mikefox whiskey
Accomplished DX-er
Registered: 02-2009
Location: Northern Ireland
Posts: 403
Karma: 1 (+1/-0)
|
|
Reply | Quote
|
|
 AUDIBLE HUM FROM MICROPHONE.
I wonder if anybody can help, I have an Astatic 1104c base microphone which I have just wired to my Kenwood TS850s, when I transmit audio there is a loud hum on my speech, when I touch the metal base of the mic or the shield of the mic cable when opened the hum goes down quite a bit but is still audible, through the monitor I can here that the mike is making an electronic clipping sound too.
I have followed the same wiring diagram as other astatic mics I have.
Has anybody any ideas what is wrong or experiences of using astatic mikes and a kenwood TS850s?
Last edited by mikefox whiskey, 11/Mar/2009, 9:35 pm
---
(Forum user name is now SuperNasty)
|
|
11/Mar/2009, 9:34 pm
|
Link to this post
Send Email to mikefox whiskey
Send PM to mikefox whiskey
|
yamanx1
Head Honcho
Registered: 09-2007
Location: In a world of my own
Posts: 4894
Karma: 40 (+41/-1)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
Hi Pat, I know this sounds obvious, but are you absolutely sure there is no shorting across the terminals?
And GRD and earth are two different pins, so Shield and BLK (earth) are not wound together , this is from memory Pat and I think pin 8 is blk and shield is common (Casing).
Sorry if that doesnt help 
---
By all means think yourself big, but never think others small.... R.F.Scott |
|
11/Mar/2009, 10:13 pm
|
Link to this post
Send Email to yamanx1
Send PM to yamanx1
|
Hot Fusion
Management
Registered: 03-2008
Location: South West England
Posts: 1389
Karma: 7 (+7/-0)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
I'm not familiar with the wiring on this setup, but it sounds to me as though the case of the microphone isn't earthed.
You can check this by holding a wire between the metal of the mic and metal on the rig - the hum should disappear. If it does, you need to identify the earth on the mic lead, and make sure it is connected to the earth on the rig.
Do you get any RF feedback? This can happen if the case of the mic isn't earthed and screening it properly.
---
Andy - 26 FB107
|
|
11/Mar/2009, 10:24 pm
|
Link to this post
Send Email to Hot Fusion
Send PM to Hot Fusion
|
mikefox whiskey
Accomplished DX-er
Registered: 02-2009
Location: Northern Ireland
Posts: 403
Karma: 1 (+1/-0)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
Hi Dave and Andy, Thanks for your replies, I have tried what you suggested and checked the earth wire and the other wires in the lead and it seems to all be fine, the problem is still there, is it possible that a resistor or diode inside the amplifier circuit in the mic be broke? I dunno, maybe there is another wiring configuration I can use?
This is how the wiring is:
Astatic 1104c Microphone (all astatic mics have these colours)
White - Audio
Shield - Ground
Red - TX Control
Blue - Switching/Common
Black - Receive Control ?
Yellow - ?
Kenwood TS850s (8 pin plug)
Pin 1 - Mic
Pin 2 - Stby
pin 3 - Down
Pin 4 - Up
Pin 5 - 8V/approx 10mA
Pin 6 - NC
Pin 7 - GND (Mic)
Pin 8 - GND (Stby)
Now this is the way I have the 1104c mic wired to the TS850s:
White - Pin 1
Shield - Pin 7
Red - Pin 2
Blue - Pin 8
Black - not connected
yellow - not connected
I don't know if this wiring code makes any sense or any help to anybody, but I thought I would put it on anyway.
Perhaps I will get in touch with the seller (eBay) though there was no returns stated on the mic listing.
On another point, I have an Astatic 575-M6 mike with the same wiring, from the info I have given could somebody tell me how to wire the mic up to take the power from the Kenwood transceiver and not the internal 9V battery in the mic?
Thanks.
Last edited by mikefox whiskey, 12/Mar/2009, 7:32 pm
---
(Forum user name is now SuperNasty)
|
|
12/Mar/2009, 7:25 pm
|
Link to this post
Send Email to mikefox whiskey
Send PM to mikefox whiskey
|
John193
Freebander
Registered: 11-2008
Location: South Glos
Posts: 260
Karma: 3 (+3/-0)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
Patrick have you tried combining the un-used leads and attaching them to the radio ground ie the case, it could be harmonic length? is the screen intact? are the decoupling ceramic disc caps in good elec contact with ground? Other than that Dunno! John fb193
|
|
24/Mar/2009, 4:00 pm
|
Link to this post
Send Email to John193
Send PM to John193
MSN
|
mikefox whiskey
Accomplished DX-er
Registered: 02-2009
Location: Northern Ireland
Posts: 403
Karma: 1 (+1/-0)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
quote:
John193 wrote:
are the decoupling ceramic disc caps in good elec contact with ground? John fb193
Hi John, thanks for the reply, I tested all the wires and the screen with a multi meter and they seem fine.
Where in the microphone do I find the decoupling ceramic disc caps you mentioned?
Thanks
---
(Forum user name is now SuperNasty)
|
|
25/Mar/2009, 6:40 pm
|
Link to this post
Send Email to mikefox whiskey
Send PM to mikefox whiskey
|
John193
Freebander
Registered: 11-2008
Location: South Glos
Posts: 260
Karma: 3 (+3/-0)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
They are across the mic socket in rig Patrick they help present the right load to the audio amp, Different impedance mics need different values ideally, normally the manufacturer fits a middle of the road 100n in there but some mics need less power mics normally need more. Bye the way is the hum 50hz mains by any chance? john193
|
|
26/Mar/2009, 8:14 pm
|
Link to this post
Send Email to John193
Send PM to John193
MSN
|
mikefox whiskey
Accomplished DX-er
Registered: 02-2009
Location: Northern Ireland
Posts: 403
Karma: 1 (+1/-0)
|
|
Reply | Quote
|
|
 Re: AUDIBLE HUM FROM MICROPHONE CURED!
The audible hum from my Astatic 1104c desk mike is now cured, HOORAY! it turned out that there was a pin prick hole in the microphone's ceramic element (how it got there I don't know) I have replaced that element with one from my Astatic 575 m6 microphone and all is working now. 
Thanks for all the suggestions.
---
(Forum user name is now SuperNasty)
|
|
5/Apr/2009, 5:02 pm
|
Link to this post
Send Email to mikefox whiskey
Send PM to mikefox whiskey
|
Hot Fusion
Management
Registered: 03-2008
Location: South West England
Posts: 1389
Karma: 7 (+7/-0)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
Glad it's cured, but that pin prick hole may be there to allow atmospheric presure equalisation if it was in the actual diaphram - it may not have been the fault.
---
Andy - 26 FB107
|
|
5/Apr/2009, 7:16 pm
|
Link to this post
Send Email to Hot Fusion
Send PM to Hot Fusion
|
mikefox whiskey
Accomplished DX-er
Registered: 02-2009
Location: Northern Ireland
Posts: 403
Karma: 1 (+1/-0)
|
|
Reply | Quote
|
|
Re: AUDIBLE HUM FROM MICROPHONE.
You could be right Andy, that hole is maybe supposed to be there, if it was though there must of been a problem inside the diaphram itself maybe? I don't know enough about microphones to know what is even in there, anyway replacing that diaphram with another one (though slightly different) has cured the problem.
I don't know if I have another problem now, but when I am transmitting after about 20 minutes I think I can here RF in the headphones and a roughness on the audio, I seriously don't know if it's real or in my head! I have been working too hard recently! I wonder could it be the 9v battery though I've tried a few.
I wish I could find out what wires to use to take the power for the microphone from the radio and do away with the need for a battery.
---
(Forum user name is now SuperNasty)
|
|
5/Apr/2009, 11:06 pm
|
Link to this post
Send Email to mikefox whiskey
Send PM to mikefox whiskey
|
