Markbass CMD121P high pitched noise when operating

[MarkA]

Very good points sir. Thanks for the input.

Just to try and rule things out.... mechanical noise from anything fan related, it's probably not that because the noise is there even with the fan unplugged.

Vibrating transformer...maybe, because the noise seems to come from a very specific area inside the amp.

Noisy power...maybe. I tried different outlets around the house and the noise is still there. The thing is...I haven't changed houses, I bought the amp a few years ago at it was always sitting on top of the cabinet ever since. never gigged.

The only whing that changed recently was that I plugged a MarkBass compressore on the effects loop. Could that have fried something???



Chirp and rattle thats surely from the room. It's the electrical type noise at the beggining of the reccording.

Attached is a reccording of the noise without any instrument plugged in.

Okay, I didn't hear that (clearly) last night (I was trying to listen at low levels on my desktop speakers, late at night -- should've plugged in headphones).

If that's happening with the speaker AND the fan disconnected, without any instrument plugged in, all I can think of is some sort of transformer noise, but my formal electronics training stopped with my last elementary school science fair, so it might be time to consult someone more qualified.

Take care if you're poking around inside the amp.

 

[woodworm_dan]

Take care if you're poking around inside the amp.

Yes, staying away from capacitors and such. Thanks, one can never be too carefull.

Now...if it's transformer noise...What can be done? I guess the "qualified tech" is my best bet. Just wondering if there's a way to repair without the "you need a whole board" solution.....

 

[agedhorse]

With switchmode power supplies, this kind of noise can occur when there is a timing error or drift that results in micro-seconds of cross-conduction, or when there is a snubber failure resulting in uncontrolled ringing of the gate drive signals.

These are all difficult things to diagnose even for a highly qualified tech and generally the amount of labor required exceeds the value of simply replacing the power supply (once it's correctly diagnosed that the noise is coming from the power supply's primary side switches and/or transformer.

A qualified MarkBass service center should have the experience to correctly diagnose this kind of problem and determine the bast (least expensive) way to proceed. A non-qualified service tech or shop could easily jerk you around (intentionally or unintentionally) because of lack of troubleshooting skill and experience.

 

[Bright Midnight]

Okay, I didn't hear that (clearly) last night (I was trying to listen at low levels on my desktop speakers, late at night -- should've plugged in headphones).

If that's happening with the speaker AND the fan disconnected, without any instrument plugged in, all I can think of is some sort of transformer noise, but my formal electronics training stopped with my last elementary school science fair, so it might be time to consult someone more qualified.

Take care if you're poking around inside the amp.

It is coming from the amp itself, with cab and fan disconnected. The high pitched noise sounds like a very high flute or something

 

[woodworm_dan]

Ok so...not wanting to hijack the thread but just got some news from the repair center...

They are quoting me a SM231.007 Poweramp DA-200 part @ 240$CAD + labor. So the total repair is going to be somewhere in the region of 350$CAD.

What do you guys think...? worth to repair or not.

 

[agedhorse]

Sounds to me like they have correctly diagnosed the problem. "Is it worth it" is a question that only you can answer.

 

[woodworm_dan]

I understand. Just wondering if others had a similar experience. They told me that since it's a new PCB, it's essentially a new amp, same cosmetics.

 

[agedhorse]

I understand. Just wondering if others had a similar experience. They told me that since it's a new PCB, it's essentially a new amp, same cosmetics.

Agreed

 

[Ken Hall]

Ok so...not wanting to hijack the thread but just got some news from the repair center...

They are quoting me a SM231.007 Poweramp DA-200 part @ 240$CAD + labor. So the total repair is going to be somewhere in the region of 350$CAD.

What do you guys think...? worth to repair or not.

Dan, did you get the repair done? I have a similar one in my shop right now. Thanks, Ken

 

[bassonovo]

It's the piezo tweeter - replace it with a HT30 and the noise is gone

 

[agedhorse]

It's the piezo tweeter - replace it with a HT30 and the noise is gone

How did you possibly come to this conclusion after the service center had diagnosed it as a faulty power supply.

If you actually read what was posted, the amp makes the noise with the cabinet DISCONNECTED.

Or is this an AI generated conclusion?