DCR Change after crossover rebuild ?
VSAT88
Posts: 1,257
On my SDA SRS 2 speakers I have rebuilt the crossovers. I did one crossover at a time. I used the same value resistors and capacitors. I jumped out the 750uF and the poly switch. Now the DCR is 2.6 (both speakers) on a 200 ohm scale Simpson True RMS VOM. Causing the Amps fan (Kenwood M2, completely rebuilt by Dan at DRM) to come on pretty quick as I would think it should ! I documented everything I did and have double and triple checked everything I did. My documentation says these speakers should sit at " more than 4 ohms" . What have I done wrong please. The fan did not operate ever before the crossover rebuild.
Comments
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Did you change the SDA inductor in the rebuild and doesn't that lower the impedance while increasing he bass slam?
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There were no inductor changes. And I would think that an inductor change would affect the resistance.
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What do you mean you jumped the 750uF ? Are you talking the bypass cap on the old caps?I jumped out the 750uF and the poly switch.
So you replaced the poly with wire or resistor?
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The poly was replaced with a jumper. The bypass cap (750 pF) was removed and replaced with a jumper as well.
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Sorry, my bad..Not 750uF...750pF -
I did that on my SDA 1Bs. Desperately needed. Are yours the SRS 2 pin-blade, or blade-blade version. The Blade-blade version is extremely similar to the 1B.The poly was replaced with a jumper.
Oooops. You've just shorted across that capacitor, taking it out of the circuit.The bypass cap (750 pF) was removed and replaced with a jumper as well.
Remove the jumper. Re-test the DC resistance.
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^ Yep ^Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
I want to say GOD how did I do that ! I was thinking again...I sat there telling myself not to put that jumper in and did it anyway. That is the solution, no doubt. Thank you for rattling my brain around ! I will post back anyway. Thanks again.
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I did that on my SDA 1Bs. Desperately needed. Are yours the SRS 2 pin-blade, or blade-blade version. The Blade-blade version is extremely similar to the 1B.The poly was replaced with a jumper.
Oooops. You've just shorted across that capacitor, taking it out of the circuit.The bypass cap (750 pF) was removed and replaced with a jumper as well.
Remove the jumper. Re-test the DC resistance.
Re read your post, mine are SRS 2 with two blades.
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You are very lucky you didn't let the magic smoke out. You may find that the tweeters are now very bright if so you may want to consider a .5ohm resistor.The poly was replaced with a jumper. The bypass cap (750 pF) was removed and replaced with a jumper as well.
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You were sending essentially a full signal to the bottom tweeters. The top tweeters are protected by the 4.4uf caps. I would listen carefully to the bottom tweeters, and make sure they're OK. A TP or PT tube placed over the dome with your ear to it, will help isolate them.Home Theater/2 Channel:
Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
dhsspeakerservice.com/ -
Excellent, incredible now. All smiles. And yes, with my often made mistakes of recent I keep a PT roll near. All the tweeters work great, guess I got lucky on this one. I may entertain the idea of the .5 ohm resistor in the PS slot later. As of now and until I find suitable nylon standoffs I am not going to change anything more. Thanks because I was stumped.
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You have to follow your ears...but...the primary difference between the SDA 1B crossover and the SRS 2 Blade/blade crossover is that the SRS 2 uses a bigger resistor in the treble section than the 1B, which has the effect of reducing the volume of the treble.I may entertain the idea of the .5 ohm resistor in the PS slot later.
The 1B didn't have enough treble for me even after I jumpered the polyswitch. I can't imagine being satisfied with the treble of the SRS 2 B/B.
My intention is to remove the 2-ohm resistor for the treble section, and replace it with a 1.5 or 1.8 ohm resistor to boost the treble a little more. I bet your SRS 2 B/B would benefit from about the same. As I recall, the SRS 2 B/B uses a 2.7 ohm resistor.
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Yes, it is 2.7 ohm however I have these speakers in such a small room (so small I would not even post it) that the treble sounds pretty good. I am running two Sl 2000s and two "hybrid" RDO 194s that I kind of built myself by sourcing diaphragms off the net. All four of the 194s I had in them went up in smoke in less than a second when I hooked up a Parasound pre amp in the system that went terribly bad the instant I turned it on. I had been using it not too long before so it was "known good" but I suppose that anything can happen with electronics that are that old. I am definitely going to keep in mind what you said about that resistor considering that i will eventually buy four more RDO tweeters. The RDO 194s I had in them did seem a bit soft to my taste however that was before I rebuilt the crossovers. I really wish i had the RDOs so I could listen with the new networks and see if the treble was still as soft as before. Are you using SL 2000s or RDO tweeters ?
