7A Monitor Upgrade
tbrainerd
Posts: 10
New to the forums.
I have a pair of 7A monitors (7.1, serial numbers in low 2000s) that I bought before I got out of my undergrad in 1978. I think the tweeters may have been fried before then, too.
I bought the replacement tweeters Polk recommended from Midwest Speaker Repair, and went looking online to see about putting them in. After reading about 7A upgrades in the forum, I purchased new caps and resistors from Parts Express, and I am now taking the guts out in anticipation of their arrival. And I have some questions:
The wadding is in back of tweeter, midrange and passive radiator. Should I remove it from behind the radiator?
The wires from the speaker posts and fuse are not long enough to get the circuitry out of the box. Would it work to just put in extensions, or would it be important to solder in longer wires from contact to contact? What gauge is this wire? Would it be any improvement to go with a larger gauge? Any downside to that?
I assume the white stuff that the drivers used to be sealed into the box with is the dreaded Mortite. I assume that I scrape that stuff out of the openings and put in speaker sealing tape instead?
Never done anything like this before, but there's always a first time. Can't be any worse than putting new calipers in my '01 Yukon XL...which has Polks in it. I can hear things driving in that vehicle that I can only hear in headphones otherwise.
Thanks for any counsel you can give me.
I have a pair of 7A monitors (7.1, serial numbers in low 2000s) that I bought before I got out of my undergrad in 1978. I think the tweeters may have been fried before then, too.
I bought the replacement tweeters Polk recommended from Midwest Speaker Repair, and went looking online to see about putting them in. After reading about 7A upgrades in the forum, I purchased new caps and resistors from Parts Express, and I am now taking the guts out in anticipation of their arrival. And I have some questions:
The wadding is in back of tweeter, midrange and passive radiator. Should I remove it from behind the radiator?
The wires from the speaker posts and fuse are not long enough to get the circuitry out of the box. Would it work to just put in extensions, or would it be important to solder in longer wires from contact to contact? What gauge is this wire? Would it be any improvement to go with a larger gauge? Any downside to that?
I assume the white stuff that the drivers used to be sealed into the box with is the dreaded Mortite. I assume that I scrape that stuff out of the openings and put in speaker sealing tape instead?
Never done anything like this before, but there's always a first time. Can't be any worse than putting new calipers in my '01 Yukon XL...which has Polks in it. I can hear things driving in that vehicle that I can only hear in headphones otherwise.
Thanks for any counsel you can give me.
Answers
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Hey welcome to the forum! Lots of good advice here!Basement: Polk SDA SRS 1.2tl's, Cary SLP-05 Pre with ultimate upgrade,McIntosh MCD301 CD/SACD player, Northstar Designs Excelsio DAC, Cambridge 851N streamer, McIntosh MC300 Amp, Silnote Morpheus Ref2, Series2 Digital Cables, Silnote Morpheus Ref2 Series2 XLR's, Furman 15PFi Power Conditioner, Pangea Power Cables, MIT Shotgun S3 IC's, MIT Shotgun S1 Bi-Wire speaker cables
Office: PC, EAR Acute CD Player, EAR 834L Pre, Northstar Designs Intenso DAC, Antique Sound Labs AV8 Monoblocks, Denon UDR-F10 Cassette, Acoustic Technologies Classic FR Speakers, SVS SB12 Plus sub, MIT AVt2 speaker cables, IFI Purifier2, AQ Cinnamon USB cable, Groneberg Quatro Reference IC's
Spare Room: Dayens Ampino Integrated Amp, Tjoeb 99 tube CD player (modified Marantz CD-38), Analysis Plus Oval 9's, Zu Jumpers, AudioEngine B1 Streamer, Klipsch RB-61 v2, SVS PB1000 sub, Blue Jeans RCA IC's, Shunyata Hydra 8 Power Conditioner
Living Room: Peachtree Nova Integrated, Cambridge CXN v2 Streamer, Rotel RCD-1072 CD player, Furman 15PFi Power Conditioner, Polk RT265 In Wall Speakers, Polk DSW Pro 660wi sub
Garage #1: Cambridge Audio 640A Integrated Amp, Project Box-E BT Streamer, Polk Tsi200 Bookies, Douglas Speaker Cables, Shunyata Power Conditioner
Garage #2: Cambridge Audio EVO150 Integrated Amplifier, Polk L200's, Analysis Plus Silver Oval 2 Speaker Cables, IC's TBD. -
Thanks for the welcome.
