Electronics > Beginners
Op amp based preamp supply. Charge pump, single vs symmetrical & ripple
dazz:
OK, how about this for a dual rail supply? It's based on two MC34063. The first one boosts the voltage to 18V, the second inverts it to -18V, then I can regulate them with some 7815 + 7915.
Or maybe I can do what b_force suggested here and get rid of the inverting 34063?
--- Quote from: b_force on November 26, 2018, 03:01:05 pm ---Another idea i to get a basic 9-12 or 9-15 boost converter and use a flyback or 1:1 coupled inductor to form the negative voltage.
--- End quote ---
I have no idea what a flyback or 1:1 coupled inductors are, but that's what google is for, isn't it?
Pros and cons of this last solution seem to be:
-PROS-
1. MC34063 & 220uH inductors and of course the obiquitous 7815 & 7915 are pretty cheap and readily available
2. Noise free regulated rails
-CONS-
1. Component count increases. I still have two DIP8 IC's, and i don't need the voltage divides and the coupling caps for the opamp bias, but the power supply section gets significantly more complex with 7 resistors, 10 caps (including the ones in the regulators) 2 diodes, 2 inductors and two linear regulators. If I could do the flyback thing this may not be an issue
2. What the hell are those 0.22R & 0.24R resistors all about? Apparently they need to be that precise at those ridiculously low values or else the converter doesn't work.
ETA: Of course I wasn't the first one to come up with this idea: https://www.diyaudio.com/forums/chip-amps/206788-using-2-mc34063-cmoy-virtual-ground.html
Dave even has a video on it apparently:
dazz:
--- Quote from: dazz on November 27, 2018, 05:52:05 pm ---then I can regulate them with some 7815 + 7915.
--- End quote ---
Wait a minute, there's feedback in those MC34063, so they're regulated, and if I calculate my values to have a high enough ripple frequency that it's not audible it won't matter for my application and I won't need those linear regulators, is that right? Because that would significantly simplify my circuit
Zero999:
You could build your own power supply but it's a pain. Just use a DC:DC converter module. Some examples are linked below, which have a regulated, isolated output. Additional filtering will probably be necessary to prevent audible noise, due to rectification of the RF in the op-amps. No doubt there are cheaper modules available off ebay, Amazon etc.
https://uk.rs-online.com/web/p/isolated-dc-dc-converters/1714747/
https://docs-emea.rs-online.com/webdocs/168f/0900766b8168f657.pdf
https://uk.farnell.com/xp-power/itw0515s/dc-dc-converter-1w-15v-0-033a/dp/2422847
http://www.farnell.com/datasheets/1847138.pdf?_ga=2.154705917.435636270.1543350785-1037805362.1481052103
John B:
Don't use the MC34063, far too much quiescent power wasted.
I'm in the middle of some similar experiments with the 7660s, to see if I can reduce the switching noise. Probably a mix of both input and output filtering.
It's going to be far more complicated than anything implemented in a commercial musical product, like pedals or guitar preamps, but for a DIY application, parts count isn't the problem, its noise and efficiency.
You're going to have to filter the MC34063 anyways.
I'm a little confused with your input power requirements. So you're not going to run it off batteries ever? Always an adapter? If that is the case, simply supply your pedal with a wide enough +/- range in the first place. Either with 2 floating DC adapters or an AC transformer supply. The input can be filtered and linear regulated, both on the + and - rails.
Your dual power supply idea seems like the way to go at first, but you end up spending far too much time, effort and space trying to make it work, not to mention probably about 30% efficient :-DD
dazz:
--- Quote from: Hero999 on November 27, 2018, 10:08:53 pm ---You could build your own power supply but it's a pain. Just use a DC:DC converter module. Some examples are linked below, which have a regulated, isolated output. Additional filtering will probably be necessary to prevent audible noise, due to rectification of the RF in the op-amps. No doubt there are cheaper modules available off ebay, Amazon etc.
https://uk.rs-online.com/web/p/isolated-dc-dc-converters/1714747/
https://docs-emea.rs-online.com/webdocs/168f/0900766b8168f657.pdf
https://uk.farnell.com/xp-power/itw0515s/dc-dc-converter-1w-15v-0-033a/dp/2422847
http://www.farnell.com/datasheets/1847138.pdf?_ga=2.154705917.435636270.1543350785-1037805362.1481052103
--- End quote ---
Those are just great simple, compact solutions, than you. If I can find those for cheap it's a done deal
--- Quote from: John B on November 27, 2018, 10:22:43 pm ---Don't use the MC34063, far too much quiescent power wasted.
--- End quote ---
According to the datasheet the quiescent current is 3mA. 6mA if I was to use two chips... just as much as the opamps themselves, so yeah, not ideal at all I guess.
--- Quote from: John B on November 27, 2018, 10:22:43 pm ---I'm in the middle of some similar experiments with the 7660s, to see if I can reduce the switching noise. Probably a mix of both input and output filtering.
It's going to be far more complicated than anything implemented in a commercial musical product, like pedals or guitar preamps, but for a DIY application, parts count isn't the problem, its noise and efficiency.
You're going to have to filter the MC34063 anyways.
I'm a little confused with your input power requirements. So you're not going to run it off batteries ever? Always an adapter? If that is the case, simply supply your pedal with a wide enough +/- range in the first place. Either with 2 floating DC adapters or an AC transformer supply. The input can be filtered and linear regulated, both on the + and - rails.
Your dual power supply idea seems like the way to go at first, but you end up spending far too much time, effort and space trying to make it work, not to mention probably about 30% efficient :-DD
--- End quote ---
Well, I have an adapter cable to plug a 9v battery or two Li-Ion cells to the 3.5mm socket in case I need it but what I was referring to is that I personally hardly ever use anything but a wall wart 9V supply. There's no requirement in the design for that though, If someone else wants to build the pedal and power it with batteries, that should be an option. I'll just provide a 9V/DC input in my board, at least that's the initial plan.
Are you having trouble with noise with those 7660S's? Even using the boost to 30KHz pin? Bummer. I was hoping I wouldn't need to filter my supply if I could get the ripple frequency above 30KHz or so
BTW, I said before that for my application (dual opamp) I would have an almost constant current draw from the supply, which I now think is BS. Wouldn't that be a problem with something like a 7660S since it would sag pretty bad (a couple of volts) if you get a 5mA spike in your current draw?
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