Mesa mini 25 buzzing problem

Hi,

my son has a Mesa Boogie mini rectifier 25, that has developed a buzzing noise from the input transformer area. this is apparent on both channels. All the valves appear to be working properly.

Q, is the transformer on it's way out?

Q, could it be a faulty valve?

Q, or a capacitor, or other failing components?

Any info would be gratefully received.

Cheers,
Martin

Martin Ryan said:

Hi,

my son has a Mesa Boogie mini rectifier 25, that has developed a buzzing noise from the input transformer area. this is apparent on both channels. All the valves appear to be working properly.

Q, is the transformer on it's way out?

Q, could it be a faulty valve?

Q, or a capacitor, or other failing components?

Any info would be gratefully received.

Cheers,
Martin

Click to expand...

Welcome to the forum.

Some slight bit of power transformer buzz can be considered normal, but how loud is this buzz?

Does it come through the speaker, or directly from the transformer?

Are you running the correct speaker load (impedance)?

You mentioned that "all the valves appear to be working properly". How did you test them?

Dom

Hi Dom,

Thanks for the reply.

The head is plugged into the mesa speaker cab, (8 ohms); only one input socket in the cab.

The noise appears to be coming direct from the transformer; it actually sounds like it is clicking.

I checked the valves, by tapping lightly, with a pencil.

Cheers,
Martin.

Martin Ryan said:

Hi,

my son has a Mesa Boogie mini rectifier 25, that has developed a buzzing noise from the input transformer area. this is apparent on both channels. All the valves appear to be working properly.

Q, is the transformer on it's way out?

Q, could it be a faulty valve?

Q, or a capacitor, or other failing components?

Any info would be gratefully received.

Cheers,
Martin

Click to expand...

3 reports of same problem, amp makes intermittent :roll: buzzing noise, resembles ground loop, etc...
Sounded like a broken input jack or a broken input wire, broken ground connection...but have not found anything broken yet.
If anybody knows anything, please let us know.
No schematic...no pictures of inside...changing to new tubes did not solve the problems.
Will let you know what (if anything) we find out.

Do you have any other place you can take the amp to test it on a different power source? You can also get a outlet tester to check if the outlet is wired properly and giving proper voltage.

http://www.amazon.com/Sperry-Instruments-GFI6302-Outlet-Tester/dp/B000RUL2UU/ref=sr_1_1?ie=UTF8&qid=1431325784&sr=8-1&keywords=outlet+tester

http://www.amazon.com/Amprobe-PY-1A-Voltage-Tester/dp/B003NY45QK/ref=pd_sim_469_1?ie=UTF8&refRID=1QFHYTNK1KTJXNQ9C70Y

vick1000 said:

Do you have any other place you can take the amp to test it on a different power source? You can also get a outlet tester to check if the outlet is wired properly and giving proper voltage.

http://www.amazon.com/Sperry-Instruments-GFI6302-Outlet-Tester/dp/B000RUL2UU/ref=sr_1_1?ie=UTF8&qid=1431325784&sr=8-1&keywords=outlet+tester

http://www.amazon.com/Amprobe-PY-1A-Voltage-Tester/dp/B003NY45QK/ref=pd_sim_469_1?ie=UTF8&refRID=1QFHYTNK1KTJXNQ9C70Y

Click to expand...

The same symptoms are showing up in three amps in three locations...
Two in Canada and one in USA. + the amp mentioned above by bottle rocket. (That's FOUR amps total)
Yes I have a tester, I'm an electrician.

The noise comes and goes intermittently. Shutting off the amp and turning it back on sometimes stops the noise....then it intermittently returns.
Changing the tubes did not stop the problem.
The noise sounds similar to a broken connection at the input. Loud low frequency hum + high pitched squealing, depending on the volume setting.
Both Channels have the noise...when it occurs.
Using the effects loop in / out, the problem seems to be isolated to the preamp.
Using different cables, etc... did not stop the noise.

Reminds me of a broken connection in the input signal path...but we have no schematic or pictures so far.
Will update you when we have more to go on. Thanks.

From User In Canada (5 minutes ago):
"The funny thing is the issue started with my amp when I used the fx loop with the new mesa eq pedal I bought. Prior to that it was fine. I wonder if the ground connection to one of the fx jacks is the issue??? Also, like I said, the buzzing is not there without the preamp. ive only tested with an attenuator in the loop. I will test with a guitar directly into the return jack, or a media player."


My Reply:
Plug a short guitar cable between effects send jack and effects return jack.
Then re-test the amp with the bypass cable installed. Let us know if the noise returns, with the bypass installed. OR if the noise is cured...
It might be a bad switch contact in the effects jacks. The bypass cable (above) will help test that theory.
Let us know what the result is, Thanks.

