oscarhuang
Well-known member
- Joined
- May 22, 2020
- Messages
- 159
The Neumann M147 is a very expensive microphone. I checked their circuit diagram and found that the basic principle should not be difficult. There is no output transformer, and a vacuum tube is used as the impedance conversion, and a transistor and an operational amplifier are used as the output part.
The hardest part for me was his power part. There are three sets of power supplies, one is the high voltage of the tube and the filament of the tube. There is also a group for operational amplifiers and transistors. Fortunately, I found a DC-DC with an input voltage of 3.5v-35v and an output from 5v-50v!
My power transformer is AC 140v and 10v. After rectification, the high-voltage DC voltage is 207v under no load. I tried resistor divider under no load and got 75v voltage. The load is about 65v. The filament voltage through the LM317 is approximately 6v. I connected the DC-DC to the filament voltage and adjusted it to 32v after boosting it. We can see through the multimeter that the voltage is basically fine.
I assembled all the components. I didn't have a 6111 for the tube, so I used a 6072 instead. I tried a lot of K47 and M7 for the capsule, but they were all too dark for me. I happen to have Arienne's k87 v1.5. When I installed it, I felt that the sound was what I liked. Although there is no NFB circuit, the k87 does not have serious sibilance under the tube. In terms of low frequency, I controlled the bass by adjusting the size of the R12 resistor, and finally settled on 56k. For op amps, I can play around with a lot of different ones to see which one suits me better.
Below are some pictures. Article translated by Google Translator. If anything is wrong please tell me.
The hardest part for me was his power part. There are three sets of power supplies, one is the high voltage of the tube and the filament of the tube. There is also a group for operational amplifiers and transistors. Fortunately, I found a DC-DC with an input voltage of 3.5v-35v and an output from 5v-50v!
My power transformer is AC 140v and 10v. After rectification, the high-voltage DC voltage is 207v under no load. I tried resistor divider under no load and got 75v voltage. The load is about 65v. The filament voltage through the LM317 is approximately 6v. I connected the DC-DC to the filament voltage and adjusted it to 32v after boosting it. We can see through the multimeter that the voltage is basically fine.
I assembled all the components. I didn't have a 6111 for the tube, so I used a 6072 instead. I tried a lot of K47 and M7 for the capsule, but they were all too dark for me. I happen to have Arienne's k87 v1.5. When I installed it, I felt that the sound was what I liked. Although there is no NFB circuit, the k87 does not have serious sibilance under the tube. In terms of low frequency, I controlled the bass by adjusting the size of the R12 resistor, and finally settled on 56k. For op amps, I can play around with a lot of different ones to see which one suits me better.
Below are some pictures. Article translated by Google Translator. If anything is wrong please tell me.
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