Hauxon's SRS 1.2TL restoration

hauxon

Since the 1.2TL are now mine I decided to make a new thread about my intended restoration and upgrades on 'em. I don't have limitless resources, neither time or money, so I've decided the process needs to be split up into steps that focus on one at a time.

The current situation with speakers is that no mods have been done out side of gluing one of the cabinets brace back to it's place above the passive radiator since it had fallen off at some point, probably during transport. I have also replaced on of the 12uF caps with a ClarityCap CSA because the original one had fallen off. Probably as a result of the brace falling onto it. Otherwise the speakers are original, not in a bad shape but in need of some TLC. I've tested the speakers for polarity with a 9V battery (the low frequency) and all woofers move in the same direction and seem ok. Tweeters are original SL3000 and all seem to be working (tested using a cone from table towel roll ). The cabinets seem reasonably airtight, if I push and hold the passive radiator the woofers all move out and return slowly.

The sound is good, especially from midtones and up. I still don't feel they're delivering the solid, firm bass I was expecting from such a large speaker. The speakers are in my living room so the listening space is rather large, about 80m2 (860 sq ft) open space and ceiling is roughly 4.5m (14ft) high. There are no walls close to the sides where the speakers are located. Floor is hardwood with rugs and most walls and corners are not perpendicular (modern architecture building). I've experimented with speaker and seating locations and don't find major changes in the bass department. I've had Polk SDA 2B(TL) for years and years and I never felt they were missing in the bass department. So I've kind of ruled out the problem is related to room acoustics since the 2B sounded just fine from the same location. The SRS 1.2TL sound much better with a tiny little help from a subwoofer. I do have a sub and if I set the to filter about 50Hz and just add a tiny bit of volume everything actually sounds really nice, not world shaking but full. Many recordings sound too thin (with sub off), especially rock music and become almost annoying at louder volumes. If I take an example some recording I know is really powerful and has plenty of bass thump like Rage Against the Machine first record ..it just does not sound right! I now have the 2B speakers in my home office/man cave, a much smaller space and they sound just terrific (with only 40W amplification!!), I often get goosebumps, just terrific speakers the TL modded 2B's. One possible fault could be the power amplifier not being powerful enough for the large 1.2TL's. It's a possibility but I highly doubt it. The power amp is a NAD C272 2x150W into 8ohms, not the 500W amp the 1.2TL deserve but should have no problems with delivering what's needed for moderate listening levels. There were no problems with the amp when it was paired to the 2B speakers and that combo just sounded powerful and neutral. So I've decided to take this one step at a time and see what happens.

The first step would then be upgrading the crossovers. Probably won't make much of a difference with bass response but these caps are old anyways and one of the crossovers were damaged when I got the speakers. As I've already mentioned I did buy a 12uF ClarityCap CSA capacitor to replace the one that broke off. I used ClarityCap ESA with my 2B and with good results so I decided to also use ClarityCaps for my 1.2TL crossovers. I also have good experience shopping from hificollective.co.uk and it is convenient to shop from the UK to Iceland. Since the 1.2TL are more "posh" I have decided to use CSA caps for the highs and the ESA for the low end. The 12uF cap I bought for the fix can reused for the new crossovers. I ordered the Gimpod boards (just arrived) form Dave and the connectors from Mouser. I've ruled out Duelund resistors because of cost and will probably either go with Jantzen Superes or Mills (both available at HiFi Collective). My original plan was to reuse the original inductors but they're cheap (besides the 16mH) so I might just buy them ans save me the hassle of desoldering the originals off. I've done a lot of reading here on forum and other diy forums and found lot's of great info that will make my quest a lot easier.

So I have few questions before I can finish my parts order at HiFi Collective.

1. Regarding the Mills resistors, are Mills and Vishay Mills resistors the same thing? I know Vishay merged with Mills but HiFiCollective list what they have just as Mills. I see Sonic Craft have Mills and Vishay Mills as different lisings.

2. The 1.2TL crossovers have five different resistors, 2R7, 7R5, 11R5, 15R and 22R5. The 22.5 I can only find at Sonic Craft (Vishay Mills). Is it wise to use two resistors in series to achieve the correct impedance? Will it have any (negative) effect on the sound or heat generation? Would it be better or worse using 10R and 1R5 in series than ...5R1 and 5R6 (insted of a 11.5ohm resistor)? I've read that people often use just a close number, like a 12ohm in place of the 11.5 and 22 in place of the 22.5. However I have seen how much a little change in resistance can have on the frequency response (and thus sound) in the few crossover design videos I've seen on YouTube I'm likely to try keep the values as intended.

