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Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 04/09/2008 : 18:24:09
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Yep yep... What Dr. Bob said!
My ealrier comment stands - "Don't try it unless you know your amp can take it though... increasing the load impedance on tube amps can sometimes cause problems."
zentropa's experience where he "managed to blow out a speaker trying" is all too common. There is no question - amps and cabs work best when matched.
I'd be matching the impedance of amp and cab and trying to find some other way - the mods Dr. Bob suggested, or a power brake, or something.
When I bought the marshall head that I'm currently very happy with (JCM600), I purposely bought an amp rated at 50W rather than 100W for just these reasons. I haven't looked at winding it back to even less power because I'm not currently using it in a band - just in the basement.
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FRANZONI
Double Platinum Member
Ireland
3543 Posts |
Posted - 04/09/2008 : 20:22:28
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http://www.londonpower.com/faq.htm ..... i emailed kevin at london power years ago before i was a member here about a problem with the marshall head and he was very kind with his emails back..... i thought his FAQ section is pretty good so i posted the link ...
Dr Bob...... whats the problem with coming to ireland it's only about 22 hours on the plane... .. i have a spare soldering iron you can borrow..... ..... i know a few(quite a few) places that serve a good pint of guinness...... ....... |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 04/09/2008 : 20:27:37
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Count me in too for the Guinness...!!
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pedals 4 pv
Platinum Member
Canada
1351 Posts |
Posted - 04/09/2008 : 21:03:46
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Party at Franzoni's place   |
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FRANZONI
Double Platinum Member
Ireland
3543 Posts |
Posted - 04/10/2008 : 03:05:17
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one of these days we ought to have a bossarea convention..make sure you bring that big gibson acoustic pedals4pv...us irish like a song or two when were drinking. ..what do ya think lauries...i know you know your way around temple bar... ... |
Edited by - FRANZONI on 04/10/2008 03:09:28 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 04/10/2008 : 04:07:58
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I'm in... seriously. If we set a date sometime far enough ahead  |
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FRANZONI
Double Platinum Member
Ireland
3543 Posts |
Posted - 04/13/2008 : 03:11:52
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i took on board the advice of the people here who know a lot more of the theory of electronics and kevin from london power who advises against mismatching speaker loads with marshalls so this is what i decided to do instead....i put the greenbacks in the cab their rated at 25 watts each and their SPL is 96db over the vintage 30's 100db and 60 watt rating,later on i'm going to cut a big hole in the back of the cab to let it 'breathe' more...this should lower the volume a bit.....remember i have tube adapters in the marshall for EL 84's so in theory the power amp section can only put out 32 watts.....
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Edited by - FRANZONI on 04/13/2008 03:12:20 |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 04/13/2008 : 04:38:16
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Hi Franzoni & guys
Can I make a suggestion?
Or just something to think about.
When you cut the opening in the rear panel, can I suggest that you make it, like a trap door, on couple of hinges or a piano hinge,
That way you will be able to close it off & have a slightly leaky sealed cabinet, with a snib/s or latch/es, to lock it off when in closed back configuration.
--edit-- or good quality Velcro ---
Best of both worlds, open back & closed back.
Plus it will afforded a lot more protection to the speakers when you're transporting them, to have the vent closed off.
The now normal sized opening on open backs is about (1/3) one third open back.
With the seal-able trap door, you may have to cut another piece of 12 ply or MDF, to make it a better fit.
Maybe a bit of foam rubber behind the opening to make it a better seal, when closed?
And perhaps some extra brace or bracing?
I hope I have explained, what I was trying to convey?
Else PM me...
When I saw the Rola/Celestion LTD, it brought back lots of memories.
Rola were a company I aspired to work for, when I was a teenager at technical college, & just 15Km down the road.
I have a Rola/Celestion LTD 18 inch driver, in my first stadium sized cabinet, & boy is that a monster, takes 2 people to lift if onto its mounting bolts, inside the cabinet, & it still runs today.
Regards Dr. Bob
PS. Those read & black speaker wires look a little on the light-thin side.
Double them up, if you don't have any thicker wire.
Remember, that if you double the diameter, you get 4 times the conductive area, & (1/2) half the resistance.
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Edited by - Dr. Bob on 04/13/2008 04:39:37 |
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FRANZONI
Double Platinum Member
Ireland
3543 Posts |
Posted - 04/13/2008 : 12:28:21
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| Thanks doc...i changed the cable to a thicker grade audio cable i had in storage..... good idea about the opening at the back..i have some brass mesh out in the shed i will use to cover the hole i'm going to cut in the back..more pics coming soon.....i'm going to be using it on a gig later this evening so i will report back on the outcome.... |
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FRANZONI
Double Platinum Member
Ireland
3543 Posts |
Posted - 04/14/2008 : 11:41:51
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| I used the cab on the gig last night and it sounded great......the greenbacks don't have that mid range 'scoop' to the sound that the vintage 30's seem to have even though on the celestion chart they are shown having a midrange similar to the greenbacks.... it was noticably quieter but the clean sounds seemed to have more 'body' to them..i don't know if cutting the opening in the back of the cab is the cause but i like what i'm hearing....i took Dr Bobs advice on putting something over the back to protect the speakers,i found some brass mesh very similar to what gibson use on the front of their goldtone amps to protect the speakers,i cut a fairly big rectangular slot with a curve on both ends and the drummer said it sounded really good from where he was sitting.....i also was getting a lot less feedback when i turned the overdrive on....all in all it seems to have worked out well....thanks for all the input guys............ |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 04/14/2008 : 12:57:55
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Hi FRANZONI & Guys
I'm really glad, it worked out for you as well as it did.
How much of the back did you remove, percentage wise?
The brass mesh was a great idea, & I bet it looks good as well.
Did you staple or glue it into place?
Regards Dr. Bob
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FRANZONI
Double Platinum Member
Ireland
3543 Posts |
Posted - 04/14/2008 : 13:09:25
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| I reckon i took out over 50% of the back on the cab doc...and your right about the mesh..it nearly looks better than the front....!!! i used some screws and clips to secure it in place and to stop any rattles fronm it at volume.....my amp and cab are in the van at the moment but as soon as i get a chance i will take some more photos if anyone is interested..... |
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pedals 4 pv
Platinum Member
Canada
1351 Posts |
Posted - 04/14/2008 : 16:22:36
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| Yes. Post a pic and we'll have a look |
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Topic |
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wiring speaker cabs...
