Topic: Correction Amp

[Urbanus]

Hello everyone,

I introduce myself considering I’m new here
my name is Frank Hoogeveen
I’m 20 years young
and from Holland

now I’ll like to order a Correction Amp but don't have a credit card.
To order It from http://hacylon.case.edu/ebay/laser_diode/LaserBoy_Correction_Amp.php
*Google checkout needs a credit card*
are there other possibilities to order?

Frank

[James]

Hello Frank and welcome to the LaserBoy Forum! 

If you want to make one that is a bit more accurate, easy to adjust and capable of handling a wider range of sound devices, you should just get a copper proto board, order the parts you need and make your own.

I have made several variations of the correction amp this way.

I would be glad to help you do this!

The kit works well with the blue-box 6 ch. USB sound device with the C-Media chip in it.

James. 

[James]

First, you should get a Dolby 7.1 sound device! It will have 8 channels. You can get either a PCI card or a USB device.

If you want to make a correction amp for all 8 channels (you really only need 5) then you will need...

(8) 10K ohm 1% resister
(8) 15K ohm 1% resister
(1) 120 ohm resister
(8) 100K ohm trim pot, 15 or more turns
(9) 500 ohm trim pot, 15 or more turns
(6) 10uF tantalum capacitor
(4) 8 pin dip sockets
(4) TLO72 dual op-amp
(1) DC/DC converter (GND, +5) to (+9, GND, -9)
(1) LM337 adjustable negative voltage regulator
(1) copper clad proto-board
     and a bunch of pin headers and sockts

If you go with a PCI card, you do not need a DC/DC voltage converter. You can get -12, +12 and +5 from the PCI slot.

http://akrobiz.com/laserboy/forum/index.php/topic,8.0.html

James.  :)

[Urbanus]

Hello,

I’m sorry i don’t told the hole story,

I like to control my 400mw green ttl laser
With 20kpps galvo’s and ilda port

First I was struggling with an lpt dac
That diddend work for me.

Then I found laserboy and the soundcard dac.

So I bought a pci 5.1 sound card
With a c-media CMI 8738 chip

And already solder wire’s before the caps

I have a  +/-12v from the psu
So don’t need the dc/dc converter,

I have some solder experience
So I want to give it a go.

Is this the right drawing?
http://www.akrobiz.com/laserboy/graphics/huge/laser_h_95.jpg

Frank

[James]

For what you have, that will work just fine!

If you get a PCI card with a VIA chip on it for 7.1, you will have 8 channels. Channels 7 & 8 can be for stereo audio left and right.

C-Media 8738 (6 ch.) is OK.

I have tried the C-Media 8768 and it is not very good.

The VIA is much better.

The difference between my current amp design and that schematic is that I like to use a variable negative voltage regulator for the constant negative offset reference and I used a finer value of trim pot for the offset adjust. I also use 100K pots for more gain.

What OS are you running?

Once you get this all figured out, then all you have to do is learn how to use LaserBoy! 

James. 

[Urbanus]

Hello,

I’m been busy the past couple days,

I manage to make the correction board
After blowing one tl082 *love that smell* and a lot of adjusting its working properly.

Al I need to do now is make a nice casing to protect it.

I test the correction amp with He-laserscan and the EzAudDac
That workt better than expected.
Tomorrow I give laserboy a go!

I hope to make some pics and post them here!

Frank

[drlava]

Good job, Urbanus.  It's always nice to hear or people's successes with this solution

[James]

Tomorrow I give laserboy a go!

Make sure you have the last few versions ready to go.

2009_10_31 sucks, so don't bother with that one! 

I update it frequently and there is WAY too much stuff there for me to test everything.

However, I try to keep everyone informed about what works, what just got fixed or added and what just got busted! 

Please ask questions, make comments, complain, whatever!

It is the best way for me to know what to fix!

http://akrobiz.com/laserboy/code

James. 

