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Let's Get Technical => Troubleshooting Problems => Topic started by: revhed666 on April 17, 2016, 09:54:20 PM

Title: MP-1 volume drop
Post by: revhed666 on April 17, 2016, 09:54:20 PM
gday guys have had this problem for a bit and its preventing me from gigging my rack setup. random volume drops from the MP-1. i cant reproduce this problem and it seems whenever i try and troubleshoot it, it wont occur so i am yet to determine the MP-1 as the exact cause. i do run it in stereo with a marshall jmp-1 which does not experience the same issue. with no patch changing the MP-1 volume will drop a noticeable amount, sometimes flickering back and forth. sometimes it seems almost a permanent drop and i compensate by upping MP-1 master gain from 2.0 to 3.0 to even things out. it may stay like this for some days or weeks but sooner or later it changes back again and i readjust the patch levels. dont go crazy trying to work this out as i cant be absolutely sure its the MP-1 but i'm hoping u may have a solution. will try different tubes but they are mullards only a few years old and had very little use. cheers and beers
Title: Re: MP-1 volume drop
Post by: Soloist on April 17, 2016, 11:29:46 PM
Hello revhed666,
What else are you running in your rack? I too run an MP1 and JMP1 simultaneously from time to time.
Are you using a mixer? Does it happen just running the MP1 alone?
To make it easier just post your signal path, it may be something other than the MP1.
For example I was running a Gmajor 2 after my pre's. The noise gate setting that worked great for the JMP1 choked out the MP1.
Or it could be an issue with the way you split your signal.
Either way someone here will be able to figure it out.
Title: Re: MP-1 volume drop
Post by: rnolan on April 18, 2016, 02:37:10 AM
Hey mate, how'sitgoin ? (I'm assuming you're a fellow Australia  :wave: ). Hey no worries,we'll help you sort it out. A Soloist said detail your patching (this goes with that at Susan's...) and we'll work through it with you.  I can think of a few possible culprits (input jack (it takes the most wear and tear), output pot, needs a clean) but I need to know more how you plug it together (which will lead no doubt to further questions LoL).

Some basic maintenance though, clean input jack (well all jacks) and pots with some decent contact cleaner (may well fix it), a good thing to do regardless.  At this age it's worth changing out the input jack (well all of them really but that's a bit more ambitious).  Now we can't source them (MP1 input jack) anymore but you can do the input jack mod (changes the back input from line level to inst level) and replaces the front jack.

Cheers R
Title: Re: MP-1 volume drop
Post by: revhed666 on April 18, 2016, 03:44:27 AM
Yeh mate Aussie all the way ;)
Signal path
EMG 81/707》
Behringer rack tuner 》
digitech GSP1101 》
GSP 1101 mono fx loop out split with Y cable 》

LEFT: JMP-1 》DBX stereo 15 band EQ 》STEREO Sonic Crapuliser 》GSP 1101 loop return left 》Gsp 1101 line out left 》 Marshall EL34 100/100 Power amp left

RIGHT: MP-1 》DBX EQ 》Sonic Crapuliser 》 GSP1101 loop return right 》 GSP1101 line out right 》 marshall power amp right

Its a bastard intermittent problem that no amount of cable or jack  jiggling can reproduce. Hopefully its a tube. Obviously i thought the Y cable was a potential trouble spot. I bought every Y cable on ebay and worked my way through them. Of course the cheapest had the most solid connection. The sockets were slightly larger and loose fitting on the more expensive cables go figure.
U guys helped out before when a chip controlling the eq was faulty. I also upgraded the eprom at the same time. Will put tubes in now and try the maintenance tips and see what happens. And report back when i have something...or nothing haha
Title: Re: MP-1 volume drop
Post by: MarshallJMP on April 18, 2016, 08:54:50 AM
Do you have a gain (distortion) or volume loss?
Title: Re: MP-1 volume drop
Post by: revhed666 on April 18, 2016, 04:41:19 PM
Only volume to my ears but there may be a gaim loss masked by the JMP pumping along just fine. IIt happens so infrequently its hard to be exactt. Played for an hour with different tubes. Stripped down to MP-1 and power amp. No issues. Except crappy tone haha. it really needs all the other gear to make this thing work for me. Will keep playing and troubleshooting and see what happens. Thanks forcthe help
Title: Re: MP-1 volume drop
Post by: Soloist on April 18, 2016, 04:52:37 PM
Try swapping sides... JMP1 to the right, MP1 to the left. See if issue persists. I never had any luck with "y" cables.

