R/E/P Community
R/E/P => Klaus Heyne's Mic Lab => Topic started by: gepposound on April 07, 2013, 10:03:55 AM
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Yesterday i plugged to my gml preamp 2 mic cad100s for a recording session and i found that both mic are not working properly , they produce a very low volume i think -30 to -40 db to normal, they also lost a lot of low frequency .......Can you help me to understand where is the problem ? why this problem has affected both mic that are always in their box ?
I attach a photo of the mic electronic.
Here there is a recorded sample with 50db of pramp gain.
https://soundcloud.com/giuseppe-loriga/cad-e100-troubleshooting (https://soundcloud.com/giuseppe-loriga/cad-e100-troubleshooting)
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why this problem has affected both mic that are always in their box ?
1. Your setup is correct?
2. 48V phantom power on the GLM.
2b. Plug in a dynamic mic (SM58 or whatever is handy).
3. Check CAD's PSU if both mic's use a combined one (I could not exactly identify what type of mic you are talking about, so this tip might be obsolete).
4. Try any other preamp.
5. Check your setup again :)
Regards
Kai
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Thanks Kai,
I tried both mics with differents preamp and cables and nothing change ,
when i use the -10db switch the volume is the same and when i turn on the high pass filter a low frequency
hiss is added to the floor noise.
can understand why both mics have this issue !!
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why both mics have this issue !!
It's extremly unlikely that both mic's break at the same time the same way except they suffered the same damaging circumstance.
This is what could damage both mic's at a time:
- Strong overvoltage on the phantom power.
- Lightning strike nearby (VERY close).
- Extreme moisture like fluid water going into the case.
- Extreme high SPL like from an explosion or gunshot nearby or a very hard hit on the closed case.
- Very hard drop to the floor without dampening like from case foam inserts (relatively unlikely).
All not very likely and partly quite obvious (water) - so the question remains:
did you check your setup against a simple dynamic mic?
I mean, replace the CAD in your setup with a dynamic to check functionality.
Regards
Kai
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Thanks Kai ,
I replaced in my setup the cad with dynamics and other condensers and they
work perfectly !!!
I also tried both mics with an A&H small mixer for some tests and i found very low volume and tiny sound.
The last time i used both mics was i think for a recording test with drum toms.
Anyway i don't think that the spl of a tom percussion could damage the capsules.
And about the moisture i didn't have problems with the other mics i have.
Probably it could be the phantom power, but i have i power conditioner that make
protection over peak voltage , and probably the gml preamp has a voltage regulator for the phantom 48v
Any suggestion about testing the electronics of the mic ?
Should i test the capsule bias voltage ?
Regards
Giuseppe Loriga
www.docsound.net
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make sure the two internal 9V batteries are fully charged! If in doubt, replace them (temporarily) with Alkaline batteries and test the microphones without 48V phantom power.
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Thanks ,
I have checked but i doesn't have any battery inside, it's the new cad E100s
made in USA .
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Provided that you're a bit familiar with electronic repair:
Feed an audio signal into the point, where the capsule is connected.
Use a ca. 1nF cap and a 2k series resistor to do so (values do not need to be exact).
The usual amplification of a healthy cond. mic amp is between -6 to +6 dB, so the mic should send out about the same level that is feed in.
If this is the case, it's likely that the polarisation voltage is missing or (less likely) the capsule is broken
If you have a schematic of the circuit you could measure the internal voltages at several points to find the fault.
If you have a scope, you can trace the signal.
If you're not familiar with this put the schematic in here and I can give you some hints.
If you're not familiar with electronic repairs, let it be repaired by the factory.
Regards
Kai
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Thanks Kai ,
I have some experience with electronics repair,
but don't have the schematics of the mic board ,
so this week-end i will check the amp the way you suggest me.
Anyway i'm thinking that it's a problem to amp of he mic related to phantom power.
Regards
Giuseppe Loriga
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Look at that pcb. It's a small, tight surface mount design. You can attempt to trace and fix it, but at CAD they wouldn't waste their bench time. They would swap that pcb and send you the bill. Surface mount designs are not made to fix but replace.
Even if you find the problem do you have the skills needed to successfully remove the bad parts and replace them? Look at those transistors, all stuffed up against each other.
Like the Gambler says:
"You got to know when to hold 'um, know when to fold 'um".
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... successfully remove the bad parts and replace them?
I've done those SMD repairs quite often.
The main problem is to locate the broken part - you can't just replace parts to try out as easy as with wired elements.
On the other hand this forces you to analyse the fault more seriously instead of fooling around - not that bad a thing.
Once removed, the SMD element can be replaced by a small wired one usually, if an SMD isn't handy.
An newer CRT-monitor can be a good source for small wired electronic parts if you don't have a dealer around. But don't use the electrolytic caps from it - they are half dried out mostly.
Regards
Kai