The theater owns two consoles: one Mackie 8-channel and one Allen and Heath GL2200 24 channel.
The A&H isn't healthy. When I originally started here, it was living in the shop uncovered and had some dust on it. I blew it off externally (didn't disassemble) and it worked well for a year. Now all of the inputs (I think I checked 14 channels before assuming that they would all behave the same) are heavily distorted; 1/4" and XLR both. Almost like you have the gain cranked the whole way, but it isn't. Small inputs from the fader will peg the LEDs even at very small volumes and the sound (even when quiet) is clipping badly. Problem seems to be the same for all channels. It's not a source problem because I plugged in a laptop, CD player, and a few other sources into both consoles and the problem only exists in the A&H box. No cracking or fuzz from the Pots or faders.
The actual SPLs seem to be logical. That is to say the volume seems right with the gain and fader positions, but the LEDs peg on clip as soon as you bring up the fader and the program is distorted.
There is zero budget for a pro fix but we have a show coming up in March where I'll need more than 8 channels from the Mackie. What can I test/try/clean? I'm no stranger to repairing things, just haven't ever done a console before and don't want to mess it up. Tips? Pointers?
Try a deoxit treatment on the main audio buss. Is the channel inputs in fact distorted or is it just through the monitor system? If the board has PFL (Pre-Fade Listen) buttons on the channels try clicking them down to monitor what's happening in each channel before the fader. If the input(s) is/are good, I'm thinking there's a bad pot/fader in the audio output chain somewhere. Also, look for a switch marked "+20db" somewhere and make sure it's not engaged. That will add another gain stage and cause distortion like you describe.
Nugi
New Reader
1/18/18 6:31 p.m.
+1 on DeOxit
There are often hard to notice gain controls for mic vs line gain. Look around on the back of the a&h. Otherwise, it could just be some old capacitors, which needs a guy handy with a soldering iron.
Nugi said:
+1 on DeOxit
There are often hard to notice gain controls for mic vs line gain. Look around on the back of the a&h. Otherwise, it could just be some old capacitors, which needs a guy handy with a soldering iron.
Caps would be humming like a mofo. It's either a bad pot/fader or a gain mismatch. Less expensive workhorse consoles like A-H are used in a variety of situations so they have all kinds of whacko stuff plugged into 'em so they have more than their share of gain-matching gizmos. Also time to check output gain for "+4" or "+20" switches too.
Is there anywhere I shouldn't touch, use deoxit, or otherwise disturb? I feel like right now I have a console worth $700 that needs a little repair. I don't want to turn it into a useless pile and have to spend more money.
