Noise and feedback

[rickeb1]

I am having a terrible noise problem with my MP-2 setup, and I'm not sure what to do about it.  As detailed in another thread, I initially had some issues with the unit, and sent it off to JMP, who fixed whatever needed fixing and sent it back to me in perfect working order.  This past year, I moved from the Chicago area to Phoenix but kept a home in Illinois as we plan to come back to visit friends and family often.  I wanted to put together a small second rig to use in Illinois for jamming with friends while I'm there, so I wrapped the MP-2 in a lot of bubble wrap, stashed it between clothes in my suitcase, and took it with me when we flew from Phoenix to Chicago this week. 

When I pulled out the MP-2 and hooked it up to a power amp and speakers, I started getting this dreadful noise and feedback from it.  Note that this is only on high-gain settings; clean settings and even voice 5 seem to work ok.  The gate helps some, but on some high-gain settings, there is a huge midrange feedback.  Without the gate on, you can also hear some motorboat oscillating.  Not sure of the frequency of the feedback, but it's more midrange than high-pitched, I'd say it's around C played on the second string, and very full and bassy. 

I thought at first that a tube had gone bad during the travels, so I replaced the tubes, but nothing changed.  Then I thought that maybe the guitar (a Schecter C1 Blackjack that I picked up cheap as a second guitar), which has active pickups, needed a battery replacement, but that didn't help. either.

The odd thing is, sometimes the noise goes away, but then if I move, it starts up.  Also, if I turn the volume of the guitar pickup down a bit, it stops (or the gate covers it).  I started thinking maybe a bad guitar cable, but you'd think I'd hear that on other voicings, not just the high-gain ones.  Or maybe a ground or shielding problem with the guitar, but again, you'd think I'd hear it on other voicings.

I guess I don't want to believe there is an issue with the MP-2, as it was working fine before I transported it from Phoenix to Chicago, and it will likely be the most difficult to fix. :(

Anyway, given all that, does anyone have any thoughts as to what the problem might be and where I should begin in trying to fix it?

~Rick

[MarshallJMP]

Does this happen when nothing is plugged in into the mp-2 (input)?

[rickeb1]

No, with nothing plugged into the MP-2, it is dead quiet, no matter the setting.

[MarshallJMP]

Then i think it's something outside the mp-2,cable maybe?? If it was the mp-2 it would also do it with nothing plugged in.

[rickeb1]

Thank you so much for the quick responses!  That's actually good news, as it narrows things down to things I can more easily address.  I will find a different cable and go from there.  Thank you so much JMP, as always, for your help!

[MarshallJMP]

No problem,keep us updated!!

[rickeb1]

Well, I can rule out a bad cable, I think.  I just went and bought a brand new cable, brought it home, plugged it in, and... exactly the same problem.  :(  The odd thing is, when I get the noise and feedback, if I turn the pickup volume down a bit, it stops.  This happens with either pickup, they both behave the same.  I guess my next step is to take the guitar in to a repair shop and see if there is some issue with the jack or wiring or something.

[rickeb1]

Ok, I did some more research on my guitar and its pickups, Seymour Duncan Blackouts, and found a number of people talking about feedback problems.  I should have thought of this before, but when I turn on a high-gain setting and start getting the feedback, if I hold the pickup between my thumb and forefinger, the feedback stops.  So evidently, the pickup is vibrating enough to cause feedback on high-gain settings even when the power amp is turned down to a near whisper quiet level.  This probably explains why turning down the pickup volume helps, and also why I didn't have this problem initially (I was using a different guitar).

I have read some recommendations to install foam of some kind under the pickup to stop the vibrating, which I will probably look into. I also saw some talk about potting the pickup, but others say you can't or shouldn't do that with these active pickups. 

Any other thoughts anyone may have on this are most welcome!

[rnolan]

Hey Rick, I've never been a fan of active guitar PUs though I know heaver players like EMGs etc for the articulation at high gain and dropped tuning.  Also I've not looked into the internal design of them but conceptually (well a bit) they are a bit like a condenser mic compared to a dynamic mic, so much more sensitive as they include a powered preamp (active).  Thus at high gain more prone to microphonics.
To me this seems like a short coming in the PU preamp circuit design? Potting PUs (dip in wax) is to quieten microphonics in passive PU coils.  Would potting help ?? depends whats inside them.  If holding the case to stop it vibrating helps, then it stands to reason that a layer of wax between whatever is inside and the case should help (if you can do it and it doesn't wreak anything).  The foam idea would absorb some of the case vibration and also help but you shouldn't need to.
I'd look to sell them (unless you like them too much) to someone who uses less gain and put in some nice passive humbuckers (single coil shaped or humbucker shaped) or EMGs if you really want active.
It seems the case vibration is amplified by the PUs (quite sensitive) preamp circuit and sets up oscillations. So not great design (circuit) or not great manufacture.

[El Chiguete]

Try your setup with another guitar that plays great in another rig and see if it stays or not the noise.

[rickeb1]

Richard (and El), thanks for the reply!  I've never been a fan of active pickups, either, but I needed a second guitar to keep at my other house, didn't have a lot of time to get it, and I got a super good deal on this guitar, so I went for it.  I'm going to take it to a local shop today and get an opinion on what it would take to sort it out, and compare it to the cost of replacing the pickups.  I really don't want to put much money into this as it is just a second guitar that I will play very infrequently.  Still, it needs to be playable, so I'll have to do something.

[rnolan]

RG bought some decent PUs and they were really cheap $18 (http://adadepot.com/index.php?topic=1250.0) would be the most cost effective option I recon.

[Systematic Chaos]

The most cost effective option would be to contact the Seymour Duncan customer support, tell them what the problem with the pups is and let them take care of it.
Whenever one of my DiMarzio pickups turned microphonic (happened twice) I contacted their customer support and they repaired/exchanged the malfunctioning pickup at no additional cost (just had to pay for the shipping from me to them).
AFAIK SD has the same policy....

http://www.seymourduncan.com/seymours-knowledge-base?tip_id=31426&tax-slug=noise

http://www.seymourduncan.com/contact-form

[rickeb1]

Well, I've gone round and round with this problem for several weeks, and to make a long story short, I ended up trading in the guitar for a different guitar with passive pickups.  I got a good deal on another Schecter, a C-1 Classic with a Duncan JB in the bridge and a Duncan Jazz in the neck.  Looks nice (although the "Vine of Life" inlay is a little over the top), plays very well and sounds very good.  Totally took care of the feedback issue I was having (although there is still a lot of noise on hi-gain settings without the noise gate).

I tend to believe that the MP-2 is not good at handling too hot of a signal coming from the guitar.  It could have been entirely the pickups, but when the shop I traded the guitar to tested it through a Peavey 5150, it sounded just fine, with no hint of feedback.

In any case, everything is sorted out now.  Thanks for all of your tips and advice!

~Rick

[rnolan]

Hey Rick, good to hear  :thumb-up: . I've not tried active PUs with MP2, I have found turning the vol pots to 2.5 to 3 on the JPLP and the warm vintage voice works very well (first time ever in over 40 years I don't have the vols on 10 LoL). The MP2 has lots of gain, pretty much all the high gain voices (6 to 10) need the noise gate (i.e. any voice that includes OD2 (1 to 5 only have OD1)).