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Multi-Way Conventional loudspeakers with crossovers

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Old 8th September 2007, 10:22 PM   #41
timbert is offline timbert  United States
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Default Still having tweeter or xo problem

The previously posted schematic matches my xo. Where justblair has a 5.5ohm resistor, I have two identical-looking ones glued together in series, and the one I can read says 2.2 ohm. In-circuit it measures 5.7 ohm.

I have soldered in the new xo resistors mentioned in a previous post and replaced the voice coils with ones from another set of tweeters. I have fabric ones on standby. I am now engaged in isolating a tweeter/xo problem. I hooked up my amp outputs only to the tweeter terminals on each speaker. Now, one tweeter is about ten times louder than the other, and when I bridged the high and low freq speaker terminals, the woofers/mids are even but one tweeter puts out almost nothing, even at 1/2 volume or more on the amp. I put the meter on both tweeters, with music playing, and one was 6 mV when at the same volume setting the other 80 to 150 mV, so I guess there's a crossover problem. I swapped the tweeter magnet with another, and it was still very low output. I measured the capacitance of the tweeter cap in the xo and it's about 6.4uf when the schematic calls for 6.8, which I assume is within range, and since I don't have an inductance meter I can't test the coils. I tried bypassing the resistor and cap and using only the inductor in parallel with the tweeter, and it appears the inductor is what is causing the decreased volume. When the amp is connected directly to the tweeter, the volume is where it should be. What do I do next?

Meanwhile, I noticed the 4.7 ohm resistor on the woofer section is bad on this xo, but not on the other. Could this affect the tweeter section of the xo, even though they're not on the same circuit and when the amp is only driving the tweeter?
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Old 9th September 2007, 09:25 AM   #42
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Default Re: Still having tweeter or xo problem

Quote:
Originally posted by timbert
The previously posted schematic matches my xo. Where justblair has a 5.5ohm resistor, I have two identical-looking ones glued together in series, and the one I can read says 2.2 ohm. In-circuit it measures 5.7 ohm.
From memory mine has two resistors in series to make up the 5.5


Quote:
Originally posted by timbert
I have soldered in the new xo resistors mentioned in a previous post and replaced the voice coils with ones from another set of tweeters. I have fabric ones on standby. I am now engaged in isolating a tweeter/xo problem. I hooked up my amp outputs only to the tweeter terminals on each speaker. Now, one tweeter is about ten times louder than the other, and when I bridged the high and low freq speaker terminals, the woofers/mids are even but one tweeter puts out almost nothing, even at 1/2 volume or more on the amp. I put the meter on both tweeters, with music playing, and one was 6 mV when at the same volume setting the other 80 to 150 mV, so I guess there's a crossover problem. I swapped the tweeter magnet with another, and it was still very low output. I measured the capacitance of the tweeter cap in the xo and it's about 6.4uf when the schematic calls for 6.8, which I assume is within range, and since I don't have an inductance meter I can't test the coils. I tried bypassing the resistor and cap and using only the inductor in parallel with the tweeter, and it appears the inductor is what is causing the decreased volume. When the amp is connected directly to the tweeter, the volume is where it should be. What do I do next? [/B]
If you are sure that the inductor is the issue, you can order up a new one, though I would look at buying a matched pair. It is possible that the inductor is shorted out. You could check this by measuring the DC resistance of both inductors. If one is a lesser value of the other, then that is probably what it is. Madisound do inductors. Keep to an air cored one.

Quote:
Originally posted by timbert
Meanwhile, I noticed the 4.7 ohm resistor on the woofer section is bad on this xo, but not on the other. Could this affect the tweeter section of the xo, even though they're not on the same circuit and when the amp is only driving the tweeter? [/B]
I would not think so. Each section works as an independant filter in this design.

And to prove it, you have tried attaching the tweeters with the woofer section disconnected and still have the issue.
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Old 10th September 2007, 01:35 AM   #43
timbert is offline timbert  United States
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Looks like the "bad" inductor is not actually shorted but while the resistance on the good one is .2 ohm and the other is 1.5 or so. I removed both and sure enough, the bad inductor will attenuate either tweeter by about 10x volume, to my ears. There is enough melted plastic in both to make an ordinary person think they should both be replaced.

Madisound has two different .3 mH inductors, one 19 gauge wire and the other 20. I am taking JB's word that the originals are .3 mH. I have an old oscilloscope that I don't really know how to use other than doing signal traces to diagnose bad amps, but if I really knew how to use it maybe I could measure inductance on the "good" inductor I have.

I am inclined to buy the physically smaller .3 mH inductor so it will fit, plus replace all 6 caps in each crossover for peace of mind's sake. Is that a problem?

