Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Equipment Usage, Soldering, Techniques, and Reviews
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 07-06-2021, 05:56 PM   #41
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,081
Default Re: Signal Tracer - Requesting input on requirements

I have one comment about the capacitor across the other pads ( in the second picture) is you might want to put heat shrink tubing on the component leads so nothing bad happens ( just a thought )

Nice work
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
sam_sam_sam is offline   Reply With Quote
Old 07-06-2021, 07:40 PM   #42
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,202
Default Re: Signal Tracer - Requesting input on requirements

It shouldn't get really quiet like that. Unless the speaker GND is shorting out the input signal or something?
I couldn't make out all the wiring, this pic might help. The hookup wire is a bit thick and awkward, I take wire out of old junk stuff like inkjet printers are reuse it. In case this starts to drive you nuts.

The PCB has the speaker ground (JST) trace go around and over to the input jack, and the IC GND is at the the other end of the trace. Sigh. It's not the greatest.

I would the leave the 2.2uF cap where it is, and move the DC power GND up to where the DC jack GND is or C6(-).
Then the signal ground is from the pot GND that goes to pin 4. The input jack GND is far away so I would prefer to not use it. If you must use those input jack pads, I would cut the trace to it and the LED/or to it and at the corner, and run a jumper from the pot GND at pin 4 to the input jack pad. Getting rid of the long loop this board has there, look at the path from input jack GND to the IC lol.

Ideally you want to have the four major grounds: DC power, loudspeaker, IC, signal input - all connect to one point or the star. It's not usually a big deal but some LM386's I built up get finnicky and I have to redo things. The IC has no markings on top?
R2 4k7 is only in if really strong signals coming in, I would leave it out.

It's normal for this to pickup noise and hum when nothing is connected to the input. Putting your hand near it will bring AC hum. It should always be quiet if the pot is turned down though.
Attached Images
File Type: jpg LM386_pcb1.jpg (218.8 KB, 7 views)
redwire is offline   Reply With Quote
Old 07-08-2021, 11:24 AM   #43
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

Quote:
Originally Posted by redwire View Post
It shouldn't get really quiet like that. Unless the speaker GND is shorting out the input signal or something?
Thank you!!! I have been trying to trace out what has been going on, and I'd unplug the speaker from the board so I could flip the board and take a look, turns out the speaker plug was reversed. Woops.

Quote:
Originally Posted by redwire View Post
I couldn't make out all the wiring, this pic might help. The hookup wire is a bit thick and awkward, I take wire out of old junk stuff like inkjet printers are reuse it. In case this starts to drive you nuts.

The PCB has the speaker ground (JST) trace go around and over to the input jack, and the IC GND is at the the other end of the trace. Sigh. It's not the greatest.

I would the leave the 2.2uF cap where it is, and move the DC power GND up to where the DC jack GND is or C6(-).
Then the signal ground is from the pot GND that goes to pin 4. The input jack GND is far away so I would prefer to not use it. If you must use those input jack pads, I would cut the trace to it and the LED/or to it and at the corner, and run a jumper from the pot GND at pin 4 to the input jack pad. Getting rid of the long loop this board has there, look at the path from input jack GND to the IC lol.

Ideally you want to have the four major grounds: DC power, loudspeaker, IC, signal input - all connect to one point or the star. It's not usually a big deal but some LM386's I built up get finnicky and I have to redo things. The IC has no markings on top?
R2 4k7 is only in if really strong signals coming in, I would leave it out.

It's normal for this to pickup noise and hum when nothing is connected to the input. Putting your hand near it will bring AC hum. It should always be quiet if the pot is turned down though.
R2 4k7 was replaced with one of the ceramic caps shown in your schematic.
I cut the ground trace in the top left and top right corners. I ran a jumper wire straight to the cap from pin 4, and ran another jumper wire from pin 4 for the led and where I grounded the two diodes.
Then I soldered all the grounds to a large blob attached to pin 4. Pic attached. Not proud of this.
The chip is marked "16CXY LM386 M-82". It doesn't show unless you get the camera angle just right.

