What crossover is this?

fiddlerman

Just bought a pair of Polk Monitor 7Bs with SL2000 tweeters. I got a pretty good deal at $35, probably because one of the banana terminals in the rear was shorn off.

I have since purchased on eBay what I thought was a matching crossover. Ostensibly taken off a Monitor 7, it's labeled # BEO700-B.

After removing the broken original, I discovered the two are completely different in appearance.

I swapped out the crossovers today, hooked up the speaker, and it sounds fine to my ears.

The original crossover lacks a part number is. It's marked "July 23 '83" and nothing else.

I'm guessing that the BEO700B (dated "10-24-91.") is meant for a SL-2500. Can anyone confirm this?

I've attached a photo of the original crossover.

My next question is: if I were to upgrade tweeters with this crossover, would it be a RDO-194 or a RDO-198?

Thanks in advance for your help,

Fiddlerman

fiddlerman

Here is a photo of the "new" crossover, the BEO700-B, that I installed. As I said, it sounds fine. But I'm wondering if it's the wrong crossover for my SL-2000 tweeter, as it appears to be completely different from the original crossover.

westmassguy

If you look at the schematics for the Monitor 7 here : http://www.polkaudio.com/forums/showthread.php?38755-POLK-AUDIO-Speaker-Wiring-Schematics-amp-More-ALL-MODELS-except-SDA
You'll see your original schematic_m7_rev, and the newer crossover's schematic_m7s_rev2.
The values for some components changed. Why not just install new binding posts, instead of replacing the entire crossover?

StantonZ

I recently re-built my Monitor 10B XO's, one pair from around 1985 and the other from around 1991: the Printed Circuit Boards were completely different (although the component values were the same). In fact one set had NO component markings/silkscreen and the other set was well marked; they even had different mounting posts/screws. The good news is, the component count is low enough that you can figure out what's what from the schematics. As was pointed out, focus on the (proper) component values and make use of the PCB's as best you can. Good luck!

fiddlerman

Hi Westmassguy,

Replacing the binding post would be the obvious answer, but I didn't know that could be done. Do you just torque on the post with a pliers and it will come free, or does it have to be detached from the other side?

There isn't much left to the shorn binding post -- it's just a stub about a wire's width. Not much purchase for a set of pliers.

Please advise --

P.S. I assume those yellow things are capacitors. Are the blue things resistors? If I add up the printed values and they are the same, am I in the clear?

txcoastal1

blue and yellow are caps, the white block is a resistor

westmassguy

fiddlerman wrote: »

Hi Westmassguy,

Replacing the binding post would be the obvious answer, but I didn't know that could be done. Do you just torque on the post with a pliers and it will come free, or does it have to be detached from the other side?

There isn't much left to the shorn binding post -- it's just a stub about a wire's width. Not much purchase for a set of pliers.

Please advise --

P.S. I assume those yellow things are capacitors. Are the blue things resistors? If I add up the printed values and they are the same, am I in the clear?

The binding posts are removed from the back side. The circuit board must be released from the nylon stand-offs on the older crossover, and on the newer one, remove the four Philips head screws. You'll most likely have to remove some hot glue to get to the nuts that secure them. I used a small flat screwdriver, and a utility knife to remove the old hot glue. Just remove as much as you need around the one nut, and be careful not to cut or damage the wiring.
As for the Caps, the Yellow "things" are Mylar Capacitors, and the Blue "Things" are Non Polarized Electrolytic Capacitors. The small rectangular items are the Sandcast Resistors. The small, round, yellow disk is the infamous Polyswitch.
The values are different for the NP Electrolytics, and the newer crossover has an additional capacitor. The large Inductors (Coils) wrapped around the outside of the crossover are also different.

fiddlerman

Thanks for your patience with my newbie-ness. ; )

From your description, WestMassGuy, the new crossover is the revised model. I think I'll just repair the old one and swap them out again.

Going in and replacing this crossover popped my cherry as far as fiddling around with the components. Definitely getting my nerve up to repair the binding post.

