monitor 12 crossover

krogersclan

Appears I have a non-functioning crossover, anyone have a solution? I'm having a difficult time finding replacement.
Thanks
Kerry

krogersclan

here's a picture

krogersclan

agfrost

Symptoms? Would like to understand it what way "it's not working." No sound at all, or tweeter cutting in and out, or no tweeter at all, or "?" Details will help diagnosis and trouble-shooting.

No replacement crossovers to be purchased new (Polk stocks drivers and upgrade tweeters, but not passive radiators or crossovers for speakers of this vintage), but they can be rebuilt if that's what's needed. On the whole, the Monitor 12 has a relatively simple crossover that isn't too expensive to replace parts (capacitors, resistor) on. If the tweeter is intermittently cutting out, the polyswitch (yellow disc) is a likely culprit and can be deleted or replaced with a 0.5ohm wirewound resistor.

Welcome to Club Polk, best forum on the internet. I always found the Monitor 12 to be a visually arresting speaker--I lusted after it ~25 years ago, although my budget at the time left me purchasing Monitor 5jr+!

Polk&Beans

Replace all those caps with MPT's and you're probably good to go. Electrolytic caps do die after time and those are very old.

pitdogg2

Do not believe poly can be omited on these. Its in line with a cap.

F1nut

You can remove the poly, no problem, but I would replace it with a .5 ohm resistor.

krogersclan

Thanks to all who are pitching in, the tweeter is not intermittently cutting out - just appears to be nonexistent or really faint, but not cutting in and out

agfrost

It's possible that the tweeter may have been fried by too much (clipping) signal. Some place a paper towel tube next to tweeter dome and listen at tube's end to more effectively hear whether that tweeter is functional or not.

If tweeter makes no (or diminished) sound, I'd carefully swap the tweeters between the two speakers. If the problem moves to the other speaker, then the tweeter is definitely bad. If the same speaker is bad, then we're looking at a crossover or wiring issue in that speaker. (You may even find that the tweeter has become disconnected internally! Tweeters on that model are connected by faston tabs, a little pulling will allow you to disconnect the tweeter from the internal wiring. Easy does it; you don't want to break the tabs on the tweeter itself.

The tweeters on the M12 are SL2500. Polk still sells a replacement/upgrade, the RD0-198, which is a drop-in replacemnt for the SL2500. Call customer service, tell them you're a forum member and you get a small discout/free shipping to the lower 48 states. I'd order a pair if I was needing to replace one--you'd be able to hear a difference between speakers otherwise.

krogersclan

Would I just remove the mustard colored "block" and replace with resistor? What size? And does it need to be soldered?

krogersclan

agfrost - thanks for info, I will start with testing tweeter (and make sure connected)

agfrost

If you do remove it:

1) Most commonly used: a Mills 12W 0.5ohm resistor http://www.soniccraft.com/index.php/mills-12-watt-c-29_53_63

2) Yes it should be soldered in. Removing that polyswitch will desolder the capacitor it's paralleled with (schematic here)--at this point, I'd be like "Hmm. Might as well replace them capacitors, too!" Then budget becomes a question; a budget (Film, not electrolytic) capacitor selection might include Daytons or Clarity PX; better/moving up the $$ might be Sonicaps or Clarity ESA. The main resistor would also be a prime target for replacement (again, Mills 12W).

Such decisions are dependent on your love for/goals for the speakers, and your willingness to pick up a soldering iron!

Edit: All upgrades should be done in parallel (done to both speakers)--you don't want imbalance between the two.

agfrost

...If you want to use them & love them & keep them a while, crossover upgrades are a great way to increase your enjoyment of them.

If you're just trying to get 'em up and running because you want to sell them or they're not for careful listening, I wouldn't spring for the upgrades. I've upgraded crossovers two pairs of my Polks (RTA 11TL and SDA 2B) and don't regret it--but I've kept them for 7 and 5 years after the work and expense. A person selling upgraded speakers won't recoup the money put into them. That's just a fact. But if it upgrades your listening experience for a good period of time....That's worthwhile!

krogersclan

I'm planning to keep, purchased new in 1990

agfrost

Awesome!

krogersclan

you've been a great help! will let you know what I find tonight with tweeters

westmassguy

F1nut wrote: »

You can remove the poly, no problem, but I would replace it with a .5 ohm resistor.

No! Do not remove the Polyswitches on those. They're revised. Note how it's shunting the small cap. See Schematic_M12_REV

pitdogg2

westmassguy wrote: »

F1nut wrote: »

You can remove the poly, no problem, but I would replace it with a .5 ohm resistor.

No! Do not remove the Polyswitches on those. They're revised. Note how it's shunting the small cap. See Schematic_M12_REV

I was pretty sure we had discussed this before Dave. Glad you chimed in. Sometimes these schematic's run together in my mind.

F1nut

F1nut wrote: »

You can remove the poly, no problem, but I would replace it with a .5 ohm resistor.

I need to correct the myself. WMG and pitdogg are right, do not remove the polyswitch and do not replace with a resistor.

[Deleted User]

I've got the crossover main board without the big inductor under it from my Monitor 12 series 2's. All wiring from crossovers to drivers is still intact. You can have them for cost of shipping if you want them.

[Deleted User]

BTW, the replacement tweeters mentioned above (RDO-198's) are worth every penny in Monitor 12's. I was a little doubtful they'd make much of a difference but some how the made the entire speaker sound better. Simple plug-n-play down to the correct spade connector sizes.