USB Powered Pimeta - Page 2

or you can use a 5v inverter chip to get -5, so you have +/-5V for the opamps. Don't need a rail spliter anymore.

by the way, how well can the TL750 linear regulator handle the 800KHz noise?

I didn't see any other mention of dac in this thread, but I had been wondering how feasible a Pimeta/Bantam USB combination would be.

Sounds like running the Pimeta alone from USB is pushing it though, without adding a dac..

Kinda have something similar in the works, though I'm using a simpler solution and drawing 18v from the wall (TREAD is inside the case too).

Consequently, I don't have the option of driving the amp straight from a laptop.

Keep this up rds. I'm curious to see how this goes

My apologies if you think this is harsh or arrogant, sometimes I'm just that way.

I hope my information is worth putting up with me.
If you are building a pimeta you need a negative supply.

Unless you get REALLY fancy&creative with isolating the USB line, USB ground will be signal ground. This becomes problematic when you look at what a virtual ground does when it is fed a voltage source which is grounded at one end (say the negative end is grounded).

First off you triple the USB supply voltage to get 15V above ground, and as mentioned later "clean" it down to say 12V which is plenty of voltage for a pimeta. It may not provide any current but the use of a powered hub was mentioned. If your going to cart along a 5V wall-wart for nothing but the powering the hub (which you only need to "power" because your powering this beast) why not just carry along a 18-24V wall-wart (no hub! 1 less bit of junk in the bag!) instead and avoid all this effort?

Lets just say for fun that you REALLY want to use USB with a voltage multiplier and a tread set to 12V above ground. The railsplitter in the pimeta FORCES signal ground to the mid-point of the power rails. In this case, we have signal ground (on the pimeta) at 6V above earth ground*. We can assume that signal ground from the source is at earth ground. They are 6V apart and connected with wire.... I smell smoke. Its the railsplitter, they dont catch on fire (IME) but they do smoke. Sometimes the smoke comes from somewhere else. That smoke is usually more expensive, but the odor and color is similar

You need to be VERY careful when combining virtual and real grounds. It is very important that virtual ground be allowed to float to equal real ground. If it can not, disaster is eminent. The technique of floating wall-warts and transformers (with no electrically good connection to earth ground on the secondary/DC side) avoids this problem in home systems, but its apt to sneak up on the unprepared.

You need a negative rail, even if its technically made by taking a single floating supply and straddling ground with it.

*when the system (assuming a portable laptop computer) as a whole is not technically grounded, consider the laptops ground reference to be earth ground. you can see the virtual ground in the pimeta and laptop grounds are still quite a few volts apart and your gear is doomed.

Ahh Nikon.. gotta come in hear and shatter my dreams! Of course your right. I'm sticking to dedicated PS and batteries. It's easier and less crap to lug around in the end.

Perhaps when USB 3.0 rolls around we will have the current specs to make this a possibility. I still don't see it working with any amp that requires more than +/-2.5v without a load of headache. Even then, what Opamp sounds decent at +/-2.5v. Not one I am aware of.
Edit.
The only info on usb3.0 that I could find is from wikipedia. Ugh.. It comes up with this.
Anyone know what a configured device is?

usb 2.0 powered is fine, have similar project in past, wm8740, tpa6120, fpga, oled, usb or wallwart powered. usb supply is fine.

add another lc after the ldo. pick the l based on the filtering frequency, but larger works like 150uH.

btw, i know you're pretty determined to use the pimeta, but if you can use SMD parts (etch your own pcb, etc.) you can do much better in terms of dc/dc.

MPS1517 with a Coiltronics transformer can give you +-12V with *real* ground.

While you can use a 24V wallwart, I would pull the vground circuitry out of the pimeta and make the source of the pimeta a split rail supply. You may have to pull out the vground circuitry entirely, but IIRC Tangent covers that on his site.

I would probably go that route instead of the vground. Issue, power via USB but feed the amp an input from the computer sound card. I believe that is the issue that nikongod was referring to.

sorry, we crossposted.

Well, here's another method...tried and true by many a head-fier.

Meier-Audio

LM2662 SOIC-8, can browndog mount for DIP-8 for through-hole. I would still go with the MPS1517. I can attest that the MPS method is very good, but it was filtered this way....dc/dc->lc->ldo->lc->ldo->lc The 2 ldo drop from +-12 to +-10 then +-8. You can drop the second ldo if it's an issue for you, it's unlikely you will hear the hash. the mps1517 switches @ 1-2MHz.

none in that mode, but if you use the input of the pimeta from an external source and that source is real grounded, it can be a short and fry the tle. if you wire output only, it's fine. if you want to have the option of external analog input then you need to either be very careful and warn those you sell it to, or center around real ground.

I admit, it's an oddball case, but you never know what people may or may not try. I can definitely see something like that happening at a meet. when guys see holes, they have to put stuff in it. must be nature.

yeah, that's fine, lest you tie the grounds when you do it.

took a quick look at the dc/dc you are going to use, that error401 recommended. there is a dual output version that can generate a negative rail as well, but with more ripple. what's cool is you can stack multiple converters together.

nice recommendation error401. I never looked at this one before.

man, tempted to make a usb powered jisbos or something like that, just need to rig up a usb device that requests all 500mA and some serious power smoothing.