3. That brings me to the next question.. Have any of you tried putting the Polk crossover designs into software like Vituix? Are there any FRD files (frequency Responce Data) out there for the Polk drivers? It would be great to have better understanding of the design intents and also the effects of slight changes from the original schematics.

4. And last. I found two discussions with great info regading inductors. One being a table of inductors in most Polk SDA models and their properties made by Gimpod (and DarqueKnight). From that table I could find what Jantzen inductors I can order for the tweeter part of the crossover but for the bass past are just Solen part numbers. I've seen pictures of newly built crossovers with all Jantzen inductors so I ask if any knows the correct part numbers for the 1mH and 2mH inductors I need.

5. Last question is regarding lower DCR with the Jantzen inductors. Polks says in the manual that the speakers can be used with amps at the 8ohms setting. If I understand correctly the 1.2TL impedance is however closer to 6omh and probably with dips much lower than that. Will the use of inductors with lower DCR move 'em closer to 4ohms? Making bridging near impossible? That would however cause your amp to operate at higher power, more powerful ..making my current amp less wimpy???

Thanks for the reading!

Hrannar

hauxon

The Gimpod boards. Bigger than I thought.

westmassguy

hauxon wrote: »

The Gimpod boards. Bigger than I thought.

Lots of room Hrannar. @gimpod did a great job on them

DarqueKnight

hauxon wrote: »

1. Regarding the Mills resistors, are Mills and Vishay Mills resistors the same thing? I know Vishay merged with Mills but HiFiCollective list what they have just as Mills. I see Sonic Craft have Mills and Vishay Mills as different listings.

As far as I know, Vishay makes their Vishay Mills resistors per the original Mills spec. You might want to inquire at vishay to be sure. As for Sonic Craft listing Mills and Vishay Mills resistors on their website, Mills no longer exists, so I assume the Mills resistors are old stock that they will sell until they are all gone. Ask Sonic Craft to be sure.

https://www.vishay.com/company/brands/mills/

hauxon wrote: »

2. The 1.2TL crossovers have five different resistors, 2R7, 7R5, 11R5, 15R and 22R5. The 22.5 I can only find at Sonic Craft (Vishay Mills). Is it wise to use two resistors in series to achieve the correct impedance? Will it have any (negative) effect on the sound or heat generation? Would it be better or worse using 10R and 1R5 in series than ...5R1 and 5R6 (insted of a 11.5ohm resistor)? I've read that people often use just a close number, like a 12ohm in place of the 11.5 and 22 in place of the 22.5. However I have seen how much a little change in resistance can have on the frequency response (and thus sound) in the few crossover design videos I've seen on YouTube I'm likely to try keep the values as intended.

You can put resistors in parallel to get a higher value, but for audio applications, you typically want as few components and as few circuit connections in the signal path as possible.

A small change in resistance can be audible, depending on where the resistor is located. However, the original ceramic metallic resistors were 10% tolerance parts. For the 22.5 ohm resistor, the range of resistance is 23.25 to 24.75 ohms. I initially used a 22 ohm Mills resistor. When I replaced the Mills with Duelund resistors, I was able to get the exact 22.5 ohm value.

hauxon wrote: »

3. That brings me to the next question.. Have any of you tried putting the Polk crossover designs into software like Vituix? Are there any FRD files (frequency Responce Data) out there for the Polk drivers? It would be great to have better understanding of the design intents and also the effects of slight changes from the original schematics.

I have put the crossover designs in PSPICE and ran frequency response simulations. I did this when I was curious about the effects of different resistor values on frequency response.

hauxon wrote: »

4. I found two discussions with great info regading inductors. One being a table of inductors in most Polk SDA models and their properties made by Gimpod (and DarqueKnight). From that table I could find what Jantzen inductors I can order for the tweeter part of the crossover but for the bass past are just Solen part numbers. I've seen pictures of newly built crossovers with all Jantzen inductors so I ask if any knows the correct part numbers for the 1mH and 2mH inductors I need.

