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david83 8th July 2021 03:57 PM

Restoring / Modifying Goodmans Magnum K2s Advice Needed
Hi all

I’ve recently been given some Goodman’s Magnum K2’s and they are in quite poor condition as is to be expected for something dug out the back of a garage.

Overall cosmetic condition is poor, and I have been advised the crossover would probably benefit from a recap. The mids have been damaged then repaired with PVA and lack brightness - or are they just like that anyway?

The tweeters look a bit shabby but appear to be ok and the woofers also appear to be ok and cosmetically are perfect probably due to the plastic wrapping on their paper cones.

Obviously it would be nice to be able to restore these to a workable state just because they’ll stay out of landfill, but I am at a crossroads. I have no problem with the cosmetic side of things, mending / filling varnishing the housing etc, recovering the grills, replacing seals that sort of thing, but I need some input and advice on the drivers and crossover unit.

My questions are:

1. What capacitors do I need to replace these with? Someone has said Alcaps? I can solder but I need to guidance on what to buy - doesn’t look like I can see the numbers written on these without desolating.. does anyone happen to know what these caps are? Here is a pic of it:

2. The mids are probably going to need replacing… is it worth trying to source K2 mids or is there something else that would go nicely in there? I can find many threads of peeps who have loved these units and an equal amount that have hated them. I’m not dead set on it being original spec unless the mids are actually good? Any suggestions for replacements and pros/cons would be appreciated

3. Same for tweeters, worth replacing? Suggestions? Pros/cons? I have heard the original tweeters are probably more worth saving than the mids, but I’m open to any and all advice. They certainly sound crystal clear to me, but if I’m dipping into non-purist with the mids, I’m open to suggestions for the tweeters too.

If I am to replace the mids and tweeters, it has to be something that will come through those woofers. It might just be that they are damaged, but they are definitely drowned by those woofers as they stand.

Cheers, Dave

Galu 9th July 2021 02:18 AM

Answer to question 1.

Undoing the metal clamp should allow sufficient access to the capacitors to read their values without immediately having to unsolder them.

I would replace them with bi-polar electrolytics like these ones available from Wilmslow Audio:

Mundorf Electrolytic ECap Capacitors

Galu 9th July 2021 02:25 AM

2 Attachment(s)
I've attached your crossover photo here for ease of reference, as well as an image of the loudspeakers for those unfamiliar with the model and drivers.

Galu 9th July 2021 02:41 AM

And here's some, probably unhelpful, specs of the Magnum K2:

Impedance: 4 - 8 ohm
Max. RMS power: 50W
Frequency Range: 30 - 22,000Hz
Retail Price: £46.20 (in 1971)
Sensitivity: 2W produces 96dB in the average domestic listening room.

david83 9th July 2021 10:44 AM

3 Attachment(s)
Hi Galu. Thank you for your help.

I have undone the clamp as you suggest and gently turned them to see what is printed on them. See attached photos. The 2 red ones appear to be the same. So they are 10uF and 5uF so I will need these: 10 fd ECap100 Electrolytic Capacitor and for the 5’s I guess the closest thing is 4.7 here: 4 7 fd ECap70 Electrolytic Capacitor not sure if this is acceptable or do I need a 5? How Will dropping it to a 4.7 change the sound produced?

One thing I am unsure about is what the 3 “doughnut shaped” parts are? They look to be some kind of coil, one for each driver. Do these also need replacing? One of the things I wanted to do was increase the internal wiring. Something thicker and copper, but looks like I’ll have to solder to each of these coils too.

Galu 9th July 2021 12:57 PM

4.7 uF is just fine and will make no audible difference (other than being fresher than the old 5uF!).

The coils do not need replacing as they do not deteriorate over time like electrolytic capacitors.

There's no need to go overboard with the thickness of the internal wiring.

david83 9th July 2021 01:10 PM

Ok that’s great thanks. :) Are these caps the same thing?

Ie, am I looking for just bipolar electrolytic? The only reason I ask is because I need some other stuff from CPC and I would get free delivery if I could bump up the order a bit.

I am still not sure if I should try and acquire the original mids or if I should replace them. I was hoping someone who has a pair of these and had swapped out the mids could recommend something.

Galu 9th July 2021 01:32 PM

You can order bipolar electrolytic capacitors from cpc if you like.

It is extremely difficult to suggest replacement mids without knowing the specifications of the originals.

You say the mids are "probably going to need replacing". Have you tested them and are they in working order?

I would see what effect the capacitor replacement has before considering changing out working drivers.

EDIT: I see you said the tweeters are "crystal clear".

You also say that the mids and tweeters "are definitely drowned by those woofers as they stand". This may not be the case after the capacitor replacement.

david83 9th July 2021 01:51 PM

Yeah I’m sorry that does come across as contradictory.

The mids do produce sound, but they are lost in something with bass, even without they seem dull. I assumed this was the result of the PVA.. you think it’s more likely to be the caps? The tweeters are crystal clear but I still feel the output is not balanced - so they are ‘just acceptable’. Maybe the first point is the caps as you suggest. I’ll get those ordered today.

Galu 9th July 2021 02:00 PM

Sorry David, although I re-read your description, I failed to note your comment/question about the mids - "The mids have been damaged then repaired with PVA and lack brightness - or are they just like that anyway?".

What do you mean by "repaired with PVA"? Perhaps a photo may help.

Severely deteriorated electrolytic capacitors would cause a lack of brightness.

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