[johannesgj]

is this correction amp you are talking about the same object as i see on the pictures connected to the dac in this post:
http://akrobiz.com/laserboy/forum/index.php/topic,8.0.html

is it to be understood like this:

dac has cables attached to its ports for unmodified output.
this goes into some sort of little pcb that does some sort of thing and then goes into another big pcb with chips that does some other stuff.

eeeeehr sorry if i sound nooby. i have no trouble understanding the schematic and components its just the overview of the different pcb's i lack.

[James]

Yes. That is a correction amp.

If you look closely, you will see that there are wires tacked onto the back of the USB sound card. These wires are attached to the positive side of the output decoupling capacitors. This means that the signals are coming right out of the DAC and not going through those caps. The output jacks on the card are right after those caps. So, if you leave the caps in place and just tap the signals from the positive side, the sound card will still work exactly as it should and you can still use the jacks as DC decoupled audio outputs.

Each one of those direct-from-the-DAC signals goes to its own section of the correction amp. There are actually 6 amps, one for each signal. Each dipp you see is two op-amps. The amp is designed to be as simple as possible. It is only one op-amp per channel. Each one of them serves exactly the same purpose. A signal comes in from the sound card DAC that is all positive voltage. A negative reference voltage is provided on the correction amp board from either a 5.1v zenor diode or a negative voltage regulator. This negative voltage is mixed (summed) with the all positive voltage from the sound card to center the resulting voltage over the zero volt line. A little bit of gain is applied to bring the voltage up to the level where it can accurately control the laser projector.

That little board between the sound card and the correction amp in the first picture was just an idea to be able to rearrange the order of the signals coming from the sound card without having to resolder anything. Since then, I just use sockts and 24 gage wire on the correction amp board.

I also made my amps with 8 channels..... just because! 

Actually, I could use all 8 channels to control more lines of color; like with a PCAOM.

This is an early version of the amp. I have made a few adjustments in the resister values and added a varible negative voltage regulator instead of the zenor diode.



James. 

[meandean]

I manage to make the correction board
After blowing one tl082 *love that smell* and a lot of adjusting its working properly.

 I'm glad to see others from far away having fun with this thing... Welcome to the Forum!
A few years back, I smoked an audio card at James house while trying to modify it for DC
operation- I think he's still yet to forgive me!

                                                                       Dean

[James]

It still smells like burt electronics around here! 

James. 

[johannesgj]

thanks for the welcomming mean dean.

well this correction amp feels like a good idea, however i dont get the function just yet. (which is maybe caused by the lack of coffee in my blood )

well this circuit board for the correction amp is having fine pictures up on the forum.
however i lack a precise schematic to be able to fully understand the circuit.

actually we have the tools to make some pcb's at my school. so if anyone can provide a precise schematic for the pcb of the correction amp, then i can make some pcb's actually probably a lot of them and then maybe if somebody is in need send them to usa and then one of you could distribute them.
well thats just thoughts of a guy who feels he wants to pay back for all this nice help
and sorry the spelling im quite tired.

well schematic and precise explanation of function would make my day

[James]

You need to make one of these for every channel of the sound card you intend to use for laser signals.

James.   

[James]

You only need to make one of these. This is where -Vref comes from. It is the same for all of the amps.

-Vin comes from the negative side of your differential power supply. If you use PCI slot power, it's -12VDC.

The 500ohm trim pot on the voltage regulator is a course adjust to get as close as possible and the 500ohm trim pots on the inputs of the amps get you down to the last ±0.0001 volt. This is WAAAAAYYYYY overkill! But it works quite well for just about any kind of multi-channel computer sound device you might come across.

You should adjust your negative voltage reference to be about -1.5 times the positive offset you are trying to null. This comes from 15K / 10K.

You can add up to 500ohms to the 15K fixed resister with the trim pot that is in series with it, so you can change the combined value by about 3%. That's why all the fixed resisters need to be 1% or better.

The 100K trim pots give you a possible gain of up to 10X (100K / 10K).

James.