thr33p4c Posted January 23, 2015 Report Share Posted January 23, 2015 Gentlemen,-Model Fives - All new Caps and Resistors on Boards - Running fine for almost 9 months...I have been noticing lately that my Model Fives have sounded a bit off. One of the speakers appeared to be lacking bass. At first I assumed it was related to a new preamp that I had put in. I swapped my pre and the problem persisted. I swapped the speaker wires between speakers and the problem did not follow. After this, I was convinced the problem was with the speakers themselves. I measured impedance on both speakers, disconnected. The one that sounded correct measured at about 4ohm, that is what I am used to seeing on my updated XO boards. The problem speaker measured at about 8ohm! They used to be identical.I pulled the woofers. Both measured at 3.9 ish. The series mids both around 14ohm. The tweets also both around 4ohm. I measured all resistors and caps in circuit and they are reading the same on both boards. With the woofers out, I twisted the woofer positive with its negative to get that part of the circuit back to the terminals. I measured impedance again and found .3ohm on the good speaker and 5ohm on the problem speaker.I think I have something going on in that crossover that is adding resistance to the circuit causing that speaker to sound noticeably less bassy. I cannot track it down. All I can think of is a bad, shorted inductor or something wrong with the switches. I tried the switches in all positions on my last test and the reading stayed at 5ohm...Any ideas? Link to comment Share on other sites More sharing options...
thr33p4c Posted January 24, 2015 Author Report Share Posted January 24, 2015 I had a spare set of Five boards and parts waiting for a rebuild so I took the night and rebuilt and swapped the XO board. Back to 4.4ohm. Sounds great. I will have to troubleshoot the problem board another day... Link to comment Share on other sites More sharing options...
kehern15 Posted February 3, 2015 Report Share Posted February 3, 2015 Maybe post a picture of the correct board and the faulty one? May help with diagnosing the problem area/part. Link to comment Share on other sites More sharing options...
thr33p4c Posted February 3, 2015 Author Report Share Posted February 3, 2015 The boards are Identical. The one that failed had been working fine for months. I think a component may have failed during a spike. I recently changed my preamplifer and it has no power up delay relay. I turned it on out of order a couple times and it sent a nasty pop through the speakers. I am starting to think more and more that this was the root of my issue. When I get a moment I will disconnect the inductors and check for continuity at least. If I don't find an issue there I will start isolating other components. Link to comment Share on other sites More sharing options...
thr33p4c Posted February 11, 2015 Author Report Share Posted February 11, 2015 I did some testing on my trouble board today. I found something very strange and am looking for a second opinion. Basically what I have seen is an increase in overall crossover resistance. With my speaker leads shorted together (Tweeter + , mid +, and woofer + shorted to ground) I usually see about .3ohm. I confirmed this on an untouched board. My trouble board measures close to 4ohm. All things equal. I have discovered through trial and error that if I move my woofer (+) lead to an alternate grounding point the overall XO resistance drops to a normal range. I can touch on any other terminal strip ground point or anywhere on the chassis but as soon as I touch the wires to the terminal tie down point normally used for the woofer I see the jump in resistance. Is it possible that this piece of metal has somehow developed a resistance? It is so odd. NOTE - This point is normally shared with an inductor but I removed the inductor lead and did this test with that lead unattached and grounded to an alternate point on the chassis. I always see the same result. Added resistance on normal tie down point. Normal resistance on any other chassis ground. Link to comment Share on other sites More sharing options...
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