Swapping capsules - weird experience

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kingkorg

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Joined
Apr 15, 2017
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Location
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Hi guys!

Today i had another round in trying out capsules in ''standard modded'' Apex460/Nady1050 etc...

It has 120v B+ and russian 6n16b-v.

Mic works nice with chinese 32mm, 35mm brass ring capsules and 797 audio CK12. When i try CK12 Rayking (Microphone Parts analog) it doesn't work at all. When i try 797 audio k67 it works with background sea waves noise, and those wave noises get worse and change when i twist microphone cable.

Needless to say, all of the capsules work great in my FET mics, i use them mostly in modded Behringer B2 circuits. And if i measured right B2 has 100V + capsule polarization voltage. My tube mic has 60V. Do these capsules need higher voltage to operate, or am i missing something? Resoldered all joints, checked voltages, electrolytics, swapped sides of capsules that misbehave.
 
100v is not 'normal' in the traditional sense. I cannot think of any vintage capsule that would not collapse at >80v. These must be some kind of 'supercapsule', no? I'm guessing they might be designed with greater diaphragm tension, or larger spacers, or both? Not something I've ever heard of, though.

Have you tried upping the voltage?
 
I thought i might do it tomorrow, restoring B+ to 150v. I am just thinking if something else could go wrong.  Here's B2 pro schematic, and if R20 is good spot for measuring capsule polarization then it's 108VDC with regular voltmeter.  CK12 and k67(797 audio) work like a charm at that voltage.
 

Attachments

  • B2_SCHEMATICS_REV_B (1).pdf
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You mention a polarisation voltage of 100 V, but... R20/R21 form a voltage divider, so the voltage between diaphragm and backplate is only 50 V, a very reasonable voltage. Or do I overlook something?
 
My bad then! It could be then that  60v and even higher stock on tube mic are to high. I will lower them and see what happens.
 
A value of 60 V is usually acceptable for most condenser capsules.
And the difference between a polarisation voltage of 60 V and a voltage of 50 V is only 1.6 dB!
 
Guys, what am i doing wrong here? It was not a bad cap. No matter what cap i connect from plate to ground i get sea waves when i twist microphone cable. With cap removed it's all fine.
 
kingkorg said:
Guys, what am i doing wrong here? It was not a bad cap. No matter what cap i connect from plate to ground i get sea waves when i twist microphone cable. With cap removed it's all fine.

Cap from plate to ground? HF smoothing - right?
What is the voltage rating of the caps you are trying and which point you choosed to connect it (assuming it is CCDA).
Is it plate follower stage or cathode follower stage?  What's the value of the cap?
"Sea waves" are usual from dropping voltage by zener diodes. What's AC of B+ in your PSU? 300V or 200V?
 
Yes, HF smoothing. I used various caps, 220-1000pf, ceramic, styroflex, pp, all being 630v or more. Same result, but waves are gone when i remove them, could that be zeners still? And waves are present only when i move cable. I connect them at tube pin 1 and 9.

It is ccda cathode follower. Classic china psu with 60v zeners for 120V. Will have to check voltage in the box.
 
It was the tube, for what ever reason it doesn't like that EQ cap there. I have no idea why. When i change to 12ay7 it works.
 
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