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Old 9th July 2015, 10:39 AM   #1
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Default Problem with fostex fw105

Hi all I recently put a new pair of fostex fw105 in a FH3 powered by a tripath 2020 board I have been using for years with no problem.

The system was fine for a day or two using my ipod as a source then my amp started to cut out.

I measured the cd resistance with a meter and could see one driver was measuring about 1ohm the other 6 ohms.

The one with the low dc resistance was cutting the amp off.

I assumed the driver was fried...

Then I tried powering it out of the cab, and I got Un distorted sound.

Over the course of the week I progressively turned the vol up with Music playing.

There is no distortion I can hear. When I go high volume the amp cuts out.

Do you think the driver is fried? Is there anything I can try to fix this?

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Old 9th July 2015, 02:53 PM   #2
TMM is offline TMM  Australia
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Did you measure 1ohm directly across the driver or on the terminals on the back of the speaker enclosure? If the latter, check for loose/shorting wiring inside the speaker enclosure and if you can replicate the problem again, try disconnecting/removing the driver and measuring directly across the drivers terminals.

If you measure 1ohm directly across the drivers terminals with nothing else connected then something has gone wrong with the driver. Possibly there is an intermittent short that only occurs when the driver is subjected to high excursion or the voicecoil heating up. You can also try manipulating the cone (gently pushing it in and pulling it out) while measuring the resistance to see if you can replicate the problem. If that is the case, there is likely not much you can do about it non-destructively.

Last edited by TMM; 9th July 2015 at 02:56 PM.
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Old 9th July 2015, 04:24 PM   #3
chrisb is offline chrisb  Canada
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Do you mean current FF105WK, or some heritage model?

TMM has pretty much covered it - if the driver in question measures and works fine outside of the box, it's most likely either the wiring or connection at terminals that are the cause.

FWIW, I've noted that when using PVC sleeved CAT5 wiring that's been untwisted only far enough to reach the driver or input terminal solder tabs, it's possible to melt the insulation on both wires if holding the soldering iron / gun longer than absolutely necessary - that could cause a short, but not likely to be intermittent.

If you can measure the VC resistance while excursing the cone as TMM suggests (not connected to amp), you should be able to isolate the problem.
"Perception is a highly non-linear function" - Earl Geddes
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Old 9th July 2015, 09:59 PM   #4
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Thanks guys

To clarify I am measuring the resistance directly at the speaker tabs rather than at the cable.

I agree about the short at high excursion - the thing that got the driver working again was some gental cone manipulation - pushing and the cone when outside of the cab.

I was hoping by using it at progressively higher volumes the fault would fix itself.

What is crazy is I can't hear any difference between the dodgy one and the good one.

I will keep playing

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Old 11th July 2015, 02:26 PM   #5
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Hi all

I played a 30hz sine wave trough the driver for half a day, progressively louder and it didn't trip the amp, now resistance is 7.8 ohm.

I've worked with speakers for along time but never seen anything like this.

I will see how it holds up for the week and if any problems pop up I can swap them out with some fe103 sol drivers I have.

All the best

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Old 11th July 2015, 05:28 PM   #6
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Originally Posted by 12345chris View Post
now resistance is 7.8 ohm
Most weird… but good.

some fe103 sol drivers
If by fw105 you mean FF105 i will be very interested in that compare. We only have FF105wKeN to compare our SOLs to.

community sites,, ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
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Old 11th July 2015, 05:35 PM   #7
Gyuri is offline Gyuri  Hungary
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I dread the self-healing defects.
They are always greet back.
Those who would have deserved the life they are all dead already. "Oh, my dead dears!" - Captain Cat
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Old 2nd August 2015, 05:36 AM   #8
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Hi guys, they have been working fine for 3 weeks and now both show the same dc resistance. Very strange but happy.

I still haven't tried the 103 Sol's


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