bradb
Well-known member
Hello everyone,
I've got some 7th circle preamps (A12, N72, J99) that have been giving me hum problems when I use them with dynamic and ribbon microphones. With condensers, the preamps are quiet as can be. Here are some observations:
1. Pre-amps CRANKED with no input mic cable, the pre's are quiet, typical low hiss noise signature. This is what I would expect.
2. UNTERMINATED (no mic plugged in) mic cable plugged into the pres' input gives a loud hum.
3. condenser mic plugged in, totally quiet, no hum. This is what I would expect.
4. ribbon mic plugged in, i get a hum that is the same as the unterminated hum, but its quieter, the hum changes in intensity when I move the mic and cable around.
5. dynamic mic plugged in, i get a hum that is the same as the unterminated hum, but its quieter, same as the ribbon mic hum, the hum changes in intensity when I move the mic and cable around.
The pre's have an internally mounted powersupply. This will give you an idea of what they look like: The pre cards and power supply are mounted horizontally.
http://www.seventhcirclestudios.com/SCA/CH01/ch01_about.htm
Some suggest that an externally mounted power supply would help but observation 1 suggests that this is not necessary. Does anyone have any advice on this or any more test that I could do?
Thank you
I've got some 7th circle preamps (A12, N72, J99) that have been giving me hum problems when I use them with dynamic and ribbon microphones. With condensers, the preamps are quiet as can be. Here are some observations:
1. Pre-amps CRANKED with no input mic cable, the pre's are quiet, typical low hiss noise signature. This is what I would expect.
2. UNTERMINATED (no mic plugged in) mic cable plugged into the pres' input gives a loud hum.
3. condenser mic plugged in, totally quiet, no hum. This is what I would expect.
4. ribbon mic plugged in, i get a hum that is the same as the unterminated hum, but its quieter, the hum changes in intensity when I move the mic and cable around.
5. dynamic mic plugged in, i get a hum that is the same as the unterminated hum, but its quieter, same as the ribbon mic hum, the hum changes in intensity when I move the mic and cable around.
The pre's have an internally mounted powersupply. This will give you an idea of what they look like: The pre cards and power supply are mounted horizontally.
http://www.seventhcirclestudios.com/SCA/CH01/ch01_about.htm
Some suggest that an externally mounted power supply would help but observation 1 suggests that this is not necessary. Does anyone have any advice on this or any more test that I could do?
Thank you