Speakerplans.com Homepage
Forum Home Forum Home > General > Electro Frying Forum
  New Posts New Posts RSS Feed - I wish my wife was as dirty as this mains supply
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

I wish my wife was as dirty as this mains supply

 Post Reply Post Reply Page  <1234>
Author
Message
mini-mad View Drop Down
Old Croc
Old Croc
Avatar

Joined: 13 July 2012
Location: london
Status: Offline
Points: 6903
Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2017 at 3:10pm
Originally posted by midas midas wrote:

Originally posted by kedwardsleisure kedwardsleisure wrote:

I used to pick up minicab drivers with my organ


Oh did you now....lol.

Does the wife know???


Ok ok... can we all stop bashing kens organ and stop being so HARDON him...

If it sounds like a gorilla is trying to escape, turn it down.
Back to Top
nev23 View Drop Down
Registered User
Registered User
Avatar

Joined: 08 September 2008
Location: Taunton, UK
Status: Offline
Points: 99
Post Options Post Options   Thanks (0) Thanks(0)   Quote nev23 Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2017 at 3:32pm
I once gave a man with a small organ satisfaction for £20.

I waived my usual minimum fee as it was a simple job, and an interesting old organ. All of the B keys were silent due to a cracked joint in the B oscillator.
Back to Top
studio45 View Drop Down
Old Croc
Old Croc
Avatar

Joined: 16 October 2007
Location: United Kingdom
Status: Offline
Points: 3863
Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2017 at 3:39pm
OK so I've done some more testing. The amps on their own is quiet. The crossovers are quiet. It's when you connect any appreciable length of XLR to the crossover input that the problem starts. So yeah, as has been said, it's probably not the mains. I have put 6 amp metal inline filters on the desk/FOH rack and crossovers though, just because it makes me feel better. I reckon I'll need them for a guitar amp sooner or later anyway.

The cable runs are really long - 2x30m from playback source to stagebox, then 2x30m *and back* in the multicore. So 180m of cable in total exposed to the field. Even if we could put the multi in grounded trunking, there will often be a need for long runs that can't be permanently installed.

However, there are still some logical inconsistencies going on. I have managed to get it set up so they can show a film next week, obviously the film soundtrack has quiet bits so a low noise floor is a must. To achieve this, I had to run the system from the matrix outputs on the desk, an A+H Zed420. Why they should behave differently to the main LR outputs, I have no idea. Before that I tried using the group outputs, which were much worse noise-wise even than the main outs. Again, no idea why that should be. The matrixes are much, much quieter. Perhaps I should check the other output sockets for bad soldering. Also, trying to use phantom-powered DI boxes is pretty impossible if you need to use any gain - *much* noise, and only gets worse with the ground lift engaged.
I've also reduced the gain at the input of the crossovers to -6dB and made the corresponding increase in the output level of the desk. For a better S/N ratio in the return lines.
Finally, I discovered that all testing to date had been done with playback from a suspicious .MKV file with a low audio track. Increasing volume to 400% in VLC Player made a big difference as I didn't have to use as much/any gain at the desk. On the night, we'll use a better source, so hopefully that will have a good strong output. 

And I mean, I haven't even tried plugging in 16 mic lines and gaining them up yet...sheeeeit.

By the way, it's actually BBC Radio Sheffield and BBC Asian Network. I've heard the channel idents enough times now. Often both at once LOL
Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
Back to Top
spongebob View Drop Down
Young Croc
Young Croc


Joined: 20 October 2010
Status: Offline
Points: 1395
Post Options Post Options   Thanks (0) Thanks(0)   Quote spongebob Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2017 at 3:43pm
Stupid question but you've checked all the XLRs you've been using to test, all wired correct and none have the XLR chassis tagged to the ground?
Back to Top
nev23 View Drop Down
Registered User
Registered User
Avatar

Joined: 08 September 2008
Location: Taunton, UK
Status: Offline
Points: 99
Post Options Post Options   Thanks (0) Thanks(0)   Quote nev23 Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2017 at 3:53pm
Outputs are also susceptible, and by varying amounts depending on configuration and component values. Something with a higher output impedance may quieter as a simple resistance in series with the output will also attenuate the interference coming in.

Do you like soldering?

A first, simple step might be to fit small resistors inside the XLRs going into the crossover. 470 Ohm would do, and even 1k probably wouldn't lose much audio signal. Also try this with the mixer outputs, but maybe 100 Ohms as they have to drive the cable capacitance.

If you are feeling brave, go inside the crossover. An older crossover, or anything with an input, may be easier to retro fit filters to if the sockets are wired rather than straight into a PCB.


Back to Top
studio45 View Drop Down
Old Croc
Old Croc
Avatar

Joined: 16 October 2007
Location: United Kingdom
Status: Offline
Points: 3863
Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 25 March 2017 at 2:31pm
Thanks for all the advice guys :)
I do likes me a bit of soldering so I does....So these resistors would go in series with the hot and cold signal wires of the XLR? Or across hot+cold, or from hot+cold to ground? I guess the aim here is to reduce the impedance of the long lines, so less voltage can be generated by the field?
I've got no problem modifying the crossovers. They are DCX2496's but I can tack components to the underside of the board. When you say a filter, do you mean just resistors or some kind of RC network?
Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
Back to Top
studio45 View Drop Down
Old Croc
Old Croc
Avatar

Joined: 16 October 2007
Location: United Kingdom
Status: Offline
Points: 3863
Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2017 at 6:17pm
Update - it is kind of working now. I retract my assumption that the mains supply is the problem. It's actually not. Well, probably. 

