Wiring 4 Scumbacks in 4/12 Cab

Decko · Post by **Decko** » Mon Aug 25, 2008 1:50 am

I am planning to buy some Scumbacks G12M 25 watters qnty 4. What is the best method to wire the drivers? Series? Parallel? This cabinet will be mated to an Express.

billyz · Post by **billyz** » Mon Aug 25, 2008 3:24 am

If you want to wire it like a vintage marshall, you'll need 4 - 16 ohm speakers wired series / parallel to get a 16 ohm total.

geetarpicker · Post by **geetarpicker** » Mon Aug 25, 2008 7:04 am

Nice pic shows just how it's done in my original Marshall cabs.

57goldtop · Post by **57goldtop** » Mon Aug 25, 2008 11:42 am

I rewired my cab using that same layout in preparation for when I receive my speakers, I have a 4 25w M75 on order..

Decko · Post by **Decko** » Wed Aug 27, 2008 7:02 am

Got it thanks! Top two in series then parallel for a total of 16 ohms.

Distortion · Post by **Distortion** » Wed Aug 27, 2008 7:46 am

Here is a link with several different wiring options which might prove useful down the road..

http://www.soundcitysite.com/sc_webpages/wire_diags.htm

Lonely Raven · Post by **Lonely Raven** » Wed Aug 27, 2008 1:38 pm

57goldtop wrote:I rewired my cab using that same layout in preparation for when I receive my speakers, I have a 4 25w M75 on order..

Man that's going to be sweet! I have two of them, and I'm saving up for two more. They sounds fantastic with the Express, and for the most part pretty good with the Rocket.

gearhead · Post by **gearhead** » Wed Aug 27, 2008 3:41 pm

Distortion wrote:Here is a link with several different wiring options which might prove useful down the road..

http://www.soundcitysite.com/sc_webpages/wire_diags.htm

And yes, the different wiring schemes do sound differently. Never believed it until I tried it when I first got my 4x12.

Scumback Speakers · Post by **Scumback Speakers** » Wed Aug 27, 2008 5:35 pm

I've drawn up a 4x12 wiring diagram for series/parallel. This is identical to how Marshall wired them in the late 60's through the late 70's.

[img:542:554]http://southbayampworks.com/wiring/SBA4 ... wiring.gif[/img]

I have tried parallel/series wiring, and it sounds thinner, with less bass, and less organic tone. The stereo switch on the back of new 4x12's (the one that offers 4 & 16 ohm in mono, and 8 ohm per side in stereo) is wired parallel series and also doesn't sound as good as the above diagram.

I have also tried the links at the Sound City wiring page listed on another member's post. These also have different tonalities with Scumbacks.

My testing of all of these wiring schemes led me back to the old Marshall style wiring I have above, and I would strongly advise you to go with that for your best tone.

In addition, changing the wiring to 16 gauge or larger zip wire (copper stranded lamp cord/power cord wire) is the minimum I would advise for wiring your cabs. The 18 gauge is OK, but you'll get more signal through the cab, better low end, and a bit more punch with 16 gauge or larger wire. FWIW

rooster · Post by **rooster** » Wed Aug 27, 2008 7:33 pm

Both the diagrams are identical electricly, BTW. And notice that in each diagram, each set of speakers gets its own complete path from positive to negative at the jack. This is what's important it seems, and yes, it has been tested to be sonically better by some people with good ears - so I'm told anyway.

In other words, electricly, you can create this circuit with a few less feet of wire - and cheat yourself sonically. To do this you would jumper to the other pair of terminals on the other pair of series speakers - ending up with ONE wire at the jack for positive and ONE wire at the jack for negative. This is what should be avoided because the speakers respond better given their own complete path.

And this being said, the bigger the wire the better, as was mentioned.

martins3325 · Post by **martins3325** » Thu Aug 28, 2008 12:08 am

Southbay Ampworks wrote:I've drawn up a 4x12 wiring diagram for series/parallel. This is identical to how Marshall wired them in the late 60's through the late 70's.

[img:542:554]http://southbayampworks.com/wiring/SBA4 ... wiring.gif[/img]

I have tried parallel/series wiring, and it sounds thinner, with less bass, and less organic tone. The stereo switch on the back of new 4x12's (the one that offers 4 & 16 ohm in mono, and 8 ohm per side in stereo) is wired parallel series and also doesn't sound as good as the above diagram.

I have also tried the links at the Sound City wiring page listed on another member's post. These also have different tonalities with Scumbacks.

My testing of all of these wiring schemes led me back to the old Marshall style wiring I have above, and I would strongly advise you to go with that for your best tone.

