Mixer into mixer causing distortion

wolfman005

Active Member
In our school's "performance center" the sound system can be configured in two ways. One is where a simple 8 (?) channel mixer runs three wireless mics, a CD player, and MP3 input. The other configuration is for more advanced users and runs through a snake into a 12 channel mixer. Then the 12 channel mixer goes back through the 8 channel mixer into a DSP, Amps, speakers. The problem we are having is when using the 12 channel mixer, the master volume has to be kept around -30 db otherwise it distorts horribly. If you turn down the 8 channel mixer and turn up the master on the 12 channel mixer, it still distorts. To get the signal from the 12 channel mixer to the 8 channel mixer, we use XLR outputs of the 12 channel, into the snake, and into a set if XLR inputs on the amp rack. From there I assume it continues in XLR form into the 8 channel mixer. The 8 channel doesn't have a gain control, but it does have a mic/line button. I'm not sure if it is configured as a mic or line input right now, but could this be the problem? If it isn't what can I do to remedy this?
 
Try toggling the input on the 8 channel to the other setting and see if it improves things. I'm going to guess its in mic mode right now, and switching to line will probably get you another 20dB of gain. What are the models of the two mixers?
 
Thanks I'll be trying this Monday when I can open the back of the rack. Now If I wanted to run say 6 shotgun mics, 7 lapels, and two keyboards, you will notice that the total number of inputs exceeds 12 channels. If I take another mini mixer similar to the 8 channel mixer mentioned above, can I run the shotgun mics into that and then run the mini mixer into the 12 channel mixer? I don't need auxs or effects and in a older forum, from what I remember, that was the only reason they discouraged doing such a thing.
 
It could work though the more mixers you add the more points of failure as well as interference that is added. Almost always the internal electronics are going to be better than running cables and inputs between more mixers. There are a few reasons over just ease of use why people by more channels instead of just more mixers.
 
add it as an additional input on the 8 channel
If I do this will I have the same problem I'm having with 12 channel? I know the 8 channel has a limited number of inputs that can be mic/line but I'm not sure how many. Also the 8 channel is hardwired into our main rack. I'd have to strip down XLR and screw it into the mixer connections, which I'm more then ok with doing, but I don't wanna be liable for anything going wrong
 
If I do this will I have the same problem I'm having with 12 channel? I know the 8 channel has a limited number of inputs that can be mic/line but I'm not sure how many. Also the 8 channel is hardwired into our main rack. I'd have to strip down XLR and screw it into the mixer connections, which I'm more then ok with doing, but I don't wanna be liable for anything going wrong

Well, you can plug as many other mixers into your 8-channel as you have line-level inputs, but that could get awfully cumbersome for operating and troubleshooting that setup. If you need more channels for a particular show than your 8-channel + 12-channel mixers can provide, I would suggest that you look into renting a 24- or 36-channel board for the gig so that you can run everything on one mixer and just use the 8-channel as a convenient way to patch into the house PA. Simpler is better in this situation, IMHO.
 
That is something I did consider, however when I asked our drama teacher he was quite surprised that people even did things like that. If it comes to this not working, I will just cut some of the shotguns and tell the chorus to sing louder.
 
Nice DI boxes w/~30dB pad anyone?
 
If the one mixer is the Crown 28M then each input has a mono screw terminal Phoenix connector for which there is a mic/line switch and a pair of RCA jacks that are internally summed to mono. There apparently a significant (i.e. around 48dB) difference in gain between the mic and line position for the Phoenix inputs so if you are running the line out of the Soundcraft into an input on the Crown and it is set as a mic input then it is probably not surprising that you are experiencing some problems.
 
If the one mixer is the Crown 28M

Unfortunately It isn't the 28M but it's very similar. I can't find it anywhere online and I don't have access to the rack till Monday but when I get to setting up I'm gonna open it up and see if the line/mic switch makes a difference. I think it should but I wanted to run it by you all before I went through the trouble of opening the rack. The people who installed the system didn't think out the space all that well and I've had to fix a lot of other install errors so it wouldn't surprise me if it's just a matter of the mic/line button not set properly. Thanks all for your help I'll update on Monday. Wish I would have found control booth 2 years ago when I started working in this space. Would have saved a lot of headaches and trial and error, although I have learned a lot that way.
 
Unfortunately It isn't the 28M but it's very similar. I can't find it anywhere online and I don't have access to the rack till Monday but when I get to setting up I'm gonna open it up and see if the line/mic switch makes a difference.
Just for reference, on the 28M the mic/line switch is right by each input on the rear panel. Some other mixers may have them all grouped together for all inputs on a single mutli-switch DIP switch. And yet others may have the switches inside the mixer chassis.

The people who installed the system didn't think out the space all that well and I've had to fix a lot of other install errors so it wouldn't surprise me if it's just a matter of the mic/line button not set properly. Thanks all for your help I'll update on Monday. Wish I would have found control booth 2 years ago when I started working in this space. Would have saved a lot of headaches and trial and error, although I have learned a lot that way.
Just to be fair, unless you have documentation showing that was how it was installed you may not be able to assume it. Many of the items I find during system commissioning are things like improper settings, however I've had end users start reconfiguring installs before the install was even complete, I had one job that every time I came on site the first thing I did was go and check some of the switches that the user kept changing so they could listen to music while they ate lunch in the Auditorium. On another project the TD pushed for us to get through system commissioning and acceptance so that he could then start changing everything to be the way he rather than what the Owner had defined, he was literally rewiring things before we could get out the door. I even had one case where I changed companies and a few years later was hired to 'fix' a system I had initially designed, which we did by simply pulling out the original plans they had in the rack and undoing all the changes and alterations that the Owner and others had made over that time, with their liking the result so much that they immediately hired us for other work.

I guess my point is there are lots of silly errors often made during installs but probably just as many made after an install is complete or in a misguided attempt to 'fix' or change something.
 
Got everything sorted today. Opened the rack, found the line/mic switch and problem solved. Thanks for your help.

@museav- Your right I don't have documentation about the original install so I shouldn't make conclusions like that. Just a lot of unexplained issues such as the line/mic switch being set to mic instead of line. Seeing as how I had such a hard time getting the rack open, I doubt it has been opened much if at all after the original install.
 

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