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The wadding (polyfill) should be behind just the tweeter and midwoofer.
It is a good idea to get rid of the mortite. Parts express has a good foam gasket tape.
https://www.parts-express.com/parts-express-speaker-gasketing-tape-1-8-x-3-8-x-50-ft-roll--260-540
I too just ordered caps and resistors to do my first crossovers. So im not sure on the fuse question but I will be needing info on that soon. There a few members more experienced in crossovers that can chime in on that.Monitor 4.6, 5jr, 5, 7, 10, 11. RTA 8TL. RTA 11T. SDA 2B. -
Welcome. Post some pics of the 7A's. That may help with answers. I would guess yours have the Peerless tweeters and have the fuses on the binding post cup. In regards to the fuse holder, hopefully member F1nut will chime in as he had some good input on that subject a while back on a pair of 7's he brought back to life. I would also guess the internal wiring is soldered to the tweeters and the mid woofers. You could pull the drivers and cut the wires, desolder from the drivers, and then use new cabinet wiring. If I remember correctly it is 16 gauge wire. Hopefully someone else will chime in on that. The dacron fill in the cabinet on the early Polk's, tends to fall down over the years. It should NOT be behind the passive radiator, but rolled up and secured above it. Lots of other mods to be done on those old girls. Search around the forum for other info.
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Your fuse wires may look like this....not good.
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 -
Faustin...
I am including a picture of the inside of the cabinet, in the area behind the Passive Radiator. If you look at it, the wadding was clearly placed as it was intentionally.
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Try againPolitical 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 -
Based upon the thread linked below, I b
ought this list of replacement caps and resistors from Parts Express:
027-430 Dayton DMPC-12 12uF 250V Polypropylene Capacitor
005-2.5 Mills 2.5 Ohm 12W Non-Inductive Resistor
005-4.5 Mills 4.5 Ohm 12W Non-Inductive Resistor
027-441 Dayton DMPC-33 33uF 250V Polypropylene Capacitor
The caps are huge compared to what is there now, and I am not sure that they will fit without some adjustment. Is there any problem with going to a larger piece of board and tying all of this together with primary wire if need be? Does the board need to be special material, or can it be 14" plywood?
Here's a picture of the crossover, with one of the new 33uF capacitors laying on it.
https://forum.polkaudio.com/discussion/71447/monitor-7b-capacitor-replacement
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Here 'tis
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It may of been put in there intentionally, but Polk didn't do that.
That is my .02 -
Bought these brand new from a high end dealer in Ann Arbor mid/late 70s. They've never been open before.
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Bought these brand new from a high end dealer in Ann Arbor mid/late 70s. They've never been open before.
Interesting I stand corrected. Every passive radiator design I've seen nothing has been below the mids or behind the passive. -
Faustin...
I am including a picture of the inside of the cabinet, in the area behind the Passive Radiator. If you look at it, the wadding was clearly placed as it was intentionally.
As others have stated, roll up the wadding and place it above the passive. You can staple it so it doesn't fall down. As pitdogg mentioned, on all of the Polk models with passives, all the dacron should be above it. In regards to the c/o, yes the caps are huge compared to the old ones. A lot of people will relocate the resistors to the bottom of the board to free up some room for the caps. And, use caps and resistors that are the same value as what is currently used on your speakers. I will see if I still have some pics of my 7 c/o rebuild. -
Here are a couple of pictures of a 5a crossover that I did a few years ago with the resistors mounted on the bottom of the pcb.
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The caps appear to be 12u and 34u, both 50v. the ones I purchased were 12u and 33u, 250v instead of 50v. Is that going to be a problem?
The resistors are sand block, 2.7 ohm and 4.7 ohm. I was able to find 2.5 and 4.5. Will that be a problem?
As far as wiring the caps under the PCB, the large inductor coil is on the bottom of the board. I can see if I can purchase a bigger board, but I'll have to string things together a little bit with wire connection to get it all to come together.
Thoughts? -
Once I have some tape and can label the wiring, I'll get the board out of the cabinet and see if I can figure this out a little bit better.
Never done this before. A first time for everything, I guess. -
I assume, BTW, that the PCB is really just a piece of bare phenolic, with no actual printed circuit?
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