I don't know if this information is useful, but I dragged out my computer speakers and a probe, and traced the signal on this new one. Signal was clean to the pot, but at the pot wiper terminal, I couldn't hear anything, possibly because the pot reduced the signal. No noise at pin 3 on the lm386 either. At pin 5, plenty of noise, even with the volume turned way down. From my readings, this is likely still a grounding problem.

So my options seem to be:
1. Shielded cable for the pot (do I ground the shielding?)
2. Shorten the pot cables to the point I'll have to completely redesign the case
3. Take the 10uf cap out to reduce the gain to 20x instead of 200x.

Also, I noticed that all the other LM386 noise filters on the output have the cap first, then the resistor connected to ground, yours is the only one I have seen that has the resistor (R3 10R) first and the cap (47uf) attached to ground. Does the order matter here?


IMG_20210708_115305.jpg
clearchris is offline   Reply With Quote
Old 07-08-2021, 01:31 PM   #44
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

Quote:
Originally Posted by sam_sam_sam View Post
I have one comment about the capacitor across the other pads ( in the second picture) is you might want to put heat shrink tubing on the component leads so nothing bad happens ( just a thought )

Nice work
If you liked that, you should see the new pic! If I could get this working, I'll probably coat it with some liquid tape. Either way, it will be 4 point mounted in a protective plastic box with 10mm of space underneath so it should be safe once installed...
clearchris is offline   Reply With Quote
Old 07-08-2021, 03:11 PM   #45
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

Quote:
Originally Posted by clearchris View Post
So my options seem to be:
1. Shielded cable for the pot (do I ground the shielding?)
2. Shorten the pot cables to the point I'll have to completely redesign the case
3. Take the 10uf cap out to reduce the gain to 20x instead of 200x.
I shortened the cables on the pot to around 1 inch, no change in noise. Then I took out the 10uf cap to change gain to 20x instead of 200x, replaced the 1M pot with a 10k pot and bypassed the 4R7 resistor. Still noise.

Quote:
Originally Posted by clearchris View Post
Also, I noticed that all the other LM386 noise filters on the output have the cap first, then the resistor connected to ground, yours is the only one I have seen that has the resistor (R3 10R) first and the cap (47uf) attached to ground. Does the order matter here?
Unless this makes a difference, I'm going to have to rebuild the circuit on perfboard or get a different amp. I think I'll get both the perfboard and a new amp on order and see which I can get working faster.

Does anyone have a suggestion for a more user friendly style amp module? Even if I don't use it myself, when I release the design, I'd like to have a more friendly option available, I'm not sure I would recommend the LM386 to anyone else unless they really wanted the challenge to level up their skills.
clearchris is offline   Reply With Quote
Old 07-08-2021, 10:56 PM   #46
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,202
Default Re: Signal Tracer - Requesting input on requirements

I'm not sure what the noise is, can you describe it a bit more.
The grounding is as good as it can get, so it's something else.

Because you are powering this from a wall-wart, the SMPS might be making a lot of common-mode noise/interference that the LM386 is picking up. Try run it off a battery 9V or something.

The LM386 output 10R/47nF the part order does not matter, it's a series circuit.
redwire is offline   Reply With Quote
Old 07-09-2021, 09:27 AM   #47
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 6,523
Default Re: Signal Tracer - Requesting input on requirements

are we talking about white noise or picking up ambient/PSU noise?

IIRC the LM386's noise floor is fairly high, but it's been a while since I had a LM386 on its own...
eccerr0r is offline   Reply With Quote
Old 07-09-2021, 11:02 AM   #48
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

It's white noise. Same level of white noise if the volume is all the way down or turned all the way up (audio input hooked up, but no sound playing). My compuer speakers have white noise if I put my head next to them with the volume all the way down, becomes slightly louder if I turn them up. Can't hear it from 1ft away. The LM386 has constant white noise that I can hear, with the speaker facing away, from at least 5ft away. The noise is loud enough I don't think I could use it to chase down noise in a system I would be troubleshooting.

I peeled the components off the board and put them in my breadboard (pic attached) for troubleshooting. I swapped out the caps that came with the kit for nichicon / kemet and I do think the sound is a touch better, but the noise didn't change. I didn't add in the protection diodes, the led or the resistor from pot to pin 3. When I add the 10uf cap between pins 1 and 8 (200x gain), the noise is overwhelming, so my breadboard layout is probably worse than the PCB, but results without the cap (20x gain) are similar.

