Polk rti a7 crossover problem

billbillw wrote: »

I am hoping you have the crossover schematic. If not, the PDF is located here: https://forum.polkaudio.com/discussion/202480/rti-a-series-crossovers#latest
Regarding components, Mills MRA 12W are generally a standard for crossover resistors. Some will argue that the Dayton non-inductive wirewound resistors from Partsexpress are close in quality, but significantly less expensive. Either will be better than the original sandcast resistors. I would use decent capacitors in the tweeter circuit. Jantzen Cross Caps, or Clarity Cap PX at a minimum. Size is a factor on the larger capacitors in the woofer section, and since they are shunt caps, they don't have as much of an effect on sound quality. Non-polar electrolytic is what the factory came with and using new equivalents will give you similar sound to what you had.
One thing to look out for, is the inductors could have been damaged by overcurrent. You'll need an LCR meter to measure those. An out of spec inductor can make a big difference in sound between channels. I've had it happen to me on a vintage set of Mirage M3.

Thank you for your interest @Gardenstater And thank you, too. , ı emailed to guy who has it own topic which is you have sent before and he said that even if the values and tolerances are the same replace with a new capacitors and resistances , there will not be equality about the stereo scene , so he recommended the both side changed just like you have said

@billbillw actually ı just wanted to make it equal stereo tonage related to both side voice and ı wanted to protect polk audio rti a7' sound characteristic and ı dont wanted to upgrade these speakers , tehrefore ı thought that if ı changed the elements of the crossover replace with in same values of elements provide the protecting of the rti a7's sound characteristic , The schematic for my A7 is included in the topic you sent.There is a 8.2uf y.c brand 50v eletrolyc capacitor and 2.4ohm %5 tolerance resistor on the treble side , Moreover there is a 18uf y.c brand 50v capacitor and resistance on the mid side , I wanted to replace the components with ones having the exact same values—albeit from a different brand - thinking that, as you suggested, I could achieve the same character and sound rather than just something "similar." I hoped to do this without touching the other original speaker, but it seems things might work a bit differently in electronics. What approach did you take to ensure consistency?

@Gardenstater I have personally examined the circuit board, both in terms of its schematic and its individual components—yes, it is the board shown in the photo. While the only way to be 100% certain would be to remove every component and test them one by one, that is beyond my current capabilities. Based on my own assessment—supported by input from an AI (to which I had sent a photo of the board)—and the fact that the coils appear to be in good condition, I suspect the issue lies with the capacitors and resistors. The sound quality problem, specifically affecting the mid and high frequencies, points toward these components; the AI ​​also suggested focusing primarily on the capacitors, noting that Mylar capacitors, in particular, rarely fail.

For instance, the circuit shows that an 8.2 µF capacitor—paired with a bypass capacitor—and a 2.4-ohm resistor are used for the mid-range section. I reasoned that by using components with the exact same values—an 8.2 µF capacitor and a 2.4-ohm resistor from the brand Jantzen—I could closely replicate the circuit design implemented by the Polk engineers and achieve the same sonic characteristics.

Of course, even without taking any measurements, the fact that the artificial intelligence specifically highlighted the mid and treble sections—where I’ve been experiencing a "veiled" or "muffled" sound—suggests that replacing the components in these parts could largely resolve the issue. Even if the coils appear to be in good condition, their actual values ​​might have drifted, making it logical to simply purchase a new crossover. This is especially true considering that, to perform accurate measurements, one would have to desolder every single component anyway; if I were to replace the capacitors and resistors with new ones of the same nominal values ​​but still fail to achieve the desired sound character, then buying a new crossover would definitely be the most sensible approach.

I hope this explanation is clear and that my message didn't come across as annoying.

@Gardenstater @billbillw @gp4jesus

I’d like to respond to all of you at once, yes, I live in Türkiye, and finding spare parts here, especially for an old speaker, is quite difficult. That said, before starting this thread, I had already placed an order using that same eBay link; since Turkish customs can be tricky, a Turkish friend of mine living in the U.S. will bring it over for me when he visiting to turkey to 3 months later, so that part is all sorted out.

Since the old, repaired filter will just be sitting on the side once the new one arrives, I wanted to build a replacement ,using components with the appropriate values that maintains the same sonic character as the original Polk filter. I’ve mentioned this all along, but it’s becoming clear that taking measurements and modifying the circuit will be necessary. If I can’t overcome these challenges, I will likely just give up, but I do have this persistent urge to tinker with it.

Since I am not very well versed in the subject, I cannot offer a precise comment; however, I am reading what you have written with great care and considering it , thank you.