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Main tweeters are 198s using the pseudo-TL mod (5.8uF cap replaces 4.4uF cap)
Secondary tweeters are SL2000. I suppose somday I'll order more RD0s, but I really hate buying from the Communists when I don't have to. -
" I really hate buying from the Communists when I don't have to."
God, I am glad to hear that from someone else. I think there are a lot of folk that have forgotten. I had SL2000s in all four holes when I got em and they really did not sound so bad to me. I may try what you said and put 198s in the top holes and just see. One day anyway. I just put new Clarity Caps in the 4.4uF position so I really would hate to take them right back out though. May well try 194s there first. I am beginning to see what you mean about the treble by the way. I am not altogether happy with the sound. I reversed the SL2000s to the bottom holes and put the "hybrid" 194s in the top holes and that seemed better. I guess in a way I do not have Polk speakers any longer with all the work I have done. I cannot say I dislike the sound. Good recordings sound really good but poor recordings sound well, poor I suppose that is to be expected with upgraded parts. I would like the sound much better if I could get some of that S sound out of them. I do not know the correct term for the sound I hate and the way to fix this but it is in the Sss es. As in if the singer sings the word self. Hurts my ears big time. It seems it almost completely go away when I was using four 194s in the SRS 2 speakers and the same in the SDA b's. -
It's called sibilance and can be caused by any number of reasons. Start with dumping the SL2000 tweeters entirely. If still there then the problem is upstream, such as your source, pre amp, pover amp and especially your cables. It can also be caused by your room if it's not well damped.
Just noticed that you didn't replace the poly with .5ohm resistor......yeah, that will result in the tweeters being too hot, which results in sibilance.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Cables are a must. All of the interconnects I have are very old or were picked up at the local thrifts. The room is terrible and there is nothing much I can do there. And I guess that when I pull the networks to put in nylon/plastic standoffs I will go ahead with the .5 ohm resistors, I have been using Dale so I will go with those again. I will order the new tweeters as time go's along and I have the cash. Trying to do what I can with in house materials for now. Any idea where I can source the nylon/plastic standoffs ? We used to use them to mount our body on our RC cars but I cannot find them now, of course that has been many, many years ago and I am sure there using a different way to fix them to chassis now.
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Do yourself a favor, use Mills resistors.
I'm not sure about those stock standoffs, but you can use threaded round or hex standoffs with stainless steel screws. Mouser and Digikey carry a large selection.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
OK, got that. I do not know why I posted that I used Dale because that is incorrect, I did order and use Mills resistors. I will check Mouser as I buy from them when I can. Thanks for the info...Again.
Looked on Mouser site and they have many options. Thanks, I would have never thought to look there. -
The 1B and SRS 2 Blade/blade are extremely similar. They use the same drivers, although the passive is larger on the SRS as is the cabinet. The crossovers are identical except that the 1B uses a 2-ohm main treble resistor while the SRS uses a 2.7 ohm main treble resistor. The treble is therefore reduced in volume in the SRS 2 compared to the 1B. An SRS 2 b/b with the polyswitch jumpered will still have more resistance than a 1B does from the factory.It's called sibilance and can be caused by any number of reasons. Start with dumping the SL2000 tweeters entirely. If still there then the problem is upstream, such as your source, pre amp, pover amp and especially your cables. It can also be caused by your room if it's not well damped.
Just noticed that you didn't replace the poly with .5ohm resistor......yeah, that will result in the tweeters being too hot, which results in sibilance.
As I have said so many times before, I believe that the 1B has too-little treble; the SRS 2 would have even less treble volume. Eliminating some resistance in the treble circuit is almost certainly a GOOD thing. Your point about the tweeters being too "hot" and causing sibilance is taken--I don't believe that's the root cause of the problem in this case. My system doesn't have an excess of sibilance, and I jumpered the polyswitch and have a lower-ohm main resistor than his SRS 2s.
I'm not sure where the sibilance is coming from. I tend to think of amplifier common-ground issues since I have had some excess of problem with that. I am guessing that # 2 on the list is damaged tweeters. However, it could be anywhere in the system, and maybe in the speaker-room interface.
If I were in his room, I'd be using a multimeter to test the resistance between the negative terminals of the amplifer...but perhaps that's already been done and confirmed as "OK".
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Eliminating some resistance in the treble circuit is almost certainly a GOOD thing.
