joulupukki
Well-known member
I’m wondering if someone might help me figure out some things to check in a pair of KM84 clone mics I’m building. They both produce sound, but the second one I built (let’s call it “Mic B”) outputs about 6-8dB lower volume than Mic A. Unpowered and in-circuit I’ve tested about as many components (resistors and caps) that I can and nothing is that far off from each other. I‘ve tried swapping the capsules and that doesn’t make any difference.
Other things I’ve checked:
- continuity from the spring pin to the JFET drain (and a resistance of 0 ohms)
- the terminal posts aren’t touching the nose cone
- all solder joints look great as far as I can tell and I reflowed them just to be on the safe side
- voltage measurements between the two mics seem very close at the FET source and drain, after the main diode, the input voltage, etc
- no components appear to be touching the mic body
- the resistance between the primary windings of the transformer are within 5% of each other. Mic A has a resistance of 703R and Mic B 668R. That wouldn’t be enough to cause a volume difference, would it?
I was so excited to have a pair of excellent mics for recording a new album. I can adjust the preamp on the quieter mic and they sound close to the same, but with the increased gain on Mic B, there’s also increased noise (which is still low). It’s just disappointing and annoying to have to not just “grab one of them” and expect them to be the same.
Anything else I should look for?
Other things I’ve checked:
- continuity from the spring pin to the JFET drain (and a resistance of 0 ohms)
- the terminal posts aren’t touching the nose cone
- all solder joints look great as far as I can tell and I reflowed them just to be on the safe side
- voltage measurements between the two mics seem very close at the FET source and drain, after the main diode, the input voltage, etc
- no components appear to be touching the mic body
- the resistance between the primary windings of the transformer are within 5% of each other. Mic A has a resistance of 703R and Mic B 668R. That wouldn’t be enough to cause a volume difference, would it?
I was so excited to have a pair of excellent mics for recording a new album. I can adjust the preamp on the quieter mic and they sound close to the same, but with the increased gain on Mic B, there’s also increased noise (which is still low). It’s just disappointing and annoying to have to not just “grab one of them” and expect them to be the same.
Anything else I should look for?