| Matt Carr wrote on Mon, 03 January 2011 22:37 |
I recently became involved in servicing a 13 year old Church audio system that consists of a Mackie 1604-VLZPro and a 70 volt auxiliary zone that feeds the main mix to offices, basement gathering, narthex, and entry areas. Aux is powered by an Architectural Acoustics UMA1502 amp that seems like it would have enough power to serve 10 speakers tapped at 5 watts each, but I just can't get enough output to achieve an acceptable listening level. When I adjust the input gain the amp starts to clip. When I adjust the output gain the amp starts to clip. Switched the input to be controlled by sub fader 1 for more input gain flexibility but amp still shuts down after clipping, all the while never producing an acceptable output level. Tried different inputs on the amp but same outcome. So far I have tried using the main mix output and sub-fader output with no success. Since the company that installed the church system is no longer around I'm trying to help out a very good customer with their issues. Any suggestions? |
| Matt Carr wrote on Tue, 04 January 2011 10:46 |
The real tricky side to this is the church claims the aux zone used to operate real loud until they had a guy come and adjust the eq settings on the inputs and the aux send outs that are being used for monitor amp inputs. Nothing physical was changed. I was a witness to the eq adjustments. |
| Sidney Pilien wrote on Wed, 05 January 2011 20:52 |
The speaker wire size sounds correct. The system runs higher voltage-low current at high impedance for long wire runs and less heat so increasing the wire size may worsen the problem. |
| Matt Carr wrote on Thu, 06 January 2011 18:44 |
Sidney Pilien wrote on Wed, 05 January 2011 19:52The speaker wire size sounds correct. The system runs higher voltage-low current at high impedance for long wire runs and less heat so increasing the wire size may worsen the problem. Sidney, why would it be worse? Is it because in a sense I'm switching it from a high impedance to a low impedance system if I use 16awg wire, therefore, making the amp work harder to push current through that much wire? I've always been taught that undersized wire meant more resistance and more heat which is exactly what you don't want your amp to have. I certainly don't consider myself a pro sound guy so I'm just asking the question. |
| Matthias Heitzer wrote on Mon, 10 January 2011 10:39 |
If there really is a short somewhere in the line, bigger wire could make things worse, but that's the only situation i can think about. If we are talking about AC, the electrons aren't acutally travelling through the wire, they just move back and forth. That's a good thing, because they are as slow as 0,3 mm/s. Let's take Sidney Pillen's straw and fill it with water. Now we fill our mouth with orange juice and pump the juice through the water-filled straw. What will come out of the straw? It's water, and if we beginn to draw back the liquid fast enough, the juice won't drip out of the straw. (if we exclude that water and juices blends in real life) |
| Matt Carr wrote on Mon, 10 January 2011 10:40 |
Well, it has been interesting and informative reading all the replies. Thank you. I discovered Saturday when I disconnected the speaker run at mid point I was able to identify a problem with the first section. I discovered one speaker connected to the 25V side of the transformer in an old office that's not currently being used. The church didn't even know it was in there. Once it was connected to 70V everything worked great, even on the 22awg wire. Thanks for all the feedback. |