Rebuild Goodmans Magnum K speakers ... 1965 English

[mfforever]

Hi my much respected Stereonetters DIY / rebuilders .......    

 

Have some Goodmans Magnum K speakers from around 1965 ....England build .........    totally original ( you feel like  Lord Carter looking into Tutankarmon's  tomb when you open the backs with its 20 screws ..... but note that I circumvented the terrible DIN speaker terminals with some modern temporary speaker terminals ) ......   beautiful bookended teak cabinets in great condition .... original stands ......    drivers in immaculate condition ).  Please note they are not the later K2 versions that followed.

 

So.... now ready to bring them into the 21st Century so they can be the best they can be.......

 

 

First things first ........    will give the full treatment to the cabinets .......    totally brace all edges and ply reline with screws with Fintech Fix 15 adhesive sealant ( my fav as remains so flexible to absorb movement / vibrations ).  Bevile out driver baffle mounts, add ply faceplate to baffle face..........   finish with Scandi Oil on that original teak  .....    replace ( sadly , as a little bit torn )  the original 1960s grills with period appropriate material.    

 

Secondly, totally rewire with some nice strands

 

 ********.        BUT the BIG issue is the internals :    2 schools of thought ( and quite debated on UK audio sites ).

 

1)    One approach :

 

- Totally strip out everything and start again . ( Dr Bunsen Honeydew is evidently a Goodmans guru  on hifisubjectivist  ) .  He recommends to strip out all the original crossover and Lpads ( hey, it's 55 years old and everything would be out of spec anyway )

 

He then recommends after the total strip out :

 

- Leave Bass Driver full range and dope it to control its HF ( using Bison doping material ..... instructions supplied on the site and seem pretty straight forward )

- For the mid range - leave the high pass filter on the midrange driver and add doping to cone if it has coloured HF output and then maybe padding the resistor ( but / and another person said LF protection on mid( electrolytic ) and doping.   ( Please note that the above process I really didn't understand ???? )

-Just LF protection on tweeter ( 3.3 mfd ).   and a padding resistor to taste.

 

On this approach of stripping everything out and getting rid of the L pads as well........   probably my preferred approach BUT THE LEAST I KNOW ABOUT / UNDERSTAND.

I would be looking for some serious guidance from some very informed contributors ........ as on many posts before my understanding of CROSSOVERS is decidedly stupid.

 

2) Second approach :

 

Just replace everything in the existing crossover  and L pads with corresponding new quality components.

 

On this approach I think I could do as it's just a replacement and solder of like follows like.

But would this do justice to the quality of the drivers ?

 

Last question :

Many forums / posts say that the  tweeter on the magnum K is the weak link in this speaker ( What can I say. ???    ......    I really can't verify this as I'm listening to these speakers with 55 year old crossover components ......     who would know what is in spec and of great quality .........   but it does sound very flat in the treble area )

 

Thinking of substituting the original tweeter with :

 

-  Aurum Cantus ribbon tweeter G3Si.   ( specs -  minimum crossover 2300 Hz,  6 ohms,  1400 to 40,000 ,   99db.  ( needs 20 uf cap as protection ??????? )

I have a pair of these so can experiment but realise that I need a totally new Xover which I have no idea about and thus throw myself on Stereonet combined wisdom )... Please note I have a pair of these so will try them but have no idea  how they fit in a crossover that is existing or to be totally rebuilt.

OR

 

Scanspeak Discovery D 2608/9130    have rave reviews ( 8 Ohms, 91.5 dB,   ,  3500 -20,000 Hz, resonance freq 700 Hz.

 

 

Would love some ideas on what direction to go .....   leaning towards a total strip out and therefore maybe a new tweeter with totally redesigned Xover .......    would love some Stereonet informed magic .........   All the best.

 

....

