Pyramid PA-305 Amp... I shorted the mic input and lost phantom power. I see a burnt resister, unmarked, but it sits between capacitors C106 and C107. Can anyone ID this resister or provide a schematic? Thanks

Sounds like your Phantom power supply may be defective. To be safe, 1st try moving AC plug for Phantom supply to another outlet as sometimes "sharing grounds" can be a problem. If this doesn't help, try using another phantom power source ...many PA mixers have built-in phantom power. If the buzz disappears with a new one, it will be a filtering issue (capacitors) with the old phantom supply.

There is really no way for a condenser mic to damage the board UNLESS you break the ground and get a static discharge into the input. That can happen with any microphone and has NOTHING to do with the phantom being on or off. As phantom power goes on and off slight bias at the input preamps can make amps non-linear causing the raspy sound you heard. The Phantom LED means NOTHING as it shows the state of the phantom switch by connecting a 12 volt source through a resistor to the LED... It shows NOTHING regarding the state of the 48 volt supply. Each input circuit has two 6.8Kohm resistors to the swinger of the phantom switch 2nd pole that either grounds those or connects them to a filtered 48 volt source. As long as you don't have a static buildup there is NO need to turn phantom power on or off while connecting a condenser microphone. At each input when using the XLR jacks are two per side 470pf capacitors for RF bypass. For the XLR's there is a 10Kohm between the signal lines and two series 10mfd/50 volt caps in series of each input to block the DC, when using phantom power, from reaching the preamp stage. These caps have to charge and discharge when changing the state of phantom power so you should AVOID having the main amps being driven while changing the state of any phantom power. Always have the fader(s) down and any monitors down to avoid a thump and also the non-linear raspy transition as the input caps charge/discharge. So fix the microphone... don't know what type you have, but DO check the cable (first) as ALL three conductors MUST be good for a condenser mic to work on phantom power. A ground leakage or noisy connection will cause your symptoms. Use a SHORT known good cable right at the board to test the mic. The 48 volts is applied through the two 6.8K resistors between both the signal lines to the shield of your XLR cable. The microphone picks off the 48 volts with a similar circuit.
Now let's cover a very important thing regarding system safety: ALL, and I do mean ALL interconnected equipment MUST be powered from the same source. Professionals run a power cord back to their mixer right alongside the snake. This is to avoid ground bounce damage due to bad building grounds or ground faults.

I don't believe the GXL2200 has a power switch directly on the microphone itself. Would you be able to tell me how you are supplying phantom power to the microphone?

I don't have the exact schematic... however sometimes they have RF bypass capacitors to ground on the balanced input lines and one side gets shorted. The schematic I do have is for an AC100. It shows a rather unconventional input circuit. You can download it here and it MIGHT be close to your unit:

http://elektrotanya.com/roland_ac-100ut.pdf/download.html

I note that this unit does NOT have Phantom power so you CANNOT use a condenser type mic with it unless you use a preamp with Phantom power... Maybe that is the problem?

Make sure you have Phantom power turned on on the Lexicon... Oh,oh... it appears that the Alphs may NOT have phantom power which IS a REQUIREMENT for most condenser mics...

The Lexicon Omega does have this but apparently the Aplpha doesn't have it.

That leaves you with the choice of either getting a dynamic mic that doesn't need Phantom, or replacing the Alpha, OR using a preamp ahead of the mic before the Alpha...

Sorry, but those are the only solutions I see for you.

REMEMBER that condenser mics pick up everything and you cannot run them into a PA or they will feedback.

A little testing is required to nail this down.

1) Will a standard mic work in either channel?
2) Will a line level source work in either channel?

It is likely that either the power supply for the phantom power or the supply for the mic pre-amp IC has failed or the IC itself has failed. If a standard mic works, then it is the phantom power supply that is faulty.

I am not aware of any service manual available other than from Yamaha directly (for a price of course...)

If you can update this with the test results, perhaps we can walk through this repair.

Dan

You will need a pre amp that supplies whats called phantom power which is power that feeds the mic .. This will come from either mixers [small cheap ones..but check it has XLR mic input with phantom power] or from a stand alone pre amp or audio interfaces with built in inputs for mics with phantom power.. Also you will need an XLR mic lead..Buy a good one with neutrik plugs or similar..

Well, it is hard to find new 15" LCD monitors these day, new one are so cheap (and cheaply made also), it can be a good learnibg experience for some one who is learning electronics to try to fix it.

Does your microphone have it's own built in phantom power? If it's just a regular mic, you should be able to connect into any MIC inputs on your Amplifier. Otherwise, you'll have to utilize a mic/line mixer to provide the phantom power your mic needs. Then you would connect your mixer to the amplifier.

Which SHS Audio amp do you have? The ones that I am familiar with do not have any MIC inputs.

- OPTiC
Master Tech
DJ PRO AUDIO
Pro Audio Equipment : Pro Audio Repairs

The CO2 is a condenser mic (also called capacitor mic), and as such, requires phantom power to operate. Ensure that your system is providing phantom power to the microphone, usually accomplished by flipping a switch near your mic input on your sound board.