Squealing sound right balanced channel DJM-S7

There was a high-pitched squealing sound in the sound system during the DJ set.

It was noise in sound system, so it was equipment related.

Epic Equipment:

• Laptop
• 2 Tech-12 turntables
• Pioneer DJM-S7 mixer

Sound Reinforcement Equipment:

• Sound system was provided by a sound tech service, so I’m not aware of all of the equipment. Will list general from what I saw.
• A Shure SLX wireless handheld mic was handed to me.
• 2 x XLR cables were connected to Epic’s mixer Main outputs from a snake on the stage behind the DJ position.
• There was a FOH station under a canopy, which I presume had a mixing desk. (There was also a station off stage right. I didn’t pay much attention to what was there, but the techs did spend some time there as well.)
• There was a stack of Crown amplifiers placed off stage-left.
• There was a JBL line-array stack flown on each side of the stage, with low frequency cabinets on the ground beneath the line-arrays.
• The band’s instruments, and microphones and other equipment were already set up when I arrived.

1. There was a high-pitched squealing sound in the sound system. It didn’t occur continually, but it did occur often right from the beginning of the set.
2. I did receive support response from the sound techs, so I had to try to troubleshoot the source of the noise in the sound system while playing the set. 
1. Note that this was difficult, as I had to make song selections, attempt to mix, announce, as well as listen to and remember song requests while troubleshooting a sound issue. I was missing mixes, bumping needles while playing with cables, trying to dampen the tone-arm with my hand, etc.

Since the issue wasn’t further investigated by myself or the sound technical staff after the discovery that disconnecting one of the XLR’s on Main output of the mixer, I am unable to provide a definitive answer to this.

When the noise was present (and I wasn’t tied up with something else), I attempted to troubleshoot the source of the sound, from my position at the DJ console.

1. I disconnected the stereo RCA cables on each turntable from the mixer - No change
2. I disconnected a Stereo RCA to 3.5mm TRS cable from Aux In on the mixer - There was no noise at that time, but I was able to leave this disconnected permanently, so I pulled it. …later, the sound reoccurred.
3. I hesitated to disconnect Main outputs, as this would have audible impact noticeable to guests at the event. Especially without cooperation of the sound technical crew controlling the sound system. However, there was a high amount of concern from the Employer, and since I had 2 connections to the sound system, I would still have audio if I unplugged one at a time. So i tried this:
1. I disconnected Main output Left - No change
2. I disconnected Main output Right - This resolved the noise!
3. I tried reconnecting the output - Noise returned
4. I disconnected again - Noise resolved

There are 2 parts to this:

FIRST PART - The ‘POP!” in the sound system and burning electronics smell

1. First, directly about the noise:
1. I don’t think this is related, but while filling this form I am reminded of this and I should mention it. I’ll explain why I think I should mention it after some context. 
2. There was a loud ‘POP!’ from the speakers shortly after the turntables and mixer were set up and connected to the sound reinforcement.
3. This raised concern from myself as well as the 2 techs that were on stage with me at that moment. One of the techs said ‘that came from our speakers’. 
4. Immediately after that noise there was a disctinctive smell of burning electronics. One of the techs said ‘it came from further away’, and gestured out towards the parking lot. In my mind I thought, we smelled that burning electronics immediately after the ‘POP’, so it seems to be something very close to us. I did say somehthing outloud to effect of ‘Where could that have come from? (meaning if not from on or near the stage). It came through the speakers. …I don’t see any transformers or anything (in the parking lot around us)’

1. There is a small possibility that there was an equipment failure in one of my 3 pieces of equipment or the sound tech’s equipment. This failure could have become evident later, when I started playing.
2. This brings up the question for myself, ‘what could cause this if the source of the ‘POP’ and burning smell was my equipment?’
1. Potential cause 1: The output stage or some component of the audio path on the Right channel of the mixer blew. The symptoms of a loud pop and burned electronics smell would indicate that spurious voltage was induced somewhere where it shouldn’t be. (By spurious voltage, I mean higher than ~1.2 volt expected from line-level circuits, or DC voltage.) 
1. If this scenario is the case, then the next quesion is ‘did the voltage get induced inside the mixer, or from the connection to the sound reinforcement system?’
2. The chances of a fault at that moment from the mixer itself is extremely unlikely. But possible.
3. The chances of the fault being a component failure of the sound reinforcement system is also extremely unlikely.
4. There is one other thing thay comes to mind. Potentially, if phantom power was mistakenly active on that channel, this would send DC voltage to my mixer’s output. This is also unlikely, for the reason that 24 or 48 VDC will not necessarily damage a balanced line output. And it would also require human error of connecting to a channel with active phantom power on that channel. (Channel 7 of the snake)
   Of the 3, this would be the most likely, in my opinion. Mostly because of the timing, and human error is more likely since we’re dealing with what should be very low line-level audio voltage.