Edited March 27, 2023 by mfforever

[Shaunmaxr]

Hi there,

having done your 2). and listened to them in my system for 10yrs or so I would say it is a worthwhile project.  Changing the caps, rewiring and cleaning the lpads (or changing them out) will give you a very nice sound indeed. They’re transparent and well balanced - I run a Sugden Masterclass Class A amp which drives them very well. They will show you every change upstream, cartridges, sources, cables etc.  
The birch ply cabinet is built like a tank. I ran without the covers and flush veneered the fronts (the whole cabinet actually).

lastly I had advice from Jerry at Falcon in the UK who supplied the caps. He told me not to use ‘audiophile caps’ just good replacement ones. 
he also advised not to change out the tweeter at all as he said it would upset the balance. I like you wanted to, but decided not to in the end. Like I said I dont miss any treble as far as I can tell with a Townsend super tweeter sometimes int he mix when I feel so inclined. 
good luck with it and let me know if you do decide to swap out any of the drivers- I’d take them off your hands in case any of mine go up in smoke in the next 25years..! 

great project. 

[Shaunmaxr]

Ps the black lpad on the right is original, the one in the left looks like a replacement. 

[Shaunmaxr]

[mfforever]

Hi Shaunmaxr ........   that veneer is absolutely gorgeous ...... is it ambrosia wood ?     and where did you source it ? I'm a fan of great cabinet work and this is top notch.....   well done.

 

Some really good personal advice here .....    will be in contact with Falcon UK for their  advice on crossover components.  

 

Your experience with the original treble is interesting .........    when you hold it in your hands it's such a non-descript thing.....    small and lightweight..........    but that you have combined it with  a Townsend Super Tweeter is , I imagine, where things would start to get really interesting.   If I go down this path I would like to contact you with the specific details on how you wired it in........   from what I know, it is pretty well self adjusting without the need of any additional external crossover. ( Now very costly here in Aust ......     could kick myself as a nice second hand pair turned up about 2 months ago on the classifieds here )

 

Early days yet in terms of my final direction, but am really appreciative of your input ......    am in no hurry so have plenty of time to gather advice and experience from informed, generous spirited members like yourself.........   all the best.

[Shaunmaxr]

Hi there, 

I got the veneer from a guy locally and he told me how to do it. I just followed his directions and then I gave them a coat of French polish. 
the Townsend tweeters just connect across the input terminals and are adjustable.

 I’m not sure I can hear the difference but it seems to attract the fruit bats from the local bush..

Jerry is excellent and very well regarded. They stock a comprehensive range of parts for speakers and postage if I recall was very reasonable.

S

[mfforever]

Hi Shaunmaxr ......  opened up the replacement L pad to have a look ........    pretty ugly with a fair bit of corrosion inside.....   makes me more determined than ever to take them right out of the X over all together.

 

Will contact Jerry at Falcon and ask for advice ......    I'm hoping that Goodmans in England are like Holdens in Australia in the 70s ........ tons of them with an active Goodmans community doing mods / improvements ....   anyway, will start on bracing/lining/reinforcement of cabinets and this will keep me off the streets for a while.

 

Anyway, been listening to them as they are  in all their faded glory and can only say it is a project definitely worth pursuing.............   thanks for your input........   will go quiet for a while as I seek UK advice as unable to find some here......  all the best.

[dcathro]

looks like an interesting project, good luck.

[mfforever]

Thanks dcathro .........    they are a very nice retro speaker but the area I need to upgrade is in  " the dark side  "       ; in other words, the Cross-over.    Can do most other things but when I read cross-over DIY forums and technical sites I just turn into a mush-eyed green -pead zombie ........    am now trying United Kingdom DIY audio sites for some higher wisdom .........    stay watching but it will be a slow build as I like to do things well and only once so I get it right the first time.   Thanks for the support.

[mfforever]

Hey Shaunmaxr .......   seems like that silver L-pad is original ......    found the exact same L-pad on 2 other Goodmans Magnum K on German sites that had been opened for the first time .....  evidently  Goodmans quite commonly changed internal parts in their models to use up spare parts / parts from other models / hard to get or priced increased parts ......    will now clean up both L-pads with DeuxIT.

