Correction Amp needed

[trotz]

I want to buy/build a correction amp. I'd prefer an assembled one but a full kit is also ok.
I live in Palma de Mallorca (Spain).

Any suggestions?

Thanks a lot!

[mixedgas]

Run away from sound card based DACs as fast as you can, unless you have a very specialized use.
Its an outdated way of doing things. Be very careful to watch card and driver settings in Windows and Linux.
Riya, Lumex, Etherdream and other output devices exist and are far more stable.

Steve

[trotz]

Hi, thanks for the advice.

I'm afraid my setup will fall into the "specialized use" category. I plan to connect a modular (sound) synthesizer to an ilda laser, and I would like to make sure that the x/y ilda signal is differential, protected from excess voltage, etc...

Do you think a correction amp is what I need?

Regards,


Pere

[The_Doctor]

I'm afraid my setup will fall into the "specialized use" category. I plan to connect a modular (sound) synthesizer to an ilda laser, and I would like to make sure that the x/y ilda signal is differential, protected from excess voltage, etc...

Do you think a correction amp is what I need?

Some sound interfaces are worth running toward, not away from. Run from most of them though... Once you find one that;s viable, stick with it, or go with dedicated laser-based hardware.
I'll only suggest one sound device, based on the following:
Differential output. Voltages between -13.6 and +13.6 volts.
Jitter free performance, provided you use its WDM driver, and NOT the standard wave driver.
Its sample rate can be set to anything between 2000Hz and 96000Hz in ONE hertz increments, so you can specify exact matches for other systems, and probably sync with them too, as it has a lot of very good sync tools built in.
Installs on most well known mainboard/BIOS combinations.
Installs on PC and Mac machines.
Gives 8 inputs and 8 outputs, plus S/PDIF if you want it.
Uses MIDI, which is very useful for scan control.
DAC voltage reference is at 0V, instead of the more common +2.25V, so you can replace the output capacitors with wire links to get DC coupling.
For what you get, it's VERY cheap. It's very high quality as well, it was a professional standard for many years.

It's called Layla 24/96, by Echo Audio. You will not need a correction board if you can intercept digital signals to set amplitude in volts precisely. Scaling operations will be fine in digital domain because Layla 24 gives you 24 bits, and most laser controls will be fine with 12. With headroom like that you can get away with a lot.

What you probably will need is a filter somewhere. Scanners do not like strong HF. Try setting a cutoff for low pass filter at 1KHz. Unless you have very fast scanners I doubt you'll need to raise that, and more likely you'll want it lower to protect them when driving them hard.

If someone offers you a little 15 buck USB 6-channel sound card, do what Steve said. Run. Layla will cost you a hundred bucks but she is not high maintenance.


Edit: There is a second worth suggesting, it's very closely related: Gina 24/96, also by Echo Audio. The difference is it's cheaper, but it has all its analog electronics on the PCI card. Digital noise should not be a problem, but be very careful because it has a 25pin D connector that looks exactly like an ILDA connector, and isn't.

[absolom7691]

What you probably will need is a filter somewhere. Scanners do not like strong HF. Try setting a cutoff for low pass filter at 1KHz.

Yes! Honestly, I never seem to even make it past 700 or 800hz. I normally never need to. Even at 500hz, I notice my galvos start to get a bit warm. Running them higher will drive the heat up. Just be careful not to cook them. 1Khz is a good cut-off

[mixedgas]

I've got a Gina, but she only has two inputs and eight outputs. Find a better, newer, Gina with eight in and eight out, or get her fatter sister Layla. .
There are some Mark of the Unicorn boxes that are useful as well.


For what your doing, single ended drive is feasible unless you need a 30 meter cable run. Ground one side of the scanner amp differential input and drive the other. It will not hurt the amp in the least.

The only reason for differential is if the projector is on noisy power lines or far away. Some Asian projectors have poor input circuits or bad ground wiring, but the great majority will fully accept a single ended input.

If you are unsure of your console's output level, a clipper with back to back 10V zener diodes and a 200 ohm series resistor will protect the galvo amp.

