My 2c:Hi, designing a power supply for a modular preamp box I'm putting together - I'm currently running +/-15vdc out of a center tapped transformer for power for the pres themselves, and was a little curious as to your guys' thoughts on the impact running phantom power through a cheaper switching supply would have on the sound - I'm assuming any small sonic difference from a switching supply on a mic's internal circuit would be amplified once it hits the pre stage, but I know Douglas Self's small signal audio design recommended a voltage tripler hooked up to the positive rail.
You're correct. This thread has drift into a anti vs. pro SMPS tirade; and lost both the original subject and the original poster.My 2c:
I agree 6800uF is overkill. My 2011 design used 4700uF but that was only required if you needed the maximum of 100mA of phantom current ( for a 16 channel mixer ofr example). For most designs 2200uF is plenty. You need at least 48VAC supply to the bridge so you get close to 70V of raw dc feeding the TL783 ( it needs about 20V across it to regulate and ripple reduce properly). Schematic attached (the 1N5407 diodes are sever overkill).6800uF 80 Volt is a massive overkill for this where a couple of say 2200 with a resistor of 47 Ohms between them would give a cleaner supply into the TL783, which needs to have it's minimum current catered for which realistically requires a 1 watt (minimum) resistor to ground. (about 10milliamps of 'bleed should be allowed for. You could do this with two resistors and have a LED in one of them to show the phantom is on if you wished.
Besides, the startup current for 6800uF is getting rather 'fierce' for a small transformer and rectifier.
I wanted to be in accordance with the standard that specified +/- 4V. Some splitter manufacturers used this tolerance to remotely control a pad
Very many years ago mixers were built with all the active electronics in an external rack and the board itself was 100% passive but that was in the days when all the amps were fixed gain. In the late 70s? Neve developed several consoles ( I think they were for George Martin) which had remote mic pres but the gain controls were still on the console and which remotely controlled mic pre gain.Stop me if I've shared this one before...
Back in the early 80s I kicked around the idea of transmitting gain control instructions to remote phantom powered preamp stages using very slow changing voltages on the + and - XLR wires, that could be easily filtered out of the audio signal.
I abandoned this idea as not commercial.
For the 100th reply, can I ask why you want to use SMPS for phantom power at all? Why not use a voltage tripler like the one used in Soundcraft consoles or similar?Hi, designing a power supply for a modular preamp box I'm putting together - I'm currently running +/-15vdc out of a center tapped transformer for power for the pres themselves....