7b's crossover help

jakelm

Hey guys and gals. I've decided to referbish my old xovers in my 7b's. I ran into a confusing situation. Here is a pic of one of my 7b's xover.

A = 4.5ohm 5watt
B = 2.7ohm 5watt
C = 12uF Maylar
D = 34uF or 27uF Electrolyc (I can't see, the cap is turned under)
E = .23mH coil

Now here is the problem. There is no schematic on this xover here @ Polk. All of the schematics in the trouble shoot thread have only one resistor (generally 2.0ohm). My 7's are dated '81. They do have the peerless. Why can I not find the schematics on this xover?

I know this has been covered a billion times. But just to refresh my memory,
Solen would be a best replacement for both the 12uF and 34uF. Or should the 12uF be the only cap I would need to upgrade?

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=027-572

I dont think reistors break down, do they?

I'm trying to stick with PE for everything. But I dont think I need to change everything on the xover, do I?

Jake

ben62670

You have to do the big caps also. It makes the mids soo much less muddy. Not that I thought they were muddy before, but after side by side comparisons the mids were much cleaner, and snappier with new caps. Mills doesn't have a 2.7 ohm res at PE, but originals were only 5% which puts the 2.5's within specs.
Ben

jakelm

The resistors are still showing to spec, so I think I will leave them be. I will change out the 2 caps, this Solen for the 12uF Maylar.
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=027-572

What do you recommend for the 27uF cap (since you just did a similar upgrade)? I'm not quite sure what type of cap it is. If I could find a schematic sheet with details on the crossover parts. But it seems like in my Polk world, my xover doesnt exist.

jakelm

The 10watt 2.7ohm dayton resistors will fit. So I can upgrade the resistors with those, if I want to upgrade the resistors in the future.

ben62670

The price difference is only about $7 for the mills. Also the stock resistors are only 5watts. From electrical experience when a resistor gets hot it looses resistance. The ones you have may read fine, but are rated at lower watts, and are about 25 years old. for $15 or so I would rather just have piece of mind with the replacements. I wouldn't worry about .2 ohms either. If you look at many of the wiring diagrams from Polk the switched resistors around quite a bit.
Enjoy your project
Ben

jakelm

They did switch resistors around a bit. Do the Mills work better than the non-inductive Dayton resistors?

I wish I could find the schematics of my xover.

As for the caps, what would you replace the 12uF and the 27uF with?

ben62670

jakelm wrote:

They did switch resistors around a bit. Do the Mills work better than the non-inductive Dayton resistors?

I wish I could find the schematics of my xover.

As for the caps, what would you replace the 12uF and the 27uF with?

I have absolutely no idea, but I have read a ton of times that nearly everyone uses the mills. I am kinda a freak when it comes to working on my speakers. I would have a little Demon running around in my head saying you should have used the mills ,you should have used the mills ,you should have used the mills. Now that I said that I did use solen caps instead of sonicaps because of the large monetary difference between the two. For $7 I don't want to hear voices till I turn the stereo on:eek:

I'm not Paul Harvey
Good Day

jakelm

LOL....

As when caps are concerned, I know they all do the same thing, I just dont understand (becides one lasting longer than the other), what the difference is.

I guess I will need to read up on the differences between Solen metalized and polyfilm and foil and electrolytic.

Ricardo

Change both caps for Solen metallized plypropylene (PB). While you are at it, change the resistors also; use Mills 12watts.

Edit: Why? because that's what most people have used with great results

dorokusai

An upgraded path is simply better, just choose a decent component and the actual brand matters little. Be different, do something new.

jakelm

dorokusai wrote:

An upgraded path is simply better, just choose a decent component and the actual brand matters little. Be different, do something new.

So basicly what your saying is : It really doesnt matter wether you go with polyfil or metalized polypropylene or metalized film or electrolityc or any of the others, just as long as its the same or close specs?

But the Solen have been found to work best.

Ricardo

Experimenting is good, but there are differences in different caps types/brands. Solens are good, but Sonicaps are better, and if you want to be adventurous and have the money, use Mundorf caps and Vishay resistors.

jakelm

I understand....

But actual makeup inside the caps doesnt necessarally mean anything?

dorokusai

jakelm wrote:

So basicly what your saying is : It really doesnt matter wether you go with polyfil or metalized polypropylene or metalized film or electrolityc or any of the others, just as long as its the same or close specs?

But the Solen have been found to work best.

