Installing Non Polarized caps in a circuit correctly.

[WRGKMC]

Most beginners will think only Electrolytic caps have polarities. If you connect them to a circuit they will likely explode.

The fact is even your non polarized caps have a right and wrong way of installing them. In the old days manufacturers used to

put a band or a dot on the positive end of a non polarized cap. in cases where a cap is connected to ground, the outside foil layer

acted as a shield to block noise and the inside foil would see and impedance.

 

This marking system has been abandoned by many manufacturers over the years because many of these caps get installed robotically

and the robots are too stupid to know which end is which. The results is you may get one amp that has them in right and sounds great while the next amp can have many or all in backwards and be a beehive for ac hum and noise.

 

I've taken amps myself and gone through them and corrected all the caps and the differences in tone and clarity can be amazing.

The problem is how do you know which side of the cap is the inner foil and which side is the outer.

 

I learned this handy trick many years ago from an Ace tech who really knew his stuff. You take an oscilloscope and set its voltage sensitivity to the lowest level.

Then you connect to both leads. You next hold the cap in your fingers tightly and read the meters amplitude. Then swap the leads around.

 

When the positive lead is connected to the outside foil, your body which has all kinds of EMF traveling through it, will induce more hum in the cap from the outside in and the scope rill read a high level. If the positive O scope lead is on the inside layer and the ground lead is on the outside layer, there will be much less hum read by the scope. That outside layer blocks hum when its grounded and if the out leads on the outside it acts like an antenna to pick up hum and noise.

 

If you don't have a scope you can probably use an amplifier and AC source. Connect the cap to two leads of an amp. (Something that has a meter like a Mixer might be better)

Put the cap close to an AC coil and see how much hum it has, then swap the leads. The one with less hum means the hot lead can be marked with a dot of white out or a Marker pen. Then when you build your project you always place the ground side towards the lesser potential. For example, if the cap is used as a coupling cap, make the ground the input and the dot the output.

 

If the caps are connected somewhere between the frame and signal path keep the dot side pointed towards the signal and the ground towards the ground.

 

The effect of one cap being in backwards is likely going to be negligible. When you have many caps the effects are collective and by the time the signal makes it all the way through the amp, you can have all kinds of harmonic hum and distortions collecting along the way. If you want the highest quality sound caps are a huge factor to getting good sound quality. Also keep in mind many of those hand built tube amps followed these guidelines and its likely a good reason for their coveted sound and longevity.