MXL603s weirdness :confused:

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reshp1

reshp1

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Was doing a little recording last night when I noticed a strange hiss from one of my MXL603's. It would only come when there was silence, after picking up a little sound, the hiss would go away and swell back as the sound faded, almost like I was "ducking" the noise with a slow release setting. I checked all my connections and they were good, but noticed that immediately after turning on Phantom power, the mic would work normally for 15 seconds or so before the hiss swelled back.
Not knowing if it was the mic or the pre (M-Audio Octane) or cable, I swapped the hiss mic and the other working 603. The hiss followed the mic. I also tried another set of SDC's on the Octane and they worked fine, so it didn't seem to be the preamp or the cable.
Now here's the really weird part.... I tried both 603s on the pres of my Digi 002R and they worked fine, which would suggest it wasn't the mics. :confused: :confused:
The only thing I can figure is that the Octane and 002R put out different Phantom power levels, and it seems to make a difference for only one of the 603's. The part about how the hiss would "charge up" and "charge down" does seems like a capacitor charging and discharging.
Anyone seen this before or have any ideas? or should I just avoid using the 603's with my Octane? Thanks in advance for any help
 
reshp1 said:
The part about how the hiss would "charge up" and "charge down" does seems like a capacitor charging and discharging.
Anyone seen this before or have any ideas? or should I just avoid using the 603's with my Octane? Thanks in advance for any help
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I'm not an expert and we do have an in-house Electrical Engineer which could probably answer this question more adequetley than I will.
However, if you tested a different mic and it didn't do the test, and you tested the mic by itself (Am I correct?) using the same setup and it didn't do the hiss.
Then you power is none of the components but your power. Although, it's really hard to know what you tested by your message.

1. Try the 603 with the set-up that makes the hiss (ensure you hear the hiss).
2. Remove one thing (another mic - perhaps) see what happens.
3. Turn everything on in your room that you had previously turned on and see if the hiss returns.

IMHO I think that it's your power. If the hiss has a cycle (I'm guessing 60Hz cycle) then it could be from a power source, or perhaps your computer. What bothers me is that you say that the hiss follows the mic, when you swapped it for the other 603. You would either need to list more detail information and what has/has not caused hissing.
 
reshp1 said:
Was doing a little recording last night when I noticed a strange hiss from one of my MXL603's. It would only come when there was silence, after picking up a little sound, the hiss would go away and swell back as the sound faded, almost like I was "ducking" the noise with a slow release setting. I checked all my connections and they were good, but noticed that immediately after turning on Phantom power, the mic would work normally for 15 seconds or so before the hiss swelled back.
Not knowing if it was the mic or the pre (M-Audio Octane) or cable, I swapped the hiss mic and the other working 603. The hiss followed the mic. I also tried another set of SDC's on the Octane and they worked fine, so it didn't seem to be the preamp or the cable.
Now here's the really weird part.... I tried both 603s on the pres of my Digi 002R and they worked fine, which would suggest it wasn't the mics. :confused: :confused:
The only thing I can figure is that the Octane and 002R put out different Phantom power levels, and it seems to make a difference for only one of the 603's. The part about how the hiss would "charge up" and "charge down" does seems like a capacitor charging and discharging.
Anyone seen this before or have any ideas? or should I just avoid using the 603's with my Octane? Thanks in advance for any help
Click to expand...

It sounds like it was/is that mic. A filter cap could be responsible, but the easiest starting point would be the likliness that there was condensation on the capsule. Dry out the mic using one of the dozens of different methods and try again.
 
Sorry, I just read my post again and it's a little unclear. Here's my series of experiments. Hope this is clearer

MXL #1 > Cable 1 > Preamp 1, channel 1
MXL #2 > Cable 2 > Preamp 1, channel 2

Hiss heard on channel 2

MXL #2 > Cable 1 > Preamp 1, channel 1
MXL #1 > Cable 2 > Preamp 1, channel 2

Hiss heard now on channel 1.

Other SDC #1 > Cable 1 > Preamp 1, channel 1
Other SDC #2 > Cable 2 > Preamp 1, channel 2

No hiss

MXL #1 > Cable 1 > Preamp 2, channel 1
MXL #2 > Cable 2 > Preamp 2, channel 2

No hiss

Repeated
MXL #1 > Cable 1 > Preamp 1, channel 1
MXL #2 > Cable 2 > Preamp 1, channel 2

Hiss still on channel 2

So it seems like MXL #2 has a problem, but only with preamp1
 
reshp1 said:
So it seems like MXL #2 has a problem, but only with preamp1
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Or the other way around, but it's probably the 603 if preamp 1 is working well with all the other mics. Sometimes moisture causes that, but it's still confusing since your other mics are ok. Sounds like a faulty component. Send it back to MXL - they have a great warranty!
 
Well, it's certainly weird. I know your title said that, but it warrants repeating. I am assuming that when you change the mic from channel 2 to 1 you also switched cables (meaning all you moved was the mic).

Where the mics actually moved from a certain location to change the channels or did they remain in their shockmounts? I know it's stupid, but is perhaps you mic stand touching something the other one is not, and hence the noise 'follows' the mic.

I'm just thinking of stupid crap that could be a potential problem. What get's me is that if it were moisture it should make the hiss on either pre. Where the setting set the same on both pre-amps?
 
