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Need technical help.
Old 26th February 2014
  #1
Here for the gear
 
๐ŸŽง 5 years
Need technical help.

Thank you for anyone who can provide some advice with this issue. I have a Blue Baby Bottle that is running into a GAP Pre 73. From there I am going into a Saffire pro 24. The other day I started getting a static that was intermittent. When I first powered on my pre 73, it made a shooting static sound. Almost like someone saying, "shhhhh". Lol. Best way to describe it. It was present most of the time but it really kicked up when I would speak on the mic. Any ideas? Thanks again.
Old 26th February 2014
  #2
Lives for gear
 
Lotus 7's Avatar
 
1 Review written
๐ŸŽง 10 years
You need to determine if the problem is being caused by the mic, the mic pre or even the mic cable.

The easiest way to do that is to substitute a different mic.

You said "When I first powered on my Pre-73, it made a shooting static sound." Do you mean when you turned on the power for the GAP Pre-73, or when you turned on the phantom power for the mic? If it was the former (high noise level with the mic pre on, but phantom power off), then it's probably the GAP Pre 73 having problems. If the noise occurred when phantom power was applied to the mic, then it's more likely the mic is causing the noise. There is also a small possibility that your mic cable has developed a defect.

If the latter (noise with phantom power on only): Has the mic been exposed to any excess moisture? Has a cold mic been brought into a warm room? (possibility of condensation in the capsule). If so, place the mic in a warm, dry place for 24 hours to dry out any moisture.

Hopefully, you are not turning the GAP pre73 main power on and off with the phantom power (The front-panel switch marked "48V") on. The GAP Pre-73 should always be powered on for a few seconds and allowed to stabilize before switching the "48V" phantom power on. The phantom power switch should always be switched off and allowed to "bleed-down" for a minute or two before switching the Pre-73 main power off.

Again, the best way to isolate the problem is by substitution: Try another mic cable, borrow another mic.

Generally, if you get an excessive amount of noise when phantom power is applied the most likely problem is a defective mic. Capacitor mics can "die" for a number of reasons, and are the most fragile component in most audio signal paths. If the noise problem can be isolated to the mic, then a trip back to Blue is in order. Unless you have mic repair experience and expertise, capacitor mic repair is best left to those who do.

The next most likely problem is probably a damaged mic pre. They can go bad, but also can be damaged by connecting/disconnecting mics with phantom power on, and can also be damaged if a defective mic cable is used. Yes, a bad cable can "break" a mic preamplifier.

Third possible cause: Defective mic cable. Even new cables can have bad solder joints, and cables that are abused can fail. This happens more often on cables used in live performance than those used in home studios for obvious reasons.
Old 26th February 2014 | Show parent
  #3
Here for the gear
 
๐ŸŽง 5 years
I can honestly say that I am guilty of powering pre on with phantom engaged. I didn't know about the powering on technique. That's a rookie mistake on my part definitely! Thank you! I did remove the pre from the chain and routed straight from mic into the saffire pro and the static went away. I didn't care for the quality without the pre in the chain but none the less it did sound better. I hate to know that I messed up the pre but I can't make excuses. I like the pre 73 with the blue but I have been thinking of getting something different as far as pre's go.
Old 26th February 2014
  #4
Lives for gear
 
Lotus 7's Avatar
 
1 Review written
๐ŸŽง 10 years
Sorry about that.

Mic pre inputs are very sensitive because of the very small voltages they must deal with. Mic signals range from 100's of microvolts for weak sounds to only 10's of millivolts for louder signals. Phantom power applies a 48 volt transient pulse to the input every time it's turned on and off. Most mic pres have "protection" circuits that attempt to protect the mic input stage components (usually a integrated circuit of a couple of discrete transistors). The protection circuits limit the current surges in the input coupling capacitors and the damaging high voltage transients that can be created across the input terminals of the semiconductor components.

The protection circuit components often include "clamp diodes" and sometimes Zener diodes that divert excess transient currents into the power supply "rails" (power carrying buses). If the power supply is not up to full voltage and stable, the protection circuits don't function correctly. The 48V phantom supply probably turns on faster than the main power rails. On phantom power turn-off, letting the phantom power drop down slowly as it will when it's turned off will reduce the power transient, both to the mic and the mic pre input.

If the pre is definitely causing the noise and distortion you're hearing it may be input damage related, or it may be from some random component failure that you had no control over. Either way, it should be a relatively simple repair for GAP.
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