Official C12 Clone - Build and Support Thread

[Tim Campbell]

The noise you hear switching patterns is most likely caused by contamination somewhere. Try cleaning everything (The pcb and solder joints. Do not use any solvents on the capsule. A dry q-tip around the conections). Make sure all the connections to the capsule are good. Does the dark rear membrane sound normal after the noise stops? The dark rear membrane is either caused by a loss of polarization voltage or collapsing of the rear membrane. To check this try to observe the rear membrane without the headbasket on and no audio connected. Do not hot plug the mic.  Connecting the power supply to the mic while it's turned on  increases the risk of collapsing membranes.
Check your polarization voltages. For my capsule I recommend 55v/110v.

 

[MatthiasAnton]

Hi Tim, thank you for your reply!

Visually, I can't see the back diaphragm collapsing.

On the power supply side I am measuring roughly 60% of B+ on pin 4 for the polarization voltage when set to figure-of-8. So, 65V while B+ is at 120V. Is this correct or should the voltage be divided down to the correct polarization inside the mic, meaning that I would measure the full 120V at pin 4 (polarization) of the 7-pin connector inside the PSU when in figure-of-8 setting?

Thank you for your help!

 

[Tim Campbell]

Well I'm glad to hear the capsule isn't collapsing. I'd say check the connections to the capsule, make sure you don't have any cold solder joints and clean the pcb inside the mic. It sounds like a bad connection or a partial short somewhere ( maybe even to the body).

 

[stelin]

I had a problem with one of my C12-mics, very similar to yours.

One of the screws that connects the wire to the back plate had become lose.
After tightening the screw the mic was ok again.

Be very careful if you need to tighten the screw; it’s very small and made of brass and can easily break.

 

[Banzai]

Omni 0V
Cardioid ≈ 60V
Fig8 120V (full B+)

measured inside PSU

 

[MatthiasAnton]

Thank you all for your help!

I tightened the screws that connect the wire hooks to the backplate and now the microphone is working fine. No noise when switching patterns anymore and both sides of the capsule sound almost the same now. Let's hope it stays that way

Thanks again everybody!

 

[Tim Campbell]

I'm glad you found the problem MatthiasAnton.
This isn't that uncommon. The heating and cooling of the screw can cause it to loosen.
In the instructions that come with the capsule it mentions that you should check that all connections are tight after installing the capsule.

 

[Wordsushi]

A few months ago, I built Dany Bouchard's D12, which I believe is fairly similar to Matador's C12, and I ended up selling it to a producer in S. Korea on the other side of the planet. He loves it, but today he said he tried to switch tubes before letting it discharge long enough after shut down and now he says he has no sound. I wish I was more knowledgable in this situation so I'm hoping someone here can point me in the right direction of what to look for to troubleshoot and what components could possibly have been fried by taking the tube out too soon.
Thanks!
M

 

[Matador]

Was he sure that the replacement tube was good before he swapped it in?

 

[Wordsushi]

Was he sure that the replacement tube was good before he swapped it in?

Good question. I don't know. He said it was new, but that could mean many different things.

Hypothetically, if was good, which component would be most likely to fry first?

 

[rmburrow]

Good question. I don't know. He said it was new, but that could mean many different things.

Hypothetically, if was good, which component would be most likely to fry first?

Always let the power supply discharge for at least 2 minutes and unplug the AC power before going into the microphone for any reason.  Depending on how the capsule is biased, hot switching the tube may subject the capsule to excessive voltage.  It's also dangerous to hot switch a tube with the power on; a accidental shock from HT won't be comfortable and you may uncontrollably drop or throw the mic and damage it.

Get out the DMM and check voltages.  No HT or no heater voltage means inoperative mic.  If both voltages are present and correct, then carefully test at other points in the mic.

 

[Tim Campbell]

I have also seen people misalign tubes and still force them into a socket, bending legs. Just ask him to re-install the original tube and see if it starts working again. This sort of fault is difficult to solve by email unless he's technical.

 

[Wordsushi]

Thank you, rmburrow and Tim Campbell. Much, much appreciated.

You're so right. It is totally impossible to do this via email, especially given that he's in S. Korea, many time zones away from L.A. I had sent a sheet of instructions detailing waiting at least 15 minutes after turning off the mic to even unplug it, since I had previously measured current still in the mic for at least that long during shut down. I can see someone impatient to try a new tube possibly rushing it. It's a shame too, he told me he was loving the mic on KPop vocals. So much so that he had me build a second one for another studio owner over there.

