Mesa Boogie Amp Diagnosis - Help?

6th Stringer

Strat-Talk Member
Jan 30, 2014
56
Rogers AR
The Amp : Mesa Boogie Subway Rocket Reverb 20 watt Combo

The Problem : The amp makes a static - like rustling and popping sound when it is first turned on (after several minutes of warm up on standby). The best way to describe it is like the sound is being played on a dirty vinyl record. Sometimes there is a volume variation as though it is going through a tremolo effectl. After the amp has been on about 10 minutes or so, it goes away.

The sound started a while after I got the amp. I replaced all 4 of the 12AX7 pre-amp tubes with 4 new Electro-Harmonix tubes and that didn't fix it. Yesterday, I replaced the 2 EL84s with new JJ's tubes and that didn't fix it. What else could be the cause of such a noise? Our local music store wants $50 just to check it out. It would be great if anyone can help me narrow the problem down. If it is something I could fix myself, then, that's even better. Thanks!
 

Stevem

Senior Stratmaster
Sep 3, 2014
1,497
NY
X2 with the above!
To help your tech out your can narrow down which preamp gain stage / circuit it's coming from by removing the preamp tubes one at a time and then turning the amp on and listening.
Start with the preamp tube closest to the input jack and work your way towards the one near the output tubes.

These amps have the output tube sockets soldered right to the circuit board which is a very bad way to build a amp since with enough play time the heat takes its toll on the socket to board connections.

When I get one of these amps in for repair I always use some wire to jump from the socket pin way back onto the circuit board trace and then if does not matter if the original solder connections go bad.

If I recall right there is also a resistor that tends to burn up some when these connections on the output tubes get flaky.

While the tech is in there he may find some power supply filters showing there age, and those should get replaced also.
 

Uncle Jimmy

Senior Stratmaster
Aug 22, 2011
1,748
Connecticut
Just in case the above is not it: Get some de-oxit spray the jack inputs and repeatedly put the jack in and out. Do the same for the speaker jack. If you get a little corrosion on those connections, you can hear all sorts of what you're hearing: snap crackle pop, volume drops and surges, etc.
 

6th Stringer

Strat-Talk Member
Jan 30, 2014
56
Rogers AR
Try to find a certified Mesa Tech. The website has a list based on where you live. It is well worth it.
Bummer. The closest authorized dealer / repair shop is over 100 miles away. That is probably out of the question. I called our local shops. One shop has $50 bench fee + ? and they outsource it to someone who is not on site, so I couldn't ask them any questions. I don't like that. Another shop wants a $95 bench fee + ?. That's a lot. The last shop said they would charge like $30/hr plus a couple dollars for the resistors. I will probably give them a try.
 

Tremdaddy

Strat-Talker
Sep 18, 2020
153
North Hollywood, California
Stevem's on it. Those cheaper Mesa amps with the tube sockets wired to the PCB circuit board have a lot of cheap components, kinda like the Fender Hot Rod Deluxes. Any number of things can go wrong, you need a qualified amp tech to fix it. You'll likely have to spend some money but if you don't you'll be left with a 20 watt paper weight.
 

Guitar Hobbyist

Strat-Talk Member
Oct 25, 2021
78
Virginia
Try replacing the first preamp tube with a 5751 that has a lower gain stage than a 12AX7. A 12AT7 is another option. Likely your amp has cascading gain similar to my Studio 22+. Twist the knobs back and forth as was suggested or use contact cleaner on all the pots. My mid control is the leading dust catcher in my amp.
 

demilieu

Strat-Talk Member
Mar 5, 2012
48
houston
The Amp : Mesa Boogie Subway Rocket Reverb 20 watt Combo

The Problem : The amp makes a static - like rustling and popping sound when it is first turned on (after several minutes of warm up on standby). The best way to describe it is like the sound is being played on a dirty vinyl record. Sometimes there is a volume variation as though it is going through a tremolo effectl. After the amp has been on about 10 minutes or so, it goes away.

The sound started a while after I got the amp. I replaced all 4 of the 12AX7 pre-amp tubes with 4 new Electro-Harmonix tubes and that didn't fix it. Yesterday, I replaced the 2 EL84s with new JJ's tubes and that didn't fix it. What else could be the cause of such a noise? Our local music store wants $50 just to check it out. It would be great if anyone can help me narrow the problem down. If it is something I could fix myself, then, that's even better. Thanks!
with all the tubes changed the options are limited. without opening it up you can try contact cleaner in the tube sockets. after that it has to be opened up and diagnosed, perhaps with the power on. what you describe can be anything from a resistor going bad to a cold or cracked solder joint. it can't be diagnosed without going inside.
 
