lylehaze

OK, it dumped my first reply.. What you're proposing is not ideal. If you ground at the transformer, you'll be creating both positive and negative voltages. Since you only need positive, that's a waste. Since you only need positive voltages, you should rectify it first, as I described previously. I REALLY hate working in windows, and now you've got me trying to draw with "paint". Warning: Ugly.. I mean REALLY ugly drawings are attached. You have been warned. LyleHaze

If you're only doing positive voltages, I would do it like this: Keep S1 and S2 connected in series, like before. Use a single bridge rectifier, from the bottom of S1 to the top of S2 (12 VAC) Ground the negative side of the bridge rectifier (0V for all voltages) Big capacitor from bridge V+ to 0V (smoothing the DC) Use positive regulators from there, with the option of a dropping resistor if the heat is too great. Use heatsinks. They're cheap. positive regulators may be attached directly to a metal case (0V) Also, you may use multiple 7805's to spread the heat load. Sorry, no means for artwork today, I'm too lazy. What's next? LyleHaze

Ouch. I just reviewed your earlier posts, we may have another problem.. You connect the secondaries in series, get 12VAC. You rectify that to DC, you get (12 * 1.4) VDC - (2 * Diode vF) There is a small "forward voltage drop" across any diode in conduction. Even with "perfect" diodes you only get 16.8 volts (no load) available. What's the minimum input voltage of your 7815? You are dangerously close to starving that regulator. Or maybe I just screwed up the math, I do software better than hardware. LyleHaze

Actually, to be more accurate, I don't know that you'd have a meltdown. Perhaps I was being dramatic there. I am sure that it would generate a lot of unexpected noise in the power supply. (noise being stuff you don't want mixed in with the power you expected) If you are building an audio circuit, you'll want the cleanest, purest power supply you can get. I'm building one now with -8V, -5V, +5V, +8V for the analog stuff, and another +5 digital to power a core board and VFD. Even though I want to keep the digital +5 apart from the analog supplies, they all MUST have a common ground, or it just won't work. How much current do you need on each supply? Good Luck, LyleHaze

OK, now I've switched over to my better browser. I'll do my best to answer your questions, and I welcome anyone to jump in and correct me. In most DC electric systems, including the kind of circuits we play with here, all voltages are measured against a common reference, often called Zero Volts or even ground (whether or not it's really grounded). so +5 Volts means 5 volts above 0V, and -12 volts would be 12 volts below. IF both have the same 0V reference, then you'd expect to see about 17 volts between them. (The difference between +5 and -12 is 17) However, if these two voltages are "isolated"(not sharing any common reference), then there could be ANY difference beween them. even 2000 volts would easily be possible. Obviously this could be hazardous to IC's that have an upper voltage limit. Now back to your drawing. There are two separate secondaries on the transformer. In your drawing, they are joined (between S1 and S2) This means that they are not isolated. They are connected in Series. This is fine.. so far. Now we add a bridge to create DC, powered from the sum of the secondaries, S1+S2. Cool. Higher voltage. We add another bridge, but it's only using S2. That works, but the 0V connection we have created is now higher than the 0V of the first supply (by the voltage in S1) Now out in the final application, all the 0V lines will be connected together, as the "universal common return" if you'll forgive my description. Now, because the 0V connections have been joined, BOTH sides of the S1 primary are just one diode away from the same potential. in short, you've shorted your secondary. Suddenly current consumption goes up, lots of heat gets generated, and the beautiful supply goes into theatrical meltdown mode. My explanation is a compromise, due to me trying to be non-technical, or possibly to me being completely wrong. If some reader is laughing at how stupidly I've described the problem, PLEASE jump right in and do a better job. Also, I offer this to help, not to criticize. I'm new here, and if I'm not helping then I'll just shut the *&^% up. Good Luck, LyleHaze

Normally all the 0V connections would be joined, and they probably HAVE to be if they are working for the same project. Connecting them in your drawing would bring bad things.

Thanks TK! Parts are arriving every day now.. Lots to build. LyleHaze

It will definetly work some of the time... The optocoupler is an analog device, and so is your transistor. Putting a few logic gates between them forces the signal into a digital state, either full OFF or full ON. Connecting without them could "soften the edges" of the signal, making it a bit less well-defined. (increasing the gain should help) I'm sure it will work some of the time, maybe even most of the time. I'd like to look at the output on a scope before promising anything more than that. Good Luck with it. LyleHaze

I'm building a new application. I've searched the forum and Wiki, I can't seem to find an answer to this.. My project needs just one encoder + one button. When I study the skeleton project, It seems to require me to identify which DIN register the encoder is connected to. Can I use the MIOS encoder handling without using a DIN board? There's plenty of available pins on the core that should work. Thanks, LyleHaze

I found an interesting page of mixer circuits. There are lots of choices for input modules. mic/line/balanced/unbalanced/Phantom power See this page http://users.otenet.gr/~athsam/Audio_mixer_6_ch_ENG.htm This project just got a little more complicated. LyleHaze

OK, I'll start with some things I forget to say before.. I am very very new to Midibox and MIOS, so if it looks like I've got something wrong, please SPEAK UP! I'm here to learn. Also, Pilo was nice enough to share the work he has done so far on the PGA4311 with me. Big Thanks Pilo! I'll do more testing when I have boards built. I'll share with anyone who asks for it, unless Pilo asks me not to. Re: Chip Selection. I agree that the 2311 is a better choice for most people. But for myself, I'm sticking with the 4311. It's not just board space, but 4 PGA4311 chips are a bit cheaper than 8 PGA2311s. I hate to be so cheap, but I really need to save every penny. Luckily, the software should be the same for everyone. I'll just let someone else design the 2311 PC board. I'll hand-wire a separate bipolar power supply board and add a few op-amps to mix into. That should be pretty straightforward. Big question on the mixer: The line mixers I've built before always had a series capacitor at every input to block DC and pass AC. I would think that this would be even more important if your sources are coming from different equipment. The datasheets for the PGA2311 do not include anything like this. Adding them after the 2311 seems silly, putting them before would make sense, but I'm not sure how it would affect input impedance. If I'm not making sense then I'll draw a schematic. Any mixer experts want to offer an opinion? Thanks. LyleHaze

OK, I started a new thread.. If I got it wrong, go there and correct it! LyleHaze

It seems we have a few different projects building on the PGA2311 and PGA4311 Audio Mixer Chips. http://focus.ti.com/docs/prod/folders/print/pga2311.html Already we have a desire for a small self-contained mixer, a controlless mixer backend, and a foundation for a more capable effects unit. Variety is a strength, but what I'd like to try is to combine what we can between these projects. Perhaps we can all agree on the same pins to control the clock and data, so we can all use the same low-level drivers. Are others going to want control over the ZCEN and MUTE inputs, or will these be hardwired into a single state? Another issue we will all face is where to get the -5Volts for the chips. And do we want to share the same digital +5 with the analog +5, or should we use separate regulators to keep the costs down? Mixers? Easy enough to lay out a board (probably separate from the PGA board to be configurable). What board design would serve the most of us with the least excess? It looks like we all want different things, but let's try to figure out what the common parts are, so we can join together! Please Comment.. Lyle Haze

Hi Everyone. New user, first posting, please let me know if I've got something wrong. :-) I've just built my first Core (and it works!) and I have been planning to build a line mixer backend. 8 stereo pairs to 1 stereo pair out. No local controls or display, just the analog end of a simple line mixer. I have been looking at the PGA 2311/4311 to get the job done. Now I'm wondering what the most flexible way to configure the PC board would be. I know exactly what _I_ want, but how can I design this to be modular and easy to reuse for other applications? If I build it all in one PCB, then it'll be a line mixer and not much else for anyone that wants to use it. What variations would be useful to everyone else? Also.. the 4311 is cheaper per pair, but the 2311 is available in DIP, which really helps hobbyist level builders. Don't expect big progress really fast here, I'm a married man, so I have a very tight budget, especially when it comes to PCB proto orders. Looking for peoples opinions here, I can detail some of my own ideas too if y'all are interested. LyleHaze