USB Audio DAC mod + LaserBoy Correction Amp

[drlava]

Only problem I see is that he says that when he connects the scanners to his DMX output board, everything is symmetrical. If that's the case, then the problem is *not* with his scanner amps.

That's assuming the DMX output is symmetrical. It's possible that it isn't and the scanners are tuned to that. DPSS, does your DMX have differential or single ended outputs?

It's also possible that he didn't set the DAC amp gains correctly with with max.wav, but he told us that he did so we can only go by that.
An oscilloscope would make it easier, but given the right technician it shouldn't be absolutely necessary to solve this problem

[DPSS]

CORRECT ! ! i had the EXACT same issue...

Just adjust the master gain until they are correct. thats what im trying to tell ya

When you refer to the adjusting the "master gain", I supose you mean the pot that adjusts the gain on the Y channel's amp board. I understand that would correct the problem, but I really prefer not to touch anything on the amps until I can make sure there isn't somthing other cousing the problem.

If your DAC gains are set properly like you say they are, both +/- 5V, then it has to be the tuning. You should try one of the free old versions of Spaghetti there are a few test frames in there. That way you won't have to rely on wav playing. Don't just use a circle, man, that only gives a small amount of info. Try the ILDA test frame for example.

Let's see, my DAC gains for both the X and Y channels are set at 0v when idle and +5v when playing the max.wav file. Tested with my meter. As far as I know that's correct, isn't it?

I have used Spaghetti's test patterns before but wasn't measuring the voltages when doing it. I'll try that when I get home tonight.

i ran in to this issue when i decided to re-tune my scanners..

i wonder myself if this is an issue with the SP20s and using single ended inputs.. but everyone tells me its not.

then i thought it was a power supply problem..

i racke mu brain for a long time till i just said F' it and set the master gains to compensate..

I just want to make sure the scanners or someting else isn't damaged in some way before I start adjusting things in the scanner amps, but if It turns out to be as hard to solve as yours I''ll probaby end up doing the same as you.

Only problem I see is that he says that when he connects the scanners to his DMX output board, everything is symmetrical. If that's the case, then the problem is *not* with his scanner amps.

I don't think this is a tuning issue. I think it's a problem with either the volume level on the sound card DAC or a problem with the adjustments on the correction amp.

True, adjusting the master gain on the Y scanner amp will correct the problem, but when he connects the DMX board, the problem will be back.

I think Alec is right... Time to get an oscilloscope.

Adam

Exactly my point.

Yeap, I think you're both right, it's time for an oscilloscope. And if after that I can't get a clear answer I'll just set the Y amp's gain higher to compensate.

By the way Keeperx, thanks for the ebay link but I'm affraid living in Spain ads quite a high shipping charge to anything I buy from the US. I'll have to check for pricing somewhere a bit closer first.

That's assuming the DMX output is symmetrical. It's possible that it isn't and the scanners are tuned to that. DPSS, does your DMX have differential or single ended outputs?

It's also possible that he didn't set the DAC amp gains correctly with with max.wav, but he told us that he did so we can only go by that.
An oscilloscope would make it easier, but given the right technician it shouldn't be absolutely necessary to solve this problem

I'm not home right now but I'm nearly sure they use 3 cables for each channel, so I guess that would be differential. I'll check tonight and let you know for sure.

Now why would I go and lie to you all about setting the DAC amp gains? That would most probably only muddle things up even more? I'm not trying to get an answer I'd like to hear, I'm just trying to figure out what's wrong.

Domingo.

[keeperx]

well i no longer use the DMX board.. but maybe the output from THAT should be measured as well...

[keeperx]

http://cgi.ebay.es/GOULD-ADVANCE-OS1...|39:1|240:1318

and this looks good too
http://cgi.ebay.es/4-Channel-DSO-Osc...|39:1|240:1318

[drlava]

Let's see, my DAC gains for both the X and Y channels are set at 0v when idle and +5v when playing the max.wav file. Tested with my meter. As far as I know that's correct, isn't it?

Yep, sounds OK.

I have used Spaghetti's test patterns before but wasn't measuring the voltages when doing it. I'll try that when I get home tonight.

Not measure the voltage, just look for distortions...

Now why would I go and lie to you all about setting the DAC amp gains? That would most probably only muddle things up even more? I'm not trying to get an answer I'd like to hear, I'm just trying to figure out what's wrong.

not lie, just make a mistake. But it sounds like you re-checked and it's OK. Are you putting both x and y signals into the + side of the input of the galvos? You could try changing to the other input and see if the size changes (it shouldn't if everything is right, if it does that's good information). Also you could try swapping X and Y inputs to see if the size changes to the other axis.

[keeperx]

OMG you just gave me an idea...

ok there are a few things to think about here..

#1 the AMP inputs are double ended (that SHOULD not matter)
#2 the Jumpers to FLIP the output
#3 the extra wire

im going to experiment tonight.. ill tell you how it goes.

[Paul]

Let's see, my DAC gains for both the X and Y channels are set at 0v when idle and +5v when playing the max.wav file. Tested with my meter. As far as I know that's correct, isn't it?

I think you make the mistake here... The max. output (peak voltage) of your DAC should be 5V. If you are testing the output with a regular multimeter, then you are measuring the effective voltage or in case of a true rms tester, the true rms voltage.
The only way to measure peak voltage is using an oscilloscope. Unless you have the possibility to generate a perfect sine wave of ~50-60Hz, then you can adjust your pots for 5/√2 = ~3.54V. (The √2 rule is only valid for pure sine waves!)

At the moment there is some amplifier clipping because you are over driving it...

[drlava]

I think you make the mistake here... The max. output (peak voltage) of your DAC should be 5V. If you are testing the output with a regular multimeter, then you are measuring the effective voltage or in case of a true rms tester, the true rms voltage.
The only way to measure peak voltage is using an oscilloscope. Unless you have the possibility to generate a perfect sine wave of ~50-60Hz, then you can adjust your pots for 5/√2 = ~3.54V. (The √2 rule is only valid for pure sine waves!)

At the moment there is some amplifier clipping because you are over driving it...

No mistake, the MAX.wav is D.C. That's the reason I made it, to allow calibration without worrying about peak, RMS, etc.

[Paul]

I just read the original message and I notice that I did not read the "max.wav" part initially. I thought the circle.wav was used.... My mistake...

[buffo]

Andrew;

I don't see how his scanner amps could have been tuned with the DMX board. As far as I'm aware, the DMX board that comes with the ScanPro scanners does not have the ILDA test pattern programmed. (The board I looked at didn't have it anyway...)

DPSS;

Do you know anyone in your area that has an Oscilloscope that you could borrow for an afternoon? Or maybe you could take your DAC over to someone's house? It would be very easy to test the output... It probably won't take more than a minute or two to set up.

Adam