Amp hum help

[roadifier]

Hello Rig-talk, I have just recently started putting my main rack together and I have run into a hum, which I thought was a ground loop and spent all day trying to get rid of it, but no luck. I tried Hum frees to isolate it from the rack, hum eliminator boxes, 2 prong plugs (my dad got a shock from touching the chassis of the amp and the rack case), nothing got rid of this hum/buzz (I don't exactly know what to call it). The amp I am using is a .50 caliber + in a rack mount chassis. The interesting thing is, the amp still hums/buzz's when it is out of the rack, nothing in the loop, and plugged straight into the wall outlet. The amp also hums/buzz's a lot when the guitar is plugged straight in, but It also still hums/buzz's when no guitar is plugged straight into the front. When a guitar is plugged straight into the amp, it hum/buzz's a lot, but this noise doesn't change much weather it is on the clean channel or the lead channel. When turning the gain knob up and and the volume up on either channel it still hum/buzz's a lot. When there is no guitar plugged into the amp, there is still the same hum/buzz but only if you turn the master up. I have tried different tubes in all the positions, and no change. Any help is appreciated!

 

[glpg80]

take it to a qualified tech, and tell them exactly what you describe here as you have done a great job in isolating the source. at this point it is time to isolate the layout and design of the power supply section and switching control circuitry of your amplifier - completely over your head and way too complex or explicit to do over a v bulletin forum. you're talking about fixing something which requires troubleshooting experience and more than just some knowledge of electronics to fix.

sorry but at this point its equivalent of a heart murmor and wanting surgery how-to's over a cell phone. its just not going to happen. good luck

 

[steve_k]

any ceiling fans with a variable speed control or lighting in the room with a rheostat?

 

[roadifier]

any ceiling fans with a variable speed control or lighting in the room with a rheostat?

Yeah, it is on the same circuit as the plug my amp is using, but I turned off the main switch to my fan and it didn't make a difference.

 

[glpg80]

any ceiling fans with a variable speed control or lighting in the room with a rheostat?

you could try a different outlet in your house running off a different circuit breaker, as it would not hurt anything, but i am 99.99% it will still be there.

to the OP - one question you have not mentioned, does the hum seem like a deep rumble of 60Hz or is it higher pitch 120Hz? does the hum increase with the increase of volume or stay constant? definitely answer these and offer them to the tech.

 

[roadifier]

any ceiling fans with a variable speed control or lighting in the room with a rheostat?

you could try a different outlet in your house running off a different circuit breaker, as it would not hurt anything, but i am 99.99% it will still be there.

to the OP - one question you have not mentioned, does the hum seem like a deep rumble of 60Hz or is it higher pitch 120Hz? does the hum increase with the increase of volume or stay constant? definitely answer these and offer them to the tech.

It is higher pitched than the deep rumble of 60HZ. I had that 60HZ hum when some caps went bad in one of my preamps. the hum does increase with the increase of volume.

 

[glpg80]

any ceiling fans with a variable speed control or lighting in the room with a rheostat?

you could try a different outlet in your house running off a different circuit breaker, as it would not hurt anything, but i am 99.99% it will still be there.

to the OP - one question you have not mentioned, does the hum seem like a deep rumble of 60Hz or is it higher pitch 120Hz? does the hum increase with the increase of volume or stay constant? definitely answer these and offer them to the tech.

It is higher pitched than the deep rumble of 60HZ. I had that 60HZ hum when some caps went bad in one of my preamps. the hum does increase with the increase of volume.

then its isolated to the guitar preamp and not the power amp/valves. who did the recap? did they recap all including filter caps or just the rectifier bank? sounds to me like its a shorted/bad filter capacitor in the preamp bank. without knowing the history of the amplifier further and having it on my bench, thats all that i can speculate. again, i cannot stress the importance of taking it to a qualified technician at this point, especially if someone else has been inside of there.