Correct. I find little sonic difference in like priced electrolytics and the high dollar stuff doesn't make any sense for an older speaker like a MON or SDA. I think there is a drastic difference in oil caps but we're splitting hairs here. Perhaps my ears have lost touch with reality but pick a decent manufacturer and I'm betting you won't be unhappy.

jakelm

Ok...Bill from PE for:

2 = 12uF Solen caps
2 = 33uF Solen caps
2 = 27uF Solen caps
2 = 2.5 Mills resistor
2 = 4.5 Mills resistor

Totoal = 70.79

The funny thing is I only spent $80 for the speakers..I hope the upgrade is worth it.

Jake

jakelm

I still cant find any schamatics of my crossover. All of Polks schamatics have one 2.5ohm resistor. None have the set-up with 2 resistors (2.5ohm and 4.7ohm) like mine.

Ricardo

jakelm wrote:

Ok...Bill from PE for:

2 = 12uF Solen caps
2 = 33uF Solen caps
2 = 27uF Solen caps
2 = 2.5 Mills resistor
2 = 4.5 Mills resistor

Totoal = 70.79

The funny thing is I only spent $80 for the speakers..I hope the upgrade is worth it.

Jake

It should be cheaper than that....you need the 27 uF OR the 33 uf, not both...right?

Only your ears will tell you if it was worth it, but chances are you'll like it; even if you used the stock components, a 25 years old capacitor is probably not in specs any more.

jakelm

HTrookie wrote:

....you need the 27 uF OR the 33 uf, not both...right?

.

I dont know. The resistor is turned upside-down and no schematics are found for my xover.

jakelm

HTrookie wrote:

It should be cheaper than that.....

Cheaper where? I have shopped many online electronics stores and I always come back to PE.

ben62670

jakelm wrote:

I still cant find any schamatics of my crossover. All of Polks schamatics have one 2.5ohm resistor. None have the set-up with 2 resistors (2.5ohm and 4.7ohm) like mine.

Thats becuase you have the peerless tweeters.
Just replace the stock components with the same values that you have in there now.
Unsolder one leg of the stock cap and read the value of the cap.

Ricardo

jakelm wrote:

Cheaper where? I have shopped many online electronics stores and I always come back to PE.

I say it should be cheaper than that, because you are listing three capacitors and you only need two. It is either a 27 or a 33, but not both, right?

jakelm

HTrookie wrote:

I say it should be cheaper than that, because you are listing three capacitors and you only need two. It is either a 27 or a 33, but not both, right?

"IF" its this schematic then the 33uF will do just fine.

http://www.polkaudio.com/forums/attachment.php?attachmentid=18772&d=1155784674

I will pull it and see for sure, but I'm 99% sure its the 34uF.

But of corse with my luck, I end up with the odd xover.:p

jakelm

The only thing is. With the additional 4.7ohm resistor, there is a possibility that it could be a 27uF cap.

Ricardo

jakelm wrote:

"IF" its this schematic then the 33uF will do just fine.

http://www.polkaudio.com/forums/attachment.php?attachmentid=18772&d=1155784674

I will pull it and see for sure, but I'm 99% sure its the 34uF.

But of corse with my luck, I end up with the odd xover.:p

As Ben says, look at the value before ordering; maybe it's neither 33 or 27.

jakelm

Being that Polk specifically labels this cap as an "eletrolytic" cap. Maybe I should get the same electrolytic cap form PE. Seems alot cheaper too.

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=027-350

jakelm

There are so many different avenues to go,,,,

This is going to be so much fun. Almost as much fun as when I built my center channel.

..Thanks for the help guys...:D

ben62670

jakelm wrote:

The only thing is. With the additional 4.7ohm resistor, there is a possibility that it could be a 27uF cap.

WHO CARES WHAT THE RESISTOR SAYS. THAT IS PART OF THE TWEETER CIRCUIT! THE CAP YOU ARE IN SEARCH OF IS PART OF THE MID CIRCUIT. READ THE VALUE OF THE CAP!!! READ THE VALUE OF THE CAP!!! READ THE VALUE OF THE CAP!!! IF YOU CAN'T READ EITHER ONE THEN ORDER THE 34uf. THEY DIDN'T USE 27uf UNTIL THE SL2500 CAME OUT. THE INDUCTOR IS THE PRIMARY SOURCE OF THE CROSSOVER. THE CAP AFFECTS MAINLY THE SLOPE. SORRY ABOUT SHOUTING BUT YOU ARE DWELLING ON DUMB ****.

ben

jakelm

Ok Ben ... Sorry for brainstorming...

I wasnt dwelling..I was just talking about it.. I enjoy talking about different componets and how they work and effect others.

But I appologize and I will drop it..

ben62670

jakelm wrote:

Ok Ben ... Sorry for brainstorming...

I wasnt dwelling..I was just talking about it.. I enjoy talking about different componets and how they work and effect others.

But I appologize and I will drop it..

No problem I just felt a little emphasizing was in order;)

The sad thing is I am more hard headed than you