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 Post subject: Optical Compressor
PostPosted: Fri May 20, 2022 11:51 am 
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I don't know why I have such a hard time with compressors. I do build other things that just work on the first try.

Is there a map somewhere that shows where the numbered components from the schematic (like R1, C3, etc.) are on the pcb?

I'm having trouble with mine (it wasn't a kit, just the raw board) and am trying to troubleshoot.


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 Post subject: Re: Optical Compressor
PostPosted: Fri May 20, 2022 1:16 pm 
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chip wrote:
I don't know why I have such a hard time with compressors. I do build other things that just work on the first try.

Is there a map somewhere that shows where the numbered components from the schematic (like R1, C3, etc.) are on the pcb?

I'm having trouble with mine (it wasn't a kit, just the raw board) and am trying to troubleshoot.


There isn't a pcb map available for that one, but it's a pretty simple circuit. Q2 is the transistor closer to the bottom of the PCB. Hopefully, you can intuit the rest from that. What is your build doing or not doing?

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 Post subject: Re: Optical Compressor
PostPosted: Fri May 20, 2022 1:49 pm 
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Thanks. I'm trying to probe it with an audio probe just based on the actual traces to see how far signal is getting, but it messes with my head to keep turning it upside down. :D

There's no sound when it's on. Bypass works, and the light comes on when the effect is engaged, but nothing is coming out.


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 Post subject: Re: Optical Compressor
PostPosted: Fri May 20, 2022 2:02 pm 
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Don't worry about tracing out the PCB signal path at this point. Just test the the main signal points. Test at pin 3 of the IC. If you have signal there move on to pin 1. If not, then look at C1 and R1, 2, and 3. If you have signal at pin 1 move on to pin 7. If you don't have signal at pin 1, then there might be a problem with the IC, so take voltages. From pin 7, check the bases of Q1 and Q2, and lug 3 of the volume pot. Those are your major signal test points. The idea is find at what major point signal fails and then you only need to trace out the signal between that point and the major point in the path that comes before it.

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 Post subject: Re: Optical Compressor
PostPosted: Fri May 20, 2022 2:54 pm 
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I have signal on Pin 3, but not 1.

Voltages on the IC:
1: 8.44
2: 0
3: 4.37
4: 0
5: 9.13
6: 1.42
7: 4.91
8: 4.56


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 Post subject: Re: Optical Compressor
PostPosted: Fri May 20, 2022 9:31 pm 
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I don't really know what I'm looking at with those voltages, but yeah, it's the IC.

It looks like
Pin 3= 1in+
Pin 1= 1out

I understand the audio test...I've got tone on the input but not the output on that one op-amp.

Regarding the voltage, I guess that number is too high?

Either way, I don't have another 4558 on hand, but I do have a 5532, which seems to have the same pinout, and when I drop one of those it there, it works.

Not sure if that would cause other problems elsewhere, but it certainly seems like it's the op-amp.

Thanks for your help!


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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 11:27 am 
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I don't think you've got the pin numbers correct. Take a look at this.

Image

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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 11:42 am 
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The NE5532 is a general purpose dual op amp, like the 4558. It's a perfectly good substitute. No reason not to leave it in there.

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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 12:14 pm 
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Crap, you're right. Sorry. I do that all the time. I retested these, and the numbers are the same, so at least it's precise if not accurate. :oops:

1: 8.44
2: 0
3: 4.37
4: 0
5: 4.56
6: 4.91
7: 1.42
8: 9.13

If the NE5532 is safe to use and wouldn't require circuit changes elsewhere, I can just go with that though. I knew that it was basically a dual op-amp with the same pinout, but still only tested it briefly in case it was subtly blowing something up.


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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 1:47 pm 
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chip wrote:
Crap, you're right. Sorry. I do that all the time. I retested these, and the numbers are the same, so at least it's precise if not accurate. :oops:

1: 8.44
2: 0
3: 4.37
4: 0
5: 4.56
6: 4.91
7: 1.42
8: 9.13

If the NE5532 is safe to use and wouldn't require circuit changes elsewhere, I can just go with that though. I knew that it was basically a dual op-amp with the same pinout, but still only tested it briefly in case it was subtly blowing something up.


You've got something going wrong at the IC. What are the voltages with the chip out of the socket?

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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 3:13 pm 
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You mean take the chip out and test the voltage at the empty socket locations?

I can check, but I'm pretty positive it's the chip. I may have nuked it or something. I put the NE5532 in there and it seems to work fine with that. If that's ok to use in there, I think I'm good.


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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 3:32 pm 
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Was that last set of voltages taken with the 5532 installed?

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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 4:06 pm 
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No, I put the 4558 back in to get you the correct numbers from the first test.

The 5532 gives me these:

1: 4.50
2: 4.47
3: 4.28
4; 0
5: 4.53
6: 4.55
7: 4.60
8: 9.13

(but most of all, it seems to be working.)

With no chip, just testing the sockets, I get:

1: 0 (it initially had something, but may have been residual and quickly went to 0)
2: 0
3: 4.36
4: 0
5: 4.54
6: 0
7: 0
8: 9.13

Which kind of makes sense? (not exactly sure how there's something on the pin 5 since there's nothing out of the input of the first op amp (since there is no op amp there) but other than that...)

These tests have all been conducted with the pedal on, the volume and compression knobs around 2:00-3:00-ish, and with a 220Hz test signal going in.

I appreciate all the help. It really seems ok with the other IC though.


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 Post subject: Re: Optical Compressor
PostPosted: Mon May 23, 2022 6:42 pm 
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chip wrote:
The 5532 gives me these:

1: 4.50
2: 4.47
3: 4.28
4: 0
5: 4.53
6: 4.55
7: 4.60
8: 9.13

Great! Those 5532 pin voltages are right on the money. ENJOY!!! :mrgreen:

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