 

[steve_k]

man, it could be anything from a loose input connection to a bad power tube to an output transformer. i don't know anything about the 50 caliber, but i assume it is self-biasing like the other mesa stuff? if this were a marshall circuit, i would be looking at the power tubes or the tube sockets, a severely under-biased output or an open resistor. in your case though, you mentioned a two prong plug and your dad getting a shock. all the old mesa marks had ground lifts on them. that seems impossible without a ground to lift. has the amp been messed with? something is going to ground that shouldn't be, if you are getting a shock. open it up and get some chop sticks and poke around with it powered up.

steve

 

[roadifier]

any ceiling fans with a variable speed control or lighting in the room with a rheostat?

you could try a different outlet in your house running off a different circuit breaker, as it would not hurt anything, but i am 99.99% it will still be there.

to the OP - one question you have not mentioned, does the hum seem like a deep rumble of 60Hz or is it higher pitch 120Hz? does the hum increase with the increase of volume or stay constant? definitely answer these and offer them to the tech.

It is higher pitched than the deep rumble of 60HZ. I had that 60HZ hum when some caps went bad in one of my preamps. the hum does increase with the increase of volume.

then its isolated to the guitar preamp and not the power amp/valves. who did the recap? did they recap all including filter caps or just the rectifier bank? sounds to me like its a shorted/bad filter capacitor in the preamp bank..

No one recapped it. It is about 20 years old and no recap I think it may be time for one.

 

[glpg80]

any ceiling fans with a variable speed control or lighting in the room with a rheostat?

you could try a different outlet in your house running off a different circuit breaker, as it would not hurt anything, but i am 99.99% it will still be there.

to the OP - one question you have not mentioned, does the hum seem like a deep rumble of 60Hz or is it higher pitch 120Hz? does the hum increase with the increase of volume or stay constant? definitely answer these and offer them to the tech.

It is higher pitched than the deep rumble of 60HZ. I had that 60HZ hum when some caps went bad in one of my preamps. the hum does increase with the increase of volume.

then its isolated to the guitar preamp and not the power amp/valves. who did the recap? did they recap all including filter caps or just the rectifier bank? sounds to me like its a shorted/bad filter capacitor in the preamp bank..

No one recapped it. It is about 20 years old and no recap I think it may be time for one.

recap that bitch and im 99% sure that will clear your ground hum follies, thats exactly what it sounds like to me - bad rectifier/smoothing/filter capacitors

 

[roadifier]

man, it could be anything from a loose input connection to a bad power tube to an output transformer. i don't know anything about the 50 caliber, but i assume it is self-biasing like the other mesa stuff? if this were a marshall circuit, i would be looking at the power tubes or the tube sockets, a severely under-biased output or an open resistor. in your case though, you mentioned a two prong plug and your dad getting a shock. all the old mesa marks had ground lifts on them. that seems impossible without a ground to lift. has the amp been messed with? something is going to ground that shouldn't be, if you are getting a shock. open it up and get some chop sticks and poke around with it powered up.

steve

The 50 caliber is self biasing, I have tried different power tubes and no luck. The ground switch on the amp did nothing so I tried a adapter that lifts the ground to see if it helped, and it didn't. I don't know of anything was messed with in the amp. I bought it from guitar center, so anything could have happened. this recently started happening when I was building my rack a month ago, before then it didn't have this buzz.

 

[glpg80]

man, it could be anything from a loose input connection to a bad power tube to an output transformer. i don't know anything about the 50 caliber, but i assume it is self-biasing like the other mesa stuff? if this were a marshall circuit, i would be looking at the power tubes or the tube sockets, a severely under-biased output or an open resistor. in your case though, you mentioned a two prong plug and your dad getting a shock. all the old mesa marks had ground lifts on them. that seems impossible without a ground to lift. has the amp been messed with? something is going to ground that shouldn't be, if you are getting a shock. open it up and get some chop sticks and poke around with it powered up.

steve

The 50 caliber is self biasing, I have tried different power tubes and no luck. The ground switch on the amp did nothing so I tried a adapter that lifts the ground to see if it helped, and it didn't. I don't know of anything was messed with in the amp. I bought it from guitar center, so anything could have happened. this recently started happening when I was building my rack a month ago, before then it didn't have this buzz.

you will still need to take the amplifier to a qualified tech to get the cap job and also a good bill of health. provide them with all of the information mentioned here before hand and also with the answers to the questions i have provided. also tell them you want a recap of the power supply and preamp smoothing/filter capacitors first and foremost. get a price quote from them too, as techs have variances in pricing for cap jobs alone.

