Monitor 5A schematics, anyone?
poutrew
Posts: 4
Back in the mid 80's I got a pair of monitor 5A speakers, free. They were being used at a local radio station and they got 'blown up' and I rescued them from the trash... The tweeters had very low output, but otherwise they worked fine. So I hooked up a pair of Radio Shack Piezo tweeters to them and have been using them ever since as a bedroom pair running 100 watts per channel. Only recently have I become aware that there is actually a community of crazies such as myself who actually like vintage gear, yeah 
And I have been motivated to finally get off my woofer and try to fix these fine speakers, and I've always known that the Rat Shack tweets were merely a band aid covering up the problem...
Problem is, I can't seem to find any schematic diagrams for the Monitor 5A crossover circuit. Does anyone know where I might get a 5A schematic? I haven't torn these down yet, but I do know they are very early monitor 5A, and the SL-1000 tweeters don't even have a Polk logo stamped on them. They have 1 amp fuses in the back, and the midrange and woofers work very well...hopefully I'll get lucky and get everything working with new tweeters only, as I would save a crossover rebuild for another day. Any help locating a schematic would be appreciated. Thanks.
And I have been motivated to finally get off my woofer and try to fix these fine speakers, and I've always known that the Rat Shack tweets were merely a band aid covering up the problem...Problem is, I can't seem to find any schematic diagrams for the Monitor 5A crossover circuit. Does anyone know where I might get a 5A schematic? I haven't torn these down yet, but I do know they are very early monitor 5A, and the SL-1000 tweeters don't even have a Polk logo stamped on them. They have 1 amp fuses in the back, and the midrange and woofers work very well...hopefully I'll get lucky and get everything working with new tweeters only, as I would save a crossover rebuild for another day. Any help locating a schematic would be appreciated. Thanks.
Comments
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Welcome to Club Polk.
Pull a crossover, the values will be printed on the components. You should upgrade the caps and resistors as they weren't great to begin with and besides, the caps are way past their prime.
That's not a woofer, it's a passive radiator.
Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
^^ as F1nut said, pull the crossover. Post a pic here if needed if some of the values are not visible. Pics of the speakers can also be helpful. There are two crossover designs for the M5A's, and schematics have not been published. Sonicap or Clarity ESA/CSA caps and mills resistors are preferred for crossover rebuilds.
The original tweeter are the much desired peerless tweeters. There are some right now on ebay, but one looks like the dome had been pushed in. There are also some new copies that people have been happy with. The SL1000 with the silver face is to be avoided. Although if you are really creative, people here have completely rebuilt them with different parts for a better sound. The silver plate with the logo is a cool look.
The very early M5's had the grills held on with velcro. The early and middle one had MW's and PR's with silver baskets and had compress paper about 1/4" thick on the front for face mounting. The later M5's had black baskets and do not have the compressed paper. -
OK, I pulled the crossovers, and aside from the coils, each has 2 caps and 2 resistors:
I checked the values of the caps against each other and they varied widely, so I guess I need to replace them...
C1: 34 uf, C2: 12uf at 50v and R1: 6.2 Ohm, R2: 2.7 Ohm each at 5w
I've been looking at some nice Axon True Cap Metallized Polypropylene caps mainly because they aren't too large and have a nice price. They have a 250 volt rating. Problem is I can't find exact replacements. How sensitive will the crossovers be if I get to a close approximation? For example, I can get two 6.2 uf for 12.4 uf total, but for the larger capacitor it will either be two 16 uf or one 30 uf and one 3.6 uf..... argh....
Is it going to be a disaster if things aren't exact? Also, considering the drift values of the original caps, I guess anything is better than what I have now...
The resistors are actually still within tolerance...
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For the larger caps, you need to go with 2x16uF, otherwise you'll have an extreme im balance, and the smaller value will act as a shunt.
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Or two 17uf but the 16uf will be close enough. If you need to go with two they need to be as close as possible or funky stuff happens. Like stated above.
Replace the resistors with wire wound stay away from cement or sand cast. Mills 12watt or mundorf 10watt -
Sonicap Gen I available at Sonic Craft has the exact values you need and they sound better too. They also have the Mills resistors.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
One other thing I forgot to mention in my previous post, these speakers (monitor 5A) have peerless tweeters in them. Am I right in thinking the RD0-194 is the drop in replacement for them, and the 198 is requiring a crossover mod, which would be difficult to do considering there are no monitor 5A crossover schematics available... right?
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The RD0-194 is not a drop in replacement. The bezel size and hole locations are different, nor do I believe the crossover values are correct.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
That....is good to know. So is there a drop in replacement available? It wouldn't be so bad if the only thing is drilling new holes, but I don't really want to change parts values in the crossover network. Or, is this when I need to call the Polk Audio people and ask them for some help?
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The only drop in replacement is a Peerless copy sold by Madisound.
It's more than just drilling holes, so just forget the RD0 idea.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Fixed it for youThe only drop in replacement is a Peerless copy sold by Midwest Speaker.
It's more than just drilling holes, so just forget the RD0 idea.
Home Theater/2 Channel:
Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
dhsspeakerservice.com/ -
For Monitor 10, the High-Pass Section of the Crossover is quite different for the later SL1000/SL2000, and the revision/model 2 with the SL2500.
Keep it simple, either buy salvaged Peerless Tweeters off fleabay, or the replacements from Midwest.Home Theater/2 Channel:
Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
dhsspeakerservice.com/ -
And if you're patient and/or lucky you might find a pair of 5As for near the same price as the above tweeters. Use the best of both and save the rest for backup.
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Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk
