Pro Audio Design Forum

Yes, you just have phantom switches for each channel. Just like a regular preamp. Each one operates independently. Ok, cool. I was concerned that once there's phantom on any channel, then the whole module flys to that. But now I see that this should make no problems for other channels. Another ques...

Wayne, Yeah, I undestand that. I'm concerned with the other thing. Let's suppose I want to make those 4 channels as flexible as possible. That is, I want to be able to switch phantom on the per-channel basis. Is that possible? For ex., today I'm doing a classical stuff and I need all 4 channels to h...

I wonder if it's possible to implement this as a multichannel preamp.

Let's say, I have a box with 4 of these DC preamps. I want phantom power on 2 channels, the other 2 should have no power (let's assume that the ribbons go there). Would this work?

That looks like dropping out of regulation. Consider making reservoir cap larger to reduce ripple voltage as easier and cheaper fix than buying bigger transformer. or not... JR JR, I've just checked this and you're correct. I've simulated mains voltage drop with my auto transformer and there it was...

I've got another strange behaviour. Every once in a while on the positive rail I've got the following going on: pos.jpeg Is it LM317 oscillating or what? I can't find out what causes this. It seems that moving the reg leads sometimes helps, but I'm not so sure. The regs are mounted off board. The le...

Ok. J.R. nailed it. Wayne, thanks for chiming in. It was indeed a layout issue. Snice negative rail LM317 output was connected to GND and its GND pin was referenced to -V, I checked where that connection was physically made. Stupidly enough, the output was taken directly from the rectifier bridge. Y...

Well, Basically, this is a front end for some console modules. Yes, my mains is 50Hz, so 100Hz really sounds like a ripple thing. Audio signals are treated respectfully, as well as grounds. I think I found the possible culprit. I've measured DC voltages and my positive rail shows 0V AC, and negative...

Hello gents. I've finished one particular build and I'm getting a very tiny amount of 100Hz hum. When I say "tiny" I mean just that - I have to boost the input of my soundcard 60dB to hear it (I'm injecting the signal in a universal input that can take both line and mic levels). I wanted t...

Wayne, Thanks for comments. I was distracted by optional caps and thought that you did the opamp HPF circuit, and I tried to figure out how that worked! Now I see that the HPF switch parallels 2K and 8K8 with 1M and everything is much more clear to me now! Thanks for pointing out the reversed 1646 o...

Wayne, I've got some question regarding the second part of the circuit: 1. There's a 1M resistor right after the 1uF/250V cap. In the other circuit it is 100K instead. What value is correct? 2. In the filter section there are two optional caps. If they have to be omitted, should they be short-circui...