When I replaced the low frequency 1 mH and 2 mH inductors in my 1.2 TLs, I used Solen perfect lay inductors. Here are some guidelines regarding DCR for those inductors:

hauxon wrote: »

5. Last question is regarding lower DCR with the Jantzen inductors. Polks says in the manual that the speakers can be used with amps at the 8ohms setting. If I understand correctly the 1.2TL impedance is however closer to 6 ohm and probably with dips much lower than that. Will the use of inductors with lower DCR move 'em closer to 4ohms? Making bridging near impossible? That would however cause your amp to operate at higher power, more powerful ..making my current amp less wimpy???

With the exception of the 16 mH SDA inductor, Polk recommends using upgrade inductors with the same wire gauge and DCR as the originals.



I replaced the 16 mH/18 AWG/2.8 ohm DCR stock inductors with 16 mH/10 AWG/0.8 DCR Solen inductors.

hauxon

Thanks for a detailed answer DK. So for the 11.5 and 22.5 resistors I'd be close enough with 12 and a 22. Funny you should mention few parts as possible philosophy since today I was looking at the KEF 103.2 crossover and it got an amazing number of components for such a simple speaker. I'll take better look at the inductor during the weekend. VR3 gave me the part numbers for the Jantzen inductor he uses. It would convenient to use the Jantzen ones since HiFiCollective carries them allowing me to save some on shipping. When I ordered the connectors from Mouser I had swallow $30 for shipping a package worth less than $10. The total with VAT to me roughly $60! So I will order caps, resistors and inductors all at once IF I can.

pitdogg2

DarqueKnight wrote: »

As far as I know, Vishay makes their Vishay Mills resistors per the original Mills spec. You might want to inquire at vishay to be sure. As for Sonic Craft listing Mills and Vishay Mills resistors on their website, Mills no longer exists, so I assume the Mills resistors are old stock that they will sell until they are all gone. Ask Sonic Craft to be sure.

That is correct Jeff has NOS Mills he will sell until gone and new stock Vishay/Mills. In the beginning of the new business of Vishay/Mills he had some problems but that has since been worked out and feels there is little if any difference between the two now and carries a large assortment. I actually had to get my .5 ohm 12watt Vishay/Mills from Hi-Fi collective as Sonic Craft did not carry them. The closest was .47 12watt. IIRC he does carry the .5ohm in 10watt Vishay/Mills.

DarqueKnight

hauxon wrote: »

Thanks for a detailed answer DK. So for the 11.5 and 22.5 resistors I'd be close enough with 12 and a 22.

One thing I forgot to mention is that the four 1.2TL's tweeters are a progressive point source array which acoustically act as "one" tweeter. Fractions of an ohm one way or the other will typically not be as audible as with a single tweeter design.

This contrasts with the tweeter protection polyswitch, which is in the signal path that feeds the entire tweeter array. I found the differences among the polyswitch, no polyswitch, and various small value resistors are very audible:

https://forum.polkaudio.com/discussion/128258/resistor-replacement-for-the-sda-srs-1-2tl-polyswitch

westmassguy

DarqueKnight wrote: »

You can put resistors in parallel to get a higher value, but for audio applications, you typically want as few components and as few circuit connections in the signal path as possible.

Raife, should be in Series, not in Parallel

DarqueKnight

Yes, I meant to say in series. Thanks for catching that. I had been working on resister ladder calculations and still had parallel resisters on the brain.

westmassguy

DarqueKnight wrote: »

Yes, I meant to say in series. Thanks for catching that. I had been working on resister ladder calculations and still had parallel resisters on the brain.

No worries

hauxon

Just made an order for $450 at HiFiCollective!!!

...I'm a bit shocked how expensive the parts were when I had put everything in the cart I needed for the new crossover build, and I did not even buy really expensive parts.

The Jantzen inductors are special order items so I expect to wait for few weeks before everything is shipped.

westmassguy

Last time I ordered from HiFi Collective, took about 3 weeks

hauxon

The Mate-n-lok connectors arrived from Mouser today. First soldering job done..

F1nut

You put them on backwards.




























J/K

hauxon

You got me worried there! Probably looks wrong because they are upside down in the pic.

I double checked the layout. Looks right to me when compared to the layout printed on the Gimpod boards.

F1nut

hauxon wrote: »

You got me worried there! Probably looks wrong because they are upside down in the pic.