When the tubes in my Mesa 50/50 power amp started to go I had a volume drop intermittently but I think it was both sides. How old are your tubes in the Marshall power amp?
Title: Re: MP-1 volume drop
Post by: rnolan on April 19, 2016, 12:56:23 AM
Hey mate, well interesting way to patch it so you are combining the JMP1 and the MP1 tones and sending one to left and the other to right.  If MP1 -> poweramp L/R works without issue, the seems maybe a drop in GSP1101 send level into the Y cable. Hey MJMP, could a difference in the JMP1 and MP1 input impedance be an issue ?
Title: Re: MP-1 volume drop
Post by: MarshallJMP on April 19, 2016, 03:50:10 AM
No I don't think so.
Title: Re: MP-1 volume drop
Post by: rnolan on April 19, 2016, 09:14:05 AM
Ok so Y lead should be fine (albeit there will be a bit of a volume drop splitting the signal)
Title: Re: MP-1 volume drop
Post by: Systematic Chaos on April 19, 2016, 09:27:28 AM
Could also be the respective channels of either the DBX EQ or the Sonic Crap thingy.....
Remove both DBX and Crapuliser from your signal chain and run only the GSP1101, JMP1, MP1, Poweramp....see if that cures things.
Add first the DBX, play and check, then the Crapuliser....
Title: Re: MP-1 volume drop
Post by: revhed666 on April 27, 2016, 04:46:34 AM
Cheers for the help guys ive been on the road. I did pull the MP-1 from the rack replaced the tubes with Mullards purchased at the same time. No other cjanges or cleaning as yet. Straight to power amp. Same tone. No volume issues over a few hours of jamming over a few days. but now theres a single loud pop every 15 mins or so.  Reassembled rack setup. No volume issues. Pop still occurring. Curiously to balance the preamps i now have the MP-1 master on 2.5. Before it was either 2.0 or 3.0 depending if the volume drop had occurred or not. Maybe it is just tubes. So i should look at an A/B splitter box to replace the Y cable? Good tips guys thanks
Title: Re: MP-1 volume drop
Post by: rnolan on April 27, 2016, 06:32:54 AM
Mmm, that pop doesn't sound good, may be indicative of the original problem, could be a cap going off ?
Title: Re: MP-1 volume drop
Post by: revhed666 on April 28, 2016, 06:32:42 AM
Stranger and stranger. Full rack setup today. Nothing changed. Loud pop every 15 mins replaced with dull thump every 5 mins. Pulled everything one at a time till it was nothing connected to power amp. Power amp connected to speakers. Still there. Both sides. Ok was gonna get it serviced as the presence knob is dodgy. Soooo at this stage it seems original problem was pre tubes. Saw an A/B box on ebay. Sorry fone wont let me paste the URL. battery only powered the LED for A or B channel indicator. $30. Is this any diferent to a Y cable? If it matters have just moved to an old house. The power box looks literally 100 years old. Does not even have a modern safety cut off switch. Might this cause some anomalies? Just wanna jam jeebus
Title: Re: MP-1 volume drop
Post by: revhed666 on April 28, 2016, 06:35:15 AM
Same thump with old or new speaker cables too. So definitely appears power amp related....maybe ;)
Title: Re: MP-1 volume drop
Post by: Kim on April 28, 2016, 07:11:31 AM
Take it to a friend's house and try it?  That should rule out crap house electric....
Title: Re: MP-1 volume drop
Post by: rnolan on April 28, 2016, 07:37:35 AM
Well it's good your getting worked out/isolated  :thumb-up:
Thump/pop definitely sounds like the power amp, can sometimes just need re-flowing the solder joins around the power supply (though doesn't hurt to re-flow all the joins).  I fixed my B200s (loud crackle in one chan) by re-flowing the whole thing (at MJMPs suggestion  :thumb-up: ) But as Kim says, try it elsewhere to be sure (but I thought you got this pop in other places (rehearsals ??))