In addition, changing the wiring to 16 gauge or larger zip wire (copper stranded lamp cord/power cord wire) is the minimum I would advise for wiring your cabs. The 18 gauge is OK, but you'll get more signal through the cab, better low end, and a bit more punch with 16 gauge or larger wire. FWIW

So does that work out the same as the cab in this picture..supposedly an all original '67? If so looks like it gets there in a slightly different manner...the positive from top speaker seems to go to the neg of the speaker below rather than straight to the jack as in your drawing.
[IMG:480:360]http://i34.photobucket.com/albums/d137/ ... bSpkrs.jpg[/img]

Scumback Speakers · Post by **Scumback Speakers** » Thu Aug 28, 2008 1:08 am

martins3325 wrote: So does that work out the same as the cab in this picture..supposedly an all original '67? If so looks like it gets there in a slightly different manner...the positive from top speaker seems to go to the neg of the speaker below rather than straight to the jack as in your drawing.
[IMG:480:360]http://i34.photobucket.com/albums/d137/ ... bSpkrs.jpg[/img]

As you can see from this picture, the negative wire bypasses the bottom speaker to go back to the jack on one side. It comes off the bottom speaker on the other side when it goes back to the jack. This is a 71 straight cab wiring pic. So it's the same as yours, my pic is just a lot closer so you can tell.
[img:800:600]http://www.southbayampworks.com/71strai ... CN4070.jpg[/img]

gearhead · Post by **gearhead** » Thu Aug 28, 2008 1:30 am

Southbay Ampworks wrote: I have tried parallel/series wiring, and it sounds thinner, with less bass, and less organic tone. . .

I have also tried the links at the Sound City wiring page listed on another member's post. These also have different tonalities with Scumbacks.

My testing of all of these wiring schemes led me back to the old Marshall style wiring I have above, and I would strongly advise you to go with that for your best tone.

The whole series/parallel vs paralle/series nomenclature gets a bit confusing. Eventually found it easier to refer to it as the "six" vs "seven" wire connectivity. I too like the solution you outlined (which is one of the six wire ones), but found that out by just trying them. Wish I woulda seen a post like this years ago, LOL.

Decko · Post by **Decko** » Thu Aug 28, 2008 3:45 am

Thanks for the input and links everyone. This will be interesting to try different wiring and hear the tones.

martins3325 · Post by **martins3325** » Thu Aug 28, 2008 5:04 am

Southbay Ampworks wrote:As you can see from this picture, the negative wire bypasses the bottom speaker to go back to the jack on one side. It comes off the bottom speaker on the other side when it goes back to the jack. This is a 71 straight cab wiring pic. So it's the same as yours, my pic is just a lot closer so you can tell.

Got it..Thanks! Looks like I got mine right now..the pic below is mine. I have a couple questions for you..not to hijack the thread..but the wiring question is pretty much put to bed anyway.

1) I know you are much more a Marshall cab expert than I am..Is there anything that would make you think my cab is not a late 60s cab? Looks near identical to the one I posted earlier which I know for sure is. Reason I ask is I got it of ebay from a local guy..Tradarama..might know of him from TGP. Hes obviously wealthier than I'll ever be..if you saw his house you'd know what I mean..so no reason for him to scam on a relatively cheap cab. Some bidders emailed him --and one emailed me too-- saying it wasnt a real deal 60s cab..but they never explained why they thought that..I know it is a retolex..but everything else looks pretty dead on..old wood for sure..bracing looks right ..screwsinside are oxidized..everything..im fairly certain the grill is original too. Metal handles..silver inserts..even speaker mounting screws look right..but im not the end all expert..so thought id ask your opinion. Not a big deal because I got it at repro price..but if its real deal and im pretty certain it is..then I got at a great price. I cant imagine someone long ago went to great lengths to repro a cab that probably back then wasnt that pricey.
[IMG:647:550]http://i34.photobucket.com/albums/d137/ ... P_2588.jpg[/img]

2) I have a really nice clean Tweed GA-08 Discoverer --and nice new to me '96 Gibson Yamano R8.. a nice pair!

-- ..I know your a big Gibby fan from seeing your posts on TGP --and you like the non T, GA9 in particular --. I like this GA8 amp alot..sold my Victoria Tweed Deluxe because I liked it more. But I recall you stating that with a few tweaks the Discoverer was badass..I think its pretty badass as is but wondered what tweaks you were reffering to...and their effect? Not sure id do any because its SO original and clean. Got it off a riverboat captain of all people! lol
[IMG:288:449]http://i34.photobucket.com/albums/d137/ ... 87copy.jpg[/img]

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