SDA-1A Xover caps?

Adam Czepiel

SDA-1A Xover caps?

I am considering a local pair (that needs work)
and looked over the xovers... They appear to be bypassed with 750pF silver micas..

From my experience silver micas are not the best for 'sound' and are more suited for antique radio RF circuits

anyone use different ? or favorite brand of cap, coil, resistor ?

F1nut

The forum is full of info about SDA crossover upgrades, take a look.

PolkieMan

Sonic Caps & Mills resistors.
http://www.soniccraft.com/index.htm

DarqueKnight

Older threads are best searched for on Google rather than the forum search function, use a search term like "SDA modification club polk".

One of our forum members, VR3, does SDA modifications. His website is http://vr3mods.com/.

westmassguy

Adam Czepiel wrote: »

SDA-1A Xover caps?

I am considering a local pair (that needs work)
and looked over the xovers... They appear to be bypassed with 750pF silver micas..

From my experience silver micas are not the best for 'sound' and are more suited for antique radio RF circuits

anyone use different ? or favorite brand of cap, coil, resistor ?

Welcome to Club Polk!
The Silver Micas are bypass caps, used to improve the sound of the mediocre Mylar caps that were used back in the day. The Mylars, and NP Electrolytics should all be replaced with Metalized Polypropylene caps. Sonicaps and Mills Resistors = Audio Bliss. The inductors were carefully chosen for their mh value and DCR. Don't mess with them unless you know what your doing. In most cases it's not necessary to replace them. As others have noted, the forum is full of info on crossover upgrades, as well as upgrades that can be done to the cabinets, drivers etc.

newbie308

westmassguy wrote: »

Welcome to Club Polk!
The Silver Micas are bypass caps, used to improve the sound of the mediocre Mylar caps that were used back in the day. The Mylars, and NP Electrolytics should all be replaced with Metalized Polypropylene caps. Sonicaps and Mills Resistors = Audio Bliss. The inductors were carefully chosen for their mh value and DCR. Don't mess with them unless you know what your doing. In most cases it's not necessary to replace them. As others have noted, the forum is full of info on crossover upgrades, as well as upgrades that can be done to the cabinets, drivers etc.

I second this! I rebuilt the crossovers in my SDA 1A signatures. When I did, I eliminated the mica caps and did as others suggested by using Mills resistors and Sonicap capacitors. I replaced the SL1000 tweeters with the RD0194's, and I am very happy with the results. Some folks prefer to disconnect the dimensional tweeter, but I left it connected. If the cabinets have the big square access covers, you may want to replace the fuse holders and binding posts while you are in there.

chuckeroo

newbie308 wrote: »

I second this! I rebuilt the crossovers in my SDA 1A signatures. When I did, I eliminated the mica caps and did as others suggested by using Mills resistors and Sonicap capacitors. I replaced the SL1000 tweeters with the RD0194's, and I am very happy with the results. Some folks prefer to disconnect the dimensional tweeter, but I left it connected. If the cabinets have the big square access covers, you may want to replace the fuse holders and binding posts while you are in there.

Hey newbie308 (or anyone else who can help!),
I am about to attempt to upgrade the xovers on my signature series SDAs as well, but this will be my first soldering project, so I am pretty nervous. Did you document what you did anywhere, or do you have a list of the exact components you used that you could provide? Also, I know there is a 25w resistor that is kind of weird, do you know what you used to replace that?

Thanks for any help you can provide!
Chuck

Schurkey

chuckeroo wrote: »

this will be my first soldering project, so I am pretty nervous.

Practice soldering on some scrap wires of small gauge (similar to the capacitor leads) prior to performing the work on the actual crossovers.

1. Soldering is EASY...when you've got some experience. With the leads and contacts properly heated and fluxed, the solder practically flows by itself.

2. While not totally un-related, soldering wires is NOT the same as soldering copper plumbing pipes. Just because you can make a water-tight joint in copper tubing does not mean you can successfully connect a capacitor to a circuit board without some thought and some practice--and the appropriate soldering iron, flux and solder. Specifically DO NOT use acid-based flux, or acid-core solder on electrical projects.

chuckeroo

Schurkey wrote: »

Practice soldering on some scrap wires of small gauge (similar to the capacitor leads) prior to performing the work on the actual crossovers.

1. Soldering is EASY...when you've got some experience. With the leads and contacts properly heated and fluxed, the solder practically flows by itself.

2. While not totally un-related, soldering wires is NOT the same as soldering copper plumbing pipes. Just because you can make a water-tight joint in copper tubing does not mean you can successfully connect a capacitor to a circuit board without some thought and some practice--and the appropriate soldering iron, flux and solder. Specifically DO NOT use acid-based flux, or acid-core solder on electrical projects.