Dracon said:
IMHO I think that it's your power. If the hiss has a cycle (I'm guessing 60Hz cycle) then it could be from a power source, or perhaps your computer
Click to expand...

That would be a 'hum' a 'buzz' or a 'tone' depending on what way you look at it - 'hiss' is an entirely different beast and is spread over a range of frequencies - see white noise
 
paddyponchero said:
That would be a 'hum' a 'buzz' or a 'tone' depending on what way you look at it - 'hiss' is an entirely different beast and is spread over a range of frequencies - see white noise
Click to expand...
You are right. It would be more of a humm, but what I was thinking was the cycling.

Also, and on a side note. Some people may describe it differently. For example my civic has a Whine at 25MPH, 35MPH, and 42MPH. I did a search couldn't find anything. Then I read about a rattle on a civic that was having the same problem. Being that's the Whine started when it was winter here (35 - 50 Degrees F), I didn't open the windows.

So, I opened my driver side window and listened to the noise when parked. Yep, it was a rattle. I know that a rattle and a whine may seem like two entirely different things. However, when the window was closed and the rattle is high pitched and really fast it sounded like a whine. Granted, the situation is different.
 
i have to concur with acorec--it sounds to me like there's condensation in the mic somewhere. i had this exact problem with one of my 603's when they got waterlogged at a gig, grrr. the hiss was quite noticible and one was significantly worse than the other.

i opened em up, dried em out and the hiss went away--and they work just fine now.


cheers,
wade
 
Looks like a condensation problem. I left the mics on the stands overnight and today they both worked fine. Eh, as long as it's working. Thanks everyone.
 
reshp1 said:
Looks like a condensation problem. I left the mics on the stands overnight and today they both worked fine. Eh, as long as it's working. Thanks everyone.
Click to expand...
.........

Cool :)
 
Hmmm, maybe not....

Okay, so I jumped the gun on saying this was fixed. Forgeting that the noise took around 20 secs after phantom power was applied to develop, I only listened for a few seconds and was so excited that the hiss was gone, I turned everything off.
I was recording again today and noticed the hiss again, same as before. I had a little more time tonight, so I pulled out my trusty DVM and measured the phantom power on both preamps.
The preamp that the suspect MXL603 worked with no hiss on has a phantom of 45V, the preamp that caused the same mic to hiss had a phantom power of 48V, but it took (guess what) about 20 seconds to build up to that voltage. I listened and watched the meter simultaneously and sure enough as the voltage went above 47V or so the hiss developed. Since this preamp works fine with the other 603 that I have (matched pair).. I deduced that something about the suspect mic made it hiss when higher phantom voltages were applied. I'm not really familiar with the circuitry inside a 603, but is there any one faulty component that would cause something like this? Thanks in advance.

Edit: I also tried the pre's in a Behringer board I have, the phantom voltage was 45V and the mic did not hiss. Outta other pre's to try, I wish I had another one that put out 48V just to test my theory.
 
reshp1 said:
...I'm not really familiar with the circuitry inside a 603, but is there any one faulty component that would cause something like this?
Click to expand...
That is certainly a strange problem, and yes, it could be a number of things. Again, you need to call MXL and ask them about it. This pc board is no fun to repair. The traces lift like crazy! They will more than likely repair it and ship it back to you free, whether you bought it new or not. You can't buy parts for that...
 
Hmm, you're probably right. I'm just worried that they won't find anything wrong with it because it only seem to have issues with some preamps. I'll give 'em a ring and see what they can do. Thanks for everyone's help.
 
Reshp1,

I actually already posted, but it was a minute after you said that it was cured (it was a surprise for me), so I deleted my post.
It looks like the problem is one of the signal capasitors is leaky. Most likely one of your preamps has a lower phantom power voltage, so it works OK with that preamp. Another preamp gives more charge voltage, and that's when hiss occures.
 
I have the same problem w/ my 603. I fixed it for a while by messing with the little thumbwheel on the inside. Then it came back. I now store it on the heat vent to keep it dry, and that seems to be doing the trick for now...
 
Marik said:
Reshp1,

I actually already posted, but it was a minute after you said that it was cured (it was a surprise for me), so I deleted my post.
It looks like the problem is one of the signal capasitors is leaky. Most likely one of your preamps has a lower phantom power voltage, so it works OK with that preamp. Another preamp gives more charge voltage, and that's when hiss occures.
Click to expand...

Thanks Marik, I think that's what's is going on too.
I was interested in doing this mod anyway
http://www.3daudioinc.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=1&t=001142

Do you think changing out these caps would fix the problem.
If anyone has a schematic for this mic that would be really helpful.
Thanks, I love this fricking place :)
 
reshp1 said:
Thanks Marik, I think that's what's is going on too.
I was interested in doing this mod anyway
http://www.3daudioinc.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=1&t=001142

Do you think changing out these caps would fix the problem.
If anyone has a schematic for this mic that would be really helpful.
Click to expand...

This mod should fix this problem, unless it is something else, which is unlikely.
Make a search on "The Lab" forum:

www.groupdiy.com

You will find muuuuch more on this mic mods, including schematics.
 
Hmm, not it either

Changed out the caps today, still the same problem. Maybe a bad FET or BJT maybe? I've got a schematic that has the pnp trany as 2N5551, the 2 npn's as 2N5401, and the FET as 2SK170GR. Any idea if these are the correct part numbers and if it's worth swapping out?
Thanks again.
Mike
 
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