One thing I told him when he was first asking about buying the mic is that he should find a tech guy there in case something happens, so I'm hoping he took me up on my suggestion. I haven't heard back from him yet, so I'm taking that as a good sign. I really don't know how technical he is. Hopefully at least enough to use a DMM. I did send him the schematic and the calibration voltages. If/when I hear back I'll ask him to put the old tube back in, just in case he hasn't tried that yet. Oy vey!

 

[Matador]

The worst case is when you unplug the microphone hot, where you need to rely on the the 499k bleeder in the stock PSU to discharge the B+ voltage.  The time constant is about 4 minutes, meaning you need to wait about 20 minutes to be safe.

 

[Wordsushi]

The worst case is when you unplug the microphone hot, where you need to rely on the the 499k bleeder in the stock PSU to discharge the B+ voltage.  The time constant is about 4 minutes, meaning you need to wait about 20 minutes to be safe.

Just a random thought: Would/should/could there be a way to implement an LED that could be installed into the PSU front panel that would glow to indicate the presence of voltage until the voltage has sufficiently drained?

Well, so far I still haven't heard back from the producer so I'm gonna keep my fingers X'd he managed to get it sorted somehow.

 

[Matador]

Just a random thought: Would/should/could there be a way to implement an LED that could be installed into the PSU front panel that would glow to indicate the presence of voltage until the voltage has sufficiently drained?

Well, so far I still haven't heard back from the producer so I'm gonna keep my fingers X'd he managed to get it sorted somehow.

I had thought about that: the problem is the 1mA draw of the LED is more than the current draw from the tube itself.   You could add one in series with the bleeder resistor, provided the bleeder resistor is reduced down to about 100k.  The series dropping resistors would also be cut in half, making the RC filtering half as effective.

 

[vinylwall]

SOLD

 

[Matador]

Just a random thought: Would/should/could there be a way to implement an LED that could be installed into the PSU front panel that would glow to indicate the presence of voltage until the voltage has sufficiently drained?
]

Some more thinking: one could add a small DPDT switch on the front panel to server as a standby switch.  Much like on a guitar amp, it would allow the heater voltage through to the microphone, but keep the B+ disconnected while the tube heats up.

The second leg of the DPDT could be used to switch a discharge resistor + LED, which would drain the filter caps down to a safe level in a reasonable time one the switch was flipped into 'standby' mode.  Paper napkin says a yellow LED in series with a 33K / 0.5W resistor would discharge B+ to less than 10V in about 10 seconds.  Essentially, the LED would be a 'DANGER' light, when the mike was flipped back into standby it would light the LED until the discharge was done (and render the mike silent as well).

 

[Wordsushi]

Some more thinking: one could add a small DPDT switch on the front panel to server as a standby switch.  Much like on a guitar amp, it would allow the heater voltage through to the microphone, but keep the B+ disconnected while the tube heats up.

The second leg of the DPDT could be used to switch a discharge resistor + LED, which would drain the filter caps down to a safe level in a reasonable time one the switch was flipped into 'standby' mode.  Paper napkin says a yellow LED in series with a 33K / 0.5W resistor would discharge B+ to less than 10V in about 10 seconds.  Essentially, the LED would be a 'DANGER' light, when the mike was flipped back into standby it would light the LED until the discharge was done (and render the mike silent as well).

Dude! That's a really super cool idea! I have this sense that folks who build these mics have a greater awareness and understanding of things like voltage dissipation in the circuit. But in the hands of a casual user who may view a DIY mic like this as they would any other switch-on appliance, safeguards such as this are very helpful in keeping the mic in optimum health.

Given that I'm not as electronically inclined as I would like to be, I can say personally that any sort of additional documentation as to implementation of such a "standby" switch mod like  you describe above would be very welcome and helpful.

 

[RPC360]

Some more thinking: one could add a small DPDT switch on the front panel to server as a standby switch.  Much like on a guitar amp, it would allow the heater voltage through to the microphone, but keep the B+ disconnected while the tube heats up.

The second leg of the DPDT could be used to switch a discharge resistor + LED, which would drain the filter caps down to a safe level in a reasonable time one the switch was flipped into 'standby' mode.  Paper napkin says a yellow LED in series with a 33K / 0.5W resistor would discharge B+ to less than 10V in about 10 seconds.  Essentially, the LED would be a 'DANGER' light, when the mike was flipped back into standby it would light the LED until the discharge was done (and render the mike silent as well).

Hmm, why not do it with a relay powered by the filament supply? That way the HV would automatically bleed off when the AC was removed.