Audacity Forum

stevethefiddle wrote:There's a more sophisticated one on this page that uses a LM317 regulator. http://www.uneeda-audio.com/phantom/

That one with the LM317 sounds interesting... I'm already starting to cook something in my mind using those schematics and the phantom power example on the SSM2019 datasheet... I think the most expensive components there would probably be the capacitors (if I want to get decent ones), but maybe I should start a new thread to discuss that

In other news... I was playing around with gnome wave cleaner and I liked its noise removal. I didn't know this app but I think it performs pretty well. The gui has some bugs but it's usable.

<<<That one with the LM317 sounds interesting.>>>

It seems overkill to me, and I don't see how they're getting rid of rapid charge and discharge. Although that circuit would do it. Initially, I couldn't see where they were getting enough DC to run everything, the monolithic regulator needs at least three volts across it to work, then I saw they were using two power supplies one + and one -.

But they're both half-wave rectifiers. Wouldn't you get better and stiffer raw DC with bridges or full wave? Then you might not need lab grade regulation or such large caps.

I didn't look up the international spec on 48v phantom. I'm pretty sure there is one. It's scary that people are not just using the juice to run a small amplifier inside a microphone. I have a new microphone that has three LEDs on the case as well as direction management and filter generation. Given all that, I'm sure they regulate inside the case. They were firm that they couldn't do all those jobs on less than 48v.

Koz

kozikowski wrote:But they're both half-wave rectifiers. Wouldn't you get better and stiffer raw DC with bridges or full wave? Then you might not need lab grade regulation or such large caps.

I'm still not sure what I'll use for source of power... I might go for a DC-DC converter. I have plenty of old power supplies ranging from 5V to 12V (DC) so I might use one of those and just make the voltage conversion to 48V plus some caps for filtering...
I can also try to use the 5V or 12V from the PC's power supply, or even the USB's 5V...

bgravato wrote:

whomper wrote:i ended up with two external interfaces that way
but the extra software was a big plus
and i *could* use one on the other pc i guess

...

Meanwhile I'll try to find or build a simple 48V power supply for the phantom power and check how the mic will sound directly connected to my soundcard's line/mic input.

why not just buy one of the commercial 48v supplies ?
do they have a problem we should be aware of ?

bgravato wrote:

kozikowski wrote:The worst curse of phantom power is not what happens when it's running, although that can be fun. When you turn it off, it dumps a sudden 48 volt charge into the amplifier system. This would be the delicate, noise tuned, super low distortion amplifier system. I can't find it immediately, but someone made a phantom system that faded the battery supply on and off to avoid that sort of damage.

I've seen a couple of schematics where they use some zener diodes for that matter I believe...

technique ??

turn them on before the amp is turned on
turn them off after the amp is offed

If I had a dollar for every time I've seen (or heard) a microphone being plugged in or unplugged with the phantom power on and the gain turned up on the desk I'd be moderately wealthy. Equipment needs, whenever possible, to be designed to withstand such abuse. The LM317 data sheet provides example schematics for how to protect the PSU from damage due to output short circuit. It also gives an example for a "soft start" regulator.

stevethefiddle wrote:... Equipment needs, whenever possible, to be designed to withstand such abuse. ..

woulda coulda shoulda
and toyotas should prioritise brakes over speed/petrolpedal

time for congress to mandate a panic button on the dash
push it and the car stops asap engine off brakes locked (no abs!)

stevethefiddle wrote:If you get round to making one, good quality capacitors are essential as many off-the-shelf electrolytics will produce an unacceptable amount of leakage noise.
Black Gate caps are probably OTT and are hard to get hold of. Elna Cerafine and Nichicon FG are good and more reasonably priced, but again are difficult to get hold of in Europe, but Panasonic FC are good and readily available (CPC, Farnell, RS, ...)

Trying to make my shopping list for farnell... Capacitors are probably going to be the most expensive components...

Farnell has many Nichicon's but no FGs or KGs... For 63V rated caps they have Nichicon TVX series... dunno if they're any good. I'll probably go for the Panasonic FCs which they have, but only sell in packs of 5 units minimum...

Not all of the capacitors are "critical" though it's unlikely to do harm to user over-specified parts (other than harm to the wallet). Capacitors in-line with the signal path (for de-coupling DC) are probably the most critical. Hopefully the microphone itself will have a reasonable degree of immunity to noise on the supply line and a regulated supply should be pretty quiet without using expensive capacitors, but if you have a capacitor across the power supply output I'd use a good one there.

Farnell have a second on-line outlet called CPC. They carry much of the same stock but have a different pricing structure so to compare one with the other you need to factor in shipping and handling charges.

As an aside, I've just about finished the new version of the noise gate - ended up rewriting it from scratch. The actual processing is very similar to the original but with a few refinements. It automatically applies a gentle (first order) high pass filter at 20Hz which takes care of DC off-set and it now follows the absolute amplitude (positive and negative) whereas the first version only looked at the positive part of the waveform. I've also tweaked the "cross-over" for a smoother response when frequency dependent gating is used and I've added a feature for measuring the noise floor though this last feature still needs a bit of work.

I think CPC only ships to the UK... I'm in Portugal, so no good for me

For the two DC de-coupling caps I'll surely use the panasonics. For the power supply part I might buy something else... The panasonic FCs are not that expensive, main problem is that farnell only lets me order a minimum of 5 units of each capacity... I might also check local stores to see if they got any...

I was reading more thoroughly one of the reviews of my sound board and I just found out that almost all caps on it are Nichicon FGs, except for a few Sanyo OS-CON on the power connector. It's a pity farnell doesn't have the FGs.