You've reminded me I use to have a Peavey amp with hot and cold transposed!

The mixer is an Allen and Heath PA20 (unpowered):http://www.allen-heath.com/UK/DisplayProduct.asp?pview=40

The induction loop is by "Current Thinking" (I dont know which model):http://www.current-thinking.com/professional.htm

Ok.. thanks for the links.
The PA20 - not a bad unit (think A&H make them in China)- thought about getting one for a local band, but the fixed low mid eq put me off, other than that it covers all the bases.
I've had a look at the pdf manual.
It's wired the 'normal' way. In fact it has a nice cables & connectors section, worth a look as it shows every combination of connector and how to wire it for use in a balanced / un-balanced way.

It would appear that the stagebox at the stage end may have been 'home made'.
The box at the mixer end.. all XLR's yes?
I'm wondering if that was the multi-cores original stagebox, does it have male (pins) XLR's or female (holes)? If it's a 'stagebox' it will be female, and thus to connect to the desk you would have 12 female-to-female XLR leads! like wise the returns would also be a bit 'backwards' and I'm woulding if that's why the wiring may a bit 'iffy'.

A tiny problem with having all XLR's at the desk end means that the desk is 'stuck' in mic level, as the line level input on the desk is on a balanced jack. There is no 'pad' button so it might be very easy to overload and distort when plugging in stuff at the stagebox.
Something to be wary off.

The returns..
4: 1 & 2 Main outs to the PA amps?
3 - Foldback 1?
4 - now here is where things get interesting..
It might be coming off Foldback 2, or it might be coming of the aux send, and this might be your send for the loop amp.
Without seeing it, 3 and 4 might be the other way around.
The foldback sends from the desk will be 'pre-send' that is to say they offer an independent mix. The channels faders will not have any effect on these signals. That's why they are used as foldback sends. This would not be ideal for you loop amp.
The aux send however will be controlled by the channels fader. Normally these are used for send signals to reverb / echo units. Be it would be ideal for your loop amp, as it mirrors what actions are being sent to the main PA. If the loop amp needs less music, and more vocal, you adjust the aux sends levels accordingly.

Has this made any sense? I know it's sounds complicated, but it isn't really.


I don't think the guitar / amp / loop amp is too much of a problem, as this would happen more or less straight away. The feedback only occurs when you add the Laney into the equation. There's a slim possibly that the pick-up for the spring reverb (Horrid sound) might be getting the loop amp. Try killing the reverb in the amp - not that you should be using it!
I still think it's a gain, and / or cabling issue.

I also looked up the loop amp link.
All the units offer 3 XLR in's. However only one of the three in's offers a mic/line input. It's this input you should be using with the desk.

Another desk issue, and worth looking at, not so much to do with your current problems, but may improve the whole sound of the system.
Each input has a 100Hz lowcut filter. These should be mostly turned ON. It will reduce bass feedback, and 'popping' problems on the vocal mics.
The only channels I wouldn't put the filters on, would be bass guitar, kick drum, possibly snare (try with / without, and keyboards (again try with / without).

Well that should give you plenty to get your teeth into.
Would I be right if I guessed you are UK based? If so where-a-bouts?

Good-luck,



------------------
The Sonic Energy Authority - a sound investment

As suspected, and with thanks to you all but especially "Sonic" for such a compreshensive trawl of the possibilities, it's all down the the induction loop being picked up by the gear.

Turn off the loop and everything is fine. I'm looking to re-route the loop wire to try to give a "dead" area around the "stage" area, at present I thing the loop goes straight underneath. Also the intermediate stage box is currently directly on top of the loop amplifier, and this cannot be helping, so I'm looking to move things about but I'll have to make some new wires up to give the necessary freedom of movement.

I have not actually found any miswiring of connectors so far, but that's now a work in progress.

For information here's the setup now.

The wiring is using commercial multicore cabling (all cores are twin and earth, with unique idents) with XLR/Jacks at one end and a stagebox at the other.

The "intermediate" box provides 12 feeds to the mixer (1-12) and receives 4 feeds back (A,B,C,D). A and B are main PA L/R, C is now a foldback line fed from the "summed mono out" of the desk, and D is the Induction loop drive from the "Aux 1" feed of the desk. The loop drive uses the line level input of the loop drive amp, I haven't dragged the PA amps out to check them but I'm confident that they work as expected.

The "stage" box may have 16 "ins" and 4 "outs" but only 8 of the "ins" and one of the "outs" are wired up into a multicore that comes out next to the intermdiate box to give 8 XLRs and a single TRS jack respectively. The 8 XLRs go straight into 1-8 on the intermediate, and the jack goes into "C" on the intermediate box to route the foldback signal to the stage box. This is also now working as expected.

So I think this situation, if not fully sorted yet, is at least in a position where we know the issues and can take some steps to improve things.

Thanks again!

John

I forgot to mention, we are using the 100hz filters on anything microphonic and by default on everything else; as you say turned off for bass, keys, piano, drums as necessary.

And I'm in the UK, Preston Lancashire!