USB Audio DAC mod + LaserBoy Correction Amp

[keeperx]

I FIGURED IT OUT ! ! ! ! !

its the jumpers for reversing X and Y (in case Yis upside down or X is backwards)

they are funny...


i have the same scanners and was able to reproduce the problem by wiggling the jumpers.


my sugestion is to find the proper setting on the jumpers and jumper it with A: a better jumper or B:some copper wire.


have not figured out EXACTLY whats causing it but im prety sure the jumpers are just not making good contact..

[drlava]

The correction amp generates +/- 5V single ended, while differential controllers produce +/-5v on their + output and -/+5V on their inverted output for a total differential of +/-10V full swing. so, if your scanners were pre-tuned for differential they should give about half the normal scan angle with the single ended correction amp until you turn up the scanner gain (shouldn't need a complete retune if they are tuned already). That would mean they were tuned for 14 or 16 degrees, which seems too small to me.

[DPSS]

I FIGURED IT OUT ! ! ! ! !

its the jumpers for reversing X and Y (in case Yis upside down or X is backwards)

they are funny...


i have the same scanners and was able to reproduce the problem by wiggling the jumpers.


my sugestion is to find the proper setting on the jumpers and jumper it with A: a better jumper or B:some copper wire.


have not figured out EXACTLY whats causing it but im prety sure the jumpers are just not making good contact..

Congratulations!! I'm glad you figured yours out.
I'm affraid nothing happens when I wiggle my jumpers though. What I have realised is that when I set the jumpers for one of the channels to be inverted, I get a simetrical image. But if I set them for both channels to be up right or reversed, one of them scans at about half the width of the other. So there is no way of setting them correctly

The correction amp generates +/- 5V single ended, while differential controllers produce +/-5v on their + output and -/+5V on their inverted output for a total differential of +/-10V full swing. so, if your scanners were pre-tuned for differential they should give about half the normal scan angle with the single ended correction amp until you turn up the scanner gain (shouldn't need a complete retune if they are tuned already). That would mean they were tuned for 14 or 16 degrees, which seems too small to me.

Thanks for the explanation.
I PM'd Dave from Lasershowparts yesyerday so I hope he can find a minute soon to check what's been going on here and he and Adam can let us know what they make of it.

Domingo.

[buffo]

Here's the problem I have with the "scanners need tuning" theory:

They work just fine when the DMX board is connected. And while the DMX board isn't *perfect*, it's at least as good of a signal source as a sound card DAC. So if there is anything wrong with either the scanners themselves or the tuning on the amps, it should be wrong all the time, and not just when the sound card is connected.

The fact that the problem goes away when you flop scanner leads is interesting. However, what is even *more* interesting is that you say you can switch *one* of the jumpers on the scanner amp and solve the problem - except that the image is inverted.

To me, these two symptoms point to a problem with the input connections. I think you've got a connection reversed, and ground is actually being shorted to either X+ or Y+ through the scanner amps (by way of the common ground they share on the scanner amp PSU.) Why it goes away when you swap the leads to the scanners is still a mystery, but it still makes me think that you've got a signal somewhere where ground should be, or vice-versa.

I've seen all sorts of crazy things happen when you invert the ground and positive input signals on one amp when running a set of DT-40's single-ended. Basically what you end up with is a dead short on the output of your controller though the common ground of the scanners (which goes back to the scanner amp PSU). It manifested as one scanner not scanning nearly as wide as the other. (Though it also caused that scanner to get hot as hell!)

I think I'd triple-check the connections between the sound card and the correction amp, and between the correction amp and the scanners. Also, I'd connect signal ground from the correction amp to both the ground terminal on the scanner amp *and* the negative terminal. See what that does.

Adam

[keeperx]

Hrmmmmmmm ..

ok you have Red Black and White..

if you are using red and black, try White and black instead then flip the jumpers... that SHOULD give you a proper symmetrical image, no?

[buffo]

Red, Black, and White?

I thought the output from the correction amp was single ended? So he'd only have a pair of wires. Or are you talking about the connection on the scanner amp input?

Not sure I'm following you here.

Adam

[keeperx]

correction amp is voltage(+/-) and ground but the scanners take red(+) black(ground) and white(-) so if you use red black it is the opposite of using white black...

im not sure if im making myself clear, but i have the same scanners and am willing to experiment with them whenever needed .. just call 443.834.5229...

i believe that the sp20s have some specific limitations regarding single ended input, have mine running well off a sound card DAC so lets get together and figure this out...

[DPSS]

Ok, I've checked the connections from my soundcard to the correction amp and they are as follows:

Soundcard -> Correction amp input (marked as)
USB Ground -> pin nº 1 (G)
USB 5v -> pin nº 2 (5v)
C10 -> pin nº 4 (1), X channel
C9 -> pin nº 5 (2), Y channel
C2 -> pin nº 6 (3), R channel
C1 -> pin nº 7 (4), G channel
C12 -> pin nº 8 (5), B channel
C11 -> pin nº 9 (6), I channel
C17 -> pin nº 10 (G)

Pin nº 3 from the correction amp inputs (G) is connected to the Ground on the scanners power supply for the purpose of joining all grounds together.

Now, for further testing I used Sapghetti to generate the ilda test pattern withount activating any of the signal inverting options for either the X or the Y channels which, as far as I know, should produce a completely inverted pattern beacause of the USB DAC being an inverter, and next I set the jumpers on the amps to produce such a pattern, which resulted in the Y channel scanning the pattern half the size of the X channel. Then I followed Adam's indications and connected each channels signal ground from the correction amp to both the ground terminal and the negative terminal on each corresponding amp. For the X channel there was no change but, when I did it for the Y channel, it increased the scanning angle to match the X channel.
So now my pattern size seems to be properly compensated between channels, but I'm still getting about 7 or 8 degrees scanning angle, which is about 1/4 of what I get when I connect the DMX board.

Domingo.

[keeperx]

did you stretch the window in spaghetti?

[DPSS]

Yes, as big as posible.

Domingo.