Upgraded 1.2TL xovers new way & circuit error found

[RichCanDo]

This is a long post as I found factory errors during my upgrading and it is a "How to" because I mounted crossover components differently than others have done. The work involved is described.

Factory Error in 1.2TL crossover board circuit:
After completing the rebuild of 2nd xover and while checking the circuit with the schematic, I learned the 750pf bypass cap and 22.5 ohm resistor which together both bypass a 12uf capacitor, are not even connected in the circuit because Polk forgot to install a jumper wire on the board. (One jumper exists on the board, 2 jumpers are required.) These parts only effect tweeter #3. - I note this again and more about it in my listening observations below.
This required jumper is shown & explained in the photos. My guess is many 1.2TL's out there have this error. The way the board traces are laid out, there must be 2 jumper wires on the board. If your board has 2 jumper wires, it is correct. If you have 1 jumper, your xover circuit is wired wrong. Unless you have a board made for the 1.2TL which is different than mine. But I have read of no one stating they have a xover board different than mine.

Tweeters in one of my cabinets were connected incorrectly phased. It appears a 1.2 wiring harness was used by mistake. The 1.2 and 1.2TL use different tweeter phasing. On 1.2's all the (-) terminals of the 4 tweeters connect together by a trace on the xover board. On 1.2TL, the (+) terminals tie together.

The (+) and (-) markings are incorrect as painted on my 1.2TL xover boards. Markings are actually reversed. Most likely the same board was used for the 1.2 and TL model which is why marks are wrong. (Correct for a 1.2 board) To tell if your board is marked wrong and/or tweeters are properly connected in proper phase to the TL xover board, look at the trace on board that connects 4 connector pins together. On TL's the 4 pins connected together should be marked (+). All 4 tweeter (+) terminals should connect to these 4 connected pins on TL's no matter what the board markings are.
NOTE: If you upgrade your xover from 1.2 to TL model, you must also rewire the 8 pin connector on your tweeter wiring harness to match the 1.2TL schematic. (Just rearrange the pin locations) The schematic drawing of connector does not match the actual connector. Go by the pin #'s on drawing. On actual connector, Pin #1 is on one end of the connector.


Upgraded parts and mounting: See the photos which show holes drilled, relocation of parts, have notes and explain the circuit error due to a missing jumper on xover board. I do not know if photos will post large enough to read notes on them. I reduced size of posted photos. Send me a PM if you want larger photos.

I used Sonicaps for High freq side, Solens for low freq side.

The 13.5uf capacitor was replaced with a matched pair of Solen 6.8uf caps. (Pair for each crossover measured 13.47uf & 13.56uf) To have both caps mount flat on the board, one of the two large inductors on the board had to be moved. It was moved toward the outside edge of the board until the inside edges of the 2 inductors lined up. This provided 1/8" or more space for the Solen caps. Just the hot glue was removed to relocate this inductor and 2 small inductors. No unsoldering was required as all inductor leads were long enough.

R3, R4 & R5 were relocated to provide room to stand the Sonicap 12uf capacitor vertical. The 2 small inductors near each other also had to be moved a little to make room for this cap.

R3 used the factory holes in board, but the body was mounted over where the long lead hole was.
R5 body was mounted over & thru existing hole for C6 lead. (Same trace) A new hole for R5's long lead was drilled near the top of the 5 on the board printing and just on outside edge of the square for the body. (Between the inductor and R5 drawing on board.)

For R4 a new hole was drilled for the body by the 6 in C6. (C6 is not used in this circuit) The long lead of R4 attached to the hole the body was originally over, and this lead runs on top of board, under the 12uf Sonicap. A rubber washer about 1/8" thick was placed between the capacitor and the board with a cutout for R4's lead. (Washer made from plumbing sheet gasket material I had. Sold at Home Depot, it is red, two 5" sq pieces in a package.)

To mount vertical, the above 12uf capacitor required a new hole be drilled under the center of the cap. The lead that runs thru the board was insulated with tight fitting insulation removed from a piece of wire. A drop of Super Glue was placed on the wire by the cap before the insulation was pushed against the cap body. This to hold the insulation in place & prevent a short with the trace. If an insulated lead thru the board went thru a different trace, I also scraped the trace away around the hole so the lead could not short out. The rubber gasket under the capacitor allowed the leads insulation to protrude 1/8" above the board to prevent a short. The 12uf lead going thru the board connects to hole marked "L" on the board, the long top lead to "A". (Same as original connections.) Moving the 2 small inductors and resistors provided room for a space between the capacitor and resistors, needed as these resistors can get hot.

