Re: New: A Direct-Coupled Input-Capacitorless Active Mic Pre
Posted: Thu Oct 08, 2015 11:36 pm
After dismissing Wayne's design as far too complicated for dis beach bum's KISS philosophy ... I'm looking with a very jaundiced eye at my (actually Professore Angelo Farina's) MOTU Traveler Mk2 which is showing leaky P48V caps after 7 yrs.
It's galling as I have a 1970's Calrec P48V PSU which is still deathly quiet after more than 30 yrs.
The Traveler uses PGA 2500 and has 1dB NF for 150R source when new. But it also has evil Schottkys as protection that go noisy. I replace the Schottkys on one noisy channel with 1n4004 but as the originals were SMD, dis blind old beach bum ripped up the PCB.
So I'm reluctant to attempt changing the caps.
It only takes a couple of such incidents to make you paranoid about P48V caps. How about you get THAT to put your Input-Capacitorless Mic Preamp on a single chip?
1 +/-0.1 dB gain steps via simple control would nice too.
Also found THAT 1510/12s vary from chip to chip by up to 0.5dB .. probably cos although laser matched trimmed to very high precision for CMRR, the absolute values may vary. The solution if you need accurate 0.1dB channel to channel matching is to buy twice as many 1510/12s as you need & match them. I need 4 for an Ambisonic mike preamp which isn't too difficult and they are cheap enough.
MOTU is one of those companies where all design is farmed out so there is NO internal Tech support at all. They haven't a clue what's in their product. Traveler Mk1s seem to remain quiet. Dunno about the current Mk3
It's galling as I have a 1970's Calrec P48V PSU which is still deathly quiet after more than 30 yrs.
The Traveler uses PGA 2500 and has 1dB NF for 150R source when new. But it also has evil Schottkys as protection that go noisy. I replace the Schottkys on one noisy channel with 1n4004 but as the originals were SMD, dis blind old beach bum ripped up the PCB.
So I'm reluctant to attempt changing the caps.
It only takes a couple of such incidents to make you paranoid about P48V caps. How about you get THAT to put your Input-Capacitorless Mic Preamp on a single chip?
1 +/-0.1 dB gain steps via simple control would nice too.
Also found THAT 1510/12s vary from chip to chip by up to 0.5dB .. probably cos although laser matched trimmed to very high precision for CMRR, the absolute values may vary. The solution if you need accurate 0.1dB channel to channel matching is to buy twice as many 1510/12s as you need & match them. I need 4 for an Ambisonic mike preamp which isn't too difficult and they are cheap enough.
MOTU is one of those companies where all design is farmed out so there is NO internal Tech support at all. They haven't a clue what's in their product. Traveler Mk1s seem to remain quiet. Dunno about the current Mk3