XSchop's modded 5jr

xschop

I signed up to get more info and input on the early monitors. I'll chronical what I do here. All advice is welcome and appreciated.
I chose these to mod because I have a smaller set of Monitor 4's in the shop that sound great and these cabinets have more volume for that extra base, but the tweets need upgrade. Cabinets will get the XS treatment with an internal billet brace and a full billet re-face to make them bullet-proof...

xschop

First tech question is about crossover mod. In the 2nd pic above, the two ceramic resistors run in parallel to get the 1.3 ohm value. Reading up on forums here, I'm going to replace with Mills resistors and I would like to keep it simple and just install their 1.2 ohm resistor to save space.
Would that 0.1 ohm difference matter much in frequency x-over? I will also use a Dayton 1% 12 uF capacitor as a replacement for the old one and modifying the cabinets to accept the Polk SL5000 tweeters.

RandyCroissant

Had to chime in!!! is the second picture the one of the crossover a polk item it looks bad like it would short out. I would have assumed some kind of circuit board from polk.

pitdogg2

the resistor is no problem that .1 is still with the 10% that the original was so they "original" may of very well been off by more then that .1. The tweeter is something I'd say pass on as I'm sure the XO for it was much different and may cause other problems with the XO point on the 5jr. XO. Why not just use the much better RDO-194 tweeter that is much better than the SL2000 by leaps? It is a drop in replacement for all SL2000 XO's and fits.

xschop

I took that pic to confirm it was indeed 1.3ohm by cutting the wire and checking the values. So the Early 5jr do not have a circuit board.
Thanks for confirming the .1 ohm won't make much difference. I'll place the cap and resistor order shortly. I consulted with John at Mavin about what Polk tweeter to use since these old SL1000's are 8ohm and the mw6502's are 4ohm In these early 5jr. So we chose these as they are silk dome as well as 8 ohm, but just as important they are ROUND. I'm about aesthetics on this build and I have a round woofer lol.

The first pic shows what I believe is a weak spot in the cabinets with not even 1 sq. Inch of cross-section of MDF.

I have the Loc-tite Power Grab drying on the woofer magnets today....

[Deleted User]

To the best of my knowledge there has never been a Polk Monitor speaker that had a crossover not on a circuit board.

xschop

I thought the same thing, that's why I clipped the wire to double check the 1.3ohm value on the Early 5Jr schematic from this site. Which does say OBSOLETE in a bold stamp BTW....
No board and the poly glue on everything was still intact. It's matching pair is exactly same....

xschop

Like watching paint dry.....
I moved them in from shop, the Power Grab specifies over 50° F for curing....

pitdogg2

what am I missing? I see 2.5 and 2.7 ohm resistors, where is the 1.3 ohm come in?

heiney9

pitdogg2 wrote: »

what am I missing? I see 2.5 and 2.7 ohm resistors, where is the 1.3 ohm come in?

Look at the schematic he posted. It show 1.3 ohm in series with 12uF cap.

H9

pitdogg2

heiney9 wrote: »

pitdogg2 wrote: »

what am I missing? I see 2.5 and 2.7 ohm resistors, where is the 1.3 ohm come in?

Look at the schematic he posted. It show 1.3 ohm in series with 12uF cap.

H9

correct but his pictures of the XO do not show that. So it is more than likely that they have been tampered with.

heiney9

Yes, that's true. I was just answering your question about where the 1.3 ohm resistor came in.

With the sl1000 and peerless tweets there always seems to be 2 resistors in the circuit on many of the Monitor series. Based on what I've seen in the past and what I've owned the x-over looks more correct than the schematic as far as values.

As we all know the documentation from that era wasn't the most accurate or up to date and many changes happened on the fly.

H9

pitdogg2

This makes me want to go home and open mine up to see whether or not there is 1. a circuit board and 2. more than one resistor? In any case I think I'd more than likely keep it as it was built but with new caps and resistor or resistors. Mine were given to me and they have SL2000 I took them home and have only tested to see if they worked correctly and then put into storage for that rainy day.

thanks Brock

xschop

These SL1000's sound good. I've heard the SL5000's (iirc in a set of S4) and they sound great to me.

I used the RT formula to confirm the 1.3 ohm value as well. From experience modding many things over the years, the manufactures usually have odd-ball first series products, then up their game/ hardware later.

heiney9

In this case the actual x-over parts are correct. The sl1000 is a rather strident and shrill sounding tweeter compared to the updated Polk RD0 silk dome tweeters.

Do yourself a favor, don't over think, just replace with the same value parts of better quality (Mills resistors and poly film caps) and get a pair of updated RD0 tweets. Forget the billet crap and spend the $$$ on updated, better parts.