Last edited:

s5tuart

Perfecting time travel since 2525
Aug 8, 2011
16,298
All over the place!
Just in case the above is not it: Get some de-oxit spray the jack inputs and repeatedly put the jack in and out. Do the same for the speaker jack. If you get a little corrosion on those connections, you can hear all sorts of what you're hearing: snap crackle pop, volume drops and surges, etc.
This worked on my Studio 22+ And my MK 3 :thumb:
 

demilieu

Strat-Talk Member
Mar 5, 2012
48
houston
Try replacing the first preamp tube with a 5751 that has a lower gain stage than a 12AX7. A 12AT7 is another option. Likely your amp has cascading gain similar to my Studio 22+. Twist the knobs back and forth as was suggested or use contact cleaner on all the pots. My mid control is the leading dust catcher in my amp.
at7 is not for gain stage it's a phase inverter. for a low output pre amp tube the correct one to use is an ay7.
 

JimmyDee

Strat-Talk Member
Nov 5, 2019
35
haligonia
This worked on my Studio 22+ And my MK 3 :thumb:
Different amp but this also worked on my old Classic 30. It was a noisy amp anyway but I was getting worried from all the popping and such when the amp was idle. It definitely helped.

+1 on doing the pots and the jacks too.
 

Stevem

Senior Stratmaster
Sep 3, 2014
1,497
NY
Changing out a preamp tube to a lower gain type when you have bacon frying and popping sounds taking place is not the cure, it’s a very small and waste of time band aid!
 

Strat it up

Strat-Talk Member
May 10, 2018
56
Greece
The Amp : Mesa Boogie Subway Rocket Reverb 20 watt Combo

The Problem : The amp makes a static - like rustling and popping sound when it is first turned on (after several minutes of warm up on standby). The best way to describe it is like the sound is being played on a dirty vinyl record. Sometimes there is a volume variation as though it is going through a tremolo effectl. After the amp has been on about 10 minutes or so, it goes away.

The sound started a while after I got the amp. I replaced all 4 of the 12AX7 pre-amp tubes with 4 new Electro-Harmonix tubes and that didn't fix it. Yesterday, I replaced the 2 EL84s with new JJ's tubes and that didn't fix it. What else could be the cause of such a noise? Our local music store wants $50 just to check it out. It would be great if anyone can help me narrow the problem down. If it is something I could fix myself, then, that's even better. Thanks!
Sounds like resistors. They are probably fried. Go to a tech to check them out and replace these who don’t function as they should.
 

stevierayfan91

DEEPLY SHY.
Feb 20, 2011
12,236
Private.
The Amp : Mesa Boogie Subway Rocket Reverb 20 watt Combo

The Problem : The amp makes a static - like rustling and popping sound when it is first turned on (after several minutes of warm up on standby). The best way to describe it is like the sound is being played on a dirty vinyl record. Sometimes there is a volume variation as though it is going through a tremolo effect.


Bummer. The closest authorized dealer / repair shop is over 100 miles away. That is probably out of the question. I called our local shops. One shop has $50 bench fee + ? and they outsource it to someone who is not on site, so I couldn't ask them any questions. I don't like that. Another shop wants a $95 bench fee + ?. That's a lot. The last shop said they would charge like $30/hr plus a couple dollars for the resistors. I will probably give them a try.


Hi, @6th Stringer

If it was me , I would be willing to pay a bit more if the amp tech was really skilled and since there is a lot of tricky things it could be.
 

6th Stringer

Strat-Talk Member
Jan 30, 2014
56
Rogers AR
So - at this point ,after I had changed the power tubes, the amp has not made the crackling sound the last several times I have turned it on and played for around 30 min or so. It was making the noise the first time I turned it on after changing the tubes. That's when I made the post. But, luckily, the last few times I have turned it on - no noise! It totally sounded like failing resistors. Hoping it does not return.

I would still like to have the amp serviced at some point. Psionic Audio on Youtube said that the reason a lot of Mesa amps fail is because some of the components barely meet or exceed the required tolerances and they burn out. When he fixes them, he replaces the parts with higher tolerance ones to prevent the same problems. I wonder if Mesa factory service techs would do the same or use the cheapest parts possible?
 


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