Electronics > Beginners
Op amp based preamp supply. Charge pump, single vs symmetrical & ripple
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John B:
For your application I'd probably skip the 7660 since it's max input voltage is around 12V depending on the model. Good for a 9V battery powered device though. Yeah, you can do voltage doubling like it says in the datasheet, but it's more hassle and space taken up. Obviously the manufacturer is happy for you to buy 4 chips vs 1.

The boost pin brings the switching frequency to around 60kHz from memory, but its a wideband burst of noise that propagates to the output of the op amps. I have used them some simple designs (a splitter and mixer for smartphone earbuds/mics) where audio quality was not a concern, but haven't put them in studio quality gear yet.

What I was getting at is that because you do not have to adhere to any standard for power, ie 9V DC input or batteries, you can cut a lot of hassle by simply providing enough voltage in the first place, and spend your effort on the signal path instead.
dazz:

--- Quote from: John B on November 28, 2018, 01:14:25 am ---For your application I'd probably skip the 7660 since it's max input voltage is around 12V depending on the model. Good for a 9V battery powered device though. Yeah, you can do voltage doubling like it says in the datasheet, but it's more hassle and space taken up. Obviously the manufacturer is happy for you to buy 4 chips vs 1.

The boost pin brings the switching frequency to around 60kHz from memory, but its a wideband burst of noise that propagates to the output of the op amps. I have used them some simple designs (a splitter and mixer for smartphone earbuds/mics) where audio quality was not a concern, but haven't put them in studio quality gear yet.

What I was getting at is that because you do not have to adhere to any standard for power, ie 9V DC input or batteries, you can cut a lot of hassle by simply providing enough voltage in the first place, and spend your effort on the signal path instead.

--- End quote ---

I just thought that by not adhering to an almost de facto standard like the 9V supply for guitar pedals I would be limiting the user's options. I was going to put there a 9V input in case you want to implement the power supply in the pcb, or two +16V, -16V for those who prefer to use an external converter, or a dual power supply of their own in which case they don't need to populate the power supply section in my pcb.

Maybe I didn't make myself clear enough, I'm just designing the PCB, not the whole pedal. Well, it's designed to fit in a 1590BB enclosure but it could also go into a larger case with a complete power supply and power amp to make an amp instead of a pedal. Hope that clears that up
Zero999:

--- Quote from: dazz on November 28, 2018, 12:34:03 am ---
--- 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

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Those are just great simple, compact solutions, than you. If I can find those for cheap it's a done deal
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What are the budget constraints?

Is just just a one off hobby project? Will it be made and sold commercially in small quantities i.e. 5 or so? Or are you going to make 1000s? It's often cheaper to use a module, once the cost of all of the parts, assembly and board space is taken into account.


--- Quote ---
--- Quote from: John B on November 27, 2018, 10:22:43 pm ---Don't use the MC34063, far too much quiescent power wasted.

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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

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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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How about using two 9V batteries or a 12VAC mains adaptor?

A voltage doubler circuit with the 78L08 and 79L08 could provide a +/-8V supply when running off the mains and batteries can give +/-9V directly. It's possible to get sockets with a built-in switch to disconnect the batteries, when running off mains power.
b_force:
What happened to the  LT1615 , LT3460, LT1316 idea?
Zero999:

--- Quote from: b_force on November 28, 2018, 11:03:56 am ---What happened to the  LT1615 , LT3460, LT1316 idea?

--- End quote ---
Going by the prices of those ICs in Mouser, it was probably deemed too expensive.

I don't see the point in doing hobby electronics on a shoe string budget. If you really want to save money, there's plenty of cheap junk available.
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