How Much Noise Should a 50/50 Make?

[CudBucket]

Hey guys. I just received my used 50/50 from an Ebay auction. It's in MINT condition but one of the rack screw holes was bent back in shipping. I plugged it into my Mesa traditional 4x12 with the Studio Pre I just picked up. I really love the tone. I ran one channel at a time to make sure they both were working.

What I noticed is that there was a fairly good amount of hum. I'm talking about the lead channel, volume 7, master 7, lead drive 8 and master volume 3 (on the Studio), with output 4 and presence 3 on the 50/50. You couldn't hear it when I was playing but of course, when I stopped, you could.

My Studio has brand new JJs in it but the 50/50 has Mesa tubes. According to the seller, the amp is 6 years old. He put the tubes in 4 years ago but hadn't used the amp for 3 years.

Do you think it just needs tubes or do you think it could be damage from shipping. Other than the bent ear, the thing is super clean.

Thanks.

Dave

 

[t0aj15]

If it's any help my 50/50 has had that same hum since it was new (out of the box) no matter what tubes are in it.

 

[CudBucket]

Thanks. I think I also read in a recent thread that the 50/50 is a noisier amp than the 20/20.

 

[disassembled]

Yep I can attest to that. The 50/50 is much noisier than the 20/20. I just received my second 20/20 so I will probably be getting rid of the 50/50 now.

If you want to get some more oomph out of the 20/20 there's a mod that's on the yahoo triaxis group that reduces the mid spike on the 20/20 which balances out the tonal spread. I am going to do it to one of my channels on the 20/20 so I can have the option of using either.

The 290 was much quieter than the 50/50 as far as noise goes.


Greg

 

[CudBucket]

Thanks disassembled. If it's normal, I may just get an ISP decimator or something. I really love the tone of the Studio Pre and 50/50 together.

 

[disassembled]

Check the ground lift switch on the back. Mine was bumped accidentally but the band was ready to go so I didn't even take a second to troubleshoot until after we finished.

When I had the ground switch in the "lifted" position it had a nasty ground loop. I would recommend using both pieces out of the rack to eliminate any ground loops due to racking everything together (humfrees rack isolation tabs help prevent this). If you want you can try swapping the three tubes preamp tubes on the inside. Make sure you do a good once over on the inside making sure there aren't any burnt up resistors on any of the boards (mine had two that the seller claimed not to know about). If the power tubes were a problem you would hear noise regardless of the volume settings and if a preamp was connected or not.


Hopefully it's just a ground loop. I hear ya on it sounding good and is probably worth keeping. Good luck.

Greg

 

[CudBucket]

I was running them out of the rack so the ground switch was set to normal. I didn't even think of the pre amp tubes in the 50/50. I'll have to pop the cover and have a look. Are burnt resistors obviously spotted?

 

[disassembled]

I was running them out of the rack so the ground switch was set to normal. I didn't even think of the pre amp tubes in the 50/50. I'll have to pop the cover and have a look. Are burnt resistors obviously spotted?

They were for me since there was a nice black spot around the resistors and they were actually split open.

Sometimes you can't tell until they are tested with a multimeter but if everything is ok after you replace tubes or change the ground switch I wouldn't worry about it.


Change the ground switch to lifted just to try everything.


Greg

 

[CudBucket]

When I changed the ground switch to lifted it immediately made a loud clicking sound so I reversed the switch.

 

[disassembled]

You aren't going to hurt anything by flicking back and forth between lifted and grounded. But if the clicking bothers you that much then you can put the amp on standby. If switching to "lifted" adds noise AFTER the switch is in position then you can be assured it should be set to "normal."

An ISP, or any other noise suppressor, is not going to fix a ground loop. I suggest you get everything working properly before adding more equipment. When I connect my triaxis directly to the 50/50 I have to lift the ground on the 50/50 but now I have the GSP1101 hooked into the 50/50 and I have to use the ground normally.


Greg

 

[CudBucket]

Gotcha. That's assuming what I'm hearing a ground loop and not a loose tube right?

I just read in the manual that Ground Loops can be caused when more than one of rack units(pre, power) are connected to the power source's ground. That in this case, one of the plugs should have it's ground lifted by using a 3 to 2 prong adapter. Both the pre and power amp in this case were connected to the power source's ground so I'm going to try the adapter. Also, while I didn't have the units racked at the time, I did have them sitting on top of each other. I've got a few things to try tonight.

 

[disassembled]

Gotcha. That's assuming what I'm hearing a ground loop and not a loose tube right?

I just read in the manual that Ground Loops can be caused when more than one of rack units(pre, power) are connected to the power source's ground. That in this case, one of the plugs should have it's ground lifted by using a 3 to 2 prong adapter. Both the pre and power amp in this case were connected to the power source's ground so I'm going to try the adapter. Also, while I didn't have the units racked at the time, I did have them sitting on top of each other. I've got a few things to try tonight.

The ground lift does the same thing but is much safer. In reality using the 3 to 2 prong adapter is only for testing and should not be used on a regular basis.

You are right the ground switch only works if the problem is a ground loop and not a bad tube or bad component.

Greg

 

[CudBucket]

Thanks Greg.

 

[CudBucket]

Hey Greg,

I just did a test where I just plugged the 50/50 into my 4x12 cab but no preamp connected to the 50/50. First channel A into the 4x12 and then channel B. With no inputs I can crank the outputs on the 50/50 and get virtually no noise at all. When I add the Studio Pre, with no guitar plugged in, I get the hiss when in the lead channel only. Lead drive at 8. Rhythm channel is super quiet with volume on 8.

Would you say the noise is coming from the pre and not the power amp?

Dave

 

[disassembled]

Yep sounds like the studio pre is making the extra noise. You should also try it with the 20/20 just to rule out the 50/50 being the problem.


Greg

 

[CudBucket]

Yep You should also try it with the 20/20 just to rule out the 50/50 being the problem.

Haha. I would if I had a 20/20. I just got off the phone with a Mesa tech because I had to order a replacement reverb tank for the Studio and we talked about the test I did. He agreed that the noise I'm getting is from the lead channel on the Studio.

I'm going to try changing the V1 and V2 preamp tubes to see if I just have a noisy tube in those slots.

 

[disassembled]

I am sorry I confused you with CoG (Cudbucket....CoG....some days I wonder myself what the hell I am thinking).


You should try moving the tubes around (maybe V4 into V2) to see if you can fix the problem that way.




Doesn't sound like it will be too hard to diagnose.



Greg

 

[FastRedPonyCar]

Dave did you ever get this sorted out?

My pre should show up today. I've got a gig at church right after work so hopefully my wife can bring it when she shows up and I can get a chance to fiddle around with it. I brought my backup case of preamp tubes to use in the studio if she does.

anyways, I was going to see if you got the noise issue fixed yet.

 

[CudBucket]

Drew, you know it's funny. Last night I installed the new reverb tank I got from Mesa. My Studio didn't have the reverb plate in it when I got it. So after I put that in, I put a JJ ECC81 in V5 and ran it through the 50/50 and Mesa 4x12. This was about 11pm last night. And when I did, I didn't hear the same level of noise. Whatever noise I heard was on the lead channel and it was what I think anyone would consider normal for a high gain setting. So right now, I'm not considering it an issue at all.