Do you have any power filtering ? a good idea if the wiring is very old.

Glad the tubes sorted the vol drop, easy fix

A/B box, so unless you go for something with some electronics in it, the Y cable will do the same thing as the A+B setting an A/B A+B box. If you replace your Y cable with this, you would choose A (say JMP1), or B (MP1) or A+B (JMP1 + MP1). As you go mono into each poweramp channel (JMP1 L and MP1 R), so neither unit in stereo.  Where an A/B box would be handy is if you re-patched it all like a PA with a small mixer. Is there a reason you want the GSP1101 in front ? Seems it's there so you can mix it all together (as I said earlier, interesting patch).
So my suggestion is use 6 or 8 chan desk with at least 2 FX sends so the patch would be:
Guit > A/B A+B box > A > JMP1 > desk ch 1 & 2 (pan L/R) | > mixer out
                                                                                         > FX send 1 & 2 > GSP1101 loop rtn L/R > GSP line outs (or mixer outs) L/R > desk ch 5/6 | >>> mixer out L/R > amp               
                               > B > MP1 > desk ch 3 & 4 (pan L/R) | > mixer out
Turn up FX send 1 on ch 1 & 3 and fx send 2 on ch 2 & 4 (so now FX will be in stereo (don't tun up FX send on ch 5 & 6 or GSP will feedback). And set GSP FXs to full wet (no dry sound)
This then will all be in stereo (and will blow you away with how good it sounds).  You control the overall volume of both preamps and FX via the desk faders.
To slot back in your DBX eq (I'm assuming you only have 1 of these and you use L for JMP1 and R for MP1) and your sonic crapsuliser (does this add any value ??, it will add noise) feed them from the FX sends and rtns on the JMP1 and MP1 so: JMP1 send & MP1 send > DBX > Crapsuliser L JMP1 rtn R > MP1 rtn.
Title: Re: MP-1 volume drop
Post by: revhed666 on May 19, 2016, 03:42:32 AM
Just thought id give a progress report. Original volume issue is gone. So was most likely tubes. Pops and thumps are random and most likely dodgy power. I go into the GSP 1101 first cause im using a distortion pedal model to boost both preamps as theres not quite enough gain in either preamp. The gsp1101 only has a mono FX send but stereo return so FX Are also applied to both preamps while maintaining seperate pres left and right. Sounds crap with pres combined in mono
Title: Re: MP-1 volume drop
Post by: rnolan on May 19, 2016, 06:04:03 AM
Thanks for the update  :thumb-up: Though have a think about my suggestions (hey drive the front of the preamps with the 1101 to get extra distortion but I recon you could patch the rest better (IMHO)
Title: Re: MP-1 volume drop
Post by: Harley Hexxe on May 19, 2016, 05:24:02 PM
That popping sounds like a filter cap going bad. They make weird noises like that when they go.

Harley 8)
Title: Re: MP-1 volume drop
Post by: MarshallJMP on May 20, 2016, 12:59:38 AM
Harley has a point here
Title: Re: MP-1 volume drop
Post by: Harley Hexxe on May 20, 2016, 08:24:13 AM
That sounds similar to what I was getting out of one of my B200S poweramps. It would start as a low hiss, and increase the volume a bit then *POP* and then make some very low frequency thumps, and start over.

  I could be wrong, but the description sound like the amp filter caps to me.

    Harley 8)