RT7 crossover upgrade pictorial

Tbone289

I upgraded the crossovers in my RT7 bookshelves this morning, and I'm really enjoying the results of the project, so I thought I would share the process with anyone here who might be interested.

As a reference, please refer to the RT7 crossover schematic here. Note that the labeling of C2 & C3 are reversed on the circuit board silkscreen, but this is a minor detail since those caps are in parallel in the circuit itself. I will refer to C2 and C3 as they appear on the schematic.

In a previous mod, I had simply replaced the electrolytic capacitor in the second order high-pass filter circuit with a 9.1uf Solen metalized polypropylene (MKP) and regretted doing so. The result, even after a long burn-in, was cold, harsh treble and the loss of "presence". I had done the same with a pair of RT3s in my office rig using Dayton MKP, and loved the warmer, more laid-back treble, with expanded soundstage. So, this time I decided to "do it right", and replace all caps and inductors in the RT7 high pass filter using Dayton 1% MKP caps, meanwhile removing the mylar C2 bypass cap.

My parts list:

C1 - Dayton PMPC-2.2 2.2uF 250V MKP x2
C3 - Dayton PMPC-4.7 4.7uF 250V MDP x4 (two in parallel in each speaker)
L1 - Jantzen 0.15mH 18 AWG Air Core Inductor

Here you see the first mod, with the Solen MKP replacing the stock electrolytic. C1, C2 and L1 still exist in stock form here.:





Circuit board unpopulated, with the exception of L2 from the low-pass filter, and R1 that I'm leaving stock. I cleaned the rosin off the board with some isopropyl alcohol and a rag.







C1 glued in place.





L1 glued down and strapped in. This inductor makes the stock item look like a real POS!





First half of the C3 parallel pair glued down







Second half of the C3 pair glued down and soldered in





The finished product, soldering complete and leads trimmed. It took me quite a long time to juggle the capacitor placement around so that everything fit back into the cabinet. It just fits in this configuration.






This was all-around a fun project for a Saturday morning and, even before any burn-in, I'm very pleased with the sound.

adnankhan

Hi Tbone,
can you plz send me RT7 crossover schematic. as given link is no more available.

Tbone289

Here is the schematic: https://www.dropbox.com/s/ri9d4uu1vm401w2/Polk_schematic_rt7_xo.pdf?dl=0

VR3

Looks great, that point 15mh should be closer to 22 awg or even 24 awg

Tbone289

Maybe. The stock air core inductor is made of VERY thin wire as I recall. I'd say 26AWG isn't far off.

VR3

Yes but this is on purpose, you would need to decrease the Dcr of the midbass inductor to balance

Tbone289

I assume you're referring to my upgrade above then, from 2011, not just the recent discussion of the schematic?
I understand your point then. I switched back to the stock air core inductor years ago after I realized the same thing soon after the recap.

VR3

Gotcha, you can actually get fantastic results getting rid of that iron core in the midrange circuit

Tbone289

Indeed. I considered that as well but, alas, these are just my garage speakers so this was just a quick-n-dirty refresh.