trans4funks1
Well-known member
- Joined
- Feb 4, 2013
- Messages
- 328
Hi,
I had some time to work on a circuit I am hoping to use in a DIY mic. I have the circuit built on a bench top test rig and I finally finished the soldering and powered it up to see what happened.
Not much happened.
I have all the parts laid out and even have an XLR output that I am routing into a mixer just to see what I can hear. I expected a bunch of noise and hum because the parts aren't shielded, they are just laying on the test rig.
I never seemed to actually get a signal off of the capsule. It's an inexpensive K67 capsule I bought from Studio 939 just for making mistakes with.
I think some of my voltage readings show where the problem may lie and I am wondering if someone can offer a second opinion. I have attached a schematic with the voltage readings shown.
The circuit is an adaptation of the U47 alternate tube schematic found at AMI-Tab. I drew the pin outs for an EF86 tube and I referred to the Neumann U48 schematic while adding the extra parts to copy a U48 figure 8 option rather than the U47's omni option.
I double, triple checked the layout and I think I have everything soldered where it's supposed to go.
Looking at the voltage going to the back plate makes me think that I may have ruined the 1Gohm R1 resistor.
The voltage going to the rear capsule seems bad too. The voltages on either sense of the 150Mohm R5 seems to indicate a problem.
I can't measure either the 150Mohm or the 1Gohm resistors with my VOM... they just read open.
Are these super high resistors more fragile than others? I've never ruined a resistor while soldering, but I've never worked with these values either.
I used a jumper wire to bridge over R1 and I got 52vDC to the back plate but I still could not hear any response from the capsule... just the noise and hum.
Does anyone have any thoughts about the voltage readings?
Thank You!
I had some time to work on a circuit I am hoping to use in a DIY mic. I have the circuit built on a bench top test rig and I finally finished the soldering and powered it up to see what happened.
Not much happened.
I have all the parts laid out and even have an XLR output that I am routing into a mixer just to see what I can hear. I expected a bunch of noise and hum because the parts aren't shielded, they are just laying on the test rig.
I never seemed to actually get a signal off of the capsule. It's an inexpensive K67 capsule I bought from Studio 939 just for making mistakes with.
I think some of my voltage readings show where the problem may lie and I am wondering if someone can offer a second opinion. I have attached a schematic with the voltage readings shown.
The circuit is an adaptation of the U47 alternate tube schematic found at AMI-Tab. I drew the pin outs for an EF86 tube and I referred to the Neumann U48 schematic while adding the extra parts to copy a U48 figure 8 option rather than the U47's omni option.
I double, triple checked the layout and I think I have everything soldered where it's supposed to go.
Looking at the voltage going to the back plate makes me think that I may have ruined the 1Gohm R1 resistor.
The voltage going to the rear capsule seems bad too. The voltages on either sense of the 150Mohm R5 seems to indicate a problem.
I can't measure either the 150Mohm or the 1Gohm resistors with my VOM... they just read open.
Are these super high resistors more fragile than others? I've never ruined a resistor while soldering, but I've never worked with these values either.
I used a jumper wire to bridge over R1 and I got 52vDC to the back plate but I still could not hear any response from the capsule... just the noise and hum.
Does anyone have any thoughts about the voltage readings?
Thank You!