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Sound card DAC tutorial

ElektroFreak

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^It's a standard feature in every program that supports the soundcard DAC..
 



MISTERWILLING

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I had the same problem, for some reason windows media player forgot how to play wav files. Download the AC3 decoder for free and it will fix your problem

This might need to be added to the tutorial as I wasted an hour or so trying to figure out why I couldn't play it
 
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Xer0

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Howto: simple Differential Amp + TTL ?

Hello Folks!

I have a 6ch CMedia ready and want to build an quick & dirty correction board.

Could you help me?

I drawed a plan with the patient help of Nicolas (weartronics) and his great Differential Amp Design. As i cant get the ±9V DC Converter here, only 5 to ±12V, which wont get enought power from usb; i thought of taking one of the 12V wallwarts i have colleting dust, and creating ±5V from it by splitting regulated 10V. the dropout of the IC is 2V so it fits, or not?

Also, i have a only TTL modulated Laser (Pf-114) so i dont need real linear amplifying by now, it should just be able to blank the Laser with Spaghetti and HE. Maybe someone could give me a solution that uses only Transistors for the RGB chan or even raw unamped Soundcard Output.
Here are the input specs: Bild: 300mw_rgb_animation_lao40c.jpg - abload.de


Sorry im a total noob in Electronics. i can solder even SMD without problems but have no clue how the stuff works and how to design a circuit from scratch and what parts i need etc...

Thanks
TC
 

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ElektroFreak

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Re: Howto: simple Differential Amp + TTL ?

Hello Folks!

I have a 6ch CMedia ready and want to build an quick & dirty correction board.

Could you help me?

I drawed a plan with the patient help of Nicolas (weartronics) and his great Differential Amp Design. As i cant get the ±9V DC Converter here, only 5 to ±12V, which wont get enought power from usb; i thought of taking one of the 12V wallwarts i have colleting dust, and creating ±5V from it by splitting regulated 10V. the dropout of the IC is 2V so it fits, or not?

Also, i have a only TTL modulated Laser (Pf-114) so i dont need real linear amplifying by now, it should just be able to blank the Laser with Spaghetti and HE. Maybe someone could give me a solution that uses only Transistors for the RGB chan or even raw unamped Soundcard Output.
Here are the input specs: Bild: 300mw_rgb_animation_lao40c.jpg - abload.de


Sorry im a total noob in Electronics. i can solder even SMD without problems but have no clue how the stuff works and how to design a circuit from scratch and what parts i need etc...

Thanks
TC
Weartronics is the man when it comes to this stuff..

That circuit is sweet because it's differential.. but I understand not having the skills to build it. As an alternative, 300EVIL sells bare PCBs for his correction amp. This is far cheaper than an assembled unit, and then all you'd need to do is get the parts and build it. You may already have quite a few of them around..

Also, a 5V to +-12V converter should be able to run very easily off of USB. I'm using one on my amp right now. Using the higher voltage DC-DC converter gives you a larger scan angle, so it's beneficial.
 
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ElektroFreak

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BUMP - Updated with a new source of correction amps, both kits and fully assembled. See first post.
 

Benm

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I'm derriving the voltage for the diff amp from the scanner power supply. Since that has -24 and +24 already, its just a matter of regulating that down to -12 and +12 volts (using LM7812/7912 or similar). This gives the opamps plenty of room for output (i use common tll082 types) even if they are not rail-to-rail.

I would strongly recommend using common ground for all your circuitry - that is, the USB ground connects to the scanner power supply ground, laser driver and also the offset ground. Ground loops shouldnt be a major worry since the signles are differential from the correction amp on.

If you must, you can use 2 separate 12 volt wall wart supplies, connecting them in series with the middle point to the ground. As long as they are properly isolated from mains (and have no 'earth' connections) this will work.
 