 

[roadifier]

I'm going to have my dad re cap it. He has recapped another one of my.50 caliber +'s and it turned out well, but that one didn't have buzz to begin with, it was just old.

 

[steve_k]

sounds like a better plan. since i have no amp techs over here, i got to do it the old fashioned way........with chop sticks and a DMM

 

[roadifier]

sounds like a better plan. since i have no amp techs over here, i got to do it the old fashioned way........with chop sticks and a DMM

 

[mrkmas]

Roadifier, Looking at the manual online, it reads that a rear panel feature is the ground switch.
"GROUND This switch is often helpful in reducing buzzes which originate in the AC power wiring outside
the amplifier. Leave the switch in its center OFF position unless position A or B definitely helps. This
usually occurs only when the ground pin on the AC plug is being defeated via a ground-lift adapter at the
wall socket. In the center OFF position your Boogie cannot be the source of annoying "ground shocks" to
the microphones, etc."

Is it possible you accidentally hit this switch?

Also, never try an amp with only a 2 prong outlet unless it came with a 2 prong plug. Never use a 3prong female to 2 prong male adapter as nothing good will come of it.

One thing you can try is using the preamp and poweramp seperately from each other if you have another amp lying around to help narrow down which part of the amp is causing the problem. Do this by running the preamp of one amp into the poweramp of another and vice versa and see if either of the 2 combinations causes the hum to go away.

As mentioned by many other posts, power source does play a role, however is the outlet you are trying to use now the same outlet you always used? If not use the original outlet again and see if it goes away.

Just basic suggestions, hope it helps.

If I had to put money on it though, I would say its a bad cap somewhere in the amp. are you comfortable opening the amp for a visual inspection? Bad caps are usually easy to see depending upon how they are mounted in the amp.

 

[roadifier]

Roadifier, Looking at the manual online, it reads that a rear panel feature is the ground switch.
"GROUND This switch is often helpful in reducing buzzes which originate in the AC power wiring outside
the amplifier. Leave the switch in its center OFF position unless position A or B definitely helps. This
usually occurs only when the ground pin on the AC plug is being defeated via a ground-lift adapter at the
wall socket. In the center OFF position your Boogie cannot be the source of annoying "ground shocks" to
the microphones, etc."

Is it possible you accidentally hit this switch?

Also, never try an amp with only a 2 prong outlet unless it came with a 2 prong plug. Never use a 3prong female to 2 prong male adapter as nothing good will come of it.

One thing you can try is using the preamp and poweramp seperately from each other if you have another amp lying around to help narrow down which part of the amp is causing the problem. Do this by running the preamp of one amp into the poweramp of another and vice versa and see if either of the 2 combinations causes the hum to go away.

As mentioned by many other posts, power source does play a role, however is the outlet you are trying to use now the same outlet you always used? If not use the original outlet again and see if it goes away.

Just basic suggestions, hope it helps.

If I had to put money on it though, I would say its a bad cap somewhere in the amp. are you comfortable opening the amp for a visual inspection? Bad caps are usually easy to see depending upon how they are mounted in the amp.

Thank you for reminding me! Just a few days ago I was using my recto preamp into the return of the 50 caliber and there was no hum. so it narrows it down to the preamp section. I will plug the send of the 50 cal into another amps power section to see if there is hum.

 

[mrkmas]

Thank you for reminding me! Just a few days ago I was using my recto preamp into the return of the 50 caliber and there was no hum. so it narrows it down to the preamp section. I will plug the send of the 50 cal into another amps power section to see if there is hum.

Im glad to help, and keep me posted on how it goes.

 

[glpg80]

then its isolated to the guitar preamp and not the power amp/valves.

so it narrows it down to the preamp section.

i thought we already established this

 

[steve_k]

then its isolated to the guitar preamp and not the power amp/valves.

so it narrows it down to the preamp section.

i thought we already established this

i think the posts were coming faster than the typing.......