Nice, thanks Schurkey! Surprisingly I'm least nervous about the physical soldering part, and more nervous about desoldering and removing the old stuff. But the thing I am most nervous about, which would probably be silly to many of you, is getting the correct components to put into it. As these are the "signature series" and kind of a wierd/in between model, it is hard to find specific info on what exact components are on these crossovers. I don't really want to take them apart to find out unless I have a plan in place, my stereo is kind of my retreat these days.

Essentially what I need is a list of what to buy, and a list of which to replace with which. I know it's a bit hand-holdy, but just want to feel confident before putting these babies under the knife!

Chuck

westmassguy

chuckeroo wrote: »

Nice, thanks Schurkey! Surprisingly I'm least nervous about the physical soldering part, and more nervous about desoldering and removing the old stuff. But the thing I am most nervous about, which would probably be silly to many of you, is getting the correct components to put into it. As these are the "signature series" and kind of a wierd/in between model, it is hard to find specific info on what exact components are on these crossovers. I don't really want to take them apart to find out unless I have a plan in place, my stereo is kind of my retreat these days.

Essentially what I need is a list of what to buy, and a list of which to replace with which. I know it's a bit hand-holdy, but just want to feel confident before putting these babies under the knife!

Chuck

Have you pulled one of the crossovers yet? You say it's an in-between model, how so? Do you mean the SDA 1 to SDA 1 Signature edition?

Schurkey

chuckeroo wrote: »

Surprisingly I'm least nervous about the physical soldering part, and more nervous about desoldering and removing the old stuff.

I've used Radio Shack copper braid for de-soldering. I heard they switched suppliers, and the stuff no longer works right--but my last purchase of the stuff had different packaging yet worked just fine. Others like a vacuum-style solder-sucker. I've never used one.

chuckeroo wrote: »

But the thing I am most nervous about, which would probably be silly to many of you, is getting the correct components to put into it. As these are the "signature series" and kind of a wierd/in between model, it is hard to find specific info on what exact components are on these crossovers. I don't really want to take them apart to find out unless I have a plan in place, my stereo is kind of my retreat these days.

Keep in mind that there's a pretty liberal definition of "Correct" components. Capacitor values are + or - 5%, and I expect that resistor values have at least the same tolerance. The stuff originally used was spec'ed more loosely than that. The parts quality used by Polk was much poorer than even the budget components available today. Pretty much ANY film capacitor will be a better choice than the electrolytics used in the original crossovers.

chuckeroo wrote: »

Essentially what I need is a list of what to buy, and a list of which to replace with which. I know it's a bit hand-holdy, but just want to feel confident before putting these babies under the knife!

Study these two links. I think everything you'll need is there. Far as I know, the 1 "Signature" is identical to a 1A in terms of crossover components, but you can verify that here:
http://www.polkaudio.com/forums/attachment.php?attachmentid=74644&d=1346690117

http://www.polkaudio.com/forums/attachment.php?attachmentid=31009&d=1201824729

westmassguy

The parts are different between the SDA 1 and 1A. The Resistor in series with the Stereo Tweeter is different, and the modification from 1 to 1A requires changing parts and removing parts. Careful examination between the SDA 1 and 1A schematics is required.
I'd be happy to walk you through it, and provide a parts list. You'll need to choose which Capacitors and Resistors you'd like. I prefer the Sonicap/Mills combination, others prefer Clarity's various lines, and Mundorf resistors.
On the conservative side, you could go with Dayton 1% and 5% Caps, but if you really want to make an investment, I'd go with the Sonicap/Mills. The Clarity ESAs are also excellent, but a bit too "in your face" for my taste. The can be tempered somewhat with the Mills Resistors.

Schurkey

westmassguy wrote: »

The parts are different between the SDA 1 and 1A.

Yes. However, if the speakers have been converted from SDA 1 to 1 "Signature", that process will make them the functional equivalent to the 1A. So these speakers "should" use the same crossover components as the 1A. A reading of the 1A schematic will yield all the component values needed.

westmassguy wrote: »

On the conservative side, you could go with Dayton 1% and 5% Caps, but if you really want to make an investment, I'd go with the Sonicap/Mills. The Clarity ESAs are also excellent, but a bit too "in your face" for my taste. The can be tempered somewhat with the Mills Resistors.

I used Dayton 1% in the high-frequency section, along with Dayton 5% and ERSE 3% caps in the low-frequency/SDA section of my 1Bs; and a mix of Mills and ERSE resistors. I'm absolutely thrilled with the results. Any film cap is going to be an improvement over the ancient electrolytic caps used originally. The Mills resistors are recommended by me based on the compact structure versus the ERSE resistors, Mills are easier to fit onto the circuit-board.

westmassguy

That's why I asked if he'd pulled one of the crossovers yet, to verify what's there

chuckeroo

Thanks for the help guys! I will make a list of the components I see on the 1A, then pull the crossovers to see if I can match them out.

