Winter Maintenance 2017/18 - Removal of the Equipment Case and Electronics

[TerryJC]

All,

I've made some progress on solving the cross-talk and the 'clicking' from the Chancel speaker when playing MP3s of church music. The attached drawing is an updated version of the Audio and Solenoids Circuit which represents the current state of play. The differences between this version and the one that was deployed in April of last year are that:

1. I have added 'Audio Conditioning Circuits' to the inputs of the Audio Power Amplifiers. These:
   • Isolate the O/P of the driving device (Pi Audio jack or USB Audio Adaptor) from the Audio PA I/Ps.
   • Pot down the I/P signal to bring the levels into a range to suit the Amp I/Ps. (There was some potting down originally, but this has improved on that.)
   • Add a series resistor to help match the signal. (I'm not sure these do much but having put them in, I'll leave them there.)
2. I have added a PSU Filter Circuit to reduce the ripple on the incoming 12 V, which was much worse with the replacement PSus that were fitted in August than the originals.

The upshot of this is that cross-talk is hardly discernible, the clicking has now gone and the hum is much reduced. The hum is still the bugbear since it is possible to change it simply by touching the body of the audio jack or putting your hand near to the isolating transformers. However, it is probably no worse than it was in April and probably a bit better. I know I could get rid of it by using two USB adaptors, but that introduced new problems so I'd rather avoid that if I can.

Over the next few days I'll install the filters into their final positions and shorten the wiring as much as possible to see if I can reduce the hum still further.

[Penri]

Excellent Terry, nice to see it all coming together and working as it should.

Penri

[TerryJC]

The upshot of this is that cross-talk is hardly discernible, the clicking has now gone and the hum is much reduced. The hum is still the bugbear since it is possible to change it simply by touching the body of the audio jack or putting your hand near to the isolating transformers. However, it is probably no worse than it was in April and probably a bit better. I know I could get rid of it by using two USB adaptors, but that introduced new problems so I'd rather avoid that if I can.

Over the next few days I'll install the filters into their final positions and shorten the wiring as much as possible to see if I can reduce the hum still further.

To catch up with this, after I'd re-assembled the system, the hum became pretty awful. To cut a long story short, I managed to get two USB adaptors working together, but it turned out that this didn't solve the hum. The bottom line is that this is a hardware problem, partially caused by the physical layout of the Audio Amps inside the box, but mostly caused by the noisy PSU (they all seem much the same) and the noisy fan (electrical noise). I've reduced this a fair bit by running the fan through a limiting resistor which has the dual benefit of improving the filtering and slowing the fan down a bit, so the noise is less noticeable. Overall though, it's still there and the only way that I can think of to get rid of the fan noise is to run it from a completely separate PSU, which is a bit kludgy.

So what have I achieved? Well the cross-talk seems to have gone and the clicking from the chancel speaker is no longer there. I'm going to bring it in to the WMT tomorrow for a trial fit to see what it sounds like in-situ. We haven't got much more time, so I need to decide what I need to do before next Tuesday.

Penri, can you bring your large diameter masonry drill? The XLR connector is 20 mm in diameter.

[Penri]

Terry

Shame about the hum, as you say lets see what it's like in situ.

I've left my drill bit at WMT in preparation for tomorrow so can't measure it to make sure its the right size, I think it's there or there about and with a bit of wiggling we can make the hole meet the requirement.

Hwyl

Penri

[TerryJC]

Sitrep,

To bring this up to date; on Tuesday we attempted to install the system back into the Tower and encountered a couple of problems. Two of these were caused by my messing around with USB Audio Devices earlier and forgetting to restore the system to its original state. These were the attenuation of the audio I/P for the bells and the provision of 5 minutes of silence on the Media Stick. The software is unchanged from last April. The third problem was more difficult to fix. The solenoids failed to operate, caused I later discovered, by the XLR connector having 5 mm of 'slop' when it was supposedly inserted. Needless to say, the solenoids only worked if the connector was pushed fully home; a situation which it was impossible to guarantee.

As a result of these issues, I brought the system back home and rectified each problem. The XLR was changed for a round industrial 6-way connector similar to the ones used for the River System and the I/P gain and silence issues put right. I decided to replace the cling film protection for the QJ with a proper 'lid' while I was about it, because the round industrial connector has to be retained with a jam nut. In the event, I made use of the existing wooden block to carry a sub-panel for the connector and put a hole in the lid to provide access.

I finished construction this morning and tested everything here. I then went into WMT this morning and installed the Chancel components (Electronics Box, Chancel Speaker, PSU box, etc) and pushed the QJ connector and cable up into the Upper Tower. At that point the snow started, so I came home.

All that should be needed now is to install the QJ in the window frame and switch on. I will be in on Monday afternoon to do this.

[Penri]

Terry

We must have missed each other by a few minutes this morning.


Penri

[TerryJC]

About half an hour.

[TerryJC]

Sitrep.

The Bells system is fully installed and working. There is still some hum and it is annoyingly difficult to pin down. It is very variable, but I've been unable to establish exactly what makes it change.

Will monitor over the coming weeks and think about how I might be able to reduce this (without spending hundreds of pounds on a complete new Audio solution).