The 27uf Solen cap was mounted the same way as the 12uf cap above, on top of a rubber washer. 2 new holes had to be drilled to mount it as the larger cap covered one original hole and a hole was needed under the center to mount vertically. Moving the closest large inductor not only toward the edge of the board (for 6.8uf Solens space) but also tight against the other inductor provided enough room so the cap did not overhang the board. NOTE: With the 1/8" thick rubber washer, the cap lead does not have to run thru & under the board nor be insulated, it can run on top of board thru a cutout made in the washer. Running the lead under the board makes a much better mechanical connection and holds the cap ridgidly in place. The lead can be soldered where it comes thru the hole as is on same trace, but I ran insulated lead to original hole.

The order work was done:
Removed old parts from board, .25uf capacitor on inductor last. The 750pf Mica bypass caps were not removed as used again. (I expect to remove bypass caps after Sonicaps burn in awhile.)
Removed as much old solder as possible with a solder sucker.
Scraped old flux from solder connections & cleaned board with 90% alcohol, a toothbrush & rag to make a good solder connection.

Measured and recorded value of all old parts. Amazingly all parts except 2 caps were within about 2% tolerance, some were right on, none were bad.
I use a Fluke 189 meter which compensates for lead resistance/capacitance, though proper lab procedure calls for measurements to be taken at room temp of 72F.
New parts were measured (again) and values recorded just before they were installed. Caps in parallel & resistors in series were measured after being soldered together, before mounting to board.

Relocated inductors & glued them in place. They had to be held in new location, glued and held until glue dried. (No unsoldering was required, just glue removal.) Photos show where located to. NOTE: Make sure the leads are long enough to allow movement before you try moving them!

All holes needed should be drilled after the inductors are moved and before any parts are permanently installed other than the .25uf cap on the small inductor which should be glued in place when installed.

Next I temp mounted the pair of 6.8uf Solens side by side, flat on the board, centered in the space & against the large inductors to determine where to solder their leads together. Soldered one caps leads to the other. (They connect in parallel, only the leads from one cap go thru the board) Then removed them from the board to have room to work on resistors and 12uf cap to be mounted vertically. These cap leads do not have to be insulated.

Round cardboard templates were made the diameter of capacitors to be mounted vertical, with center hole for lead, to check fit between components. Templates were used to mark board where lead hole had to be drilled under the cap. (Do not mark or drill for long lead from top of cap until you know where other parts will be located.) R3, R4, R5 placed on board temporarily to determine where 12uf cap would fit and outline was drawn on board around cap. Resistors removed then holes drilled for cap. All installed temporarily again to make sure all fit, the parts removed again.

Determined where the 27uf Solen cap would mount vertical, marked and drilled the 2 holes required for its leads. Temp mounted cap with insulation on the leads to check fit & proper hole locations, then set it aside. Mine does not overhang the board. It intentionally sits tight against the inductor so it can be hot glued to inductor for mechanical strength. The lead hole location under the cap must be exact because it is tight against inductor.

In the 4th photo it shows a new hole used for R5. Actually this hole & hole below it was used as 2 resistors in series were used. This is shown in the photo of bottom side of board.

CONTINUED BELOW

[RichCanDo]

Installation order:

Polyswitch (S1) was relocated to underside of board for easier access if future replacement is required. This was done long before the upgrade. A new S1 was installed as 3 were mounted in parallel on both crossovers when I got the speakers!

The inductors were moved and glued.

1st part installed and glued was .25uf cap across inductor so there was room to work on it. I used a .22uf Sonicap as recommended to me stating they would send one nearest to .25 they had. Both received measure .225, right at the max low end of spec for the .25uf +/- 10% tolerance! I bought these parts over 2 years ago, so if I remember correctly, Sonicap stated .25uf was not critical where it was being used. Same for the 22.5 ohm resistor for which they recommended Mills 22 ohms. The two received measure 22 & 21.9 ohms, within 2.66% of the 22.5 ohm spec.

