SDA 2B Studio Crossover Upgrade

BlueMDPicker

While ordering bits and pieces for my planned Dynaco ST-70 rebuild, I noticed the vendor (Angela Instruments) carries the "Solen" PB series caps with their own branding. So, I thought I'd give them a try on my first acquired set of SDAs, the 2B Studio. I'm still waiting on the resistors and binding posts and I'll post more pics of the actual upgrade as it commences.

This one promises to be challenging for parts placement since the stereo and dimensional PCBs are sandwiched pretty tightly on treeloc standoffs. But, where there's a will, there's a way. The caps pictured cost about $35, which I consider a modest investment for these solid performing vintage Polk speakers.

faster100

I seriously would like to upgrade some stuff on my sda 1b's when money permits.. I already replaced all the tweeters and woofers from polk, just because... and to start off new.. would like to start with binding post and work from there...

DAGLJAM6

This will be of interest, i'm ordering new tweets for my sda2's next week and this summer i'm planning a re- cover job on the end caps could use the down time for some "other" upgrades.
Keep us posted please. Thanks.

hookedonford

I am very interested in upgrading my SDA 2B Xovers. My Xovers do not look like the pictures in the others posts. The numbers on them are:

SDA2B+CRS
BE1807-A
3/17/89 4R

How do you get a parts list for these SDA 2B Xovers? I will attach a picture of one my xovers, maybe some one can give me some insight to what components I need to upgrade the BE1807-A style xovers I have.

Thanks in advance, Jim

BlueMDPicker

Welcome to the forum, Jim.

Using your photo for reference, and starting at the top/right, these are the components to replace on each board:

"Dark" blue (in shadow) cap is a 40 uF electrolytic
Light blue cap is a 20 uF electrolytic
Yellow cap is a 12 uF mylar

All the above were replaced with 400-630VDC metalized polypropylene caps. In my 2Bs I used Angela 630V (Angela Instruments), and in the SRSs Solen PB series 400V (Parts Connexion.)

http://www.angela.com/

http://www.partsconnexion.com/catalog/CapacitorsFilm.html

White block resistor is a 2.7 ohm wirewound. I'm again using the Mills MRA-5 non-inductive resistors from Parts Connexion.

http://www.partsconnexion.com/catalog/resistors.html

There should be a 750 pF silver dipped mica capacitor on the PCB in parallel with the 12 uF cap. It's a quality component, and I did not replace this cap in my SRS, nor will I on the 2Bs.

There is also a polyswitch for tweeter circuit protection on the PCB. It should be either part number RDE050A, or RDE090A. If you've had any problems with tweeters cutting out, it should be replaced. If not, leave it alone. Available from Polk Customer Service, as is a schematic of the crossover.

Good luck! You'll probably complete your project before mine (I'm waiting on resistors for another project in a batch that includes the ones needed for this.) If so, please feel free to post your photos and observations in this thread.

Mike

amulford

Hey Mike,

This does sound interesting. Does it make that much of a difference?

I think I might have to give this a shot, along with the tweeter upgrade. I am not very good with a soldering iron, though. I might have to seek some help w/ that aspect.... Any suggestions?

Anthony

BlueMDPicker

Hi Anthony,

IMO, with similar results reported by other forum members, cap and resistor upgrades provide a marked improvement in separation, imaging, bass response, and transient speed. My SRSs upgrade was, to my ears, like receiving a new set of speakers.

The replacement tweeters are well worth the money spent, and have been discussed thoroughly here (with some hardcore traditionalists even becoming converts.)

Soldering is not difficult to master. There are numerous good tutorials on the web. Do a search for "soldering tutorial" to find one that fits your needs. Here's a nice one;

http://www.kpsec.freeuk.com/solder.htm

Holler if you need any help.

Mike

BlueMDPicker

I finally found some time to tackle this. Below is a shot of parts placement (resistor not yet replaced), which was somewhat challenging -- the new capacitors are 3-5 times larger than the originals.

