Nice Vocal Chain under $200 - MOD RECIPE

[valvehead]

[quote author="hrasco"]These chips all have the same form factor and basic function. What I can't find is what is the difference, for example, between a 2132P and a 2132PA other than the price. (Of course I picked the most expensive ones for my "samples") :wink:

Hank[/quote]

Looking at the specs on the datasheet, it appears that the difference is better matching for the input pair on the non-"A" version.. There is lower input offset voltage, better common mode rejection and higher OL gain.

It's also interesting to compare the opa132 to the opa134 series. They appear to be identical except the 134 has even higher tolerance than the 132PA. The funny thing is that TI markets the 134 as an "Audio Operational Amplifier." Hmmm, dump the 132 rejects on poor unsuspecting souls :razz: Still the 134 is a worthy upgrade from a TL07x.

 

[csonics]

[quote author="csonics"]I just modified my 990 per buttachunk's recommendations and it sound pretty darn good! Good call! I've noticed that the mic is kind of noisy. I didn't test the thing before I pulled it apart so I don't have a benchmark to test it against. Has anybody else noticed this we these mics?[/quote]

To elaborate on this noise issue. I replaced all the caps in the mic I could with WIMA polypros rated at 100v. I'm getting a pretty high noise floor (high even for this mic) and its also picking up pretty much any rf noise in the area including power outlets and local radio stations! I know this can't be normal. Anybody have any insight on what I might be doing wrong?

Thanks,

 

[SonsOfThunder]

You probably have a short to the case. I was working on one last night and noticed that the top of the electros were touching the bottom of the metal plate in there. I put little pieces of vinyl tape on top of each one to prevent problems.

I also had a problem when I put the 991 back together with low output. One of the traces on the edge of the PCB was making contact with the mic body. Tape was the answer again.

Anyone else rip out the inner mesh layers on the 990? Be careful or you'll do like I did...got a little careless and ripped the outer layer a bit.

HTH!

 

[Gus]

The MXL V67 grill gets VERY weak if you remove the inner layers of mesh. Weak to the point of not usable IMO.

The V67 and 990 look like the same grill.

 

[Gus]

Has anyone looked in the meta at the 603 mods?

 

[SonsOfThunder]

Gus,

I was being careless when I removed the inner meshes. If I had been more careful, I think the 990 would be okay. I have not used the V67 so I cannot compare. Thanks for your experienced input. It is well noted and regarded.

Peace!
Charlie

 

[csonics]

[quote author="SonsOfThunder"]Gus,

I was being careless when I removed the inner meshes. If I had been more careful, I think the 990 would be okay. I have not used the V67 so I cannot compare. Thanks for your experienced input. It is well noted and regarded.

Peace!
Charlie[/quote]

SonsOfThunder,

What would be the benifit of taking out the inner mesh? I'm guessing something to do with acoustic quality?

 

[SonsOfThunder]

Yes. :grin:

 

[csonics]

[quote author="SonsOfThunder"]Yes. :grin:[/quote]

well SonsOfThunder,

I taped up the tops of the electrolitics and all around the sides of the pcb. I'm not getting any 60hz hum anymore but I am still picking up radio stations with this thing. Any suggestions on what I might be missing here? I'm beginning to think its the mic but I could be wrong...

 

[SonsOfThunder]

csonics,

Does the mic pass signal at all? How many caps did you change at once? Perhaps after you check all of your solder joints again, you can try putting the factory caps back in, one or two at a time til the problem goes away. Maybe one of the values is off? Or a bad component.

Usually this kind of thing is due to bad solder, broken wire, or short to the case or some other component.

HTH!

 

[csonics]

[quote author="SonsOfThunder"]csonics,

Does the mic pass signal at all? How many caps did you change at once? Perhaps after you check all of your solder joints again, you can try putting the factory caps back in, one or two at a time til the problem goes away. Maybe one of the values is off? Or a bad component.

Usually this kind of thing is due to bad solder, broken wire, or short to the case or some other component.

HTH![/quote]

Its passing a lot of signal and its pretty darn clear. I can just hear radio signals popping through the noise floor. I changed all the .022 uf, 1000pf, .22uf caps out with wima polypros 100v. I've double and triple checked all my soldering and it seems ok. I haven't check the cap values so I'll to that next. Thanks!

 

[seavote]

a ferrite bead on your mic cable may help. search "ferrite bead" and "rf interference" with the word mic in this forum.theres more than a few threads on the subject.

 

[Gus]

csonics

Did the microphone have RF problems when you bought it? Did you even test it

If not, is the cable good, are you using the same preamp, are you in the same room? Etc.

when changing parts it is a good idea to change one at a time if you are changing stuff for the first time.

One needs to be logical when trouble shooting.

noise? did you touch the capsule to gate cap with your hands? did you cleanup the flux? Did you overheat the caps?

 

[csonics]

[quote author="Gus"]csonics

Did the microphone have RF problems when you bought it? Did you even test it

If not, is the cable good, are you using the same preamp, are you in the same room? Etc.

when changing parts it is a good idea to change one at a time if you are changing stuff for the first time.

One needs to be logical when trouble shooting.

noise? did you touch the capsule to gate cap with your hands? did you cleanup the flux? Did you overheat the caps?[/quote]


Gus,

I didn't check the mic before i modified it (I'm regretting that now).
Cable = good
Room = same in all tests
Preamp = same in all tests

"when changing parts it is a good idea to change one at a time if you are changing stuff for the first time."

You speak words of wisdom. In my haste I didn't bother to do a test after I installed each component. I just replaced each of the little yellow caps with a wima of equivalent value (I'm not sure if the wima caps' 100v rating is the same as the original caps). I will probably end up taking the whole thing back apart and starting from scratch.

I do notice that it takes about 10-15 seconds to produce sound after I power on fantom. I'm guessing this is due to the caps charging.

I didn't touch the capsule (it has screening on the assembly so it would be hard to).
I painstakingly cleaned up all the solder joints and double and triple checked them.
I have no reason to believe that I overheated any caps but I guess its possible.

Thanks for you insight!

 

[Gus]

noise with condenser microphones can be caused by leakage currents on the surface of the capsule to gate/grid cap.

If you handle the gate/grid to capsule cap finger oils and dirt can form a leakage path this can cause extra noise. I use clean tools to hold that cap when soldering it in a microphone. Also flux can cause noise if it is in the High R section.

 

[csonics]

[quote author="Gus"]noise with condenser microphones can be caused by leakage currents on the surface of the capsule to gate/grid cap.

If you handle the gate/grid to capsule cap finger oils and dirt can form a leakage path this can cause extra noise. I use clean tools to hold that cap when soldering it in a microphone. Also flux can cause noise if it is in the High R section.[/quote]

Gus, thanks for the suggestions. I'll go over it tonight and clean it up.

 

[csonics]

So I dimantled the mic yesterday. I tested all the caps. They checked out to within 5% of they're target values. Is there a benifit to checking out the other components too? I'm thinking I might as well pull off all the resistors and test them.

 

[csonics]

I put the mic back together after checking all of the components I could. I then cleaned any solder flux dirt off of the bottom. Turned it on. Its still loud and now its making popping noises! What am I doing wrong here? Anybody have any ideas?

 

[lookn4tone]

Have you checked the connecton to the XLR fitting on the mic? On my mic, I had some noise. The wire to ground had come off the board. I resoldered it, and noise was gone.

Just a thought.

Steve

 

[csonics]

yeah, I checked for that. Everything looks to be fine. I'm starting to think there is voltage leak across the pcb as Gus had pointed out before. I took some cleaner and a toothbrush and scrubbed it down as best I could but I may go over it again.