2nd part installed was pair of 6.8uf Solen caps. Hot glued after soldering in as cannot get to glue points after other components are installed.

Next installed resistors, R3, R4, R5.

Installed 12uf Sonicap vertically with rubber washer under it near above resistors. Glued cap to board and small inductor.

Installed C2 the 27uf Solen cap with rubber washer under it. The cap was glued in place before the long top lead was installed. (The lead would be in the way of gluing cap to inductor.)

Installed C3 the 12uf Sonicap on top of the 6.8uf Solen pair. The leads of C3 need to be insulated so as not to short with 6.8uf cap leads.

Installed C5 the 12uf Sonicap that overhangs edge of board.

Installed the rest of the resistors. Glued the above 2 caps in place and any other place that req'd glue.

I may place some pieces on Dynamat Extreme on the capacitors. Maybe strips across several at once. Doubt this will do much. The entire xover board needs to be mounted or sealed in a way free of vibrations. The board probably moves all around mounted on the nylon pegs to the inductor frame.

Circuit error on xover board:
After completing the rebuild of 2nd xover and while checking the circuit with the schematic, I learned the 750pf bypass cap and 22.5 ohm resistor which together both bypass a 12uf capacitor, are not even connected in the circuit because Polk forgot to install a jumper wire on the board. (One jumper exists on the board, 2 jumpers are required.) These parts only effect tweeter #3. (I have RDO's)
I listened to speakers as they were, then removed 1 xover and installed the missing jumper. Now I could compare the left & right channel #3 tweeter. I think it sounds better when connected wrong! To isolate the tweeter I used a toilet paper roll with about 3/4" of paper left on it and placed it over the dome of the tweeter. Played a Windham Hill Jazz CD, Tuck Andress, Title "Reckless Precision" track #10. With this CD track, tweeter #3 is the loudest of the 4. A guitar solo, I looped it to play only the 1st 7 guitar notes over and over. With the 750uf bypass cap and the 22 ohm resistor out of the circuit the sound was warm. With the parts in the circuit the sound was harsh. (Comparing between left & right cabinet tweeters.) I will let the new caps burn-in awhile, then remove the a bypass cap from 1 xover but leave the resistor in the circuit which bypasses the 12uf cap, as the schematic calls for. Then I'll compare the R & L #3 tweets again to learn if the bypass cap or the resistor made the sound harsh. (I left factory bypass caps in place as expect to remove them later anyway with the Sonicaps installed for high freq's.)

CONTINUED BELOW

[RichCanDo]

NOTES: Any parts that overhang the board at top or bottom when xover is mounted to plate, will hit the speaker cabinet when installing the xover. The board itself just fits thru the cabinet hole.

I used same size drill as existing holes on board except for insulated cap leads going thru the board which req'd a larger hole. Use a sharp drill. I turned the drill by hand to start the holes. I recommend this or the hole can wander if you try to use a drill motor. Drill from the trace side when possible. Drilling from the top of the board can force the trace from the board when the drill goes thru, though these traces hold well. (Let the drill bit do the work and do not push it through!) Lightly scrape the top coating from the trace around new hole until the copper shines or solder will not stick. Cleaning with alcohol may help also. I drilled from top of board if location of hole had to be exact, but if hole is on edge of a trace or close to another trace, better to drill from trace side. Deburr the holes after drilling with a larger drill by hand. Do not drill where you will hit 2 traces at once with the hole.

Leads that were not long enough on caps & resistors were lengthened by soldering the lead cut off under the board to the short lead. For leads insulated, shrink tubing and pieces of insulation taken from wire I had on hand was used.
Cardas Quad Eutectic Solder was used. I also used flux on all connections (Which was not cleaned from boards before I took photos.) After assembly boards again cleaned with 90% alcohol & toothbrush after scraping off excess flux.

Other work done:

I made a new Interconnect Cable from Monster Z2 speaker wire as Darque Knight had done, but I used Neutrik Speakon NL4FRX 90 degree 4 pole connectors & connected the 4 poles together for more contact area. A 1" hole was drilled in rear of cabinet to install the 4 pole Neutrik jack. I Dynamated the drivers & PR. Will use leftover Dynamat on my guitar amp speakers.