I double checked the layout. Looks right to me when compared to the layout printed on the Gimpod boards.

You missed the J/K at the bottom of my post.

hauxon

LOL

F1nut

hauxon

Whoo hoo, $440 worth and 4.5 kilos of caps, inductors and resistors has finally shipped from HiFiCollective! Scheduled to be at my doorstep in 2 days. Need to clear my desk for my biggest soldering job to date.

One question. I decided to order the big Jantzen C-Coil 16mH inductors and have been thinking about where to put it. The original inductor kind of holds everything in place, mounts to the back of the crossover board and then has a nut that enables the whole thing to be mounted on the metal front plate of the 1.2TL. I've been thinking about mounting the inductor to the brace bar below the crossover. I think I however need to secure it better since the inductor is almost 3 pounds the glue holding the brace might give in to gravity with time if not reinforced somehow. Another possibility would be putting it on the back of the cabinet above the hole for the terminals. Does the orientation of the inductor matter? Does it have a magnetic field that might interfere and cause problems with the internal wiring or other components in the speaker?? ..and does the length of the wires from the crossover to the inductor have any effect on performance?

Hrannar

hauxon

I read somewhere that toroidal inductors (like the Jantzen c-coil) have a core and interact less with other inductors since the magnetic field is self contained. Does that mean that I do not to worry too much about where I put the inductor?

westmassguy

Hrannar, the c-coil had a magnetic metal core, and should be well clear of any other inductors. You should also use non-magnetic screws (Stainless, Brass or Aluminum) and plastic hold-down clamps to secure it.



The safest place would be centered on the bottom of the cabinet.

When I eliminate the large spool inductors, I replace them with a new mount made from 1/2" MDF, 3/4" nylon standoffs, and a 1/4 X 20 Hurricane Nut.

hauxon

Thanks! I guess the bottom is a good place for it. I would then just use a regular heavy gauge speaker wire to connect it to the board. I did buy the 3 pin Mate-n-lok connector for the inductor but forgot to buy the male connector from parts-express. Do you know if a regular 3 pin male Molex (computer) connector will fit?

westmassguy

hauxon wrote: »

Thanks! I guess the bottom is a good place for it. I would then just use a regular heavy gauge speaker wire to connect it to the board. I did buy the 3 pin Mate-n-lok connector for the inductor but forgot to buy the male connector from parts-express. Do you know if a regular 3 pin male Molex (computer) connector will fit?

Pretty sure the Mate'n'Lock are completely different

hauxon

Few days ago I read a thread about a light leakage with the bolt that holds the crossover. If I remember correctly the return time for the woofers when you push the passive radiator went from 2 seconds to 5 with better sealing. I would say woofers on my speakers are closer to 2 than 5. Have you thought about using the MDF board to make the sealing better, maybe by using something like Mortite around the bolt hole and hot glue on the other side of the hurricane nut? ..or maybe a rubber gasket or something on the bolt head.

I can't find US threaded hurricane nuts here in Iceland (everything metric here) so I will have to find a way to use a regular 1/4 nut. Will probably work on this tonight. The crossover parts are here in Iceland according to FedEx but won't be delivered until tomorrow.

westmassguy

Once the hex head is tightened, there's no leakage. There are so many other places for leakage to occur, I seriously doubt it's the crossover machine screw. Keep in mind, the woofers are not sealed. The mesh dust caps and cloth spiders leak air.

Viking64

Bump.

SIHAB

Bump interesting for Ben Franklin talk

hauxon

Here's the post I was referring to: https://forum.polkaudio.com/discussion/comment/2002887#Comment_2002887

hauxon

The parts arrive tonight but last night I did some preparation work. I decided to take Dave's advice and will be putting the 16mH inductor on the buttom of the cabinet.

I did order a 3 pin MATE-N-LOK/Molex connector for the large inductor to make it easier to remove the crossover from the cabinet. I used 14AWG wire but had to strip a little bit off to be able to fit it into the connector and used some solder to further cement the connection.



I got some scarp wood I cut to length for the mounting plate and drilled holes where the original inductor was positioned. Since I wasn't able to buy a hurricane nut here in Iceland I just cut out an insert for a regular nut in the wood and glued it into the board using Zap-a-gap glue. Hope it good enough.

westmassguy

Looks great. Are those nylon standoffs I hope?

hauxon

Yup