Martin Ryan said:

Hi,

my son has a Mesa Boogie mini rectifier 25, that has developed a buzzing noise from the input transformer area. this is apparent on both channels. All the valves appear to be working properly.

Q, is the transformer on it's way out?

Q, could it be a faulty valve?

Q, or a capacitor, or other failing components?

Any info would be gratefully received.

Cheers,
Martin

Click to expand...

Martin,
Plug a short guitar cable between effects send jack and effects return jack. No effects for this test please.
Now, re-test the amp. Did the noise stop?
Let us know if this test stopped the noise.

I'm sorry soundguruman, but how do you know the issues the OP have are the same as what you have researched? The OP is describing a physical audio buzzing coming form the transformer area of the amp, not a signal noise. And just because the issue may be happening in four locations around the world, does not mean the problem can't be the same issue in building wiring or power distribution, just in four locations.

If the PT is buzzing or chirping, the problem is between the PT and the power source, or a loose coil in the PT.

vick1000 said:

I'm sorry soundguruman, but how do you know the issues the OP have are the same as what you have researched? The OP is describing a physical audio buzzing coming form the transformer area of the amp, not a signal noise. And just because the issue may be happening in four locations around the world, does not mean the problem can't be the same issue in building wiring or power distribution, just in four locations.

If the PT is buzzing or chirping, the problem is between the PT and the power source, or a loose coil in the PT.

Click to expand...

Try the bypass cable first, that eliminates the possibility.

The buzzing may be the power amp oscillating, because the input (to the PA) path is an open circuit.

We don't know anything for certain yet. That's why we're trying the most common failure point first. (bad switch contacts on effects loop jacks)
If you eliminate that cause, then start looking at the other possibilities.
The bypass cable is the easiest part - that the user can test. This test takes only a short time, and you know pretty quickly.

Martin Ryan said:

Hi,

my son has a Mesa Boogie mini rectifier 25, that has developed a buzzing noise from the input transformer area. this is apparent on both channels. All the valves appear to be working properly.

Q, is the transformer on it's way out?

Q, could it be a faulty valve?

Q, or a capacitor, or other failing components?

Any info would be gratefully received.

Cheers,
Martin

Click to expand...

Well...
the loop bypass test did not help the situation. Although it is worth a try.
(effects jacks fail frequently, causing similar noises)

From the recording, it reminds me of a break in the signal path, the power amp input being an open circuit...possibly causing the power amp to oscillate.

From the sound of it, and the fact that it is intermittent, and from the fact that it's happening in multiple amps...
I am not concerned about the electricity causing the problem.

You tried changing the tubes,
you tried inspecting the internal connections and jacks...
you bypassed the effects loop, so...you have done almost anything you could have done without test equipment. (good job BTW...)

Now these amps frequently have an FET which mutes the effects loop, and that transistor has been known to fail on other amps.
That is one thing among others that remains.

But until we have a schematic, or until somebody has one on the bench, unfortunately we have run out of simple possibilities.

I believe there is something wrong, I don't doubt it. We just don't have the means so far to find it.

To be continued,
when I have one on the bench, I will let you know whatever I find. Sooner or later I'm going to see one.

FYI
Yes I have been (previously) a Boogie service center, and have fixed many Boogie amps, for many years.
Including fixing several amps, that the factory was unable to fix.
Overall, I am not a novice at repairing Boogies. I am pretty familiar with them.
But it's true that it takes a lot of patience, above and beyond what's required for other guitar amps.

Hi,

I posted the original question for this problem, I had the amp checked out by a amp repair guy that i know, he found absolutely nothing wrong with the amp. When by son plug it back in he changed the speaker cab lead, and the buzzing/clicking noise, has gone.

Thank you all for your time, and effort in helping to resolve the issue.

Regards,
Martin.

Martin Ryan said:

Hi,

I posted the original question for this problem, I had the amp checked out by a amp repair guy that i know, he found absolutely nothing wrong with the amp. When by son plug it back in he changed the speaker cab lead, and the buzzing/clicking noise, has gone.

Thank you all for your time, and effort in helping to resolve the issue.

Regards,
Martin.

Click to expand...

I'm not sure that the problem is gone.
People who reported this said the problem was intermittent.
Other people brought their amp to a Mesa tech... the tech told them there was no problem...but then later, the problem came back.
So, I am not really convinced.

Thank you for your reply. If the problem comes back, I will add another post.

Cheers,
Martin.