Hi,
I had time to finalize my two MK7 tubemics from years back, here's the project
http://groupdiy.com/index.php?topic=30124.0
Pf86 tube, fixed bias, suggested psu. The thread says heater must be very low ripple for no hum. It is good enough since there is no audible or daw analyzer visible psu hum over background noise.
This no noise scenario is with mogami tube mic cable. For the other mic i had just made new cable with sommer cable octave tube.
The other mic had hum and it took a while to look where psu hum is coming. Much swapping and ruling out things i'm almost sure it is the cable! At least it appears to be. The mics and psus are pretty much identically built and the psu hum appears on the mic with sommer cable.
What should i be looking for to cause this phenomenon? Both should be good cables and are almost identical for electrical specs(?). I triple checked they are properly soldered and the twisted pair is used for audio, heftier wires for heater and ground. Cable shield is not connected at the mic end. Mic body is grounded to the same ground as audio inside the mic.
I tuned the sensitive heater rail in the psu for a given psu + cable + mic combination. Sommer cable is about two meters shorter so little less resistance, capacitance and inductance at play. Cables are roughly 7m and 5m long.
The hum induced is by my daw analyzer something like 20db louder than with mogami cable. I'm puzzled. Maybe it was too late last night or what, i going crazy? well now i' heading for another test round. I'll post a reply later.
http://www.mogamicable.com/category/bulk/microphone/tube/
http://shop.sommercable.com/en/Cables/Bulk-Cables-Audio/Mikrofonkabel-SC-Octave-Tube-200-0186.html
I had time to finalize my two MK7 tubemics from years back, here's the project
http://groupdiy.com/index.php?topic=30124.0
Pf86 tube, fixed bias, suggested psu. The thread says heater must be very low ripple for no hum. It is good enough since there is no audible or daw analyzer visible psu hum over background noise.
This no noise scenario is with mogami tube mic cable. For the other mic i had just made new cable with sommer cable octave tube.
The other mic had hum and it took a while to look where psu hum is coming. Much swapping and ruling out things i'm almost sure it is the cable! At least it appears to be. The mics and psus are pretty much identically built and the psu hum appears on the mic with sommer cable.
What should i be looking for to cause this phenomenon? Both should be good cables and are almost identical for electrical specs(?). I triple checked they are properly soldered and the twisted pair is used for audio, heftier wires for heater and ground. Cable shield is not connected at the mic end. Mic body is grounded to the same ground as audio inside the mic.
I tuned the sensitive heater rail in the psu for a given psu + cable + mic combination. Sommer cable is about two meters shorter so little less resistance, capacitance and inductance at play. Cables are roughly 7m and 5m long.
The hum induced is by my daw analyzer something like 20db louder than with mogami cable. I'm puzzled. Maybe it was too late last night or what, i going crazy? well now i' heading for another test round. I'll post a reply later.
http://www.mogamicable.com/category/bulk/microphone/tube/
http://shop.sommercable.com/en/Cables/Bulk-Cables-Audio/Mikrofonkabel-SC-Octave-Tube-200-0186.html