You'll need a five volt clipper for the RGB channels anyways, that can consist of a five volt zener diode, a 1n4001 diode and a 470 ohm resistor. Unless you have TTL color. TTL can cause issues, best solved with either a emitter follower circuit or a simple comparator circuit.

Absolom is right, My best galvo can take a very small 2 KHz signal, then rolls off like mad. If you use a low pass, best make it a RC lowpass, a AC coupled Sallen Key filter like in a synth will cause your image to float around under some circumstances.



Steve

[swamidog]

echo laylas are pretty easy to find on ebay if you have some patience. i got lucky and stumbled across a couple locally off of craig's list.

I've got a Gina, but she only has two inputs and eight outputs. Find a better, newer, Gina with eight in and eight out, or get her fatter sister Layla. .
There are some Mark of the Unicorn boxes that are useful as well.


For what your doing, single ended drive is feasible unless you need a 30 meter cable run. Ground one side of the scanner amp differential input and drive the other. It will not hurt the amp in the least.

The only reason for differential is if the projector is on noisy power lines or far away. Some Asian projectors have poor input circuits or bad ground wiring, but the great majority will fully accept a single ended input.

If you are unsure of your console's output level, a clipper with back to back 10V zener diodes and a 200 ohm series resistor will protect the galvo amp.

You'll need a five volt clipper for the RGB channels anyways, that can consist of a five volt zener diode, a 1n4001 diode and a 470 ohm resistor. Unless you have TTL color. TTL can cause issues, best solved with either a emitter follower circuit or a simple comparator circuit.

Absolom is right, My best galvo can take a very small 2 KHz signal, then rolls off like mad. If you use a low pass, best make it a RC lowpass, a AC coupled Sallen Key filter like in a synth will cause your image to float around under some circumstances.



Steve

[trotz]

Wow, the technical specs of these soundcards look great, even for driving analog synthesizers (there is some dedicated software to send DC from Digital Audio Workstations, such as Ableton Live or Cubase).
Do you know of any USB or FireWire alternatives?

Thanks!

[trotz]

For what your doing, single ended drive is feasible unless you need a 30 meter cable run. Ground one side of the scanner amp differential input and drive the other. It will not hurt the amp in the least.

The only reason for differential is if the projector is on noisy power lines or far away. Some Asian projectors have poor input circuits or bad ground wiring, but the great majority will fully accept a single ended input.

If you are unsure of your console's output level, a clipper with back to back 10V zener diodes and a 200 ohm series resistor will protect the galvo amp.

You'll need a five volt clipper for the RGB channels anyways, that can consist of a five volt zener diode, a 1n4001 diode and a 470 ohm resistor. Unless you have TTL color. TTL can cause issues, best solved with either a emitter follower circuit or a simple comparator circuit.

Absolom is right, My best galvo can take a very small 2 KHz signal, then rolls off like mad. If you use a low pass, best make it a RC lowpass, a AC coupled Sallen Key filter like in a synth will cause your image to float around under some circumstances.



Steve

THIS is some quality info I was looking for!

I see the principles are more or less the same as in the audio world. Is there any device that can balance an unbalanced signal ? In the audio world we use DI-boxes but I'm unsure about their DC behavior. In video, sometimes a device called bal-un is used; the concerns about DC are even greater here...

Thanks about the tip on some projectors having difficulty accepting single ended input. Really useful.

I have control over my voltages, the synth has even two oscilloscopes that can also measure voltages. The synth has attenuators, investors, offset generators, etc... You could think of it as an analog laser console in many aspects (even has quadrature oscillators) only it has not been designed with that purpose. I take good notice of your advice about the 10V, 5V and frequency 2k limitations.

The frequency limitation creates nice interference patterns in a raster image like the one I generate in my software, and I understand how in a laser projector high freq signals just cause the image to roll off...





Pere

[CountFunkula]

---snip---
(there is some dedicated software to send DC from Digital Audio Workstations, such as Ableton Live or Cubase).
Do you know of any USB or FireWire alternatives?

Thanks!

Are you thinking of Volta by MOTU?
http://www.motu.com/products/software/volta/body.html
...pretty sweet piece of software if you've got outboard analog gear that responds to CV.

IIRC, most of MOTU's interfaces are DC-coupled.
I used to have an 896...and really regret selling it.