ElektroFreak

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That's a perfectly acceptable way to do it. The reason most people use DC-DC converters is to be able to keep the DAC external by powering it with the same USB voltage source as the sound card. With your method, the DAC would need to be built in to the scanner (or very near in any case), which is a perfectly valid arrangemment. The only thing potentially problematic about that arrangement is if you have more than one scanner and you want to be able to use the same DAC with any of them. Then you would want the DAC to be external and use DB-25 cabling to connect your scanners to the DAC. Being able to power the DAC directly from USB is just extra convenient for this arrangement.
 
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Benm

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I'm sure it is - especially if you just want a nice box with the soundcard and comp amp, no external power supply, and run an ilda cable to the scanner/laser box that is interchangable. Downside is that you will most likely be using the usb port out of spec, although i dont know what current requirement the sound card reports to the pc.

Its perfectly feasible to make the supply voltages from the 5v usb power using MC34063 or similar switching regulators. It adds a little bit of complexity to the overal design though, because such switching regulators are sometimes tricky to diagnose for faults.

Personally i like linear power supplies because they are very predictable - problems like oscillations are very easy to diagnose using a scope. With switchmode supplies there always is some unwanted ac component present on the powerlines, and its sometimes hard to tell if that represents a problem or normal operation.

Also, the soundcard plus compensation amp isnt that expensive. The sound card is $20 or less, and the components have similar cost. Personally i dont consider making a $30-$40 assemby a separate box worthwhile, but to each his own in that regard!
 

ElektroFreak

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Cost isn't the sole concern, though. Let's say you want to sync two projectors. You currently can't run more than one soundcard DAC using a single instance of software so if you want the projectors synced with the same signals, they must either be controlled using software that can run more than one DAC, or the signal must be split from a single source (of course the signal can only be split once without the need for additional buffering..) You could still have this functionality if you were to split your internal DAC signals to a female DB-25 connector so it can daisy chain to another projector.

Convenience and versatility (or most people's perception of it) is the main concern. I'm just throwing information out there, it's your design.
 

Benm

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If you want to run more than one projector, it would indeed be much easier to make the dac and correction amp into a unit, and run wires from there.

Btw, i think it IS possible to run two soundcards with the same output: You could feed LFI into virtual audio cable (software, does what you think it does), and mix the output of that virtual cable to two soundcards. I'm not entirely sure this works for 5.1 signals or how much cpu load it takes, but it sounds feasible.
 

Benm

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I noticed no schematic for the correction amp is given in the opening post, so here it is:





Notes:

- this is not THE correction amp as pictured in the opening post, but something that i have tested and found to work.

- this schematic is for one galvo. You will need 2 for a X-Y system, and additional ones if you want analog modulation (more on that later).

- this amplifier requires +/- 12V symmetric supply voltage. -12 V is NOT the same as ground. Any symmetric power supply between 9 and 15 volts will suffice, 12v recommended. The ground must be connected to the souncard/usb ground.

- 10 turn pots are recommended for easier setup, but not totally required.

- both opamps are in a single TL082 IC.



Setup/tuning:

Connect the DC modded soundcard to the input, and a scope to one of the differential outputs (i'd recommend the non-inverted to check the inverting amp is working). Start up LFI, but dont display anything for now.

- put the gain pot somewhere in the middle, doesnt really matter much.

- adjust the offset potmeter such that the output voltage is zero.

- now open some ilda file in LFI and make sure it runs at full size/deflection, and that the laser is configured to be 'on'.

- adjust the gain pot to achieve a 5 volt (with respect to ground) output signal.

- stop the display show in LFI

- check if the offset is still at zero volts. If not, adjust the offset pot to get it back to zero, and repeat the steps above (not usually required).


Thats it, the output is ILDA compliant 5/5 volt differential and can be connected to your scanner set.
 

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Benm

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You're welcome - i figured this was the last piece missing to make this thread a complete tutorial.

I'm still doing some reasearch on setting up analog drivers, if the results are good i'll post those too.
 

Grix

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I can't get the sound card used in the dac to work when set to secondary sound card in windows anymore.. It worked fine before but suddenly now it doesn't. It works when set to windows' primary sound card. Anyone else had this problem?

It's not a configuration error, the soundcard won't even output sound when tested in it's own control panel.
 




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