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DJM 750 noise on headphones

I encountered a very strange problem:

Sometimes I can hear a static humming noise on my headphones that is noticable in silent parts of tracks or while cueing vinyl records.

I cannot say what the trigger is but I found out that simply re-connecting the headphones like plug out and plug back in solves the problem in 99% of the cases.

 

My investigations have just started so I don't know more about it at the moment. To me it is very curious that re-connecting the headphones solves the problem and makes the noise go away.

 

Because of surge this mixer's chipset was renewed in Dec 2020. I can remember humming noises but I am not sure if they are the same now.

3ncoder

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I am using HDJ-X10.

Currently I am testing my setup without the turntable. I am only connected to 2 CDJs and the PA system using RCA.

When the noise started it is also present when nothing is cued. Btw the turntable is connected via Line-In, I am using the turntable's internal phono pre-amp.

Atm I have not done enough testing to say if it was the turntables fault or not.

 

In one thread in the forums I read something about "static charge" that genereates humming noises. At first I was like "how can that keep going all the time after there had been collected enough charge to hear it" but then I noticed, that the noise goes away when re-plugging which will short some charge because of the plug-in process.

 

 

3ncoder 0 voti
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I contacted the Pioneer service center yesterday.

My "isolated" test with 2 CDJs and the microphone was not successful, after some time the noise, which is a low frequency by the way, occured randomly.

After turning of everything else except the mixer, the noise did not stop. It is coming from the mixer, I am absolutely sure. I clicked every button, I changed the value of every potentiometer, it had no effect.

Before I turned off the mixer I did the "re-plug" thing and disconnected the headphones, connect them again - NOISE GONE.

 

Headphones are passive elements, they cannot generate humming sounds "after some time". I am sure that this is a hardware problem because of a real "problem" on the board/in the power supply or bad circuit design.

3ncoder 0 voti
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Have you tried using the DJM (and only the DJM) at another location to see if perhaps it's caused by the electrical service at that location?

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No, it's lockdown.

I cannot believe that this is because of the power grid. It has also nothing to do with a bad earth connection (earth, not ground) because Pioneer DJ products do not have earth-pins.

A power supply's job is to filter fluctuations, if it does not do that it is either damaged or has a bad design. (if this is the cause)

I am sure that is has nothing to do with inputs from CDJs because if it would be an input-problem, I would be able to hear it ....

When a bad signal would come from a player I would be able to hear it because RCA is analog and the music would be affected...

 

The most important question to me is "who pays for the upcoming workshop hours"!

I can't stand that noise, I paid nearly 1000€ in 2011 (or so) for the mixer, paid 600€ in 2021 to get a new chipset... this is just frustrating because it's PIONEER DJ - the best of the best!

Do you [Pioneer staff] have contact to circuit designers of PioneerDJ to ask them?

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I never suggested it was due to earth; just trying to eliminate the possible causes.

If you had the unit serviced, I would contact them to investigate as you would typically get a 30-90 day warranty on the repairs.

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I did not want to offence you.

In Austria the law says that everything that got sold must come with 2 years of warranty, this does also apply on repairs but...

I know the struggle of problems that occur "after some time" because tech. support is not very interested in those problems... this is why I have mixed feelings

 

My idea would be to put in a new power supply (I would also pay for that because this is the old one that could also got some damage at the surge-event in Dec)

 

I also got the idea to connect an oscilloscope to the output to see what's goin on but before doing that I need to build an adapter-thing...

 

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The previous servicing should have / hopefully would have performed a test on the equipment to know which components required servicing or replacing, but it's entirely possible they missed something because it did not occur within short-period testing on the bench. If I had to guess, it sounds like a capacitor or other component is holding a charge that is causing the hum - disconnecting the headphones causes that charge to collapse or dissipate and as it only occurs after a certain amount of time, they might have missed it - or maybe never connected headphones at all.

Unfortunately nobody here is authorized to provide the technical service instructions to do diagnose or service the unit yourself, which is why I'll suggest you contact the previous service shop and inquire about the fact it's been making that noise since the repair.

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Today I talked to the local Pioneer service center, they gave me a call-back after I sent them the issue.

I will just post the update here:

I disconnected all CDJs and generated sound on the headphones using the built-in noise generator effect. No noise on the headphones for hours BUT then I disconnected the headphones for a few minutes, connected them again and BÄM, there was the loud BRRRRRRR again. Doing a second reconnect -> noise gone.

Tomorrow I will contact the service center again and I will tell them what I found out and that it is coming from the mixer itself.

PS: I didn't want to get technical instructions, I just wanted to know if some employees have expereinced that particular issue.

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It does not work all the time to recreate the humming noise but it worked once which is a little ray of hope for me.

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I was able to reproduce the problem:

1) Generate noise with the built-in noise generator, route it to one channel and hit cue on that.

2) turn up the volume on the already connected headphones to at least "3 dots" using the headphones volume potentiometer and make sure you can hear the cue'd channel.

3) disconnect headphones while noise is playing

4) connect headphones while noise is playing

5) hit cue again to uncue the channel -> massive humming noise in the background

 

The humming noise started because of reconnecting headphones while "loud" sound was comming out of the headphones-port.

Only turning the volume down helps when reconnecting otherwise the humming sound will not go away.

 

Now I want you to please try this on other DJMs if you do not have a 750.

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Sorry, this is not something that occurs on other products - I believe your unit to be faulty and again, I will direct you to contact the repair shop who previously serviced your mixer. Thank you,

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