Ward Beck M470A phantom power issue.
« on: May 30, 2010, 10:59:19 AM »
Hi all!

i recently got a lot of troubleshooting help here with some auditronics 110a modules (which are now running beautifully).


I've now come back with my tail between my legs, looking some help with my new ward beck m470a modules :(

i'm aware of the WBPS forum, but have been waiting for account verification for ages,,,so i thought i'd come here,,



My two modules are racked up and working beautifully, apart from one fault.

I've added my own phantom power, as per a few guides on the wbs site.

This simply provides +48 in and out of a mic/line switch, so that 48 volt is only present on mic selection.
It is then sent (via 2 6.8k resistors) to mic pins 1+2.

This works flawlessly on both units.




The units have a built in pad switch. when this is engaged, one unit is still fine, but the other only provides 12v for phantom power?!??


i've tested the voltage at various points and it seems that 48 volt is still present right the way up to the two resistors before mic pin 1+2, but on the mic side of the resistors i read 12v.
This is with or without a microphone.....


The schematic can be found here, but i think there's no amount of staring at it that's going to help me......

http://wbsps.kuzub.com/PDFs/M470A%20Input%20Module.pdf

can anyone see how this would be possible? or what kind of fault would cause it?





If it's any use the pinout is on page 21 and my phantom works like this.

1  +48 from psu into P2 X

2   with mic selected, +48 comes out of P2 U

3   this is taken, split into two, each fed through 6.8 resistors and sent to p1 w and p1 19.


P1 W AND P1 19 read 48v with no pad, and 12v with pad.


Much thanks in advance everyone!



okgb

Re: Ward Beck M470A phantom power issue.
« Reply #1 on: May 30, 2010, 11:08:35 AM »
If the only difference is the pad ,
are both of thoses equal ? check the resisters
[ or maybe just the solder connections
resistances  [ to ground ? or just across input ]
have not drifted , switch is o.k. ?

If you find you like them , it wouldn't hurt to
tightly match those resisters ahead of the xfmr
for best common mode rejection
« Last Edit: May 30, 2010, 11:13:42 AM by okgb »
GKB Audio / Greg Boboski

Re: Ward Beck M470A phantom power issue.
« Reply #2 on: May 30, 2010, 11:12:29 AM »
i'm sorry, i don't mean to sound rude, but, i don't understand what you mean...



i haven't tested the switch yet, but i have a feeling that it works,,cos if you use a mic with 48v and no pad,,,then flick the pad on,

it will work for a few seconds at reduced volume......then the input level fades away as the power runs out i guess?

3nity

Re: Ward Beck M470A phantom power issue.
« Reply #3 on: May 30, 2010, 11:14:40 AM »
you said Phantom to pin 1 and 3.
Should be 2 and 3.
Life is a path, death the destination.

okgb

Re: Ward Beck M470A phantom power issue.
« Reply #4 on: May 30, 2010, 11:16:49 AM »
check that all the resisters are what they're supposed to be
there is a center tap ground point on the pad that could be bleeding off voltage
it 's gotta be before the xfmr and there isn't much there so if you have one thats working
you have something to compare values to

Quite right 3nity , pin 1 is always ground
GKB Audio / Greg Boboski

Re: Ward Beck M470A phantom power issue.
« Reply #5 on: May 30, 2010, 11:17:29 AM »

my mistake,,,,i meant schematic mic 1+2,,,,,not microphone cable pins....





the schematic has mic 1,2 and ground so 48v goes to 1+2....



Also,,,,both units operate perfectly with phantom power on......its only one of the units that stops working with the pad on....



Incidentally, i forgot to mention,,,the pad works perfectly with dynamic mics....


Thanks :)
« Last Edit: May 30, 2010, 11:20:26 AM by steenamaroo »

Re: Ward Beck M470A phantom power issue.
« Reply #6 on: May 30, 2010, 11:18:40 AM »
ok okgb,,that's something to look into......did you see this ground point on the schematic? if so,where is it?

thanks very much!!

okgb

Re: Ward Beck M470A phantom power issue.
« Reply #7 on: May 30, 2010, 11:45:15 AM »
the two 47 something resisters on the pad are centertapped to ground ,
but if you say the pads works ..........still seems worth checking
do the two pads seem equal in attenuation ?

Sorry that's R9 & 10  91 ohm in the pad
actually now that i look harder there's a cap to ground
also worth checking out
« Last Edit: May 30, 2010, 12:35:43 PM by okgb »
GKB Audio / Greg Boboski

Re: Ward Beck M470A phantom power issue.
« Reply #8 on: May 30, 2010, 11:47:12 AM »
with dynamic mics,yeh,,the pads seem equal...

the only other thing worth noting is that without pads, one unit reads 48v and the problematic unit reads 44.8, but i only just realised this.....don't know if it's important...


i'll check out those resistors. thanks :)


are you talking about r11 and r12? i thought that was the input transformer that they are on!??

the only ones i see on the pad are 750x2 and 91x2?


**EDIT** on the problem unit, i read 44.8v on one side of r11 and r12, and ground on the other side.

on the good unit, i read 48v on one side of r11 and r12, and ground on the other.
« Last Edit: May 30, 2010, 11:57:13 AM by steenamaroo »

PRR

Re: Ward Beck M470A phantom power issue.
« Reply #9 on: May 30, 2010, 01:44:39 PM »
Snip C2 and see what changes.


Re: Ward Beck M470A phantom power issue.
« Reply #10 on: May 30, 2010, 01:47:37 PM »
found r9,r10 and c2.


r9 and 10 read 55ohms instead of 91, so i'll swap them out and do the cap while i'm at it....



Thanks all :)

Re: Ward Beck M470A phantom power issue.
« Reply #11 on: June 05, 2010, 06:22:54 PM »
a new cap did the job...
thanks very much for the help again folks!!


 

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