Replacing Panoramic Potentiometers On Subwoofer

[TLS Guy]

Great. _-_

I put on Bausch and Lomb ReNu on the knobs and turned them alot and then the crackling actually stopped but it sounded the same so then I put more and now it won't even turn on anymore...

Please help me. ;-;

Check your sub manual. Some subs have their crossover disabled as to whether the L or R sub input is used.

If your manual says the crossover is active on all connections, then somehow the crossover has failed. However this would be a really odd fault and for the life of me I can think of one way that could happen. That would have to involve the disconnection of the feedback loops and or failure of the same circuit inside multiple op amps. That would be highly unlikely. So I have to feel operator error has by passed the subs crossover some how.

The most likely failure of a crossover would be no sound.

 

[SunnyOctopus]

Check your sub manual. Some subs have their crossover disabled as to whether the L or R sub input is used.

If your manual says the crossover is active on all connections, then somehow the crossover has failed. However this would be a really odd fault and for the life of me I can think of one way that could happen. That would have to involve the disconnection of the feedback loops and or failure of the same circuit inside multiple op amps. That would be highly unlikely. So I have to feel operator error has by passed the subs crossover some how.

The most likely failure of a crossover would be no sound.

Okay. The subwoofer turns on now, but it makes almost no sound with everything turned up max.

Someone please guide me. I am a sad, lost bunny in the dark. I just want a subwoofer. ;-;

 

[TLS Guy]

Okay. The subwoofer turns on now, but it makes almost no sound with everything turned up max.

Someone please guide me. I am a sad, lost bunny in the dark. I just want a subwoofer. ;-;

It seems your sub has a progressive failure. It might be you have got some of the cleaner on the circuit board.

This is now an impossible problem to trouble shoot at long range. It likely is not possible for you to trouble shoot it either without test gear.

This hobby is now complex.

I personally think that anyone in this hobby for the long haul should learn how to use test gear. At the minimum I recommend an amplified high impedance universal meter, an audio generator and a two channel scope.

With an investment in a little study and the purchase of suitable test equipment, then light is usually shed on strange problems pretty quickly.

Having test gear is really step one on fixing just about anything these days.

I just hauled a boat off a reed bank a few days ago with a dead engine. Without ignition test equipment I would have had to send the guy to an expensive service shop. However test gear soon isolated the problem to a failed kill switch. On analysis one of the three ignition coils was bad causing an intermittent spark on number one cylinder. Everything else checked out good. So with $70 of parts he was soon back in the water. None of this would have happened if I just guessed.

The point is that in any technical pursuit, it is important to have the means to find and deal with a lot of your problems.

 

[SunnyOctopus]

Okay, if I turn up the crossover to 200 and the level on the sub to max and the volume on my pc control to 100

I can hear the sub. Turning the volume knob still seems to work, it's just the volume is extremely low... The low pass knob seems to do nothing.

 

[TLS Guy]

Okay, if I turn up the crossover to 200 and the level on the sub to max and the volume on my pc control to 100

I can hear the sub. Turning the volume knob still seems to work, it's just the volume is extremely low... The low pass knob seems to do nothing.

I think you are now facing a situation that you will not make progress with without instruments. I certainly doubt I could even if I was on site without instruments.

 

[SunnyOctopus]

I think you are now facing a situation that you will not make progress with without instruments. I certainly doubt I could even if I was on site without instruments.

Awww.... :'[

Thank you all so much for your time and effort. I really appreciate it.

 

[SunnyOctopus]

Okay! Update. This morning it sounds like it used to before I put the cleaning contact on, but the level knob wouldn't move. It was stuck until I put alot of force into moving it. It moves now, but it is difficult to move. The low pass knob still seems to do nothing, the crackling has returned, but now it also does a loud beeping sound when turning it. I kind of like it because to me it seems like a sign that someone could identify and tell me what's wrong.

If this new information is not helpful, I will just open it up later today. : 4

 

[TLS Guy]

Okay! Update. This morning it sounds like it used to before I put the cleaning contact on, but the level knob wouldn't move. It was stuck until I put alot of force into moving it. It moves now, but it is difficult to move. The low pass knob still seems to do nothing, the crackling has returned, but now it also does a loud beeping sound when turning it. I kind of like it because to me it seems like a sign that someone could identify and tell me what's wrong.

If this new information is not helpful, I will just open it up later today. : 4

In that case I would go ahead and replace the pots.

The values should be stamped on them and say whether they are log or linear taper. You must use pots of the same value and taper.

I would not get them from rat shack. I would order good ones from Mouser electronics.

You will need to desolder the wires from the pots and remember where they go. Then remove the old pots. Install the new pots and resolder the wires.

 

[SunnyOctopus]

In that case I would go ahead and replace the pots.

The values should be stamped on them and say whether they are log or linear taper. You must use pots of the same value and taper.