The 40 uF at the top right was a best fit mounted at a right angle to the PCB due to the modular connector. A jumper wire (sleeved in heat shrink) was required. A knee bend at the other lead allowed correct roll toward the coil (for stability) and away from the connector.

The 20 uF, with knee bends to hit the original mounting holes, has just enough lead length to mount between the coils and the 12 uF (which is mounted first, rolled to the left and up as far as lead length will allow.)

Generous amounts of hot glue were used between the new caps and any adjoining surface or component.

Unlike my SRS crossover upgrade, I intend to do one crossover at a time so that I may more readily (and objectively) A/B for SQ changes.

BlueMDPicker

Well, that was a no-brainer. After listening to the single modded xover and the original, side by side, it was a night and day difference. It took me less than 20 minutes to do the second one.

For less than the cost of one replacement tweeter you can have a new pair of SDA 2Bs, that sound like they were designed -- versus how they were mass produced.

Next stop: the 2As.

Polkersince85

I've got a set of SDA 1B crossovers and am slooowly collecting drivers. I will eventually tread on holy ground and build a custom set of SDA's. I may go ahead and upgrade the x-overs prior to building. The links and tips on this may come in handy. Keep us updated.

HBombToo

Originally posted by BlueMDPicker
Welcome to the forum, Jim.

White block resistor is a 2.7 ohm wirewound. I'm again using the Mills MRA-5 non-inductive resistors from Parts Connexion.

http://www.partsconnexion.com/catalog/resistors.html

There should be a 750 pF silver dipped mica capacitor on the PCB in parallel with the 12 uF cap. It's a quality component, and I did not replace this cap in my SRS, nor will I on the 2Bs.

Welcome, Jim.

is there a difference in parasitics(chspl)? why move away from carbon resistors is my question.

one less expense:p

1/4twin

BlueMDPicker

Originally posted by HBombToo
is there a difference in parasitics(chspl)? why move away from carbon resistors is my question.

one less expense:p

Henry,

The two Mills resistors used in this project cost $2.15 each.

I didn't do any science. The decision to replace them was purely a function of the age and (lack of) quality of the original components. "White coffin" wire wounds, IMO, are fine outside the signal path (voltage dropping networks, etc.) But, I'll bet this pair of SDAs that Polk didn't use these gruntball components to prototype the design. DarqueKnight had a dialog with Polk engineering that pretty much confirms that fact.

This modification is profound. Unless and until you've heard the difference in SQ it affords, you simply won't believe it. It's not like a veil being lifted, it's like a down-filled comforter being lifted. The bang to buck ratio of this $30 upgrade is at least 50:1.

Mike

sda2mike

I was wondering if anyone on the site would be interested in doing the upgrade on an exchange...plus$$$ of course...I have visions of me **** up a project like this...:p

BlueMDPicker

sda2mike,

There's really not much to worry about in the screw up department. The most tedious part of the upgrade is separating the treeloc standoffs. I'll try to do it by the numbers for you. This is for the 2B or 2B/CRS+ crossovers:

1. Order the following parts from Parts Connexion (link above)

2 - Solen PB series 39 uF capacitors (SKU: SOLEN- 52319)
2 - Solen PB series 20 uF capacitors (SKU: SOLEN- 51558)
2 - Solen PB series 12 uF (SKU: SOLEN- 51556)
2 - Mills MRA-5 2.7 ohm resistors (SKU: MILLS- 64619)

2. You will need: Medium phillips screwdriver, needle nose pliers, 25W-35W soldering iron, good quality silver solder, approx. 12" of 18-20 AWG wire, approx. 12" of 1/8" heat shrink tubing, round toothpicks or desoldering braid, hot glue gun, pencil.

3. Remove the passive radiator from the cabinet.

4. Disconnect the three modular wiring plugs. No need to mark them, they'll only fit back in the right sockets.

5. Disconnect the two black push spade terminated wires from the large coil behind the PCB (marked "P" and "R" where they are soldered to the PCB). Mark either one with a small piece of tape for later ease in replacing.