To achieve lowest amount of RF pickup, firstly the desk had to be powered from a different ring main than the amp racks. Obviously this is not normally best practice as it could easily result on an earth loop and 50Hz hum. I was just trying random things and found that if I used the sockets at the back of the hall rather than the power line that runs with the multi, it was marginally better. And, thankfully, no hum.

Secondly, I've had to rationalise the gain structure to minimise the amount of gain at the amp racks. -10dB at their inputs and +10dB at the desk faders gives me 10dB less noise. I think this will test my desk's output drive capability in some situations, so I'll probably have to find a way to solve that.

Thirdly, the source up on the balcony has to be plugged into the mains. To what might be the same ring as the desk, or possibly a 3rd ring. To ground it, you would think. However, none of the sources we have used actually have a ground connection in the plug - all the mains leads/chargers are double insulated and have a two-core lead and plastic earth prong. But, once you plug them in the last vestige of the RF disappears. Presumably down the neutral wire to earth at the substation?! It seems pretty mysterious to me.

This suggests to me that perhaps the actual earth connection at the mains at the amp racks is not so good - I estimate it is fed from at least 200m of 10mm twin-and-earth from the main incomer, and the earth conductor in that cable is pretty thin as far as I know? So that could potentially make it quite high resistance. I couldn't find any water pipes with an earth bond attached to them in the backstage toilets, or anywhere else in that corner of the building, so it would seem that the long feeder is the only place it is bonded. In fact I found what appeared to be an incoming water main (with a meter on it) and it was plastic. 
This again makes me consider installing a technical earth at that side of the building, which can be wired to the relevant consumer unit using nice thick wire. Like a copper rod or set of rods drilled into the earth outside the building wall.
Do you guys think that's a good plan? Obviously I would engage an electrician to do the work.
Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
Back to Top
nev23 View Drop Down
Registered User
Registered User
Avatar

Joined: 08 September 2008
Location: Taunton, UK
Status: Offline
Points: 99
Post Options Post Options   Thanks (0) Thanks(0)   Quote nev23 Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2017 at 10:51am
200m of earth wire is still an antenna, no matter how thick it is.
Some mains filters will also insert an inductor in the Earth line. Which would probably help. More expensive, though.
A local earth sounds good, but let the people who operate the transmitter know: a.m. antennas are usually non-resonant, inefficient, very narrow band and highly dependent on an extensive earthing system. Adding to or changing the earthing within 1/4 wavelength (50 to 150m depending on frequency) will de-tune the antenna.
Resistors in the signal lines should be in series, not parallel. Pin 2 and pin 3.
A wideband digital crossover may continue to be a problem, because any input filtering will probably be ineffective below 20MHz. If there is room to cut tracks, adding resistors in series, then capacitors to ground, and another common mode, would be a comprehensive solution.
Back to Top
_Natty_ View Drop Down
Young Croc
Young Croc


Joined: 01 April 2007
Status: Offline
Points: 663
Post Options Post Options   Thanks (0) Thanks(0)   Quote _Natty_ Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2017 at 2:39pm
can u see the silver paper on the preamp? lol one of the hardest nite of my life...alla signal cable covered by tinfoil all over, some net over me and around me to trying to made something like a farhad cage... yes we played but some noise from the radio antenna too lol


Back to Top
nev23 View Drop Down
Registered User
Registered User
Avatar

Joined: 08 September 2008
Location: Taunton, UK
Status: Offline
Points: 99
Post Options Post Options   Thanks (0) Thanks(0)   Quote nev23 Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2017 at 3:08pm
Back to Top
nev23 View Drop Down
Registered User
Registered User
Avatar

Joined: 08 September 2008
Location: Taunton, UK
Status: Offline
Points: 99
Post Options Post Options   Thanks (0) Thanks(0)   Quote nev23 Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2017 at 3:13pm
Spare chain link fence?
galvanising spray paint on the flight cases?

If you are going to do this regularly, I think you need some modified equipment. Getting line level inputs quiet is going to need some care, but getting mic and phono inputs will definitely need all equipment to be in metal boxes, with filters added to inputs, outputs and mains. Some clamp on ferrite cores would be useful, too, but you will need big ones at this frequency. But who makes CD players in metal boxes?
Back to Top
kedwardsleisure View Drop Down
Old Croc
Old Croc


Joined: 20 January 2009
Location: Staffordshire
Status: Offline
Points: 4938
Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 28 April 2017 at 10:34pm
Quote can we all stop bashing kens organ


Haven't had the Marlborough Director (organ) since I left home. One day I heard the Rediffusion engineer on a service call to next door's TV telling head office that the lady had a blocked hole in her shadowmask. The Hammond L100 would pick up next door's fridge and the current Hammond A100 is pretty silent.

It's Kev, BTW not Ken! Unless Ken has my old organ

Kevin

North Staffordshire

Back to Top
 Post Reply Post Reply Page  <1234>

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.06
Copyright ©2001-2023 Web Wiz Ltd.

This page was generated in 0.094 seconds.