Mesa DC5 combo fx loop hum issues

MikeytheG

MikeytheG

Active member
I got a massive hum coming out of my DC5 1x12 combo when I run anything through the fx loop. I tried cleaning it out with de-ox, tried changing the cables, changed the tubes. Even with the noise suppressor its still there.

Im open to any suggestions.
 
MikeytheG said:
I got a massive hum coming out of my DC5 1x12 combo when I run anything through the fx loop. I tried cleaning it out with de-ox, tried changing the cables, changed the tubes. Even with the noise suppressor its still there.

Im open to any suggestions.
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Highly suggest some pure Greek olive oil, some oozo and a pinch of lemon and garlic ..... should get you in the ball park !

Possibly some of them pastries to....
 
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If you just jumper the effects loop with a cable, do you still get the hum? Or do you have to have a pedal or rack effect unit in the loop? What if the pedal is powered on a battery versus a power supply?

Any idea on the frequency of the hum, are we talking 60Hz, 120Hz, white noise?
 
so it happens with any pedal (mutiple or single pedals) tried both PWS and battery powered. even when I jump it, same thing. its a subtle hum but noticeable, not sure what freq. but im guessing 60hz.
 
I have no technical input here. Just popped in to say I used and abused a DC5 combo for many years in my early 20’s. Even though that’s not my sound anymore, I have a fondness for that amp. It was built really well, solid as a tank. Good luck with the issue you’re working on.
 
Do you get the hum if you plug a guitar into the FX return?

Plugging a guitar straight into the FX return can be a way to sort whether a problem is in the preamp section or in the power amp section.

Jumpering it with a cable was a good idea; bummer that that didn't help.
 
Found the schematic. https://el34world.com/charts/Schematics/Files/Mesa_boogie/Boogie_dual_caliber_dc5.pdf

Only difference between jumpering with a cable and just having nothing connected, is that you put the mix pot in the circuit. So it’s perplexing that having anything plugged into the loop causes noise, versus having nothing connected. I am also wondering if the 1uf electrolytic cap right before the loop is bad.

The key to try to figure out is if the noise is coming up stream from the loop or downstream. Taking the send jacks into another amp and comparing this to plugging a guitar into the return jack is a good place to start. When you plug into the return jack, you want to put a cable in the send jack, so that the preamp of the dc5 is disconnected, also make sure you have the loop level maxed in this test.

Also if the graphic Eq effect the hum, that would suggest the noise is coming in before the loop.
 
blackba said:
Found the schematic. https://el34world.com/charts/Schematics/Files/Mesa_boogie/Boogie_dual_caliber_dc5.pdf

Only difference between jumpering with a cable and just having nothing connected, is that you put the mix pot in the circuit. So it’s perplexing that having anything plugged into the loop causes noise, versus having nothing connected. I am also wondering if the 1uf electrolytic cap right before the loop is bad.

The key to try to figure out is if the noise is coming up stream from the loop or downstream. Taking the send jacks into another amp and comparing this to plugging a guitar into the return jack is a good place to start. When you plug into the return jack, you want to put a cable in the send jack, so that the preamp of the dc5 is disconnected, also make sure you have the loop level maxed in this test.

Also if the graphic Eq effect the hum, that would suggest the noise is coming in before the loop.
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So you were right, I used the switch on the back to dis-engage the graphic eq and it went away. so then i started checking each eq fader, and its the 80hz, if i drop it, its lowering the noise. this gives me alot to work with. Thanks man. I appreciate it.
 
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