Subway Blues hum problem - when did they sort it out?
- Thread starter Zoner
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carlsoti
Well-known member
Chrissmoth said:
The hum on my clean channel IS really loud. It's so loud that, when NOT playing, it sounds like its set up for really high gain. Oddly enough, when the gain channel is dimed out, it's actually quieter when not being played than the clean channel.
Chrissmoth
Well-known member
There are however different types of loud...
Before the mod with all the controls set to zero I could plainly hear the hum through a closed door & on the floor below.
In the same room it was unbearable!
Bare in mind that the problem only occurred after the amp had been switched on for 40 minutes or so.
I was going to return it until I found this mod.
Thanks Boogiebabies! 8)
Before the mod with all the controls set to zero I could plainly hear the hum through a closed door & on the floor below.
In the same room it was unbearable!
Bare in mind that the problem only occurred after the amp had been switched on for 40 minutes or so.
I was going to return it until I found this mod.
Thanks Boogiebabies! 8)
Thanks to all on this topic for the info. I have one of very first Subway Blues units but put it away several years ago because of the 40 minute+ hum (thermal issue?). Found BoogieBabies' cap mod a few weeks ago while researching how to get unit fixed so I can use it for a rehearsal unit without having to buy another amp (leave it in studio space).
Ordered the part and had a tech friend install the new .68 cap. The photos were a big help. However, left the amp on without a guitar plugged in for a while and after 40-45 minutes the hum returned. We are going to test the amp in a "cold" environment with a fan on the Mojo Modules. My EE/tech says there are often heat issues with potted circuits. He also mentioned that there are solvents that will dissolve the potting/epoxy, but the risk in damaging the encased parts probably does not warrant doing this.
If the COLD test does not work (proves the thermal issue of Mojo module), I guess I'll call the factory and see if I can order the replacement PC board. Has anybody ordered this part, or do you have to send the whole unit back to Mesa to be reworked? I tried calling them on Friday, but they are only open M-Th. Guess I'll try again next week.
The only other solution is to somehow modify the Send/Return circuit (build a new one?). I like the Send/Return feature because I use a modelling box direct into the power amp for some sounds.
Thanks for any further insight into this issue. I always liked the amp for its size and portability.
Steve Schultz
Ordered the part and had a tech friend install the new .68 cap. The photos were a big help. However, left the amp on without a guitar plugged in for a while and after 40-45 minutes the hum returned. We are going to test the amp in a "cold" environment with a fan on the Mojo Modules. My EE/tech says there are often heat issues with potted circuits. He also mentioned that there are solvents that will dissolve the potting/epoxy, but the risk in damaging the encased parts probably does not warrant doing this.
If the COLD test does not work (proves the thermal issue of Mojo module), I guess I'll call the factory and see if I can order the replacement PC board. Has anybody ordered this part, or do you have to send the whole unit back to Mesa to be reworked? I tried calling them on Friday, but they are only open M-Th. Guess I'll try again next week.
The only other solution is to somehow modify the Send/Return circuit (build a new one?). I like the Send/Return feature because I use a modelling box direct into the power amp for some sounds.
Thanks for any further insight into this issue. I always liked the amp for its size and portability.
Steve Schultz
I have the same problem with my Subway Blues amp production #108 with no fat switch (two inputs). Was that a .68K or uF or some other value 250V capacitor.
I also have the dangling wire near pin #9 of what appears to be V1 the first preamp tube. Did anybody find out why the heck this thing is in there? Someone on the ampage web site said it would act as an antenna for RF noise. Wondering if anyone removed it and what it could have been there for?
PS how do you post a photo on here?
I also have the dangling wire near pin #9 of what appears to be V1 the first preamp tube. Did anybody find out why the heck this thing is in there? Someone on the ampage web site said it would act as an antenna for RF noise. Wondering if anyone removed it and what it could have been there for?
PS how do you post a photo on here?
Chrissmoth
Well-known member
The replacement cap is 0.68 microfarads uF make sure you get one that's the same voltage - it doesn't matter if it's higher - just NOT lower
The wire remains a mystery
cvjanick as you have the two input model have you seen this post?
http://forum.grailtone.com/viewtopic.php?f=4&t=30694
Check it out!
The wire remains a mystery
cvjanick as you have the two input model have you seen this post?
http://forum.grailtone.com/viewtopic.php?f=4&t=30694
Check it out!
