Behringer PMH300 noisy phantom

garybates · 15th February 2009, 04:09 PM

I noticed last year that the first two channels on my PMH3000 had intermittent crackles on them when using phantom powered mics. If dynamic mics are connected and the 48v switched off all is ok. All other channels are fine even with phantom powered mics.
This year channel 2 has got much worse and is completely unusable with the 48v switched on.
Has anybody else had similar problems ? I have disassembled the unit and tried to swop the larger capacitors around in the front end (between ch2 and ch3) but had no joy at tracing the source of the noise,
thanks
gary

garybates · 19th February 2009, 01:40 PM

Does anyone have a schematic diagram for the input stage of a channel on this mixer to show the phantom powering ?

Nigel Goodwin · 19th February 2009, 04:27 PM

I've got an MX802 circuit, but really theres very little in phantom powering - just two 6K81 resistors feeding 48V to the input pins.

Perhaps the coupling capacitors from the input to the ampliifer are leaky?, they have to block the 48V DC.

garybates · 18th March 2009, 01:39 AM

Thanks for your reply.
Yes Ive had a closer look and see what you mean. The curcuit is very simple around the XLR. Ive pulled the two 47uF/50v caps that couple the XLR to the mic input and some more caps are on order.I'll let you know how I get on
regards
Gary

15th February 2009, 04:09 PM	#1
garybates diyAudio Member Join Date: Feb 2009	Behringer PMH300 noisy phantom I noticed last year that the first two channels on my PMH3000 had intermittent crackles on them when using phantom powered mics. If dynamic mics are connected and the 48v switched off all is ok. All other channels are fine even with phantom powered mics. This year channel 2 has got much worse and is completely unusable with the 48v switched on. Has anybody else had similar problems ? I have disassembled the unit and tried to swop the larger capacitors around in the front end (between ch2 and ch3) but had no joy at tracing the source of the noise, thanks gary

19th February 2009, 04:27 PM	#3
Nigel Goodwin diyAudio Member Join Date: Jul 2005 Location: North Derbyshire	I've got an MX802 circuit, but really theres very little in phantom powering - just two 6K81 resistors feeding 48V to the input pins. Perhaps the coupling capacitors from the input to the ampliifer are leaky?, they have to block the 48V DC. __________________ Nigel Goodwin

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Phantom Power might be Bad?	mistermisfit	Solid State	12	10th February 2010 08:22 PM
+/-15V from +48V Phantom	Pilbromatic	Parts	4	9th August 2009 05:46 AM
whu 6800ohms for mic phantom pwr?	SemperFi	Instruments and Amps	3	19th February 2009 04:20 PM
noisy noisy noisy noisy noisy tube	dsavitsk	Tubes / Valves	50	20th February 2006 04:07 PM
phantom powering non-phantom mics	karambos	Instruments and Amps	8	3rd January 2004 09:21 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

19th February 2009, 01:40 PM	#2
garybates diyAudio Member Join Date: Feb 2009	Does anyone have a schematic diagram for the input stage of a channel on this mixer to show the phantom powering ?

18th March 2009, 01:39 AM	#4
garybates diyAudio Member Join Date: Feb 2009	Thanks for your reply. Yes Ive had a closer look and see what you mean. The curcuit is very simple around the XLR. Ive pulled the two 47uF/50v caps that couple the XLR to the mic input and some more caps are on order.I'll let you know how I get on regards Gary

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)