leswatts
Well-known member
Hi,
First post.
I'm throwing together 6 THAT 1512/1646 based mic pres shortly for my studio. Getting ready to order parts. Before I do i'd like to discuss the phantom blocking circuitry a little.
I've done a search on this and read quite a bit. Seems it boils down to these options:
1) "Menace" configuration (from the AES paper). This is shown in the 15XX development board docs.
It uses rather high 100k input bias resistors that allow a small (2.2uF) non polarized film blocking cap.
I like the idea of no electrolytics, but I wonder about current noise at very low frequencies and improper loading of some dynamic and ribbon mics.
2) polarized 47uF phantom blocking caps with 1K5 bias resistors. This is pretty much standard I guess, but I sure don't like the idea of this when phantom is off...unless it was bypassed. An alternative would be to leave phantom on with dynamics etc so the cap would be polarized.
3) As #2 but with giant, expensive 47uF NP film capacitors. Or a somewhat lower value with higher bias resistors (much less than 100k).
4) Non polarized electrolytics. Seems a bad plan to me, given what i've read about their electrical characteristics.
5) Flying rail with no blocking caps. I read about this, but it seemed to not go anywhere.
So, before I finish my bill of materials I would like to ask for opinions on these options.
Les
L M Watts Technology
First post.
I'm throwing together 6 THAT 1512/1646 based mic pres shortly for my studio. Getting ready to order parts. Before I do i'd like to discuss the phantom blocking circuitry a little.
I've done a search on this and read quite a bit. Seems it boils down to these options:
1) "Menace" configuration (from the AES paper). This is shown in the 15XX development board docs.
It uses rather high 100k input bias resistors that allow a small (2.2uF) non polarized film blocking cap.
I like the idea of no electrolytics, but I wonder about current noise at very low frequencies and improper loading of some dynamic and ribbon mics.
2) polarized 47uF phantom blocking caps with 1K5 bias resistors. This is pretty much standard I guess, but I sure don't like the idea of this when phantom is off...unless it was bypassed. An alternative would be to leave phantom on with dynamics etc so the cap would be polarized.
3) As #2 but with giant, expensive 47uF NP film capacitors. Or a somewhat lower value with higher bias resistors (much less than 100k).
4) Non polarized electrolytics. Seems a bad plan to me, given what i've read about their electrical characteristics.
5) Flying rail with no blocking caps. I read about this, but it seemed to not go anywhere.
So, before I finish my bill of materials I would like to ask for opinions on these options.
Les
L M Watts Technology