Thor Posted March 12, 2017 Share Posted March 12, 2017 (edited) Hi All, This is a bit of a weird one but I'm hoping somebody out there may be able to shed some light on a query I have with my DB750, so I recently got a Barefaced Big Twin 2 Gen 3 cab and when I tried out the amp/cab combination I was getting a horrific noise that initially made me think that the horn on the cab was faulty. I tried attenuating the horn and this did seem to ease the symptom, although I did think I could still hear it. I asked our singer to lift the amp/tuner off the cab and by doing so the noise definitely disappeared. This got me to thinking that something was loose in my rack, having checked, everything was found to be secure. The thing is I have heard a rattling noise coming from the rack when setting it down on the floor, so I've taken the rack apart and the top off the amp to try and identify what's going on - I've found out that inside the amp there's a row of resistors marked on the board as R103 - R108 and R109 - R114 that have some kind of insulator sleeve at one end of the soldered joint and it's these little insulators (or whatever they are) loose and moving back and forth slightly. So I don't really think there's a fault as such just a certain frequency (fretted D at the fifth fret of A string) that sets them off buzzing and rattling. I guess what I'm after is whether anyone else has experienced anything similar and whether I need to try and isolate the rack from the cab? Kinda like a gramma pad I guess? The frustrating thing is I really like the HF horn cranked to the max but by doing so I just get this terrible rattling noise that spoils the cab. I have take photos of the offending parts but the last time I used Photobucket it seemed to corrupt my phone, so if anyone can suggest another image hosting software that is easy to use on mobile that'd be helpful too👍 Here's hoping that someone may be able to help😊 Edited March 12, 2017 by Thor Quote Link to comment Share on other sites More sharing options...
Bridgehouse Posted March 12, 2017 Share Posted March 12, 2017 Imgur is great for hosting - and very easy - web based if you need. Quote Link to comment Share on other sites More sharing options...
Thor Posted March 12, 2017 Author Share Posted March 12, 2017 (edited) Cheers I'll check it out😊 https://i.imgur.com/d2jtOfa.jpg https://i.imgur.com/tE97Jca.jpg Edited March 12, 2017 by Thor Quote Link to comment Share on other sites More sharing options...
Thor Posted March 12, 2017 Author Share Posted March 12, 2017 Hopefully have added links to pics. Quote Link to comment Share on other sites More sharing options...
Dood Posted March 13, 2017 Share Posted March 13, 2017 If those sleeves are the cause of the issue, you could use a hot glue gun to fix them in place. (It would be wise to run it by a tech if you are unsure where to put the glue). I have to say though, It's unusual for these to cause noise unless one of the components nearby has a dry joint or is faulty. The first place I'd actually go look is at the valves in case they need reseating or one or more has gone microphonic, often the cause of vibration noise being amplified. There are three 12AX7 and one 12AU7 (ECC83, ECC82 for us in the UK). Check those by gently tapping them with a pencil whilst all is plugged in and turned up. Again, there are very high voltages running around inside the amp so if you are not happy with doing this, run it by a tech Quote Link to comment Share on other sites More sharing options...
Thor Posted March 13, 2017 Author Share Posted March 13, 2017 Thank you for the comprehensive reply - it is appreciated 😊 The weird thing about those little sleeves is that I've heard them rattling like that for probably around a year - I've never experienced any abnormal noises through my 412 or the Super 12T that immediately preceded the Big Twin - I think I need to use my back up MarkBass F1 and try it at gig volume just to make sure there's definitely nothing wrong with the cab - I've got myself doubting whether the cab sounded correct when the singer picked the amp up. I know the valves were replaced around about 2 1/2 years ago, I tend to do around 40 gigs per year - what would normal life expectancy be of the valves please? Thanks again. Pete Quote Link to comment Share on other sites More sharing options...
bertbass Posted March 13, 2017 Share Posted March 13, 2017 Life of preamp valves is years. Quote Link to comment Share on other sites More sharing options...
alexclaber Posted March 13, 2017 Share Posted March 13, 2017 It sounds like something in the amp has gone microphonic (i.e when it vibrates it generates electrical noise). The BT2 has very high accuracy sound reproduction so it'll show up any faults like that which other cabs may hide. Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted March 13, 2017 Share Posted March 13, 2017 Ceramic capacitors can also display microphonic behaviour in some circumstances, and that's what those little brown jobs in between the resistors are. If the cab seems fine with another amp or when the amp isn't on top of it, it would probably be wise to have the amp looked over. Quote Link to comment Share on other sites More sharing options...
petergales Posted March 13, 2017 Share Posted March 13, 2017 I always use Isoblok blocks to isolate the amp from those vibrations coming from the cab. I bought a couple from Bassgear after I could hear the valves rattling in my amp when it was sat on top of a BF cab. That did the trick for not a lot of money. Quote Link to comment Share on other sites More sharing options...
stevie Posted March 13, 2017 Share Posted March 13, 2017 This is an odd one. If the noise stops when you lift the amp up from the cabinet that would indicate that the cab is vibrating and passing the vibrations through to the amp. What is odd is that it gets better when you reduce the output from the horn, because a tweeter should not really be able to drive the cabinet panels into vibration. If the ceramic insulators are vibrating, they are vibrating, and there's no reason to suspect microphony. You should be able to locate the problem frequencies by playing sine test tones through your system. There are plenty of free ones available on the internet. That should help you locate the cause of the problem and fix it. Quote Link to comment Share on other sites More sharing options...
Dood Posted March 13, 2017 Share Posted March 13, 2017 [quote name='bertbass' timestamp='1489402362' post='3256547'] Life of preamp valves is years. [/quote] Yet like lightbulbs they can yield a surprise end of life sooner than you'd hope lol Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted March 13, 2017 Share Posted March 13, 2017 (edited) [quote name='Beer of the Bass' timestamp='1489411528' post='3256650'] Ceramic capacitors can also display microphonic behaviour in some circumstances, and that's what those little brown jobs in between the resistors are. If the cab seems fine with another amp or when the amp isn't on top of it, it would probably be wise to have the amp looked over. [/quote]That's true when the capacitors are in the signal path but if they are used for decoupling or HF bypassing they should be OK. Edited March 13, 2017 by Chienmortbb Quote Link to comment Share on other sites More sharing options...
Mickb1773 Posted March 19, 2017 Share Posted March 19, 2017 Hi Had similar issue with intermittent loss of volume and buzzing on certain notes . Initially thought it was valves as when connected using the slave output thus bypassing the preamp issue went away ..on second attempt to fix turned out 2 resistors went bad..problem solved All the best Mick. Quote Link to comment Share on other sites More sharing options...
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