 

Any special tracks that the Fruit Bats really dig ?  ( like Meatloaf's Bat out of Hell.... )

 

 

Edited April 4, 2023 by mfforever

[Shaunmaxr]

  
Mine have four of the black Ones but they all cleaned up well after some deoxit.

 

[mfforever]

Don't know enough about a total strip out and partial crossover rebuild as in Option 1  so .......  it is Option 2 - replacement of the Caps, deoxit L-pads, extensive cabinet bracing and internal wiring . I have a variety of nice speaker cable to suit the  Bass using Kimber Kable 4 PR   and then  The Chord Company Carnival Silver for  the treble and mids.

 

Will do above and listen ......    probably will then still buy a pair of Scanspeak Discovery tweeters D2608/9130 and wire in for a comparison with original Goodmans tweeter........    the Scanspeak seem a fantastic drop-in replacement involving no crossover adjustment ( I believe with my limited Xover understanding )......  as both are 8 Ohms, both around 91 db sensitivity, and the Scanspeak has an incredibly flat response between 3000 and 20,000 hz  that suits the Goodmans crossover at 6000 hz...... and as a bonus, it will drop straight in the front baffle ( albeit sitting on the face of the baffle rather than mounted from the inside on the front baffle )

 

If I have missed / overlooked something then would love further advice .......   will be a while before posting progress. as I do everything pretty slowly, but enjoy immensely.

 

 

 

 

Edited April 8, 2023 by mfforever

[Shaunmaxr]

Thought you might be interested in this review of the Magnum K

from 1966. Cheers 

[mfforever]

Thanks Shaunmaxr .......    an interesting read....    everything I've read on the Magnum K rates them very highly indeed ...    just about to disassemble mine for the full treatment ........    I know you were very happy with the results so hopefully the Audio Gods will smile down on my endeavours.  Will post progress photos .....   slowly.

[mfforever]

Hi StereoNetters.   ........    I know I stated that I am snailikelyslow in my builds, but I've had a really bad Covid  .......    anyway , bought Caps ,resistors and new tweeters to compare  .......... so ready to go ...........    but the delayed holiday to South Australia is now beckoning ........   will show progressive build later in July .......    ( and can I say, the initial listening to the English Magnums without any rebuilding  is quite exciting .........    the English sound and the Japanese sound ( multiple Yammies NS 1000 and now NS 5000 ) are really very different and apparent .......    but different is good.....   both are quite marvellous in their own ways  ).    Will pursue this build to it conclusion..... and do a comparison with the original  Goodmans tweeter with the  Scanspeak Discovery tweeter ( D2608/9130 ) .         Cheers......

 

Over and out until  mid July .

[Powerglide]

Looks like fun.

 

I’ve resurrected a host of vintage speakers and the rewards, to me, are great. Love to get my hands on a nice pair of Goodmans even though I’m double parked with ‘’to do’s’’ 

 

I think you’re taking the right approach, definitely run them with the original tweeters for a few months before trying the scanspeak’s you don’t want to loose what they were unless you have to.  

[mfforever]

Hi guys .........    back into this build after all-the-life-stuff-going-on and being really bogged down in Crossover - Dark-Arts - trying-to -understand-WTF ? -  ----   now have  a schematic diagram of a Crossover that removes the L-pads ( with great thanks ellnic and chrisng  immensely ).    I have been SLOWLY reinforcing/bracing/modifying the cabinets  ........   plus had to go the SkanSpeak tweeter as one of the original Goodmans tweeter was totally dead.

 

After all the bracing and the original DAMN HEAVY drivers, this speakers now weighs a ton. Will post the internal bracing pics ...........   and after looking at the internals of a Yamaha NS 1000 ( one of my idols ...... had a few for many years )     I will totally fill the cavity with diffraction foam and then sheep wool.    See pics below as to progress.