I found a good thread about this model:

http://www.polkaudio.com/forums/showthread.php?54342-SDA-1-crossover-schematic

Can you guys tell me what they are talking about regarding the "cermet" resistor in posts 7 & 8, and what could be used as a replacement? He talks about what he will use in post 8, but I am not fully understanding what kind of resistor he is talking about...

westmassguy

He's referring to a cement or sand-cast resistor. The SDA 1s had 130uf electrolytic capacitors. The 1As replaced all four 130uf caps with 2.5 ohm, 25 watt sand-cast/cement resistors. Once you pull the crossover you'll know exactly what you have. Those 2.5 ohm, 25 watt resistors can be upgraded to two, 5 ohm, Mills MRA-12, 12 watt resistors wired in parallel. They will equal a 2.5 ohm, 24 watt resistor of much better quality.

chuckeroo

Hello!

Ok, I went into my speakers last night, and the crossovers for my SDA1 Signatures are exactly the same as the ones shown here for his SDA2:

http://www.polkaudio.com/forums/showthread.php?28024-1st-generation-SDA-crossover-upgrade


A few questions:

1. Would you just swap everything out one to one component wise, or are there any changes that would be beneficial? (for example, changing out the 12 uf cap for the 25 watt resistor)

2. Where is this tweeter polycap everyone talks about removing? Also, I've read some people just bypass it with a wire, and others insert a resistor. Is there a "best" method?
edit: I have fuses on the back of the speakers, does that mean the fuses take the place of polycaps? Can I/Should I bypass the fuses somehow?

I'm putting together a parts list now...

Thanks!
Chuck

westmassguy

chuckeroo wrote: »

Hello!

Ok, I went into my speakers last night, and the crossovers for my SDA1 Signatures are exactly the same as the ones shown here for his SDA2:

http://www.polkaudio.com/forums/showthread.php?28024-1st-generation-SDA-crossover-upgrade


A few questions:

1. Would you just swap everything out one to one component wise, or are there any changes that would be beneficial? (for example, changing out the 12 uf cap for the 25 watt resistor)

2. Where is this tweeter polycap everyone talks about removing? Also, I've read some people just bypass it with a wire, and others insert a resistor. Is there a "best" method?
edit: I have fuses on the back of the speakers, does that mean the fuses take the place of polycaps? Can I/Should I bypass the fuses somehow?

I'm putting together a parts list now...

Thanks!
Chuck

If your crossovers look like the SDA2s with all the same values, then your 1s were either modified previously, or are 1As.
In either case, there's nothing to modify. You'll be changing all the caps and resistors with the same value that's in there now.
The only caps that are routinely removed however, are the little 750pf silver mica bypass caps. You don't need them with Metalized Polypropylenes. I'd also recommend replacing the Polyswitches with 0.5 ohm resistors as well, unless yours are still fused.

chuckeroo

So I'm pretty sure I don't have polycaps at all, just fuses, can I just bypass the fuses somehow? Should I do that?

I have also put together the following parts list if you wouldn't mind checking it over:

Crossover -- qty -- cost -- total
12 uf Cap -- 4-- 22.5-- 90 -- sonicap soniccraft.com
27uf Cap -- 4-- 14.23-- 56.92-- solen partsexpress.com
.5 uf Cap (.47)-- 2-- 8.58-- 17.16-- sonicap soniccraft.com
2.7 ohm 12 watt resistor-- 4-- 4.95-- 19.8-- mills soniccraft.com
4 ohm 12 watt resistor-- 4-- 4.25-- 17 -- mills soniccraft.com


Thank you so much again for all of your help!

westmassguy

chuckeroo wrote: »

So I'm pretty sure I don't have polycaps at all, just fuses, can I just bypass the fuses somehow? Should I do that?

I have also put together the following parts list if you wouldn't mind checking it over:

Crossover -- qty -- cost -- total
12 uf Cap -- 4-- 22.5-- 90 -- sonicap soniccraft.com
27uf Cap -- 4-- 14.23-- 56.92-- solen partsexpress.com
.5 uf Cap (.47)-- 2-- 8.58-- 17.16-- sonicap soniccraft.com
2.7 ohm 12 watt resistor-- 4-- 4.95-- 19.8-- mills soniccraft.com
4 ohm 12 watt resistor-- 4-- 4.25-- 17 -- mills soniccraft.com


Thank you so much again for all of your help!