Painted 4-5 coats of polyurethane around driver and PR cutouts in MDF to provide a smoother, flatter surface for gaskets to mate to. MDF was rough in the cutouts. Used Mortite on one cabinet and will remove it. Factory gaskets seal just as well. Will replace all gaskets if I find new, one piece foam gaskets the same thickness.

For possible air leaks: Ran a bead of wood glue around all interior cabinet seams that did not have a bead already. Placed pieces of duct tape inside cabinet over all driver & xover screw holes that went thru the cabinet. Made sure binding posts plate and posts were well sealed with silicone as well as bolt going thru xover plate to hold large inductor. Removed top and bottom end caps & wrapped Mortite around the 4 studs to seal air leaks around bolt "thru holes" in cabinet.

I have new grill cloth but this will wait until I find wood to replace the end caps and side wood strips. Been looking on eBay for months for some solid wood, but hard to find enough quantity in width I want. When this is done, I may cover the old wood with polished black laminate. (Formica, etc)

[RichCanDo]

Before someone mentions I connected the pair of resistors wrong, they are connected in Parallel. I mistakenly wrote "in series" in the above posts and on the photos. A 20 & 27 ohm are connected in parallel for 11.5 ohms.

[vmaxer]

I upgraded my crossovers with all sonicaps. Are the Solens supposed to be better/different?? I also have switched to the RDO tweeters and sealed with mortite.

[F1nut]

Are the Solens supposed to be better/different??

They are inferior in any application.

[NJPOLKER]

RichCanDo sure did!!! Isn't it rewarding do something like that??? Thanks for taking an extreme amount of time sharing this information with everyone. I can't say I read it all yet but will later, I sound like a politician for some reason saying that. I bet you can't wait to hear them and after a few hundred hours you'll be set for awhile. Then you have to get into tubes :p
Thanks

[RichCanDo]

I upgraded my crossovers with all sonicaps. Are the Solens supposed to be better/different?? I also have switched to the RDO tweeters and sealed with mortite.

F1nut is correct. Sonicaps are better, there are better than Sonicaps also. Solens are a cost saving alternative as the low freq side of the xover is not as critical. I just read a post by a company that had done xover upgrades using Solens stating they are used in $15,000 speakers by some makers. The post stated they would no longer offer upgrades using Solens because customers later wanted the Solen upgrade changed to the upgrade that used higher ends caps.

The upgrade did make a big improvement in sound which was noticable immediately. The bass is much better, which is the Solens. Detailed sonic differences I can not tell you. Only listened to them about an hour so far a little while at a time. Also I have not listened to them much before the upgrade, for the past 2 years, so I cannot give a comparison. Since I've owned these, about 3 years, I always thought there was something wrong with them as they have a poor sound stage. As they were, they did not compare to the SDA SRS I had for about 10 years and got when they came out. Soundstage improved with upgrade but I now have to try getting them placed correctly. Not done this yet as I have 3 stacks of components (17) on the floor between the speakers which have to be unwired and moved to move speakers closer together.

[RichCanDo]

RichCanDo sure did!!! Isn't it rewarding do something like that??? Thanks for taking an extreme amount of time sharing this information with everyone. I can't say I read it all yet but will later, I sound like a politician for some reason saying that. I bet you can't wait to hear them and after a few hundred hours you'll be set for awhile. Then you have to get into tubes :p
Thanks

You are welcome. Doing this is the sort of thing I did working half my life and enjoyed the most. I used to troubleshoot manufacturing machinery control circuits and would often do upgrades to circuits or design a new type of circuit. Like converting analog control to computer control.

Have had tube gear in past, still have an old Dynaco amp I plan to use in my bedroom if I ever get time to set up a system there. My Fender guitar amp is a tube amp which uses digital processing for the sound effects. I prefer analog circuitry and discrete components.

[zarrdoss]

nice job!

[DarqueKnight]

Great write up Rich. Thanks and enjoy!

[RichCanDo]

I would like to know from others if anyone has TL xover boards with the correct tweeter polarity marked on the board. (If so, then there is a board designed specifically for the TL model)

I would also like to know if others have crossovers missing the 2nd jumper. It may have just been a factory oversight on my 2 xover boards, but it seems unlikely same error on 2 boards. I also do not believe this was a circuit design change made by Polk. If a design change, they would have not wasted time & money installing a capacitor & resistor that would not be used. A design change would have been made after the 1st set, or a few sets were built, and underwent listening and other tests. Also if a design change, it would have been noted on the 1.2TL schematic.