NOTE: Everything above is only a possibility of a scenario that came to my mind as I’m filling this form. If I were to guess, I would say that the “POP’ and burning smell was on or next to the stage. But I doubt that a mixer channel blew up from whatever that was. 

To add to that doubt: In pro-sound, when there is a catastrophic problem, it is almost always a cable.
However, the timing adds up for the ‘pop’ and blown channel, so it is worth investigating. That would be permanent damage, so I should be evidence by testing and inspecting the mixer.

In terms of what could have prevented the noise in the sound system, this can’t be determined until/if the source of the issue is found. 

However, if there was a soundcheck, the noise would very likely have been discovered during the soundcheck. Then, troubleshooting could have been completed in cooperation with the on-site sound support team. Pre-performance discovery that this issue was simply resolved by disconnecting the XLR cable connecting Main out R to Channel 7 of the snake, could have been easily solved by one of: 

1. Replacing the cable if it was a defective cable.
2. Using a different channel on the snake, mixer or other component in the sound system Right-Channel audio path
3. Utilizing only the left output channel of the DJ mixer, if the noise source was from the mixer channel. (easily confirmed by elimination of A & B, above and then moving the ‘good’ XLR on the Left mixer channel over to the Right channel to see if the noise ceases or still exists, but now in the sound system Left Channel instead of Right.

I do. In my opinion, and I think every sound tech I have ever worked with, sound-check at a live event should never be skipped. Any piece of equipment or change of connection should be tested before showtime unless not reasonably possible.

On this note. I felt warmly welcomed by the employers.(Caitlyn and Chad). I was also greeted politely by a helpful tech who connected my mixer to their sound system and handed me a mic.

Conversely, when I arrived to set up (I was assuming I needed to set up early for soundcheck) after placing my gear on stage, I was told ‘hey, we’re going to be doing sound check in a few minutes’. 

I realized at that point that since I was going on first, and they were evidently referring to the other act, that this meant no soundcheck for me. This raised a red flag in my mind, as I feel it is prudent to always conduct a soundcheck before a production. Plus, it made me feel like I was in the way of the sound team and not welcome.

I did shrug it off in my mind and actually almost made a joke when I first spoke on the mic along the lines of ‘I’ll be playing some music for you before our headliner arrives, but DJ’s aren’t worthy of a soundcheck, so we’re going in cold!’. …I realized before I said it that it may have been taken in a hurtful way, so I didn’t say it. Probably the right choice, but would have been super ironic if I had! Lol  

So, I had a mixed experience in that respect. However, feelings aside (this is a professional event, after all) I felt that proper etiquette in that situation was to go with the flow of the attending technical team. It is their equipment & project, and they should be left to operate under their protocols and process. So, I cooperated accordingly.

Later, once I had discovered the noise issue was resolved by disconnecting the XLR cable, I waved at the tech sitting in the FOH station. It seemed he saw me, but didn’t react. So I waived again and held up the cable, and pointed at it so he could see I need his help with something. He again watched me do that, then looked back down. I tried one more time with a big waive, and a bigger gesture pointing to the cable. He reacted by pulling down my audio and playing his background music, again with no further acknowledgement. Coupled with previous seemingly disinterest in supporting me with the noise issue while I was attempting to perform my job, was frustrating and again made me feel like I wasn’t worth their time. I coudn’t figure out if I had made them upset somehow, or if I was just overreacting. It was difficult to sort out in the moment. Thinking back, I’m still not sure. I met Jessie once before. He seemed like a really nice guy. My guess is there was just a misunderstanding. Like I do things one way, and others do things another way. Doesn’t make my way right and others wrong. And, as far as I know, the technical team has a good reputation. Anyway. I’m not generally a ‘concerned about my feelings’ kinda person. I just think that it’s just important to include this information for context for this report. 

Please take note that I’m not reporting this to cast negative light on anyone. Admittedly, I am mentioning this in defence of my position in the situation.. 

I am happy to answer any questions around this report and the related incident with full transparency. 

END OF REPORT