20 years back I used a rack containing a JMP-1 - an FX unit (Boss GP700 I think) and a Mesa 50/50 into 2 Marshall 1912 1x12s with stock Celestion speakers (G12B-150).
I gave up playing for about 15 years and recently in the last couple of years the old band has decided to get together and gig again (special prize will go to first one of us to have a coronary on stage).
I decided to try the modelling route and have all the stuff - AxeFX, Matrix SS amp, FRFR cabs etc etc ....... great stuff and all that except for the pokey gigs where my ass is parked next to my backline - just doesn't cut it with the drummer's cymbals practically touching my cabs - and turning up the volume just gives me tweeter squeal and all that crap. I think FRFR would be fine if we played more larger rooms with a decent stage monitoring system - but we are probably only going to be playing those venues 5 or 6 times a year ...... the rest will be smaller pub/club stuff.
So ...... I decided to pull out the old 'conventional' rack from storage and fire it up with view to perhaps incorporating the AxeFX into it as more an FX unit (with backup possibility to act as both preamp and FX) or just use another rack FX unit I have. I'd hoped to do nothing to it as it worked very well for me back in the day.
All was not good .... so cutting a long story short .... I had to replace the speakers in the cabs then the JMP-1 died
So - sent the JMP-1 off to Marshall for repair and got it back with apparently clean bill of health. The only problem being that they had wiped all my old presets and MIDI mappings etc.
I tried setting up a few new presets but my rig just sounded thin and quiet ........ so I blamed the Mesa 50/50 and dropped the whole rack off to a local amp repair guy. He called me a couple of weeks later and said the Mesa was actually fine (he also added a bias trim pot to it and warmed it up a bit because he reckoned the cold biasing that Mesa use is a load of pants .... not that I asked him to!).
He reckoned it was probably the old Boss FX unit - which I had wired into the JMP-1 loop that was thinning the sound. He bypassed it and sent the JMP-1 direct to the Mesa and rattled his windows.
No problem I suspected that 20 year old Boss unit was probably about to keel over so I already had a G Major 2 to replace it with ..... so basically my old rig has had everything more or less replaced or modified!
But with the G Major in the loop it's still thin sounding ....... I've set up all levels ok etc.
I'm wondering now if there's something up with the FX loop in the JMP-1. I can't remember what my FX level settings were in my old patches - but as I used mod effects like chorus I'd assume I'd have set up each patch to have a effects level of '12' - which should be 'serial' operation - IE all signal goes out of the FX send - no dry signal in parallel.
I tried using just a patch cable between the send and return L on the JMP-1 loop and monitored the signal as I gradually swept through the Effects level dial ...... it was thin tone from 1 though 5 - good strong at 6 - then it thinned out again as I moved to 12 (but I'd have thought 12 should be 'fully serial' and therefore not thin).
Does anyone else's JMP-1 fx loop do this same thing? IE Tone/signal suck at '12' in Effects level? I'm wondering if Marshall missed a problem in there with it when they were servicing it.
I'd rather use the loop in the JMP-1 than sending main outs to the FX unit ..... although I suppose seeing I also have an AxeFX it would maybe serve well in a 4CM setup with the JMP-1 and act as a modeller backup direct to the power amp if required ... although using a quick 4CM set up test it sounded noisy/muffled listening just via the AF2's headphones - I wasn't using 'humbuster' cables though which might make a difference.
Sorry about long post .... but that's the whole history.
Comments
Will that not work for you ?
Having done that I made sure that the G major was set up to be 100% wet (i.e. no dry signal whatsoever). Otherwise, if any of the dry signal gets through the G major there's a (so called pipeline delay) that will mix with the dry signal of the JMP1 and give phase cancellation type effects (which thins the sound).
Unfortunately I no longer have the units so all I can do is try to remember what I did.
Yes ... that would be my current findings ..... at '6' in the FX settings the tone in the loop seems unaltered.
I did try setting the G Major to 'Kill Dry' in the globals when the JMP-1 loop was at '6' .... but while delays and reverb do well in parallel it doesn't sound brilliant with modulated FX as there's still a strong uncontrollable dry signal passing to the main outs at JMP-1 level.
From hunting the net I see there's a mod that can be done on the JMP-1 to turn it's loop into a more conventional serial only one ... a couple of resistors need removed from the loop circuit ...... so seeing as thats reversible without too much hassle if it doesn't help it might be worth trying.
Because there's a dry signal path in the JMP 1 Fx loop (when it's not on maximum), the 100% wet modulation within the G major will mix with that dry signal to still give the modulation effect.
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If you want Marshall to inspect and service the unit you call them at their Bletchley HQ - 01908 375411 and they'll give you a Repair Reference Number - you then send the unit to them with the Ref No clearly visible and they then will get the tech to inspect and they'll contact you with a quote to repair - or to return if you think its too expensive.
Mine had a couple of ICs blown and they also replaced the 2 front input sockets (Instrument in and Headphones) and checked everything else - it was a while ago now - but I think it was around £70 all in.
The Power Transformer is probably the single most expensive part in the JMP-1 - I see them at £223 online http://www.mercurymagnetics.com/pages/catalog/manufacturers/MM_marshall.htm - so if it needs replaced and labour costs added ..... I'd be 'humming' myself on whether to proceed unless it was going to be a keeper. If I wanted shot of it I'd maybe sell it as in need of some repair
The much lauded higher end 'Voodoo' mod replaces the PT with a 'quieter/better' one (but they also build in a noise suppression circuit too because its just a fairly noisy amp by default).
If you think yours is definitely in need of repair and you want to get a quote from Marshall then you just call Marshall (Bletchley Head Office - 01908 375411) and they'll take your details and give you a repair ref number - then you sent the unit to them with the repair ref clearly visible and they'll contact you with a quote for repair or quote for return postage if you decide they are too expensive.
If it is the power transformer then that would probably be the most expensive element to replace in the JMP-1 - I see they are around 225 quid online http://www.mercurymagnetics.com/pages/catalog/manufacturers/MM_marshall.htm ..... so seeing the entire JMP-1 is probably only worth around that used these days it might be only worth paying if it's going to be a keeper for you - otherwise personally I'd probably flog it with the issue clearly stated and let someone else in the know restore it.
Mine had some blown ICs and they charged me £70 all in I think ..... but they did replace the 2 front input sockets (In and Headphones) as well because the washer nut was missing off one of them.
You can then tweak the level controls on the G major to vary the amount of effect on the fly. Sometimes, in a very live room, I'd back off the reverb and delay in that way (although the compromise was that it also reduced the level of modulation when I used that effect).
Just seemed odd that at level '12' the JMP-1 signal from the FX loop send sounded so crap even just using a patch cable between send and return L in the loop. Def some phase issues going on there it seems
I might get the amp repair guy I use to do the 'serial loop' mod by removing and bridging the R167/R169 resistors to see if it does anything interesting. Within the G Major I could still internally configure the parallel route for delays but keep serial for other stuff before returning to the JMP-1 loop and main outs if I wanted.
I'm not sure I'm loving the G Major 2 much ...... I like the look of a Digitech GSP1101 as a 1U replacement option if I can track one down somewhere.
Using the AxeFX would mean upsizing to a bigger rack - a GSP1101 would give me some preamp backup options too if the JMP-1 decided to die at a gig.
But I can recommend the GSP1101, it's really surprisingly good. Especially hooked up in 4CM.
Keep an eye on ebay and weirdly Amazon just sold some off at £130 so maybe keep checking them as well.
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I've replaced the volume pot on my and redone some joints, along with the valves. It's actually pretty easy to work on despite the complexity