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Author Topic: New Church Audio CA-11 Omni caps out of balance on older STC-11 cardioid bodies  (Read 2028 times)

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Offline andante

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I just recently bought some Church Audio CA-11 omni caps to use on my STA-11 (old version of CA-11) cardioid microphones but it seems like the new omni caps are singnificantly out of balance.

I went ahead and tested all four combinations of caps and bodies with a 1kHz test tone and the recorded results in Audacity looks like this:









FLAC audio file - ( SPEAKER > CA STC-11 > SONY PCM-M10 using PIP):
STC-11 CARDS STOCK - CARDS LRSWITCH - OMNI CAPS- OMNI CAPS LRSWITCH.flac (916kb)
[dropbox link - click "No thanks, continue to view", then "Direct download" from the upper right Download dropdown arrow]:
http://bit.ly/2aYKbVC


Other than the cardioids in original LR configuration, there seems to be only one combination of omni caps (the last one) that is even close to being balanced - but it's still quite off.  I just can't figure out why the other two combinations are so incredibly lopsided.  I don't think Chris would have sent out omni replacement caps that are this far out of whack.


I'm guessing that it might have something to do with the FETs:

In a previous thread (linked below) Chris mentions that the CA-11 cardioids have a FET (field-effect transistor) inside the Left & Right microphone bodies that is calibrated specifically for each of the corresponding Left & Right capsules.   This means that with CA-11 cardioids you must use the Left mic body with the Left cap and the Right body with the Right cap otherwise the microphone levels will be out of balance:

CA-11 Interchangable caps - Can someone explain?
http://taperssection.com/index.php?topic=159663.msg2009489#msg2009489


Can the STC-11 cardioid FET(s) also affect the CA-11 omni replacement caps to this degree?

If so, how am I to get balanced levels using replacement omni caps for these older cardioid mics?

Anyone else using replacement omni caps with their CA-11 cardioids?

Thanks to anyone who can help!  :)

« Last Edit: August 02, 2016, 02:20:48 AM by andante »

Offline andante

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FETs vary in something called "transconductance", which in a 2-wire circuit will affect gain.  The good news is that will be equal for all frequencies, so just make a note of which capsule is right and left and the difference in dB and adjust in post.

Thanks for your help Jon.

I had no idea that FET transductance could affect the levels so much.

It seems especially odd that one of the new "balanced" omni caps has such a huge difference in volume when switching microphone bodies while the other omni cap is essentially the same volume no matter which microphone body it is attached to.

If the new omni caps are measured for balance, I would think that the volume level for each Left & Right channel would be the same (though not necessarily equal to each other) no matter which  omni cap is attached.

I suppose the FET tranductance is very sensitive and its effects are quite a bit more dynamic than I can comprehend.

Probably the only way to have a perfectly balanced set of CA-11 omnis is to buy them with the cables.

I'll take your advice and mark the left microphone body and best caps with a silver sharpy and will adjust levels in post if running omnis.

Offline Church-Audio

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FETs vary in something called "transconductance", which in a 2-wire circuit will affect gain.  The good news is that will be equal for all frequencies, so just make a note of which capsule is right and left and the difference in dB and adjust in post.

Thanks for your help Jon.

I had no idea that FET transductance could affect the levels so much.

It seems especially odd that one of the new "balanced" omni caps has such a huge difference in volume when switching microphone bodies while the other omni cap is essentially the same volume no matter which microphone body it is attached to.

If the new omni caps are measured for balance, I would think that the volume level for each Left & Right channel would be the same (though not necessarily equal to each other) no matter which  omni cap is attached.

I suppose the FET tranductance is very sensitive and its effects are quite a bit more dynamic than I can comprehend.

Probably the only way to have a perfectly balanced set of CA-11 omnis is to buy them with the cables.

I'll take your advice and mark the left microphone body and best caps with a silver sharpy and will adjust levels in post if running omnis.
its most likely the metal tabs are not making proper contact with the Omni capsules.. Make sure the are centered and bent up high to make good contact with the center pin of the capsule if it's not you can get wildly different levels from left to right and a sign that this is the issue is no mater how the capsules are moved around the one side ( fet ) always seems low. If you want you can always send everything back for me to look at. The Omni capsules are matched the fets are matched to each other as well as the cardioid capsules that's how I can sell Omni capsules ;) separately. I've sold hundreds and hundreds of Omni capsules. And it's not an issue. So it's the metal tabs. I do match the fets to the capsules but also to each other that makes it necessary for me to buy hundreds of capsules at a time. To match perfectly. It's time consuming. I also match for left right distortion.... ;)
« Last Edit: August 03, 2016, 12:18:05 AM by Church-Audio »
for warranty returns email me at
EMAIL Sales@church-audio.com

Offline andante

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FETs vary in something called "transconductance", which in a 2-wire circuit will affect gain.  The good news is that will be equal for all frequencies, so just make a note of which capsule is right and left and the difference in dB and adjust in post.

Thanks for your help Jon.

I had no idea that FET transductance could affect the levels so much.

It seems especially odd that one of the new "balanced" omni caps has such a huge difference in volume when switching microphone bodies while the other omni cap is essentially the same volume no matter which microphone body it is attached to.

If the new omni caps are measured for balance, I would think that the volume level for each Left & Right channel would be the same (though not necessarily equal to each other) no matter which  omni cap is attached.

I suppose the FET tranductance is very sensitive and its effects are quite a bit more dynamic than I can comprehend.

Probably the only way to have a perfectly balanced set of CA-11 omnis is to buy them with the cables.

I'll take your advice and mark the left microphone body and best caps with a silver sharpy and will adjust levels in post if running omnis.
its most likely the metal tabs are not making proper contact with the Omni capsules.. Make sure the are centered and bent up high to make good contact with the center pin of the capsule if it's not you can get wildly different levels from left to right and a sign that this is the issue is no mater how the capsules are moved around the one side ( fet ) always seems low. If you want you can always send everything back for me to look at. The Omni capsules are matched the fets are matched to each other as well as the cardioid capsules that's how I can sell Omni capsules ;) separately. I've sold hundreds and hundreds of Omni capsules. And it's not an issue. So it's the metal tabs. I do match the fets to the capsules but also to each other that makes it necessary for me to buy hundreds of capsules at a time. To match perfectly. It's time consuming. I also match for left right distortion.... ;)

Thanks Chris :)

You were right about the contact tabs being a problem as they were pretty filthy with some sort of black substance that could only be removed with an acetone dampened Q-Tip.   I feel kind of foolish for not having checked these before testing.

Bending the contact tabs upwards probably helped as well but the tab in the right channel seems kind of weak in that it keeps needing to be rebent after every capsule change.

The levels were much more consistent this time around except for the first time switching to the omnis:





But the omnis still seem to be out of balance with these microphone bodies even when they're making good contact.

I might just take you up on your offer to ship the whole shebang up to you so you can better dail them in. :)

Offline andante

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Since the new omni caps are still consistently ~3db out of balance, Chris had me send them back to him so he can replace them with a better balanced pair. 

Offline andante

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I received the balanced caps back from Chris and the 1kHz test tone results are much better:




 

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