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Post by guitargeorge on Feb 10, 2006 6:58:33 GMT -7
My MAZ i8 Jr 2/10 was making strange noises when I unplugged the guitar from the input and strange overtones on certain notes as I previously posted in another thread. I took it apart and tightened everything and cleaned the pots and the switching jack on the input. I installed new tubes and it sounds punchy and louder, the input noise went away but I still have this strange overtone thing happening. When I bend the B string at and around the 12th fret I get a buzzing in the background with a low note overtone. It's not my speakers because I tried another speaker and it does it also. It is also present on some lower notes but it is most intense around the B on the 2nd string at fret 12. I also tried another guitar and it still does it. What in the amp circuit would cause this? I checked all the forums and pretty much checked everything as to causes and quick fixes for buzzing, rattling, etc. I thought I had it when I found my speaker mounting screws were loose but the noise is not mechanical, it's an electrical thing.Other than that, the amp is not noisy when not playing other than a little hiss when all the controls are pegged. I have: V1: Fender 7025 V2: Fender 7025 V3: Fender/Electro Harmonics 12AT7 V4: Sovtek 12AX7LPS V5: Sovtek 12AX7LPS power tubes are a matched set from Bob at eurotubes JJ EL84's. I had a Top Hat Club Royale and it had some strange overtones that would occur on certain notes and I know AC30's also exhibit this overtone thing but is this normal on a class A cathode biased amp like the MAZ? Your help would greatly be appreciated.
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Post by guitargeorge on Feb 10, 2006 16:31:06 GMT -7
Well I went round two with the maz, checking for loose solder joints and making sure no obvious stuff was wrong, I took the amp out and set the chassis on top of the cabinet and started playing. the overtone thing was there and it sounded like a mechanical vibration that was transformed into a corruption in the signal. I put a brand new Sylvania 5U4GB in the rectifier and it still made the overtone then......I put an old Tung Sol 5U4GB that I found in a TV set at my buddy's junkyard and guess what.....No noise, I play the note on the 2nd string at the 12th fret and it's clear as a bell and overall the amp sounds snappier. I think I solved the problem, I'll keep you posted.
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Post by guitargeorge on Feb 10, 2006 16:52:38 GMT -7
Back to square one, I put the chassis back in the amp and it is still happening. Anybody have any suggestions. It does seem like it's doing it a little less, before it was making the overtone on notes close to 2nd string-12th fret also now it seems to have a little less effect.
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Post by Strato on Feb 10, 2006 16:54:08 GMT -7
DUDE i totally have the same problem with my Maz jr NR and 2 12 cab. When i play my E and B string together around the twelth fret, i get this horrible low overtone... When i move up on the B string, the overtone gets lower and lower... It seems to help if i put the master all the way up and use the volume only...
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Post by myles on Feb 10, 2006 18:33:08 GMT -7
Tap the two output tubes .... this sounds a lot like a microphonic output tube and I have seen bad phase inverters as well.
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Post by guitargeorge on Feb 10, 2006 19:22:54 GMT -7
I spoke to the guy that repairs my guitars and he works on amps too. He said "they don"t make good EL 84's anymore, I can relate to that because every set I get they rattle within a week, but this isnt a microphonic tube, I had the chassis out of the amp and tapped all the tubes with a chopstick and I did'nt detect any microphonic tubes. The overtone thing seemed to go away when I switched out the rectifier tube but with the chassis back in the amp and the overtone is still there. I hooked the amp up to a different speaker and that did'nt help, the only other thing maybe a bad filter cap? The amp otherwise is loud and punchy and sounds great, its quiet when idling, it's just that b to c# bend .
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Post by guitargeorge on Feb 10, 2006 19:33:48 GMT -7
A little history here. This may help. I had the MAZ since around 1997 when I bought it from the other guitarist in my band, It was one of the early ones with the reverb ground hum and I fixed it by isolating the one reverb RCA plug from the chassis and regrounding it on the turret board. I never really noticed overtones on this amp before and also none after I fixed the reverb hum. It has only been in the last year or so that this problem has surfaced and I had it retubed with all JJ's from Bob at eurotubes, I had problems with so called matched sets that werent closely matched and the Maz will let you know if your power tubes are mismatched, it's very particular on tube matching, I always get good matching EL84's from Bob that don't hum.
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gstan
Full Member
What, me worry?
Posts: 180
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Post by gstan on Feb 10, 2006 20:28:47 GMT -7
make sure the pots are snugged tight to the chassis.
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Post by Strato on Feb 10, 2006 23:10:02 GMT -7
Id hope the pots are tight, i just got my amp brand new barely a week ago. This overtone is quite annoying. Im curious... If you have a maz Jr, plug straight in on a clean or dirty setting.(max guitar vloume) and play these notes...
e----12----12----12----12 b----12----13----14----15
Not only can i hear a really obnoxious low overtone, I can hear the overtone acctually getting lower and lower as I increase the fret increment on the B string by 1. I have 2 Strats and a 335, it does this will all of them.
Where would you recommend getting a good matched pair of EL84s from? Any suggestions would be great because right now I have $2000 head and cab that i cant really use.
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Post by guitargeorge on Feb 13, 2006 8:39:38 GMT -7
I got a tip from a repair guy on another board that the cap in the conjunctive filter may have been under sized and are prone to failure, anybody know which cap that may be?
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Post by bluzsteel on Feb 13, 2006 9:53:27 GMT -7
tighten the top 4 chassis bolts , you might be surprised. if they are loose you get all kind of wierd sounds
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Post by guitargeorge on Feb 13, 2006 10:13:35 GMT -7
I had it apart 4 times over the weekend and I can assure that the pots are snug, all bolts were tightened and all connections are right, I also sprayed my pots with de-oxit, it still produces the overtone.
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Post by guitargeorge on Feb 14, 2006 10:35:36 GMT -7
I just e-mailed Mike Zaite about the problem, see what he says, This is a great amp I sure hope I can get it back up to snuff.
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