[decato]

I listened to speakers as they were, then removed 1 xover and installed the missing jumper. Now I could compare the left & right channel #3 tweeter. I think it sounds better when connected wrong!

I had also seen this discrepancy between the schematic and actual crossover in 2 pairs of 1.2tl's. Adding that resistor in parallel with the cap gives the tweeter more signal at the low end of its range. It may appear harsher, but I think it helps to create a solidified center image. I kept it in the circuit for mine. Would you please experiment with listening to the pair rather than just a L-R comparison?

-Brian

[Lasareath]

I would like to know from others if anyone has TL xover boards with the correct tweeter polarity marked on the board. (If so, then there is a board designed specifically for the TL model)

Mine all match up, My Serial Numbers are 6381 & 6371, I'm pretty sure they left Polk as 1.2TL's

Lasareath

[RichCanDo]

I had also seen this discrepancy between the schematic and actual crossover in 2 pairs of 1.2tl's. Adding that resistor in parallel with the cap gives the tweeter more signal at the low end of its range. It may appear harsher, but I think it helps to create a solidified center image. I kept it in the circuit for mine. Would you please experiment with listening to the pair rather than just a L-R comparison?

-Brian

I am listening to them as a pair now with the jumper installed connecting the bypass cap and resistor into the circuit. I do not think my observations matter much as I made too many changes at once. I've mentioned these TL's always seemed to have a poor sound stage. I always had a good center image, but it seemed to contain only maybe a vocalist centered well with maybe a drum set just behind him or slightly left/right behind him. Other than that, the left and right speaker seemed like separate entities, I heard sound directly radiating from each speaker, as if instead of sitting in the sweet spot I was sitting directly in front of one speaker, or the recording had to much stereo separation. This with good recordings.

I will next experiment with speaker placement which always makes a large difference. Where I have them placed should be OK though as it is within recommended placement as on the labels. Cabinets are centered in the room on long wall 6'-8" apart and both 6'-8" from the side walls. I sit centered between them, my ears 9' in a direct line to the center of each speaker. Wall behind my head is 32" from my ears.

Incidently, when I had SDA SRS's, I found placing an absorbtive surface on wall behind my head made a big difference in the clarity of the music. Removing the reflected sound from the rear wall allowed for better musical detail. To check this out then, I simply had hung a heavy bed quilt on the wall behind my couch. Now I am looking for a heavy tapestry to hang on wall. I'll mount this to a frame of 1" x 2" lumber & install 1" ridgid fiberglass insulation in the frame.

[RichCanDo]

Mine all match up, My Serial Numbers are 6381 & 6371, I'm pretty sure they left Polk as 1.2TL's

Lasareath

Yours do not match up! They are like mine. The Positive tweeter wire is connected to Negative marked on the board. A board made specifically for the TL's would be marked to match the wiring.

Yours are wired correctly though as the 4 pins marked (-) on board connect together by a trace. So your 4 (+) tweeter terminals are connected together as TL's should be, even though they connect to (-) marked on board.

Do your crossovers have the 2nd jumper installed? It would be in the holes for R2 marked on the board.

[F1nut]

The Positive tweeter wire is connected to Negative marked on the board.

That's how Polk did it for the 1.2TL's. No biggie, they are wired correctly and that's all that matters.

[F1nut]

Here's one I did, R2 jumper installed.

http://www.polkaudio.com/forums/atta...5&d=1185155268

[F1nut]

Rich, it may help you to know that Polk used the same board for a number of different models including the CRS+, 2B, 1C, 1.2, 3.1TL, 2.3TL and the 1.2TL. They all start with part number BE.

[RichCanDo]

Rich, it may help you to know that Polk used the same board for a number of different models including the CRS+, 2B, 1C, 1.2, 3.1TL, 2.3TL and the 1.2TL. They all start with part number BE.