I would not get them from rat shack. I would order good ones from Mouser electronics.

You will need to desolder the wires from the pots and remember where they go. Then remove the old pots. Install the new pots and resolder the wires.

Okay. Excellent. I'll try and do this. I'll take pictures of everything and hopefully the internet can guide me through it. Do you think I should do this, or just cut my losses an save for a new sub?

 

[TLS Guy]

Okay. Excellent. I'll try and do this. I'll take pictures of everything and hopefully the internet can guide me through it. Do you think I should do this, or just cut my losses an save for a new sub?

I would go ahead. What do you do you have to loose?

 

[SunnyOctopus]

The pots said: A100k
3bw and B100k
3bw

I saw nothing that looked wrong. Here is a picture:

So I will just need to buy replacement pots from that site and then use a soldering iron to install them? Could you link me to the ones I need to buy? : 3

Edit: Is it this?
http://www.radioshack.com/product/index.jsp?productId=2062302
I like Radioshack because I can walk to it. I don't have a credit card, and I don't want to have to borrow someones. I'm probably going to need some help installing them, too...Do I even need to replace the volume one? It doesn't seem to have any problems.

 

[TLS Guy]

The pots said: A100k
3bw and B100k
3bw

I saw nothing that looked wrong. Here is a picture:

So I will just need to buy replacement pots from that site and then use a soldering iron to install them? Could you link me to the ones I need to buy? : 3

Edit: Is it this?
http://www.radioshack.com/product/index.jsp?productId=2062302
I like Radioshack because I can walk to it. I don't have a credit card, and I don't want to have to borrow someones. I'm probably going to need some help installing them, too...Do I even need to replace the volume one? It doesn't seem to have any problems.

The pots are ganged. Also they are PC mount. Look on the control to see if the pots are linear or log, the latter sometimes known as an audio taper.

The volume control will be log for sure, the crossover control could be either.

Ganged pots are getting very hard to come by. Radio Shack do have one ganged pot on their catalog and it is 100K log taper. That will work for your volume control, and will work for the crossover. However of your current control is linear, then the frequency marking will be way off.

You will have to remove the circuit board to do this repair. You will need a soldering iron and a vacuum desoldering iron to do this repair safely and neatly. Be careful not to damage the printed circuit board conductors. They are fragile. Be careful not to cause shorts on the board with spreading solder. Check all joints with a meter, and make sure you have not caused any shorts on the board.

Then reinstall the board.

 

[SunnyOctopus]

The pots are ganged. Also they are PC mount. Look on the control to see if the pots are linear or log, the latter sometimes known as an audio taper.

What is ganged? What is PC mount? What is linear or log and how do I check which the pots are? What's a control? >_>

Ganged pots are getting very hard to come by. Radio Shack do have one ganged pot on their catalog and it is 100K log taper. That will work for your volume control, and will work for the crossover. However of your current control is linear, then the frequency marking will be way off.

What does the frequency marking will be way off mean? That if I move it to where it says 50hz it might actually be something else, but it will change?

You will have to remove the circuit board to do this repair. You will need a soldering iron and a vacuum desoldering iron to do this repair safely and neatly. Be careful not to damage the printed circuit board conductors. They are fragile. Be careful not to cause shorts on the board with spreading solder. Check all joints with a meter, and make sure you have not caused any shorts on the board.

Then reinstall the board.

Thank you! I feel hopeful. : ]

 

[TLS Guy]

Thank you! I feel hopeful. : ]

Ganged means there are two pots on one shaft. PC mount means it is connected directly to the PC board and not with wires. This means you may have to get creative to make the connection to the PC board, because either the spacing, and or size of the pot connectors are different from the original.

A linear taper means the resistance on the pot wiper changes in linear fashion with rotation. In other words at the mid point the resistance of the center wiper will be 50 K to each of the connectors beside it.

A log taper means that the resistance to the wiper changes with the log of degrees of rotation. Volume controls are always this way, as to double the loudness you have to increase power 10 times. So this is why the relationship to rotation and change of resistance is log to the base 10.

So if the crossover control is linear, and you replace it with log the crossover will change log to base 10 with rotation and not in linear fashion.

I have a feeling the crossover taper will be linear, but it might not be depending on the circuit.

 

[SunnyOctopus]

Ganged means there are two pots on one shaft. PC mount means it is connected directly to the PC board and not with wires. This means you may have to get creative to make the connection to the PC board, because either the spacing, and or size of the pot connectors are different from the original.

A linear taper means the resistance on the pot wiper changes in linear fashion with rotation. In other words at the mid point the resistance of the center wiper will be 50 K to each of the connectors beside it.

A log taper means that the resistance to the wiper changes with the log of degrees of rotation. Volume controls are always this way, as to double the loudness you have to increase power 10 times. So this is why the relationship to rotation and change of resistance is log to the base 10.

So if the crossover control is linear, and you replace it with log the crossover will change log to base 10 with rotation and not in linear fashion.