Looks good to me. You don't have any Polypropylene caps in there now, those are Mylar and NP Electrolytics. I would leave the fuses, but replace them with new 1Amp fast-blow fuses, and be sure to clean the fuse holders and use a little DeoxIT on them

newbie308

Sorry! It took me a while to get back to this thread. I did what others suggested. That is, I removed the crossovers and recorded the values of the components. Take pictures so you can look back to how things were connected before disconnecting anything! Mills resistors are readily available from parts express, and so are the capacitors unless you want Mundorf or another brand that PE doesn't carry. I usually buy extras of the 5% components and then match their values to within 1% (or better) my self. This save a little money in the end since you can return the unused portion (so long as you didn't solder them or cut the leads). This is easily done with resistors, but you will need an LCR meter for the capacitors.

Remember that with resistors the resistance (Ohm's) should match exactly, but the wattage can be greater than the original without issue.

Remember that with capacitors the capacitance (micro Farad's) should match t original equipment as closely as possible +/- 5% and the Voltage rating can be greater than the original without issue. Drastic deviation in capacitance from original will likely have a negative affect on the resulting sound quality! The value of capacitors in parallel add, so if you can not find an exact match, you can piggyback two values to attain the capacitance you need! Not the best for sound quality, but it will work and cost significantly less than custom wound capacitors.

When I teach my employees to solder I tell them to remember the sequence (apply the heat - apply the solder - remove the solder - remove the heat). The other important thing is to limit the amount of time that the heat is applied (3 seconds MAX). If the component can not be fused in 3 seconds, you need an iron with more wattage! Keep the tip clean! Drag the tip of the iron across a wet sponge until the tip is shiny silver (not black).

To desolder I prefer a solder sucker.

Have fun!

chuckeroo

westmassguy wrote: »

Looks good to me. You don't have any Polypropylene caps in there now, those are Mylar and NP Electrolytics. I would leave the fuses, but replace them with new 1Amp fast-blow fuses, and be sure to clean the fuse holders and use a little DeoxIT on them

Thanks for all your input, I wouldn't have the confidence to have a go at this without your help, it really is appreciated.

I'm off to order parts, will report back when the operation begins!

Thanks!
Chuck

westmassguy

newbie308 wrote: »

Sorry! It took me a while to get back to this thread. I did what others suggested. That is, I removed the crossovers and recorded the values of the components. Take pictures so you can look back to how things were connected before disconnecting anything! Mills resistors are readily available from parts express, and so are the capacitors unless you want Mundorf or another brand that PE doesn't carry. I usually buy extras of the 5% components and then match their values to within 1% (or better) my self. This save a little money in the end since you can return the unused portion (so long as you didn't solder them or cut the leads). This is easily done with resistors, but you will need an LCR meter for the capacitors.

Remember that with resistors the resistance (Ohm's) should match exactly, but the wattage can be greater than the original without issue.

Remember that with capacitors the capacitance (micro Farad's) should match t original equipment as closely as possible +/- 5% and the Voltage rating can be greater than the original without issue. Drastic deviation in capacitance from original will likely have a negative affect on the resulting sound quality! The value of capacitors in parallel add, so if you can not find an exact match, you can piggyback two values to attain the capacitance you need! Not the best for sound quality, but it will work and cost significantly less than custom wound capacitors.

When I teach my employees to solder I tell them to remember the sequence (apply the heat - apply the solder - remove the solder - remove the heat). The other important thing is to limit the amount of time that the heat is applied (3 seconds MAX). If the component can not be fused in 3 seconds, you need an iron with more wattage! Keep the tip clean! Drag the tip of the iron across a wet sponge until the tip is shiny silver (not black).

To desolder I prefer a solder sucker.

Have fun!

Excellent advise, I would add, that when paralleling two caps, best practice is to use as close to equal value as possible, otherwise the smaller value cap will react faster. Example 34uf cap could be made using two 17ufs, and would be Ideal, however, a 30uf cap and a 4uf would be bad.
I'd also recommend 3M VHB heavy duty tape under all the new caps to secure them. Cut the strip in half, as the contact area between the cap and the circuit board is small. If two caps are touching each other, you can bond them together with brush-on Cyanoacrylate (super glue). This well help reduce any resonances. Avoid Hot Glue at all cost. You can also mount the new Mills Resistors on the underside of the board, to make room for the new larger caps.

newbie308

One more suggestion. While you are at it, get some dynamat and wrap the metal frames on your drivers. Don't plug the holes, but cover the metal to reduce ringing. This made a significant improvement in the SQ of my speakers, and the cost is minimal! It also helps to seal the drivers to the cabinet. There are many references to this on the forum.