Thanks for the info. I would expect a universal board would typically be used on which different circuits could be built. A phase reversal in a circuit requiring the board to be marked differently was probably never expected. I just wondered if there was a board made for TL's which had the correct polarity marked on it, as I do not want someone to change their wiring to what I had written, if they had a board not requiring a change. This is why I always stated "check the trace" on the board.

[michaeljhsda2]

Rich, here is a pic from my 1.2TL's. Is the blue rectangle on the far right the jumper you are referring to?

[RichCanDo]

Rich, here is a pic from my 1.2TL's. Is the blue rectangle on the far right the jumper you are referring to?

Hi. The blue rectangle is in the proper location. It could be a jumper, though a simple piece of wire would have done the job. If a jumper, the type is used as to just quicken the installation, saving assembly time. It could also be some type of component, but I doubt it is. If you board does not have a 750pf Mica cap on opposite end of the 12uf capacitor, that is what it could be, but not likely, as its leads need to connect to both ends of the 12uf cap.

[michaeljhsda2]

Hi. The blue rectangle is in the proper location. It could be a jumper, though a simple piece of wire would have done the job. If a jumper, the type is used as just quicker to install saving assembly time. It could also be some type of component, but I doubt it is. If you board does not have a 750pf Mica cap on opposite end of the 12uf capacitor, that is what it could be, but not likely, as its leads need to connect to both ends of the 12uf cap.

That's good to hear as I just put my speakers back together :D Taking photos of everything sure saves a lot of time when looking at things in retrospect.

Jerry's original 1.2 board (but now upgraded to 1.2 TL's) does not have a jumper of any sort in that position, either on top or on the underside. Do you recommend we install a jumper as you have done?

[RichCanDo]

That's good to hear as I just put my speakers back together :D

Jerry's original 1.2 board (but now upgraded to 1.2 TL's) does not have a jumper of any sort in that position, either on top or on the underside. Do you recommend we install a jumper as you have done?

Yes, I would install the jumper as that is what the schematic calls for. If you upgraded to better capacitors, you can remove the 750pf mica bypass cap as others have stated is not really required with good capacitors. I left the bypass cap in mine. I will let the new caps break in awhile and then probably remove the bypass. But the jumper is required to keep the resistor in the circuit.

Out of curiosity, what are the serial #'s on both sets? 1st 2 digits are enough. Mine are 61xx on both cabinets.

[michaeljhsda2]

Yes, I would install the jumper as that is what the schematic calls for. If you upgraded to better capacitors, you can remove the 750pf mica bypass cap as others have stated is not really required with good capacitors. I left the bypass cap in mine. I will let the new caps break in awhile and then probably remove the bypass. But the jumper is required to keep the resistor in the circuit.

Out of curiosity, what are the serial #'s on both sets? 1st 2 digits are enough. Mine are 61xx on both cabinets.

Jerry's 1.2's (1.2TL's) 5016 and 5032
My original 1.2 TL's 61xx

[Lasareath]

Here's one I did, R2 jumper installed.

http://www.polkaudio.com/forums/atta...5&d=1185155268

Mine also have the R2 jumper installed.

[vmaxer]

okay, look at mine and tell me if it is correct....

This is before the upgrade, but they are connected exactly like this...:o

[dorokusai]

"Interesting. I do not remember any such run of SRS that went out with missing jumpers. That is not to say that it could not have come from the factory w/o my knowledge but these were made at our Mexico facility and we used microphone setups at that facility which identified the proper number and polarity of tweeter impulses from the tweeter array. I will have to examine the documents more closely." - Polk Audio

[michaeljhsda2]

Yes, I would install the jumper as that is what the schematic calls for. If you upgraded to better capacitors, you can remove the 750pf mica bypass cap as others have stated is not really required with good capacitors. I left the bypass cap in mine. I will let the new caps break in awhile and then probably remove the bypass. But the jumper is required to keep the resistor in the circuit.

Out of curiosity, what are the serial #'s on both sets? 1st 2 digits are enough. Mine are 61xx on both cabinets.

Photos of Jerry's 1.2's (converted to 1.2 TL's).

[RichCanDo]

okay, look at mine and tell me if it is correct....

This is before the upgrade, but they are connected exactly like this...:o

Yours are missing the jumper also. Your board looks just like mine did. Your jumper may be under the board but I doubt it is.

What are the serial #'s on yours?