[mfforever]

Hi again .....   sorry it's been a while ........   but finally refreshed cross overs with some nice Jantzen Superior Z Caps and Jantzen Cross Caps .....    next step to cut new gaskets for drivers and fit them.

[rsa17]

27 minutes ago, mfforever said:

Hi again .....   sorry it's been a while ........   but finally refreshed cross overs with some nice Jantzen Superior Z Caps and Jantzen Cross Caps .....    next step to cut new gaskets for drivers and fit them.

Good to see you making progress again. I run the Magnum SL's (around 1975 vintage) I recapped the original crossovers using Dayton metal film audio caps. Can't tell you if they were an improvement over the original ones they replaced, I did a bunch of other work to the speakers at the same time. Both of my tweeters were blown, but luckily, they are a fairly common Philips unit which I was able to locate a pair locally. It looks like mine share the same mid driver as your Ks though. The latex surround had become unattached, so I had to reglue them using a Polymer EVA glue. They came up nice. The bass drivers look similar. One of mine, the spider has sagged causing coil rub, but if you rotate them 180° that sorted the issue (an old guitar amp trick).

 

Mine sound great, and I encourage you to keep going. It's a shame one of your original tweeters was dead though. Just because of my OCD I would try and source an original, but I'd imagine that they are unobtainium now.

 

Peter.

[mfforever]

Hi Peter .......   great to hear from other Goodmans fans / rebuilders / believers . Yes, definitely pushing ahead as the end is in sight ( for one speaker that is, as I'm doing just one up to do a comparison with the second.

 

and yes, I think the mid drivers are identical on the Magnum K and the SL ......    and they are indeed an impressive unit - very solid and weighty - expecting good things here. The Bass drivers are not identical but very similar .....   beautiful monsters  - a few English sites rate the Goodmans 201/301/401 and ours as better than the Tannoy Golds , but I think this is a little bit of biased indulgence on their part .....

 

Would have liked to have heard the original tweeter - DT3 - but one was dead and still to look at the other one .......     not too upset as reviews always said the DT3 was the weakest link  .....    to look at it is a very light and flimsy thing ...... whilst the replacement Scanspeak Discovery D2608 is very solid with near identical sound specs. 

 

Will post review when finished ( will need to burn in new caps and tweeters ).       .........   stay well.

[mfforever]

Everything rewired with Chord Carnival cable ( stripped the wires out ) .......   nice cable that I had on my HT speakers.....

 

and fitted some good Cardas Binding posts that I got on Stereonet. ......  slowly getting there.

[mfforever]

Please note that there is an error in the above cross over I made .......     I connected the positive from the Woofer to the wrong side of the 10uF cap ......   it should be connected to the large inductor side ( please see the corrected version below ).    BUT even BETTER than my arrangement is one provided by Martykt .........   please see below  (  all negative terminals on your drivers go to common negative terminal).........   Thank you yet again to the Stereonet Community.

 

Got my one completed speaker into my system and fired it up .........     WOW !!!!!! this is sounding beautiful .......   Bass is deep, controlled and very tuneful ......    the new Scanspeak tweeter is going to be a real winner.     When the second speaker is completed and they have 100 hours on the new caps and tweeters I will give a full review.

Edited April 5 by mfforever

[mfforever]

On the second speaker now  .....   some nice 9 mm ply sandwiched with silicon adhesive onto the back board ... new gasket material to seal the back ............the Cardas binding posts well bedded into the silicon adhesive so no vibration there .......    next step is to round out the baffle fronts where mid and bass bolt on the back ......   then reline with a mixture of acoustic foam,  10 mm felting and some good old Aussie wool.   Second speaker sooooooo much faster and less stressful as I can now say I know what I am doing.

[mfforever]

 Filled the holes  .....    rounded out by hand around Bass and Mid to create slight fold out as drivers attach to back of baffle .....   just some sanding  before priming/painting .......... moving along at break neck speed ( for me that is )