Back to basics capacitor question

[Joe BKNY]

I'm replacing the foam surrounds of the woofers in a vintage pair of speakers - Sound Dynamics 300ti. While I'm at it I thought I'd replace the crossover capacitors:

Do I need to pay attention to the orientation / polarization (not sure of the correct term) when I install the new ones? Should I be extra careful about overheating the capacitors when soldering?
FYI - these speakers are obviously not great, or maybe even good. Their job is to be the warm-up act for something much better. More (questions) about that later!
Thanks in advance for your help.

 

[Plcamp]

Soldering should not be a problem with those caps.
They are not polarized so either orientation ok.
Secure them physically with a glue or zip tie.
Avoid mounting them close to the power resistor.

They likely won’t make audible difference IMO.

Good luck!

 

[DVDdoug]

Are the black capacitors the original's and the off-white ones the replacements?

The black ones are non-polarized electrolytic capacitors. Electrolytic capacitors rely on "chemistry" and they can lose capacitance over time. The tolerance is probably also worse than the new (film?) capacitors.

Most other kinds of capacitors are perfectly stable and will last "forever" if not somehow damaged. The same is true for the coils and resistor.

The old capacitors probably haven't deteriorated that much and it might not make any difference, but since you have them you might as well change them...


If the old foam was rotted-away, the new foam will make a HUGE difference! And normal human psychology will make you think the capacitor replacement made an improvement too!

 

[SIY]

Other thing is that if you're replacing electrolytics with film caps, put about 0.1 ohm in series with the new caps. I learned this the hard way.

 

[egellings]

I'm replacing the foam surrounds of the woofers in a vintage pair of speakers - Sound Dynamics 300ti. While I'm at it I thought I'd replace the crossover capacitors:

View attachment 287384View attachment 287385

Do I need to pay attention to the orientation / polarization (not sure of the correct term) when I install the new ones? Should I be extra careful about overheating the capacitors when soldering?
FYI - these speakers are obviously not great, or maybe even good. Their job is to be the warm-up act for something much better. More (questions) about that later!
Thanks in advance for your help.

Either way of connecting the caps will be fine, since they are non-polar. Any physical orientation will be fine for them.

 

[Joe BKNY]

Other thing is that if you're replacing electrolytics with film caps, put about 0.1 ohm in series with the new caps. I learned this the hard way.

Thank you. I’ve already learned plenty of other stuff the hard way so I’m happy to skip a lesson. Because my middle school electronics unit was 50+ years ago I have to ask : add the resistor to one of the wire leads of each capacitor? Like so?

Also curious: what problem does the resistor prevent?

 

[fpitas]

Thank you. I’ve already learned plenty of other stuff the hard way so I’m happy to skip a lesson. Because my middle school electronics unit was 50+ years ago I have to ask : add the resistor to one of the wire leads of each capacitor? Like so?
View attachment 287571
Also curious: what problem does the resistor prevent?

The old caps had ESR, effectively an internal resistance. That will affect the crossover filter curve. Film caps have a very tiny ESR.

 

[SIY]

Thank you. I’ve already learned plenty of other stuff the hard way so I’m happy to skip a lesson. Because my middle school electronics unit was 50+ years ago I have to ask : add the resistor to one of the wire leads of each capacitor? Like so?
View attachment 287571

Yes, exactly. It's a substitute for the electrolytic's higher ESR, as fpitas said.

 

[Joe BKNY]

Yes, exactly. It's a substitute for the electrolytic's higher ESR, as fpitas said.

Thanks! I see that resistors are also specified in Watts - I’m seeing from 1 Watt up to 100 Watts… What do you suggest? My amp is rated for 84 watts per channel @8ohms…

 

[fpitas]

Thanks! I see that resistors are also specified in Watts - I’m seeing from 1 Watt up to 100 Watts… What do you suggest? My amp is rated for 84 watts per channel @8ohms…

2W resistors are cheap on Amazon. That's more than enough in that position.

 

[egellings]

Thank you. I’ve already learned plenty of other stuff the hard way so I’m happy to skip a lesson. Because my middle school electronics unit was 50+ years ago I have to ask : add the resistor to one of the wire leads of each capacitor? Like so?
View attachment 287571
Also curious: what problem does the resistor prevent?

It limits high inrush current that could damage components in circuit with the capacitor. It also just might, in some circumstances, damp out possible parasitic oscillations in applications involving amplifiers using feedback, although I would doubt the design competency of a circuit needing that kind of a fix.

 

[Joe BKNY]

Thanks to all for your help! Probably easy for you, and yet large scale help to me!

 

[egellings]

Thanks to all for your help! Probably easy for you, and yet large scale help to me!

We're both here to learn things and to share any applicable knowledge.