Goodman's Magnum K series MEGA collection... Mod advice

[lysergic-skies]

Given you've got so many , you can mod one and compare .

I bet you a tenner you don't agree with riat

I might just do that. I could start with the naff K2s when I get them back and the fish tank Ks, and if it all comes falling down I’ll shove them on freecycle. Then at least I’ll know!

I’ve ordered some low value MKP caps to start, more ofc wire (was running low), plastidip and am enquiring about steel plating. It might have to be acrylic to start then move to steel when I know it’s worth it.

I’m still confused about the contact adhesive. I realise Bison is a brand, but I meant what type of Bison was doc referring to? He linked to the car mirror in a tube stuff in one post I saw, then mentioned the kit stuff in a tin in another. I’m happy to take recommendations on alternative but part of me also thinks that I should do this the unadulterated ‘doc way’ for the full ‘doc experience’. Also need to figure out caps for the mids. Pretty sure he said 100-200mfd in-line on positive, which seems insanely high to me but I’m tired and have probably invented that. If that is how it’s got to be, I’ll probably start with 4 x 27s and just keep adding just to minimise cost.

I’ve had a long day and I’m hot and exhausted (can’t handle this heat, anything over 20c is a no go for me!) so I’m not going to do much tonight but tomorrow I’ll try and hunt down and tag some previous modders who’ve followed this and see what they say!

[Geoff.R.G]

DQ, what I would do is recap and rewire as Riat suggests and see what they sound like. As you have more speakers you could mod another pair and compare pre and post mod versions.

[Lindsayt]

Interesting how some have the drivers front mounted and some are rear mounted on the baffle.

[Daniel Quinn]

You need bison kit contact glue if your using bison . I'm of the opinion that any contact glue will do .

Start with a minimal round the dust cap and listen . The amount is driver dependant and your personal preference .

[lysergic-skies]

Interesting how some have the drivers front mounted and some are rear mounted on the baffle.

I have thought a lot about this and I think it is simply to do with the fact that when the back was removable and the grille was not (because the K grille is secured from the inside) it was easier to have the whole cab face down on a work bench. When the K2 came along with it’s sealed back, the obvious choice was to drop them in from the front instead of continuing with the rear mount design because once the cab is sealed, that’s it. The design was probably changed in the K2 to reduce the amount of gasket required and reduce the infinity bass air leak issue. The fact that the K2 grille is removable is not intentional as such, it’s unavoidable - my mate I’ve given the naff ones to reckons the mid is WAY too forward without the grille and that they were never intended to be run without it.

You need bison kit contact glue if your using bison . I'm of the opinion that any contact glue will do .

Start with a minimal round the dust cap and listen . The amount is driver dependant and your personal preference .

Thanks, I’m starting with the fish tank Ks today. They stink so much I’m just stripping them out to liberally douse them in bicarbonate and febreeze then they’re going outside in the harsh unforgiving sun for a few hours!!


Crossover is a mess. This one had 2 buggered Lpads. Trying to trace the crossover and I must say I hate these Goodmans crossovers. Such a mess!!

If anyone happens to have the original crossover diagram it would save me some time!

I’m going to bypass the lpads on this one just because they’re knackered and I prefer them open anyway. I have some 4mm posts from a pair of sacrificed missions here I’ll put in their place.

Pics: https://ibb.co/album/6Jp7Dj

I think the crossover I’ve drawn there is correct but I need to double check it!

[Daniel Quinn]

The xover is ancient , throw it away .

[lysergic-skies]

The xover is ancient , throw it away .

I will, but I need to trace it first to know what to knock up on the prototype board!!

That resistor is part of the replacement (different) Lpad. I don’t know what it does, I don’t fully understand lpads other than they are more or less 2 pots that don’t reduce impedance.

The original one on the right doesn’t have it, nor do any of the other cabs including the original ply ones.

There are no resistors anywhere else on any of the Ks or K2s.

[TheRealAleman]

1. Which Bison compound is used? I can find reference to both the car mirror stuff and the kit stuff in a tin. They seem quite different products!

Bison Kit is the glue that Richard used, and recommended, apparently it never goes hard, ( Oeerr Missus ) ... Even with 5 sets of drivers to dope, you should be able to get away with a 1L tin ... Don't do what I did, and get the 4L can

2. Does anyone have a photo of the Bison compound once 'wormed' round / drizzled down to the cap? (most the tinypic links are shot). It seems to me that there could be quite a variation on amount depending on user [in]experience and I don't want to screw it up.

These are some drivers I'm working on in my "test bed" ... I think it's about 4 or 5 iterations, with the last few being diluted with acetone, to control the amount of glue applied, Just need a few coats of Plasitdip now, Happy with the sound, and a harshness/ break up around the "crossover frequency" has been "tamed" ... It may be different when they go into the proper cabinets.

5. Can someone recommend a sealant to run round the inside of the cabs for air tightness? I'm not used to infinity bass and didn't realise the air leak thing was so important - will hot glue / liberal PVA suffice?

Bison Kit ... I was thinking about using 2 part epoxy resin.

6. Does anyone know if the K2 bass cone paper caps be sprayed with the Plastidip?

Don't know but I did mine, but they are Kevlar and plastic

[lysergic-skies]

That’s really great info and a fantastic photo - thank you very much. I’ll get some Bison Kit for when I do the second set.

At the moment, I am working on the factory spec set to compare. I thought I’d found someone on another forum who had the crossover for the Ks but they’re no longer a member. I really struggled with this crossover and just couldn’t trace it but some other kind peeps at DIY audio helped me out. I’ve just finished the first one: https://ibb.co/album/xFwQSg

[lysergic-skies]

Here is the K crossover (thanks to chrisng at DIY audio):

Goodmans Magnum K Crossover.png (15.84 KiB) Viewed 3479 times

Chris has also kindly provided the K2 crossover:

Goodmans Magnum K2 Crossover (incomplete).png (4.61 KiB) Viewed 3479 times

I didn't have the tweeter inductor value to hand, so need to add that later.


So far I have taken my "fish tank" Ks (which now smell a lot better btw) and I have rebuilt the crossover from scratch without the Lpads. They sound good. I feel the bass may be a little lacking but I think I know why....

@Lindsayt whilst disassembling the K cab and removing drivers, it occurred to me that probably the 2 most important reasons for changing the cab design to that of the K2 are:

1. Those drivers are an absolute b**** to remove from behind. The bolts are ridiculously long. It takes ages and it's fiddly.
2. Air leaks which we've already mentioned, but where? Where the grille secures through the baffle and the bolts fix from behind!

swiss cheese speaker.jpg (179.62 KiB) Viewed 3479 times

You have the potential for 8 additional air leaks. With the K2 you really only have to worry about 3 speaker gaskets. The K's rear panel is easy enough to seal, but I don't fancy these grille holes. And now having worked on two K speakers, I can say that it's a massive pain in the bum to remove 20 screws to pop the back. Despite it's cheaper chipboard construction, the K2 is clearly the superior cabinet for an infinity bass. I'd be tempted to plug the K's holes and change the way the grille secures! K2 is velcro, might be an idea. It's a shame that by the time the K2s came along they'd already started cheaping out. A pair of K2s in birch ply would make for some seriously solid cabs.

I'm gonna run these Ks for a while before moving onto the doc mods. I think the next thing I'd like to do is shove a pair of the K alnico mids in the K2s. The K2 has a superior bass that is already full range and doped with kevlar, the DT-3 tweeter is also superior. Seems like an idea would be to swap the mid!