sethinspain
Active member
- Joined
- Dec 18, 2011
- Messages
- 36
Hey guys,
I finally got my hands on an Apex 460 circuit and have done the typical mods out there. Its got a low pass and pad switch but fixed cardioid. Other than that, it's spot on the Alctron tube mic.
Here's the schematic i'll be rerencing:
I am hearing a noise and I am not sure this is the typical noise a mic makes. The self noise is a high 20dB, but I thought self noise is more like a hiss, or white noise type sound. What I am hearing almost like a PSU type noise that is in the lower freq range.
It is not a strong hum from maybe the body being improperly shielded or the psu tranny being too close to the circuit. It's more like a light 100-400hz tone that almost sounds like machinery noise. I have tried swapping tubes and the noise changed minimally, if at all.
I don't know if anyone has this mic and can confirm that this is normal or not. It is definitely audible, and for my taste too much so to record.
I removed C9 and C10 which act as RF filters. This sound doesnt strike me as RF which is high pitched. Maybe I'm wrong...
I removed C8 (output coupling cap) and changed it to a film cap and I wired the trafo directly to the cap. This actually seemed to help the noise a little bit. I thought of possibly jumping the trace from R8 and wiring it directly to the cathode of the tube socket.
I also removed C7, and put in a better capsule.
Now the PSU is still stock but I just lowered the output voltage by changing the zeners. I have read zeners can put noise in a circuit but I have one that uses them and it's noise free practically. I could put a by-pass cap (tantalum) as I heard that can help. Or I could also install an additional cap to filter more, maybe a 470uf 250V - I don't have a ton of space.
I realize also that the voltage may not even reach 120V which is the zener voltage rating. I could lower it to be 112V which would for sure clamp down the voltage and possibly eat the remaining ripple, but at the expnse of loosing some volts.
PSU Schematic:
Any ideas how I can take care of this?
Cheers,
Seth
I finally got my hands on an Apex 460 circuit and have done the typical mods out there. Its got a low pass and pad switch but fixed cardioid. Other than that, it's spot on the Alctron tube mic.
Here's the schematic i'll be rerencing:
I am hearing a noise and I am not sure this is the typical noise a mic makes. The self noise is a high 20dB, but I thought self noise is more like a hiss, or white noise type sound. What I am hearing almost like a PSU type noise that is in the lower freq range.
It is not a strong hum from maybe the body being improperly shielded or the psu tranny being too close to the circuit. It's more like a light 100-400hz tone that almost sounds like machinery noise. I have tried swapping tubes and the noise changed minimally, if at all.
I don't know if anyone has this mic and can confirm that this is normal or not. It is definitely audible, and for my taste too much so to record.
I removed C9 and C10 which act as RF filters. This sound doesnt strike me as RF which is high pitched. Maybe I'm wrong...
I removed C8 (output coupling cap) and changed it to a film cap and I wired the trafo directly to the cap. This actually seemed to help the noise a little bit. I thought of possibly jumping the trace from R8 and wiring it directly to the cathode of the tube socket.
I also removed C7, and put in a better capsule.
Now the PSU is still stock but I just lowered the output voltage by changing the zeners. I have read zeners can put noise in a circuit but I have one that uses them and it's noise free practically. I could put a by-pass cap (tantalum) as I heard that can help. Or I could also install an additional cap to filter more, maybe a 470uf 250V - I don't have a ton of space.
I realize also that the voltage may not even reach 120V which is the zener voltage rating. I could lower it to be 112V which would for sure clamp down the voltage and possibly eat the remaining ripple, but at the expnse of loosing some volts.
PSU Schematic:
Any ideas how I can take care of this?
Cheers,
Seth