Tube Mic mod (Repair)

Cujo · 20th March 2006

First of all I am pretty limited on my electronic skills, but I am looking for detailed info to bring to my tech who does tube amps like a champ but not mics,

The issue is in my Pacific pro Audio LD 2UBE Chineese OEM mic. (or its power supply)

It makes an intermitant but frequent low rumbly crackle (Self noise) the tube has been changed (it still does it), and actually this is the third mic from them, they have all done it. Someone suggested it was the PS, and something leaky in there.

If anyone has any suggestions, I would greatly appreciate them!

paully · 20th March 2006

If you have access to a scope, pull back the jacket of the XLR where the mic plugs into the PS and check the legs to ground. If the crackle doesn't show up there, it's probably in the PS after the phantom. Is the noise there without the mic plugged in? I'd unplug the cable at the mic end, then load the PS by putting a 1000 ohm resistor across the legs, with the XLR plugged into the PS (XLR jacket still pulled back). If the noise is still there, it's definately the PS.

A lot of times a crackle can be something as minor as a noisy resistor, a bad solder joint or (tube) contact. A noisy current limiting resistor in the power supply would certainly do this. Assuming that the mics are bench tested before shipping, and you've gone through 3 mics already, that pretty much narrows down the list of culprits. The only thing left is the wire.. hmmm.

Good luck, Paul

tunekicker · 15th July 2006

I had the same crackle problem.

I tightened up the connection for the XLR jack on the Power Supply and replaced the stock cable with a Mogami 7-pin. Hooked up to my gear via a Canare XLR, it sounds GREAT! Smoothed out the sound and cleaned up the highs a lot. No crackle anymore!

I also replaced the tube with an Electro-Harmonix tube- improved the sound as well. Think I'll try Telefunken next... :-)

Also, if you bought your mic more than 2 years ago and have as sneaking suspicion the shock mount sucks, it does. PPA replaced mine for free when I brough them the broken one.

I hope this helps solve your problems!

Peace,

rodabod · 17th July 2006

These cheap Chinese capsules can go bad quite easily too which causes rumbling, pops and washing noises.

20th March 2006	#1
Cujo Gear addict Joined: Nov 2004 Location: Boston Posts: 467 Thread Starter	Tube Mic mod (Repair) First of all I am pretty limited on my electronic skills, but I am looking for detailed info to bring to my tech who does tube amps like a champ but not mics, The issue is in my Pacific pro Audio LD 2UBE Chineese OEM mic. (or its power supply) It makes an intermitant but frequent low rumbly crackle (Self noise) the tube has been changed (it still does it), and actually this is the third mic from them, they have all done it. Someone suggested it was the PS, and something leaky in there. If anyone has any suggestions, I would greatly appreciate them! __________________ The Blizzard of 78 Killing Floor Records

17th July 2006	#4
rodabod Gear maniac Joined: Aug 2005 Location: London, UK Posts: 185	These cheap Chinese capsules can go bad quite easily too which causes rumbling, pops and washing noises. __________________ Roddy Bell BBC / Siemens

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20th March 2006	#2
paully Lives for gear Joined: Dec 2004 Location: Northern New Jersey Posts: 562	If you have access to a scope, pull back the jacket of the XLR where the mic plugs into the PS and check the legs to ground. If the crackle doesn't show up there, it's probably in the PS after the phantom. Is the noise there without the mic plugged in? I'd unplug the cable at the mic end, then load the PS by putting a 1000 ohm resistor across the legs, with the XLR plugged into the PS (XLR jacket still pulled back). If the noise is still there, it's definately the PS. A lot of times a crackle can be something as minor as a noisy resistor, a bad solder joint or (tube) contact. A noisy current limiting resistor in the power supply would certainly do this. Assuming that the mics are bench tested before shipping, and you've gone through 3 mics already, that pretty much narrows down the list of culprits. The only thing left is the wire.. hmmm. Good luck, Paul

15th July 2006	#3
tunekicker Gear interested Joined: May 2006 Posts: 28 2 Reviews written	I had the same crackle problem. I tightened up the connection for the XLR jack on the Power Supply and replaced the stock cable with a Mogami 7-pin. Hooked up to my gear via a Canare XLR, it sounds GREAT! Smoothed out the sound and cleaned up the highs a lot. No crackle anymore! I also replaced the tube with an Electro-Harmonix tube- improved the sound as well. Think I'll try Telefunken next... :-) Also, if you bought your mic more than 2 years ago and have as sneaking suspicion the shock mount sucks, it does. PPA replaced mine for free when I brough them the broken one. I hope this helps solve your problems! Peace,