You can thank us later. We have all been around the block plenty of times modding older Polks.

H9

xschop

I appreciate your concern for my financial well-being. But the exercise here is to incorporate a round silk dome Polk tweeter. I have not seen, read, or heard of an RDO sounding much better than an SL5000, but that's beside the point. The billet is on order and I'm starting the G-code on my trusty Hurco.

heiney9

Have at it. I guess you know more than the Polk engineers and all of us hacks that have been doing the actual mods for the past 10-15 years.

The RD0-194 and RD0-198 is a round (square bezel) silk dome specifically designed by Polk to replace the older, shrill tweeters like the sl1000, sl1500, sl2000, sl2500 and sl3000 (the later 2 being not as bad).

But your speakers, your money. It's just hard when you post asking for advice and then when given you basically say "thanks, but no thanks". Why post at all if you already are doing what you want to do?

H9

xschop

I welcome all advice and maybe the RDO do sound better than SL5000. I wasn't sure on the crossover mod that Pittdogg so kindly answered . I was going to put in a Fountek Neo Ribbon, but it is square, so I decided on staying all Polk driver and have heard the SL5000's as I said before. They sound much better to my ears than the SL1000's....and they're ROUND.
These are going in my shop with a Yamaha natural sound rec/amp.
I will be incorporating the billet fascia into a All-billet enclosure on my next build for my home and maybe I'll choose the RDO then.

xschop

Ill design my baffle accordingly to get the new tweeter in the same spot as the old one. BTW these two SL1000's are FREE to anyone that needs a pair. They both work perfectly and tested at 6.6 ohm.....Not sure how PM's work here.

xschop

It would be easy to also make an adapter plate to fit the factory square holes. The magnet diameter is smaller than the SL-1000's

xschop

Power Grab is dry. I used 60 mil EPDM with self-adhesion as a sound/vibe dampener on the baskets....

xschop

Since I am adding an extra 0.50" lenght to the 0.75" factory port hole, will it make much difference in bass cut-off if I open it's diameter to 1.125" from 1.0"
I will flute the billet plate there and my tool set -up will be perfect for 1 1/8" circ.

Also just to confirm, does it matter which way the Mills resistors are soldered in? I understand the caps don't matter as they are non-polarized....

[Deleted User]

Actually film type capacitors do have a connection directionality, the outer foil should be connected to the lower impedance side of whatever the capacitor is connected to. In some cases the capacitor manufacturer will give you the proper connection (V-Cap has one lead with a red coating and the other lead with a green coating) some having a band printed on one end. If the cap doesn't then you can connect the cap to an oscilloscope set to the most sensitive setting and bring the cap close to an AC carrying wire. Then reverse the 'scope's leads and see which direction gives the lower coupling. The ground probe will be connected to the outside foil.
While this is mostly true for caps used in active circuitry there might be an advantage in connecting shunting caps so the outside foil is to ground in speaker crossovers.

Nightfall

You're going to make the baffle out of metal and use a completely different era Polk tweeter?


Good luck.

xschop

Thanks Kenneth, thats good info to know. I don't have an oscilloscope, but planned on soldering them with the writing going in same direction if that matters/helps. I'll double check if there are bands/lines on these in morning.

To Nightfall, I have made a couple baffles before for a customer years ago in the same fashion. I'll be gluing mine directly to the old baffle, essentially making them many times more stiff. This also negates the need for baffle reinforcement rings or hurricane nuts....win/win.

As for the new tweeters, I temp hooked them up and a very noticeable improvement even with old caps/crossovers as is.

Nightfall

xschop wrote: »

I'll be gluing mine directly to the old baffle

I see, I thought you were replacing the baffle completely.

Good to hear that you liked "new" tweeter.

RandyCroissant

When you get them done post some pics, there is nothing wrong with experimenting.

xschop

I'll be posting pics of everything I do to these. Experimenting is fun, and this is kind of addictive. Plus its easier than modding a custom car or bike. I tested a large swath of the EPDM on a piece of wood and an un-milled billet plate and it is a fantastic adhesive for both, so I'm going to use the Power Grab on the billet plate also.

I used it on the Larger Dayton cap and factory inductor as well as a zip-tie. It's drying.

The long leads sure did help out with soldering and positioning without a wafer-board....

xschop

I'm looking for another set of these old 5jr cabinets. I started deburring the stock and will program some cool detail into the panels of the 2nd set....

pitdogg2

Pm sent

xschop

I had to confirm with my supplier that this was indeed T6061-T6 alloy. Usually the designation is imprinted on the stock. The T6 heat treatment makes for a more beautiful hue when ball-milling the reliefs....