I am probably not going to cannablize this part, but will try to pick it up at my local electronics store. I assume this is a standard item? Radio Shack, even?

Thanks,

F

westmassguy

fiddlerman wrote: »

Thanks for your patience with my newbie-ness. ; )

From your description, WestMassGuy, the new crossover is the revised model. I think I'll just repair the old one and swap them out again.

Going in and replacing this crossover popped my cherry as far as fiddling around with the components. Definitely getting my nerve up to repair the binding post.

I am probably not going to cannablize this part, but will try to pick it up at my local electronics store. I assume this is a standard item? Radio Shack, even?

Thanks,

F

The Rat Shack may or may not carry quality binding posts. I've got a couple salvaged Polk BPs I can send you. There were two sizes, I only have the smaller ones left, but it should get you through.

fiddlerman

That's outstanding, WestMass. Is it possible to PM on this site?

BTW, do you remember the Helsinki Cafe in Great Barrington? Played there once and have been through the Berkshires a few times in my musical travels. Great locale.

fiddlerman

I will PM you with my address, but I first need to get to ten messages, hence this.

westmassguy

fiddlerman wrote: »

That's outstanding, WestMass. Is it possible to PM on this site?

BTW, do you remember the Helsinki Cafe in Great Barrington? Played there once and have been through the Berkshires a few times in my musical travels. Great locale.

Don't remember it. Don't get up to the Berks that often. All tourists now leaf peeping.

PolkieMan

If it was up to me I would update the crossovers using components from the latest correct revision.
Those very old parts were made cheaper and not up to the quality standards available today.
Next I would replace the SL-2000's with Rdo-194's

fiddlerman

I would probably switch out the caps and resistors in my current crossovers, as they were designed for the SL-2000s and will accept the RD0-194s. I'm not sure, however, if the latest revision lines up with my current drivers.

Did the RDO-194s actually make it into production models of the Monitor series, or were they strictly an after-market phenom? In other words, was the SL-2000 the last tweeter installed on the production Monitors? That would mean the most current crossovers would work with them.

Or to put it another way, which tweeter was the latest Monitor 7 crossover designed for?

westmassguy

fiddlerman wrote: »

I would probably switch out the caps and resistors in my current crossovers, as they were designed for the SL-2000s and will accept the RD0-194s. I'm not sure, however, if the latest revision lines up with my current drivers.

Did the RDO-194s actually make it into production models of the Monitor series, or were they strictly an after-market phenom? In other words, was the SL-2000 the last tweeter installed on the production Monitors? That would mean the most current crossovers would work with them.

Or to put it another way, which tweeter was the latest Monitor 7 crossover designed for?

If you want to replace the SL2000 with the 194s, then upgrade the caps and resistors with the same values that are there now.
The 198s require modifications to the crossovers to operate properly.
The RDOs came out well after the original Monitors, SDAs, and RTAs from the 80s and early 90s were discontinued. The last Monitors received the SL2500 Tweeters, which were a big improvement, and the SDAs and RTAs received the SL3000.

Nightfall

westmassguy wrote: »

...RTAs received the SL3000.

Not the 12's I believe, those ended at SL2000's correct?

westmassguy

Nightfall wrote: »

Not the 12's I believe, those ended at SL2000's correct?

The 12s were discontinued before 1989/90 I believe. I was referring to the 11 and 15 TLs which came from the factory with SL3000 tweeters

fiddlerman

I thought I'd cut to the chase and order the RD0-194s today. I called Polk and they're on BACK ORDER. They'll have them back in stock in a couple of weeks.

I'm thinking that this is not simply a coincidence. Now I'm thinking that my errant BEO700-B crossover was originally connected to a SL-2500 or SL-3000, since it has a markedly different architecture than the crossovers that I currently have connected to my SL-2000.

If that is the case, I'm already halfway to an RD0-198 upgrade. I am now inclined to purchase a pair of RDO-198s and do the mods to my remaining crossover to bring it up to speed.

