• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Goodmans Maxim Voice Coil Shorted?

P

Pondy

New Member
I have a pair of early Maxims inherited from my mum. One of the bass speakers isn't working - disconnected from the crossover the voice coil tests good for continuity on my primitive meter but only produces the very faintest sound and doesn't respond at all to a 9v battery flicked on the terminals. The magnet appears strong and the cone moves freely. I've been looking at coil replacement and re-winding videos - can anyone please advise if this is feasible and/or is there any other possible cause/remedy?
Apart from being very neat, the speakers have sentimental value so any help would be very much appreciated.
Fingers crossed!
 
Register to hide this ad
What is the resistance reading on the voice coil? Continuity in itself doesn't tell you much.

I've never rewound a voice coil and don't know anyone who has. In theory it seems as if should be doable, but to do it correctly requires complete disassembly of the speaker, and doing that without damaging some of the components is very difficult. To my knowledge, pros who do this sort of thing only do it when replacement components are available (but of course their time is valuable).

TBH, assuming you confirm that the woofer is bad per my first paragraph, you'd probably be better keeping an eye out for a replacement woofer on the used market.
 
Thanks Swechsler TBH the meter is so old and crappy I only ever use it to test fuses and I wouldn't trust the reading. It is zero - but then it is zero across the tweeter also (presumably that should 8?)
 
If the drivers are 8Ω (not guaranteed but probably a good guess - driver impedance doesn't have to match speaker impedance) then they would probably measure about 5-7Ω DC resistance (resistance is what you're measuring with an ohmmeter). Resistance and impedance are related but aren't the same.
 
The problem could be a cold joint between the terminals and tinsel lead or voice coil. Worth eliminating these before digging deeper. Really need a reliable meter to test. Can you try your one on a known resistor or the other woofer? These may be 16 ohm but as noted above DC likely to be less.

Tweeter in circuit will include capacitor etc which invalidates the reading.

I’ve rewound a shorted voice coil at home using nail varnish to replace the burnt varnish. Horrible job without the right equipment and it looked like a mess, but the woofer worked again. These are probably worth doing properly especially with the sentimental value.
 
Thanks everyone. I concluded that the voice coil on the bass driver had to be shorted, so I have eventually plucked up courage and replaced it with an 8ohm coil of the same diameter bought online. It works and even sounds ok but it is much more responsive than the driver in the other one of the pair so even with the amp balance set fully to one side it sounds harsh and seems at risk of blowing up as you turn up the volume

I have replacement crossover capacitors for both speakers, not yet installed - so can anyone advise how to soften and attenuate the bass on this new coil? Would putting a resistor or other component in series with the new coil work and if so what sort of value?

I would be most grateful for any advice members could give......
 
I’d send the original to AKer GordonW to fix. He could probably replace just the voice coil.

The driver you swapped in that’s the same diameter probably has very different specs.

At minimum just don’t throw away the original woofer. Someone might want to fix it some day.
 
Thanks Fairlane, but I can't pay $300 plus postage to UK.
Thanks also Elitopus, but I think you misunderstand - I have "successfully" replaced just the voice coil in the faulty driver. It works but I need to damp it down - my query is, can this be done by an addition to the crossover?
 
Ok gotcha. My bad. So it seems like the sensitivity of the woofer with the new VC is higher than the old one?
 
Pondy said:
Thanks Fairlane, but I can't pay $300 plus postage to UK.
Thanks also Elitopus, but I think you misunderstand - I have "successfully" replaced just the voice coil in the faulty driver. It works but I need to damp it down - my query is, can this be done by an addition to the crossover?
Click to expand...
Yeah nothing for these little Goodmans is ever cheap. Always on the look out for a pair of them.
 
What's the measured DCR of the one with the new coil, compared to the one with the original coil? I'm betting that it's not the same. Probably will have to find some way to measure that, at least relatively accurately. Could be that the coil in the all-original one, is also compromised, causing it to be low in output?

Regards,
Gordon.
 
Thanks Gordon
I now have invested in a semi decent meter.! I have disconnected each driver and you are right - the new coil measures 6.9 ohms compared with 8.3 for the original driver of the pair.

The closest resistor I've seen is this 1.5 ohm -

"Cement Resistor SQP 20W 1.5 Ohm (axial)
High power resistor, ideal for attenuation in crossover circuits"

So - Question 1 - should I just wire one of these in series in the +ve lead to the driver ?

Question 2 (At the risk of trying your patience), here's pictures of the original speaker - it looks as if the bass and tweeter are out of phase - does it matter?
Confusingly, I have seen other pictures on the net showing the same black to red wiring.......



upload_2023-3-13_17-38-46.jpeg
 
You must log in or register to reply here.
Back
Top Bottom