Crossover on 5A Bad?

TomL

Hi -

I have a Polk 5A speaker that had a muffled sounding tweeter. I replaced the tweeter and it sounded great. Now that tweeter is muffled sounding. I switched the negative and positive speaker wires and it started working - I thought that was the problem. Hence, though, it's back to sounding muffled. I'm guessing that the tweeter is fine but the crossover is defective somehow.

Does anyone have any thoughts about this? Thanks, Tom

treitz3

Hey, another Tom! Please allow me to offer you a very warm welcome to Club Polk.

Are you sure the connections at the tweeter and all connections leading up to said tweeter are secure with no compromise?

You also want to make sure that the phase is correct, otherwise it will throw things off.

Tom

F1nut

You are tripping the polyswitch, which is tripping early due to be tripped too many times. Basically, it is worn out.

TomL

Thank you, Treitz3. I soldered the wires when I installed the tweeter but perhaps I should open it up and double check.

TomL

Thanks, F1nut. What is a polyswitch and how does that impact the tweeter?

TomL

The 5As are rated at 40w and I'm using a 100w Sony receiver.

mhardy6647

The polyswitch is a self-resetting circuit breaker of sorts.

https://www.parts-express.com/search?keywords=polyswitch&order=relevance:desc

Also known to some as Satan spawn. They have a reputation of being not quite audibly transparent.

TomL

Thanks, mhardy6647. I don't see that part on the crossover. Where would it be located?

TomL

Correction: the tweeter is not muffled - it's not emitting sound.

Gardenstater

If they truly are 5A they would have the Peerless tweeter and a fuse on the back of the crossover. I would start by checking and making sure the fuses are good and that the fuseholders and fuses are making good contact by cleaning them with some 00 steel wool or the like.

Do you have a meter and know how to use one? I would check the tweeter and see how it reads. If you can't get a reading with the ohmmeter then it has an open voice coil. You would have to remove one of the tweeter wires at the crossover to get a reading just of the tweeter since yours are soldered.

F1nut

TomL wrote: »

The 5As are rated at 40w and I'm using a 100w Sony receiver.

Ha, you can forget that nonsense. However, the Monitor 5 specs from another post of mine, "They are 6 ohm nominal. The -3dB limits are 43Hz-20kHz. Recommended amplification is 20-125 watts per channel."

With that nonsense stated what has happened to your speakers to cause the polyswitches to trip and wear out is called clipping. When an amplifier is overdriven it causes distortion, which results in clipped signals being sent to your speakers. The distortion/clipped signals generate heat, so when the polyswitch reaches its thermal limit it trips. The purpose for tripping is to prevent the clipped signal from reaching the tweeter and causing serious damage. Once the polyswitch has cooled down it resets and allows the signal to pass again. However, the polyswitch becomes hypersensitive after being tripped and each time it is tripped it becomes even more hypersensitive ending up where you are now.

To prevent clipping regardless of whatever power one is using one must know the limits of their gear. Rule number one is never go past halfway on the volume knob. Rule number two is when the sound becomes strained/harsh turn it down because the power source is clipping.

My rule, never use a Sony receiver.

TomL

Thanks, F1nut, I don't play my speakers loud (small house). Where would I find the polyswitch to replace it? From the link that mmhardy sent, I don't see that part on the crossover.

George from the great state of NJ, I will try to clean the fuse. Not sure how this would impact the tweeter and not the woofer.

Gardenstater

Your speakers don't have a polyswitch, just a fuse that protects the tweeter only. It should be 1A fast blow. Earlier model 5's probably had two fuses, one for the tweeter and one for the midwoofer.

F1nut

Ah well, if you have a fuse on the binding post plate then you don't have a polyswitch. As mentioned, clean the fuse holder and fuse ends. Use a pencil eraser or a metal cleaner. Steel wool should not be used. If still no sound the fuse is bad.

The fuse or polyswitch is connected to the tweeter circuit only.

TomL

Got it. Thanks, F1nut. Thanks, all.

Gardenstater

Correction. Ultra fine steel wool works great but it is 0000 (not 00). 1000 grit and finer sandpaper if you happen to have it also works good. Pencil erasers are good too. Used to clean the copper contacts on the Aurora HO Model Motoring race cars when I was a kid with an eraser.

TomL

So I switched the fuses - now the speaker works (this makes me really happy - thank you F1nut).

Just need to get a new fuse. Does anyone know where I can get a fuse compatible with the 5A? I think i've gotten this at a hardware store many moons ago - kind of hazy.

treitz3

The fuse rating and voltage should be imprinted/stamped on the end casings.

Tom

F1nut

You can buy them at most hardware stores as well as Amazon.

Gardenstater

F1nut wrote: »

TomL wrote: »

The 5As are rated at 40w and I'm using a 100w Sony receiver.

Ha, you can forget that nonsense. However, the Monitor 5 specs from another post of mine, "They are 6 ohm nominal. The -3dB limits are 43Hz-20kHz. Recommended amplification is 20-125 watts per channel.

10 - 60 WPC and 8 ohms nominal impedance and 40-21kHz +/- 3 dB. In the interest of accuracy, from the brochure I was given in 1979 when I purchased my 7Bs. This is for the 5A, 7B, and 10A even though they don't show the letters.