Is there a schematic for the Monitor 5A?

nspindel

Don't see one in the collection of schematics. I see the 5B's and the Jr's, but I'm grabbing a pair of Peerless 5's tomorrow, wondering what makes them tick.

Faustin

Probably the best thing to do is pull one c/o out and check the values. I rebuilt my 5a's a while back and they had a 12 uf cap, a 27uf cap, a 2.5 ohm resistor and a 2.7 ohm resistor. I did not have a schematic so I just replaced what was on the boards

nspindel

Looks great! If I can get the specs I would do the inductors as well, but I'd need to know gauge and DCR not just inductance. I guess I can always figure that part out myself but it's always good to have that confirmed on paper.

nspindel

Turns out these are 5B's not A's. Either my understanding of the model changes is wrong or these are one of Polk's infamous in-between versions. I had always thought that the A's had Peerless tweeters and a fuse, then the B's moved to SL-2000's and the polyswitches. The pair that I just bought has SL-2000's and fuses. When the seller told me they had fuses on the back I assumed there would be Peerless tweeters. So either I'm mistaken and the first revision of the B's had fuses, or Polk had a bunch of binding post plates with fuse mounts to use up. Either way, not concerned about the schematic any more.

westmassguy

I think you're better off Neil. Now you can "TL" them. 198s are better than Peerless in my opinion.

nspindel

Agree. I'm actually very psyched for 5B's. They were my first Polks.

nspindel

Dave - do you agree that a 5B with a fuse is an in-between model. The SL2000 should normally indicate a polyswitch correct?

drumminman

I have RTA 12C's that came with a manual and boxes designating them as such (I bought them new). Yet, they have SL1000 tweeters and a fuse. And the Xover board has 12B stamped on it!

Polk can be confusing, but it sounds like you got 5B's.

westmassguy

nspindel wrote: »

Dave - do you agree that a 5B with a fuse is an in-between model. The SL2000 should normally indicate a polyswitch correct?

I think it's obvious Polk used leftover parts for transitional models. If you look at the 5B original schematic, there's a revision noted where the fuse was replaced with a Polyswitch, and the resistor downstream was changed from 2.7 ohm to 2.0 ohm.

nspindel

Does that note mean that the 5B originally had the fuse and then was changed later? Or is that referring to the change in spec from the 5A to the 5B?

westmassguy

Your guess is as good as anyone's Neil. All the good people that were involved with the designs back then are long gone. I run into this a lot. Inductors and resistors are the biggest headache. You can't always go by what's on the schematics. You have to remove the crossovers and look at the actual values for the caps and resistors. Inductors I always to measure if they're being replaced.
My 2As, according to the schematic, were supposed to have #18 gauge Inductors. The Stereo Sections had #18 gauge, but the Dimensional Sections were #22 gauge.

nspindel

Yes, the more I'm thinking about it I may just pass on doing the inductors. At least in this first pass at these speakers, let's see how they sound after I do everything else.

Thanks again Dave.

westmassguy

You're still going to have to change the Hi-Pass Shunt Inductors if you're doing the SL3000 Mod

nspindel

Ah yes, that is correct. The SL3000 schematic was at least nice enough to specify the DCR should be .5 ohm for the replacement inductor, and there is a Jantzen that is .49 ohm. But the schematic doesn't mention the wire gauge, so I'm just going to cross my fingers on that one...

nspindel

Also I am going to replace the 2.7 resistor in mine with a 2.0 resistor as per the spec, and then I am going to jump the fuse connector with a .5 ohm and not use the fuse. That should match the spec in the schematic with the polyswitches. I trust myself to not need the protection in the circuit. Whole reason I got these is for apartment living where I won't be able to crank them up all that much.

westmassguy

No finger crossing The .5 ohms is critical, as it affects the overall SPL of the Tweeter.
The Jantzen part # is: 000-1640, it's #22 gauge.
Parts Express can special order them, and you'll be waiting 6-12 weeks.
Your other option, is the stock #18 gauge, .27mh Jantzen: http://www.parts-express.com/jantzen-audio-027mh-18-awg-air-core-inductor-crossover-coil--255-216
You'll have to pad it with a Mills MRA-12, .27 ohm resistor, which is what I normally do.

westmassguy

nspindel wrote: »

Also I am going to replace the 2.7 resistor in mine with a 2.0 resistor as per the spec, and then I am going to jump the fuse connector with a .5 ohm and not use the fuse. That should match the spec in the schematic with the polyswitches. I trust myself to not need the protection in the circuit. Whole reason I got these is for apartment living where I won't be able to crank them up all that much.

No. Stay with the 2.7 ohm, or 2.5 ohm, and just remove the fuse from the circuit.

nspindel

Yes I was looking at the 1640, I didn't realize that any of the Jantzens were stocked. I don't mind waiting for the 1640, these 5B's are for when I move to an apartment in Tampa which won't be for a few months. These days I'm still enjoying my SDA's!

nspindel

westmassguy wrote: »

nspindel wrote: »

Also I am going to replace the 2.7 resistor in mine with a 2.0 resistor as per the spec, and then I am going to jump the fuse connector with a .5 ohm and not use the fuse. That should match the spec in the schematic with the polyswitches. I trust myself to not need the protection in the circuit. Whole reason I got these is for apartment living where I won't be able to crank them up all that much.

No. Stay with the 2.7 ohm, or 2.5 ohm, and just remove the fuse from the circuit.