FYI - Called Mesa Engineering Customer Service and inquired about buying just the Subway Blues replacement main board. The Parts Dept. will sell you the board for $100 so you don't have to ship the chassis back to them and be charged for labor. I was told to specify part # BR.SUB.
I'll let people know how this goes if I decide to order the board and replace it myself.
Steve Schultz
I'll let people know how this goes if I decide to order the board and replace it myself.
Steve Schultz
Just wondering... has anybody tried inserting a new effects loop circuit/board in place of the Mojo module/circuit? I was wondering if you go the route of bypassing the effects loop, couldn't you insert a new buffered effects loop circuit on a daughterboard or something between the connections you cut to do the bypass?
Forgive me if this has been discussed before.
Steve Schultz
Forgive me if this has been discussed before.
Steve Schultz
badboybubby
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Frank at Zone music in Cotati told me when I bought it, that the Black Shadow was a Celestion.....Mesa website says it's an Eminence. Was Frank mistaken? Did any of the Subways come with celestions?
There are a number of places to look.durham85 said:
http://www.digikey.com
http://www.rselectronics.com
http://www.tubesandmore.com
http://www.mouser.com
Chrissmoth
Well-known member
I think it should be ok
It has the Bright / Fat switch
The early ones (like mine) had seperate inputs for Bright / Fat
Easiest way to tell is to switch it on & wait 45 minutes
It has the Bright / Fat switch
The early ones (like mine) had seperate inputs for Bright / Fat
Easiest way to tell is to switch it on & wait 45 minutes
That appears to be an early board due to the potted sections. This is what a later board looks like.Kes said:So would this (bright/fat version) have the mod or not, the guy I am buying from is a bit vague.
The board has a 1994 date stamp.
Chrissmoth
Well-known member
True - the board looks just like mine - however the hum isn't caused by the potting
Just a cap being the wrong value
Just a cap being the wrong value
I just had mine fixed the HUM was unbearable after 30 minutes First changed the pre amp tubes.. that didnt work so I took back then they changed a capsistor and let it cook after 40 minutes it started up all over again So they by passed the MO JO loop Only other option was replacing the entire board The only down side is I wouldnt be able to use my effects loop output in the back which I never used anyway This was done by a Mesa certified shop Cost me 102.00 including cleaning the pots and tubes. Amp was in a closet for about 6 years Im picking it up tomorrow curious to see if it will effect the " gain" on the mid Mine is has a fat & a bright input How can you tell the age of these babies ?
cbkuck
Member
Old blues, new blues...
I finally pulled the chassis out of my SB and had a look. From markings on the circuit board, it seems to be the 1994 model. I see two things done to it (other than the fact that the two input jack setup was changed to a bright/fat switch and a single input jack):
1. The orange wire going to the daughter board that houses the effects loop has been cut. The cut end off of the daughter board is still there. The other end is connected to ...
2. The location of the cap by the "mojo module" is now empty, and the other part of the orange wire that used to go to the effects loop daughter board now goes to the trace where the 0.01 uF cap used to be mounted, on the side away from the mojo module.
So, if I re-install a 0.68uF cap in the location next to the mojo module, and re-connect the two halves of the orange wire, I'll get the hum fix AND get my effects loop restored? That's what I'm looking for, as then I can also use the effects mix pot as a master volume with the "shorted plug" mod.
I also took photos, but I don't have any place to host them (yet)...
I finally pulled the chassis out of my SB and had a look. From markings on the circuit board, it seems to be the 1994 model. I see two things done to it (other than the fact that the two input jack setup was changed to a bright/fat switch and a single input jack):
1. The orange wire going to the daughter board that houses the effects loop has been cut. The cut end off of the daughter board is still there. The other end is connected to ...
2. The location of the cap by the "mojo module" is now empty, and the other part of the orange wire that used to go to the effects loop daughter board now goes to the trace where the 0.01 uF cap used to be mounted, on the side away from the mojo module.
So, if I re-install a 0.68uF cap in the location next to the mojo module, and re-connect the two halves of the orange wire, I'll get the hum fix AND get my effects loop restored? That's what I'm looking for, as then I can also use the effects mix pot as a master volume with the "shorted plug" mod.
I also took photos, but I don't have any place to host them (yet)...