That would be ignoring the tonal balance Polk engineered into the different models.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Yes, absolutely.Eliminating some resistance in the treble circuit is almost certainly a GOOD thing.
That would be ignoring the tonal balance Polk engineered into the different models.
But what harm is there in changing the tonal balance, if Polk didn't get the balance "right" to begin with?
We change the caps from mass-market electrolytics to specialty film jobs; that changes the tonal balance, too.
We install low-resistance SDA inductors to add more bass at the expense of reduced impedance and DC resistance. There's another change to the speaker voicing.
The issue becomes: Is the "new" tonal balance better or worse than the "original" tonal balance?
In my case, the results were clear: MORE TREBLE NEEDED. Other people's ears, other people's rooms, other people's upstream equipment...maybe other opinions. -
Changing to higher quality caps while keeping the same values does not alter the tonal balance, but changing the SDA inductor value certainly does as does making the tweeter hotter, which makes my ears hurt just thinking about it.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
I am still trying to find a drawing of what I need to do to TL with 198s. Do I add a cap or replace the 4.4 with a 5.8 if I were to do the mod ? I know there are two caps for the two tweeters, one a 12uF and the other a 4.4uF those (Clarity) are installed now, however If I replace all the tweeters should I not go ahead with the 198s ? Oh, by the way I have not and will not (in the near future anyway) be changing any inductors.
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5.8uF caps are mildly difficult to obtain. Clarity probably offers them, the lower-budget brands don't. 5.6uF is readily available, and within the 5% tolerance often accepted as "close enough".I am still trying to find a drawing of what I need to do to TL with 198s. Do I add a cap or replace the 4.4 with a 5.8 if I were to do the mod ? I know there are two caps for the two tweeters, one a 12uF and the other a 4.4uF those (Clarity) are installed now, however If I replace all the tweeters should I not go ahead with the 198s ? Oh, by the way I have not and will not (in the near future anyway) be changing any inductors.
Another alternative is to add a 1.4 or 1.2 uF cap in parallel with the existing 4.4; giving a total of 5.8 or 5.6. In fact, I think my 1Bs have a 4.4 and a 1.5 for a total of 5.9uF. Again well within the 5% tolerance.
The additional capacitance in that location on the circuit board, plus two or four '198s, and some solderless connectors is all you need. I have forgotten (and got into trouble once by getting it backwards) but between the 194 and the 198, one of them has a "small" blade for a faston connector. So either your wire harness has a large and a small blade, and you need two large blades for each tweeter, or you have two large blades and you'll need a large and a small for each tweeter. I'm too lazy to look up which is which.
The whole process of idea to confirmation to application has been detailed in a very long thread by our member inspiredsports here. The first half of the thread is contradictory and nearly useless except as a history project, but the second half is golden.
http://forum.polkaudio.com/discussion/74946/sda-srs-2-crossover-parts-list
Be aware that the "TL"-ing of the 1B and SRS 2 B/B is considered an "unofficial" mod; it bothers some folks.
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My crossovers are not like those seen in that post. I have one crossover on a board that mounts on the single big inductor. Mine are blade pin. Looks like a 1988 model crossover.
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There is more to making a non-TL capable SDA model into one than simply changing a capaitor, which is likely the reason Schurkey finds the treble needs boosting in his speakers.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
mine are SRS 2 with two blades.
Yours are the second-generation SRS 2. They're essentially the same as the SDA 1C, where the earlier generation SRS 2 was essentially the same as the SDA 1B.Mine are blade pin.
Everything I said earlier was based on your comment that you have the blade/blade "first generation" SRS 2. Therefore not much of it actually applies.
There is no method--official or otherwise--that's been posted for stuffing '198s into the 1C--SRS 2 pin/blade speakers (although I'm going to try it someday.) -
No, the treble was lacking in my 1Bs from Day One. Even after I had tweeters and crossovers replaced under warranty, the treble was soft, and it was soft in every room I moved the speakers into over the course of thirty years of ownership. MAYBE every room was over-damped. I don't think so, but I'll acknowledge the possibility.There is more to making a non-TL capable SDA model into one than simply changing a capaitor, which is likely the reason Schurkey finds the treble needs boosting in his speakers.
Changing to the 198s did not make the treble volume worse; replacing caps and resistors made the speakers sound much better, I have a suspicion that the treble was becoming VERY bad due to aged electrolytics. I had largely quit listening to them because it just wasn't "fun" any more. Then I upgraded the caps and some other mods, the speakers came alive again--but still with insufficient treble volume.