Can anyone confirm, by examining the photo above, that this crossover indeed matches to the 2500 or 3000?

WestMass assures me the 198 is a better tweeter than the 194. His opinion carries a lot weight, but I'm wondering whether anyone else has an opinion on this matter.

westmassguy

fiddlerman wrote: »

I thought I'd cut to the chase and order the RD0-194s today. I called Polk and they're on BACK ORDER. They'll have them back in stock in a couple of weeks.

I'm thinking that this is not simply a coincidence. Now I'm thinking that my errant BEO700-B crossover was originally connected to a SL-2500 or SL-3000, since it has a markedly different architecture than the crossovers that I currently have connected to my SL-2000.

If that is the case, I'm already halfway to an RD0-198 upgrade. I am now inclined to purchase a pair of RDO-198s and do the mods to my remaining crossover to bring it up to speed.

Can anyone confirm, by examining the photo above, that this crossover indeed matches to the 2500 or 3000?

WestMass assures me the 198 is a better tweeter than the 194. His opinion carries a lot weight, but I'm wondering whether anyone else has an opinion on this matter.

If you're going to upgrade to the 198s, you should do the modifications on both older crossovers, rather than use one old and one new. If you go with one newer and one older, they may sound different due to different crossover points. The large, low-pass inductors are different between the newer and older crossovers. Sticking with the 194s is a no brainer, no changes other than replacing parts with the same value. Doing the "TL" modification to both older crossovers for use with the 198s is more complicated, but the end result will be better. I would not recommend using the new crossover, and modifying the old, bad idea.

fiddlerman

The latest haps: Got Polk on the phone today and we ran down some serial numbers. My eBay crossover is from a Series 2 Monitor 7 (ca. 1991), which took the SL2500s, hence it corresponds to a RD0-198.

I ordered a pair of 198s and will search for a second crossover or try to modify my existing 1983 7C crossover.

westmassguy

Either method will work, just don't mix them

fiddlerman

I hear you, WestMassGuy, but I'm wondering where I'm going to mount the extra capacitor(s), etc., if I use the old crossover chassis. Your previous emails also referred to shunting, which I haven't a clue about (though I will ask my audiophile buddy who does a lot of this kind of work). For someone like me, it's a daunting prospect.

Seems easier to find a matching crossover for the one I've got. which is what I'm currently trying to undertake. But if I can't find one, I'll definitely use the original crossovers and retrofit both for a matching sound.

Incidentally, what does "TL" stand for?

westmassguy wrote: »

If you're going to upgrade to the 198s, you should do the modifications on both older crossovers, rather than use one old and one new. If you go with one newer and one older, they may sound different due to different crossover points. The large, low-pass inductors are different between the newer and older crossovers. Sticking with the 194s is a no brainer, no changes other than replacing parts with the same value. Doing the "TL" modification to both older crossovers for use with the 198s is more complicated, but the end result will be better. I would not recommend using the new crossover, and modifying the old, bad idea.

Nightfall

fiddlerman wrote: »

Incidentally, what does "TL" stand for?

Tri-Laminate

westmassguy

fiddlerman wrote: »

I hear you, WestMassGuy, but I'm wondering where I'm going to mount the extra capacitor(s), etc., if I use the old crossover chassis. Your previous emails also referred to shunting, which I haven't a clue about (though I will ask my audiophile buddy who does a lot of this kind of work). For someone like me, it's a daunting prospect.

Seems easier to find a matching crossover for the one I've got. which is what I'm currently trying to undertake. But if I can't find one, I'll definitely use the original crossovers and retrofit both for a matching sound.

Incidentally, what does "TL" stand for?

The new caps are most likely going to be much larger than the ones in there now, if you use Metalized Polypropylenes. The Clarity line in particular are very large.
The Resistor(s) can be relocated to the bottom of the circuit board, which will clear some room. You can also make riser boards, and or remote mount the new larger caps.