I have a feeling the crossover taper will be linear, but it might not be depending on the circuit.

Okay. I hate to be annoying, but I have close to no idea what you're talking about. I'm sorry!

I want to make this as simple as possible for myself since I don't know what I'm doing at all, do you think you could give me step by step instructions if I provided you with detailed pictures?

As I gather it as of now, step 1 is to buy the vaccum desolder and 1 of those things you linked me to from radioshack (I already have a soldering iron). Step 2 is to disconnect the circuit board ( I do not know how to do this, but might be able to figure it out). Step 3 is to desolder the crossover pot using the vaccum desoldering iron? Step 4 is to solder on the replacement. Step 5 is to put back the circuit board. Step 6 is to screw it back closed.

Is that right? Thank you so much. You are reviving my dreams of quality audio. : D

 

[TLS Guy]

Okay. I hate to be annoying, but I have close to no idea what you're talking about. I'm sorry!

I want to make this as simple as possible for myself since I don't know what I'm doing at all, do you think you could give me step by step instructions if I provided you with detailed pictures?

As I gather it as of now, step 1 is to buy the vaccum desolder and 1 of those things you linked me to from radioshack (I already have a soldering iron). Step 2 is to disconnect the circuit board ( I do not know how to do this, but might be able to figure it out). Step 3 is to desolder the crossover pot using the vaccum desoldering iron? Step 4 is to solder on the replacement. Step 5 is to put back the circuit board. Step 6 is to screw it back closed.

Is that right? Thank you so much. You are reviving my dreams of quality audio. : D

I would replace both pots.

A pot is a variable resistor. Between the outer connections is the fixed resistor, in your case 100K. The middle connection is the wiper. As you rotate the control, the resistance increases from the pin it is moving away from and decrease to the one it is moving towards. At either extreme resistance to the pin the wiper meets is zero. In a linear pot the fixed resistance at point is directly proportional to the distance from the outer pins. In a log control it varies by log to base 10 of the distance.

I doubt I can help you much from photographs. You need to jump in and get experience. Research variable resistor on the NET, and learn how these controls work.

You have an old non functional unit. It is good for you to get started now in increasing your knowledge and skills. If you muck it up, dust yourself off and vow to do better next time.

Just about any fool can buy new equipment and plug it in, although we have a had a few here lately, too stupid to own equipment, who can't even do that. The serious enthusiast gets experienced in service and maintenance to keep his gear going longer.

 

[SunnyOctopus]

I would replace both pots.

A pot is a variable resistor. Between the outer connections is the fixed resistor, in your case 100K. The middle connection is the wiper. As you rotate the control, the resistance increases from the pin it is moving away from and decrease to the one it is moving towards. At either extreme resistance to the pin the wiper meets is zero. In a linear pot the fixed resistance at point is directly proportional to the distance from the outer pins. In a log control it varies by log to base 10 of the distance.

I doubt I can help you much from photographs. You need to jump in and get experience. Research variable resistor on the NET, and learn how these controls work.

You have an old non functional unit. It is good for you to get started now in increasing your knowledge and skills. If you muck it up, dust yourself off and vow to do better next time.

Just about any fool can buy new equipment and plug it in, although we have a had a few here lately, too stupid to own equipment, who can't even do that. The serious enthusiast gets experienced in service and maintenance to keep his gear going longer.

Okay. Just one last question, I think. You said I'd need to desolder the wires replace the pots and then resolder them to the new pots, but there are no wires on the curent pots. They seem to connect another way.

 

[TLS Guy]

Okay. Just one last question, I think. You said I'd need to desolder the wires replace the pots and then resolder them to the new pots, but there are no wires on the curent pots. They seem to connect another way.

I know that I told you they were mounted directly to the PCB. That is why I said you might get creative and have to remove the board as you will have to desolder and resolder from the other side. Please read my posts or this gets tiresome.

I need a side view, to see if they are ganged or not. It might have been a reflection in the photo. Also one pot says A 100K, which means it is log taper. Does the other one have an A in front of the 100K. If not it is linear. My guess is the volume is log and the crossover linear.

 

[SunnyOctopus]

OKAY! I replaced the pots and everything seems to have gone smoothly. They no longer crackle or beep, but the bass is still easily localizable at 51hz, and the crossover on both the sub and the computer still seem more like a volume knob...

What do you guys think? Am I just a bass genius capable of detecting it when the location when it's not supposed to be detectable?

 

[TLS Guy]

OKAY! I replaced the pots and everything seems to have gone smoothly. They no longer crackle or beep, but the bass is still easily localizable at 51hz, and the crossover on both the sub and the computer still seem more like a volume knob...

What do you guys think? Am I just a bass genius capable of detecting it when the location when it's not supposed to be detectable?

Probably both crossovers are too low in order. Try setting both to 60 Hz and cascade them and see if that helps.