Re: Portable mic preamp project
Posted: Wed May 21, 2014 5:37 am
OK, yours are very interesting comments. Thanks.
One detail I should have corrected was the voltage for the zener diodes, which should be lower for my supply. Zeners were (and still are) the recommended types for the protection. But I think I'll switch to the diodes bridge.
Your also bought me on using 10R series resistors, instead of 49.9, as long as I am protected, and the diodes seem to do so.
The one I call "Single 2" is the one I would like to use, as long as the chip can be swapped and be able to listen for eventual differences, which I'm not sure if anyone has tried or found.
Let's see if we can get to a compromise with the C1 and C2 capacitors, at least on the cutoff, which goes from 160Hz to 16Hz. The first is a bit high, but it's effective with dialogue on location recordings.
The first thing I would do, sticking to film cap types, is to go to 2.2uF Siemens pol, which are small enough and reasonably priced for a film. That should reduce the cut to about 80Hz, right? Sounds like a nice improvement.
I would like to go to about 50Hz, but no increasing the cap or going for 'lytic type. Perhaps using 2.2K for R1-R2? I don't think noise would be much higher.
On my actual preamp, using the DC-DC supply I showed above, the switch is after the capacitor. BTW, THAT recommended me that the phantom switch went to V/2 instead of chassis ground.
I think I will draw two more examples, introducing the improvements, to see what you think. BTW, two things were not included on my design, and are on my preamp: the gain is through a three position switch and there is an output cap, which should be essential with rail-splitter.
One detail I should have corrected was the voltage for the zener diodes, which should be lower for my supply. Zeners were (and still are) the recommended types for the protection. But I think I'll switch to the diodes bridge.
Your also bought me on using 10R series resistors, instead of 49.9, as long as I am protected, and the diodes seem to do so.
The one I call "Single 2" is the one I would like to use, as long as the chip can be swapped and be able to listen for eventual differences, which I'm not sure if anyone has tried or found.
Let's see if we can get to a compromise with the C1 and C2 capacitors, at least on the cutoff, which goes from 160Hz to 16Hz. The first is a bit high, but it's effective with dialogue on location recordings.
The first thing I would do, sticking to film cap types, is to go to 2.2uF Siemens pol, which are small enough and reasonably priced for a film. That should reduce the cut to about 80Hz, right? Sounds like a nice improvement.
I would like to go to about 50Hz, but no increasing the cap or going for 'lytic type. Perhaps using 2.2K for R1-R2? I don't think noise would be much higher.
On my actual preamp, using the DC-DC supply I showed above, the switch is after the capacitor. BTW, THAT recommended me that the phantom switch went to V/2 instead of chassis ground.
I think I will draw two more examples, introducing the improvements, to see what you think. BTW, two things were not included on my design, and are on my preamp: the gain is through a three position switch and there is an output cap, which should be essential with rail-splitter.