A minor miracle has occurred, the electronics shop has some JRC LM386D in stock. From what I have read, that's pretty much the gold standard (if not fake), I'll go pick one up and see how it sounds...

IMG_20210709_103805.jpg
clearchris is offline   Reply With Quote
Old 07-09-2021, 11:54 AM   #49
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 6,523
Default Re: Signal Tracer - Requesting input on requirements

Problem with the chip itself not your design, at least if you make sure you're not introducing more noise for it to amplify...

Last edited by eccerr0r; 07-09-2021 at 12:06 PM..
eccerr0r is offline   Reply With Quote
Old 07-09-2021, 03:54 PM   #50
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

I went and picked up the new chip, it wasn't JRC, but it was a natsemi lm386-4 (the 1w version). I put it in, total silence at 20x gain and zero volume. At 200x gain I start to get some AC hum from nearby lights, etc. I did have some chirping, but I think it was either from my PS or from my desk lamp, further testing is required. No chirping in the dark using a battery. Candle light signal tracing anyone?

I can work with this!

So where do I go from here?

1. Dig up some shielded cables.
2. Test longer shielded cables for the volume pot
3. Reroute some wiring in the box or redesign the box
4. Research if it's feasible to add a potentiometer for adjusting the gain.

On point 4, from the datasheet, a 1.35k resistor sets the gain at the lowest setting of 20. There aren't any 1.35k pots available and the nearest ones don't accept a knob. So 2k is the closest available. Using an audio taper 2k pot could yield the most usable range.

I'm probably going to end up reprinting the box, but we'll see.

Thoughts anyone?

BTW, thanks again for everyone's help!
clearchris is offline   Reply With Quote
Old 07-09-2021, 11:33 PM   #51
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,202
Default Re: Signal Tracer - Requesting input on requirements

Glad you found it, crypto guys need pure white noise for random number generation, that bad IC could be worth a fortune lol.

The 1.35k resistor is built into the IC (across pins 1-8) to set its gain at 20.
A lower impedance between pins 1-8 increases the gain. Max gain 200 is with a 10uF cap and no resistor there. Gain of about 52 (34dB) is with a 10uF and 680R for example.

You could have a high/low gain switch that just puts in the 10uF+resistor or not.
The input pot lowers gain, the amplifier should be quiet with the pot set low and no long input cables.
redwire is offline   Reply With Quote
Old 07-10-2021, 12:50 AM   #52
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 6,523
Default Re: Signal Tracer - Requesting input on requirements

I have a 2sc458 that I coupled with a LM741 specifically to make white noise
Just need a power source and hook up an amplifier to it...and it's pure hiss...
eccerr0r is offline   Reply With Quote
Old 07-10-2021, 12:52 PM   #53
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

Quote:
Originally Posted by eccerr0r View Post
I have a 2sc458 that I coupled with a LM741 specifically to make white noise
Just need a power source and hook up an amplifier to it...and it's pure hiss...
Yeah, this chip would have worked great, except then it picks up AC hum too, probably adding too much non-randomness to it. Last I heard of this (and it has been a long time) people were cracking open smoke detectors, taking out the radioactive bit and attaching it to a sensor...

Quote:
Originally Posted by redwire View Post
Glad you found it, crypto guys need pure white noise for random number generation, that bad IC could be worth a fortune lol.

The 1.35k resistor is built into the IC (across pins 1-8) to set its gain at 20.
A lower impedance between pins 1-8 increases the gain. Max gain 200 is with a 10uF cap and no resistor there. Gain of about 52 (34dB) is with a 10uF and 680R for example.

You could have a high/low gain switch that just puts in the 10uF+resistor or not.
The input pot lowers gain, the amplifier should be quiet with the pot set low and no long input cables.
Yeah, no kidding. Super loud, only reason I didn't suspect it sooner is that everyone online seems to complain about hiss and noise with this chip and people respond to ground the chip better. But yeah, after attaching everything to the back, and it not making the slightest bit of difference...

A switch isn't a bad idea, I might even have something suitable on hand instead of trying to get a 2k reverse audio taper pot. Initial testing shows that having longer leads on the 1 and 8 pins doesn't affect the sound much if at all.

