ComodoComplex
Well-known member
Hi all. Just looking for some advice.
I built a G7 a while back. It turned out amazingly and I love it and use it all the time when recording! I have a small noise issue now, which is so slight that it could have been there the whole time but I only noticed it now. Alternatively it could be because of a few recent modifications I made (description follows). It sounds like a 60Hz hum about -50dB down (too loud for me!). It comes through on quiet vocals so I'd like to get rid of it if possible.
Essentially I was trying to make the polar pattern as precise as possible given that I used the cheapest capsule available (the microphone-parts.com RK12). So I added a trimmer between HT and the 200K polarization voltage divider to lower the fig-8 voltage to exactly twice the 60V capsule voltage.
1) The trimmer is from a grab box at my local electronics distributor, but I've inferred it's probably a 1W cermet 20K potentiometer.
Do these have noise issues? I looked up cermet and it seems to have problems with noise. In addition, I could be using the wiper near the end of the range and exceeding power dissipation. Could this be fixed by using a smaller resistance potentiometer rated at the same 1W?
2) I had been using 1% metal film 1/4W resistors in the divider until this point, but realized that the schematic called for 1/2W resistors so I replaced them with closely matched 5% carbon film resistors.
Could this also be a reason for the hum?
Those are the only two things I changed recently. I've also noticed that when I move the 7-pin cable around at the connection to the PSU, it makes some crackling noises, probably because of connectivity issues due to the cheapness of the connector. I doubt that's the cause of the hum though.
TLDR: I've got a very slight 60Hz hum coming from my G7 and think it could be due to recent modifications: A cermet trimmer added and two metal film resistors replaced with carbon film. What do you think?
If you've made it this far, thanks. I'm ordering replacements for the carbon film resistors. But I really like having the trimmer as the thought of perfect polarization voltages is attractive to me.
I built a G7 a while back. It turned out amazingly and I love it and use it all the time when recording! I have a small noise issue now, which is so slight that it could have been there the whole time but I only noticed it now. Alternatively it could be because of a few recent modifications I made (description follows). It sounds like a 60Hz hum about -50dB down (too loud for me!). It comes through on quiet vocals so I'd like to get rid of it if possible.
Essentially I was trying to make the polar pattern as precise as possible given that I used the cheapest capsule available (the microphone-parts.com RK12). So I added a trimmer between HT and the 200K polarization voltage divider to lower the fig-8 voltage to exactly twice the 60V capsule voltage.
1) The trimmer is from a grab box at my local electronics distributor, but I've inferred it's probably a 1W cermet 20K potentiometer.
Do these have noise issues? I looked up cermet and it seems to have problems with noise. In addition, I could be using the wiper near the end of the range and exceeding power dissipation. Could this be fixed by using a smaller resistance potentiometer rated at the same 1W?
2) I had been using 1% metal film 1/4W resistors in the divider until this point, but realized that the schematic called for 1/2W resistors so I replaced them with closely matched 5% carbon film resistors.
Could this also be a reason for the hum?
Those are the only two things I changed recently. I've also noticed that when I move the 7-pin cable around at the connection to the PSU, it makes some crackling noises, probably because of connectivity issues due to the cheapness of the connector. I doubt that's the cause of the hum though.
TLDR: I've got a very slight 60Hz hum coming from my G7 and think it could be due to recent modifications: A cermet trimmer added and two metal film resistors replaced with carbon film. What do you think?
If you've made it this far, thanks. I'm ordering replacements for the carbon film resistors. But I really like having the trimmer as the thought of perfect polarization voltages is attractive to me.