But spec for the TL mod is the 5.8 cap in parallel with a 2.0 that's why I'm splitting into two separate resistors. I'll have the 2.0 with the cap and a .5 in place of the fuse which should be the same as the polyswitch. What's wrong with doing it that way?

westmassguy

Nothing wrong with doing it that way, but you're using 4 resistors instead of 2. Money you don't have to spend is all.

nspindel

Understood but if I'm just using the MRA's they're just a few bucks. Between the tweeters and the caps and everything else I'll probably spend close to $400 fixing up speakers I soent $60 for!

westmassguy

Neil, keep it simple. You have what appears to be an early 5B, with a single resistor.
All you're doing is eliminating the fuse block and adding the 5.8uf shunt cap. Mount a 2.5 or 2.7 ohm resistor to the bottom of the circuit board, the 5.8 cap on top. Easy Peasy. It's a contour circuit. A .5 ohm upstream from the 2.0 ohm, or a single 2.5 or 2.7 ohm isn't going to make a difference. You're adding more work for yourself.

nspindel

I get stuck on the Ohm's law part of it. The 5.8 cap will have a resistance value as well as capacitance. So that cap in parallel with a 2.0 vs. a 2.5 will net to a different resistance than parallel with the 2.0 and series with a .5. I wouldn't be able to just remove the fuse block, at a minimum I would still need to solder a jumper in place of it, so it's not like it's much more work to solder a resistor instead of the jumper. At the end of the day, it may not make much of an electrical difference but it will make me feel all warm and fuzzy inside

westmassguy

Overthinking Neil. It's a contour circuit. The 198s have a slight rising output as the frequency decreases. The shunt cap compensates for this. Whether its shunting a 2 or 2.5 ohm resistor, it makes little difference. The fuse block has one 1/8" pop rivet, drill it out, and it comes right off. You can either seal the three holes from behind, or I can send you some 1/8" black plastic plugs to seal the holes. Wire the hot lead right off the new binding post to the circuit board.

westmassguy

Neil, do whatever you want. If you want to take the hard road, knock yourself out. I've done dozens of 5s and 7s.

nspindel

Dave, I'm not trying to be argumentative here, it's not like I'm trying to pick a fight. But I just don't understand what you're saying here. You're telling me to start drilling out pop rivets, but you're referring to me simply adding a $4.40 resistor as the hard road? I actually wasn't intending on removing the fuse block at all, I intend to leave it in place but with the leads disconnected, that way the mod becomes reversible. Disconnect those two leads and replace the connection with a $4.40 resistor. To quote you, easy peasy. I'm just not getting why this seems so offensive to you. When I do mods I like to stick to the schematic, I've never been one to wander off the reservation too far when it comes to sticking to Polk's specs when rebuilding these speakers. People here have always been replacing polyswitches with a 0R5. I'm doing nothing different than what has been done hundreds of times here.

Hope you have a happy Easter/Passover, whichever way you lean.

westmassguy

Neil, it's all good. My intent was not to be combative, just give you several options you may not have been aware of. As I said, I've done dozens of these. From a cost and time perspective, a single resistor is easier. Your Circuit Board may be any early version, and may not even have the traces and holes for a Polyswitch. You'll have to open it up and take a look.
There's also another option, if you do plan on replacing all the inductors too. The Monitor 7 Rev2 Schematic, which would be the same for the Monitor 5 Rev2,
was the last version produced. The Inductor and Capacitor values are all different, but were designed for the SL2500. This would make your crossover a true "TL" version.

nspindel

I was going to use the holes for the fuse connection. The fuse block has two wires coming from the back that are soldered onto the board. Desolder those two wires, replace with 0R5.

I will have a look at the 7B schematic you're talking about later when I'm not on my phone!

nspindel

Not to overthink things, but.....

The 7's use a .22mH coil in all of their revisions, but the 5's use a .23mH. Now Jantzen doesn't even make a .23mH in 22AWG, the closest they have is 21AWG. If I use a .22mH in a Monitor 5, I should still be within a 5% tolerance of the .23mH, so it shouldn't really be a big deal to use the .22mH. However, Jantzen has 3 different .22mH 22AWG coils, not sure which one I should use. The Jantzen 1013, 1650, and 1950 coils are .22mH 22AWG, but differ slightly in DCR and one says OD-29 / 8mm, one says OD-24 / 15mm, and one says OD-17 / 25mm.

The Polk spec for the SL2500 Monitor 7 doesn't reference DCR, only inductance and gauge, and I'm not sure what the OD/mm measurements even mean.

So assuming I were to use a .22mH coil, which of the three would be the correct one?

Also, very interesting to note that in the SL2500 schematic for the Monitor 7, there is neither a fuse nor a polyswitch. I didn't realize that they removed the tweeter protection from the circuit in the later version.

westmassguy

I'd go middle of the road, 000-1650
The OD really doesn't matter, you're going to have to move it anyway, and drill new holes for the Nylon Wire Ties.
Re: Tweeter Protection: On all the Rev 2 Monitors and RTAs, Polyswitches were removed.

nspindel

Never knew that the polyswitches were removed in the later generation.

Ah so with your comment I figured out what OD means, obviously that's outside diameter. So I'm assuming the other measurement is the thickness of the coil? As the diameter gets smaller the coil gets thicker...

But you would agree to use the .22mH and not the .23mH? More important for the gauge to be correct as long as it's still within 5% tolerance?