TIP:I bought a $10 USD Radio Shack rubber-bulb desoldering iron which has made my life much easier.
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Old 19th September 2007, 04:53 AM   #44
timbert is offline timbert  United States
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The tweeter and crossover repairs are complete. I did not use the new fabric voice coils, but the aluminum ones swapped out from another pair of Peerless tweeters. I replace all the resistors on the xo, plus the inductor (which justblair measured to be .3 mH) that was severely attenuating one of the tweeters. I replaced the inductors on both xo's with ones from Madisound.

The result is too much tweeter, to my ears.

How do I tweak this? Add resistance to the tweeter? The xo has two 1 ohm resistors in parallel, which yields 1/2 ohm, I believe. Without taking apart the crossover, can I just add diferent resistors to the tweeter and experiment?
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Old 19th September 2007, 05:46 AM   #45
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When I replaced the cap in my tweeter crossover I got too much tweet in my tweeter. Start by trying just one resistor instead of the two in parrallel, this will give you 1ohm. It should ease things for you. I am running mine with 1.1 ohms resistance just now and it is just about right.

I would try the fabric cone in there just for the hell of it. It may not be any better, but it gives you options.

The freedoms used fabric. I personally didn't like them as much as the non-freedoms. I think that the metals have more detail. With the metal "guards" in place they are a bit tizzy, but removing the guards tames this. I have some fine lambswool and some moleskin adhesive pads that I will experiment with to see if I can smooth them out further. Just finding a few hours spare to play with them is proving difficult right now. I have an amp project that is refusing to work for me!
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Old 19th September 2007, 08:53 AM   #46
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by timbert


The result is too much tweeter, to my ears.

How do I tweak this? Add resistance to the tweeter? The xo has two 1 ohm resistors in parallel, which yields 1/2 ohm, I believe. Without taking apart the crossover, can I just add diferent resistors to the tweeter and experiment?
Hi,

unless you have 4 ohm replacement diaphragms (DCR ~2.7R) you
need to add 6R in parallel with the new tweeters (DCR~5.4R).

This will correct the croosover operation and increase the effect
of the series resistors - which you can adjust up to say 2.2R.

/sreten.
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Old 30th September 2007, 08:58 PM   #47
timbert is offline timbert  United States
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Forgive my ignorance, I have confused myself. Sreten, the two 1 ohm resistors that are parallel to each other, aren't they also said to be in series on the + input to the tweeter? When you say to add a 6R resistor in parallel, exactly where do I do that? Would it connect to both sides of the tweeter? Before or after the inductor?

The new coils in the tweeter are 5.4R, so where exactly do I add a resistor, and what rating and power value, going by the above schematic? I am trying to get as close to the factory sound before continuing.

To repeat, I have rebuilt the factory XO to original, but have replaced the blown stock 4ohm tweeter coil with an 8ohm one because that's all I could find.

Many thanks and sorry for my dumb questions.
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Old 1st October 2007, 08:28 AM   #48
sreten is online now sreten  United Kingdom
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Hi,

The 6R (standard value 5.6R or 6.2R) is wired across the tweeter.
The 1 ohm resistors can be used for a 0.5R, 1R (omit 1) or 2R
series resistor.

Ideally after finding the right balance the capacitor and inductor
woulds be reworked for an 8 ohm tweeter, but above will work.

/sreten.
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Old 30th November 2007, 06:01 AM   #49
timbert is offline timbert  United States
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Well I listened on and off to the bright tweeters for a few weeks, and even tried a few episodes of rock-concert level music. I used my 100 watt NAD 2200 and drove it into clipping. I have a couple spare amps so I wasn't very careful. Everything was fine except for the neighbors. Today I finally soldered the 5.6 ohm 10W resistors as suggested to the tweeters, and they cut back the highs severely. Also, at the external speaker terminals I get 10.4 R on my digital multimeter. I think, to start, they need to be cut to a level about half of what the 5.6R cut them. Should I be experimenting with the resistors at the crossover, or with the resistors I just installed right at the tweeter?
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Old 30th November 2007, 11:06 AM   #50
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by timbert
Today I finally soldered the 5.6 ohm 10W resistors as suggested
to the tweeters, and they cut back the highs severely. Also, at the
external speaker terminals I get 10.4 R on my digital multimeter.
I think, to start, they need to be cut to a level about half of what the
5.6R cut them. Should I be experimenting with the resistors at the
crossover, or with the resistors I just installed right at the tweeter?
Hi,

it sounds like you have wired them in series with the tweeter rather than in parallel
which will be too dull and impedance wise completely wrong for the crossover.

/sreten.
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