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In Reply to: RE: Magnepan 2.7/QR image / focus issue posted by Satie on December 19, 2016 at 00:56:06
Ok I started testing. I pulled the sock off the right speaker. I disconnected the spade connections to the woofer, mid and tweeter so the crossover would not affect the pure resistance readings.
Tweeter 4.1 ohm
mid 4.2 ohm
woofer 4.2 ohm.
These readings seem to be the same (allowing for slight meter difference) as those listed in the speaker diagram attached.
No delam was found in tweeter or mid wires. There is slight delamination on the woofer. Maybe up to an inch on bottom but not all loops and up to 1/2 inch on top again not all loops. There was only one woofer trace with a delam in the middle and that wire was delaminated about 3 inches where the vibration button is.
The crossover only has one bipolar cap and that is on the woofer 50uf. would not expect the film caps to go bad on the tweeter (solen) and mid (elpac).
I hope to pull the sock off the left speaker and insepect it soon.
Follow Ups:
Inspected the left speaker. measured resistance on all drivers and all good. less delam (almost none) than the right speaker. I will make one change at a time to the crossover when the parts arrive starting with the bipolar 50uf caps.
Question has anyone heard of the magnets degrading with time?
Not really an issue with these types of magnets. It would be an issue with AlNiCo that needs occasional remagnetization - at least with the old formulations. Which is why they fell out of favor, well that and cheap high power SS amplifiers that made the high cost of stronger magnets unjustifiable..
First thanks to all who posted. I did three things that improved the sound. The first was I replaced the bipolar 50uf on the bass with a dayton film of same value. This cleaned up some of the sound but was still lacking in dynamics. The second was, and I am still in testing phase, is I bypassed all the capacitors with a 10uf MRO-2 russian PIO capacitor. I am not saying these are the ideal values but simply what I had on hand. Much more of a dynamic speaker with more detail at every frequency range. I will by trying other values and caps to see what results I can get. Third, If you remember I compared my 2.7QR with my MMG's and believed that the MMG's focused better. I moved my 2.7/QR tweeters to be in the same location as the MMG's tweeters. I believe this improved the focus of the 2.7's. Both speakers tweeters outside slight toe in. In the past when I swapped speakers I would align on the inner part of the speaker, but the tweeter was on the outer part of the speaker. I hope this information is useful to someone else who is going through a like issue.
That is a bit too big of a bypass, you actually lowered the crossover point a bit. But if you like it then it is fine. If it is practical, then try to match the values of the original crossover more closely when you include the bypass cap so that you are not departing too far from the original design.
Since you have the speakers open then outside the delam you spotted, the other ageing related shift in performance is often the decline of the bipolar electrolytic cap in the crossover. Even if it is still ok now, I would not expect it to last that much longer. Get a film cap to substitute. Does not have to be expensive. It may be the culprit in your imaging problem.
I am pulling the staples on the second speaker. I have ordered film capacitors to replace the 50UF bi-polar caps.
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