, the frustration is real.


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PostPosted: Thu May 04, 2023 9:58 am 
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Warder wrote:
...I don't mind tedious, but given my total lack of knowledge on the subject, the frustration is real.

Hey, we'll get this thing running yet! We're a tenacious bunch around here! :mrgreen:

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PostPosted: Tue May 09, 2023 9:16 am 
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I really appreciate it. This week has turned into a serious Charlie Foxtrot. Last night was the town meeting, so my evening was entirely eaten. Tomorrow I head to pick the eldest up from college, which will eat the rest of my week. Every time I look at my bench, this pedal is staring at me for not finishing it yet.


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