G7 problem 4 pins capsule

[Gachet]

Hi everyone,

I've build a g7 using tim campbell capsule, and it's not working as it should.
It probably works fine in bi directionnal mode but when i switch to omni I can hear only hi frequencies, as if I had a phase related problem.
In cardio mode the back capsule only catches low frequencies.

This is how I've wired the capsule:
The two terminals on the side of the capsule are wired to center.
The front and back terminals are wired to front and back

I've read the meta about that kind of problem and changed the two styroflex cap close to the capsule, no change.
I've checked voltages it seems fine.

Is that possible wiring should be different?
Is there anybody who successfully achieve a g7 using tim campbell's capsule?
Thanks

 

[gyraf]

I've made several G7's with the CT12 - never had that sort of a problem

G7 directionality is made like this:
Front membrane always at 0V
Backplates (both) always at +60V
Back membrane varies 0-60-120V (which is the same as +/-60V relative to it's backplate)

To sum up directional voltages:
In Omni, both backplates are at +60V, and both membranes are at 0V
In Cardioid, front membrane is at 0V, both backplates and back membrane is at +60V
In Fig-8, front membrane is at 0V, backplates are at +60V, and back membrane is at +120V

..best guess would be something like swapped centre/back/front wire from capsule to headamp.

If you test with headphones and your own voice, make sure to compensate for signal polarity (or use rather high gain)

Jakob E.

 

[Gus]

Gachet

Did the g7 work with a different capsule?

Are you sure you built the microphone correctly?

 

[Gachet]

Hi
thanks for the answers.

I've re-checked everything this morning, wiring, voltage, and components values.
Everything is fine as long as the two close terminals on the side of the capsule really correspond to center.
As I said, it seems to work fine in bi and cardio mode, just the omni pattern sound weird, very less bass and ringing at hi frequencies.
And yes i've tested it with my vocal in headphones, and i had to raise the gain a little bit in omni.
Should I leave things as they are?

 

[zahyb]

Hello, did you finally solved this problem? Dealing with simmilar stuff in my G7.

 

[gyraf]

..be aware of phasing when testing with own voice in headphones..

Jakob E.

 

[Gachet]

Hello, did you finally solved this problem? Dealing with simmilar stuff in my G7.

No and you, did you find a solution?

 

[pucho812]

Have you tried testing the circuit without a capsule?

 

[Gachet]

No I didn't

Ive check the capsule with a LCR meter and I have confirmation from jakob that it is is wired correctly.
I've tested the connections between the capsule and the tube and the different components.
I've measured the styroflex to make sure they are ok.
I reversed the capsule front and back...

But I'm still having the same problem:

When I switch directivities I have:

Figure 8:  perfect fig8 pattern with lots of lo end , a bit woofy
Cardio: perfect cardioid pattern with a great sound pretty well balanced
Omni: perfect omni pattern with no lo end at all, like a 500Hz Hi pass...

I recorded it so it's not  the phase issue beetween  headphone and mouth.

 

[pucho812]

check every joint, check every part for the correct value. Check the power supply that it has the correct value. make sure it's wired correctly. Test the circuit with a capacitor in place of the capsule. do look up that information as my memory is foggy doing that, it's been a while since I had to.