6. Using needle nose pliers, reach behind the PCB and find the treeloc that penetrates the PCB between the two larger board mounted coils. You can't see it from the top of the board. Gently compress it while exerting MILD pulling force toward you. Once it's free, gently compress the top tips of the other three treelocs where they penetrate the PCB and apply MILD force toward you to free them. The PCB should now be loose in your hand.

If you're not good at working blind on the tough treeloc, remove the bolt on the back of the speaker cabinet and pull the entire assembly (including the large coil) out. It's more work, so try the above first.

7. Heat the solder joints on the tracing side of the PCB where each lead of the capacitors and resistor penetrates, and pull the leads free. Re-heat the pad after each pull and insert a round wooden toothpick to clear the mounting hole, or use de-soldering braid to wick the hole free of solder.

8. Install the 12 uF cap first. Grab each lead close to the body of the cap and bend the lead at a right angle to the body. Hold the cap parallel to the board near your intended mounting position. That position is as far away from the two coils mounted side by side on the PCB as possible with the lead length you have. With leads aimed toward the mounting holes, determine if one or both needs a "knee bend" (a bend back tight under the cap body, then at a right angle again) to hit the mounting holes. Mark and bend the leads as necessary and dry fit (do not solder) them to the holes, bend the tracing side of the leads at a 45 degree angle to hold the cap in place.

9. Install the 20 uF cap between the two coils and the cap you just installed. Use the same techniques. Make sure the end towards the "P1" wiring socket does not interfere with replacement of the wiring plug. If the other end lead is bent closely to the bare jumper on the PCB at "L5", insulate it with heat shrink before final fit.

10. Solder both installed caps in place and trim the excess leads.

11. Install the 2.7 ohm resistor vertically, or use knee bends to mount it horizontally -- your choice. Use needle nose pliers to protect the lead where it enters the resistor body when bending. Solder it in place and remove any excess leads.

12. Bend the two leads of the 40 uF cap at right angles to the body using the previous techniques and care. It will be mounted vertically in relation to the PCB. Hold the bottom of the cap to the PCB and snug to the side of the adjacent coil. Make sure you are positioned far enough from "P2" as to not interfere with reinsertion of the wiring plug. Mark the bottom lead where it needs to be bent at a right angle to penetrate the board. Bend the lead and insert it throgh the mounting hole. Solder this lead making sure you are still snug to the coil and free of "P2".

Cut a piece of wire long enough to fit from the other mounting hole and be bent at a right angle meeting the top cap lead. Solder it in place. Slip a piece of heat shrink over this wire and bend it to the meet the cap lead. Mechanically wrap the wire and lead together. Solder. Slide the heat shrink over the joint and to the cap body.

13. Apply hot glue to every contact point between the PCB and the caps and adjoining parts and the caps.

14. Allow the glue to cool and reassemble your crossover in the cabinet. Get the "hidden" treeloc inserted first, the others are easy.

15. Enjoy your new speakers!

sda2mike

Thank you!!! Maybe I CAN do this!!!

ND13

Why couldn't Polk do this from the get go? What's another $30 in a multi thousand dollar set anyway?

hoosier21

Originally posted by ND13
Why couldn't Polk do this from the get go? What's another $30 in a multi thousand dollar set anyway?

30.00 x how many pairs, say 5000 = 150,000.00 that wouldn't be going in ol Matt's bank account, that's why.

I am sure the stock parts are average or better than average, but there is ALWAYS something better.

DarqueKnight

Originally posted by ND13
Why couldn't Polk do this from the get go? What's another $30 in a multi thousand dollar set anyway?

I asked the same question after doing my first SDA mod. Cost was only part of the problem. A Polk engineer said that it was more of a parts availability issue than a cost issue. He said that no premium component manufacturer could (at that time) quarantee the quantities required by Polk's manufacturing time frames.

Furthermore, he said that most audio consumers were not interested in, and would not pay for, the higher sound quality provided by premium parts. Bob Carver expressed the same opinion when asked why he didn't use better quality components in his amplifiers.