I have been playing some songs through this setup so I can compare when I add the longer shielded leads, and I'm now pretty impressed with this setup, it sounds far better than my logitech computer speakers. I did buy a supposedly decent speaker, IIRC, I spent under $15 for a pair, but you never know what you are going to get when you import electronics...

BTW, does anyone have any opinions on which side (or both) of the shield from the shielded wires should be grounded?

Last edited by clearchris; 07-10-2021 at 01:14 PM..
clearchris is offline   Reply With Quote
Old 07-11-2021, 09:56 AM   #54
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

So a theoretical question. Why would you, by default, want to set your gain to a static value and weaken the input signal instead? Seems to me that you would want to leave your good input signal, and adjust the gain to the minimum level required to get the sound output you want, since the amplification by the chip is what introduces noise/distortion. What am I missing here?
clearchris is offline   Reply With Quote
Old 07-11-2021, 11:05 AM   #55
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 6,523
Default Re: Signal Tracer - Requesting input on requirements

mainly for an adjustable gain circuit, as gain changes, distortion changes?
Better off attenuating input and have a fixed gain - with no distortion.
eccerr0r is offline   Reply With Quote
Old 07-11-2021, 12:04 PM   #56
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,081
Default Re: Signal Tracer - Requesting input on requirements

I have learned a lot with this post keep up the good work
sam_sam_sam is offline   Reply With Quote
Old 07-12-2021, 10:37 AM   #57
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

Quote:
Originally Posted by eccerr0r View Post
mainly for an adjustable gain circuit, as gain changes, distortion changes?
Better off attenuating input and have a fixed gain - with no distortion.
So the usual is to set your gain to a set amount with no distortion for a certain type of input. That makes sense. In this case we could be dealing with different types of input though and specifically wanting to chase down subtle noises or just general troubleshooting at full levels...

Quote:
Originally Posted by sam_sam_sam View Post
I have learned a lot with this post keep up the good work
Yeah, me too. I was really expecting this to be one of my simpler projects, and it's turning out to be a lot more complicated.

At least I found some perf board. Does anyone have a good schematic/layout tool they use? I haven't looked into it yet, but I think I'll use something like that to get the arrangement to how I like it first...
clearchris is offline   Reply With Quote
Old 07-12-2021, 04:22 PM   #58
eccerr0r
Solder Sloth
 
eccerr0r's Avatar
 
Join Date: Nov 2012
City & State: CO
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 6,523
Default Re: Signal Tracer - Requesting input on requirements

Err... no, you design your circuit for the max gain you need and fix the circuit so that it does not distort at that gain. Then you can assume for any input it will not distort - unless you're overdriving it but this is not a problem because you accounted for it already - else it wouldn't be the nondistorting max gain you need...

Anything can be made arbitrarily difficult...
eccerr0r is offline   Reply With Quote
Old 08-14-2021, 08:56 PM   #59
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

Quote:
Originally Posted by eccerr0r View Post
Anything can be made arbitrarily difficult...
This may be my new motto.

Well, I decided against using my crusty 20 year old perfboard, and the new perfboard arrived 2 days ago. It's going together pretty well. Unfortunately, my garage has to be over 100F, so I'm doing it in shifts. I should have something soon.

If I'm really lucky, I might get it into the same general form as the old board with an adapter and cutting the end of the board. We'll see...
clearchris is offline   Reply With Quote
Old 11-02-2021, 09:49 PM   #60
clearchris
Badcaps Veteran
 
clearchris's Avatar
 
Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
I'm a: Hardcore Geek
Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

I had to spend some time out of town, I'm back on the project. It's all together on the perfboard and I used shielded cable for the connections to the pot. I'm not picking up any noise from the flourescent lights any more.

However, I'm also not getting much amplification either. While connected to the 3' speaker If I turn up the volume past a quiet speaking voice volume, the audio starts dropping out at parts. I can turn it up with headphones connected I can raise the volume much further, to where the headphones start distorting.

I suspect something was damaged when I was breadboarding. I'm going to take the caps off tomorrow and test/replace, anyone have any other possible suspects?
clearchris is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2021
Powered by vBulletin ®
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 09:19 PM.
Did you find this forum helpful?