fb3 blanking voltage

[badger1666]

only taken on my mobile phone so not that great but does show the trouble i am having

[badger1666]

got it working much better stopped it jelly beaning, under the advice rob the stanwax guru (all hail stanwax) i adjusted tec cooling and hey presto
jelly beans all gone it not perfect but 100% better than it was
the freaky orangy red thing all but gone ,and now get full green circles and not 3/4s of one going to reinstall robins driver and see if its ok on analog

[buffo]

Sorry I'm late getting back to this thread, but it looks like you've found a solution. Congratulations!

Yeah, Rob (Stanwax) is a great guy. Glad to hear he was able to help.

Jellybeaning is a problem with all DPSS lasers, but some models exhibit the phenomenon more than others. I've heard good things about CNI and LaserWave DPSS units, but I haven't tested them myself to see how they perform under heavy modulation. Still, from what I understand, they're just about the best available, at least among the affordable Chinese suppliers. (The lasers from European suppliers are much more expensive, and lasers from the US are outrageous.)

Replacing your green with one of the lasers that Dave and Aijii sell on their LaserShowParts.com website would probably be your best bet, but if adjusting your TEC controls has limited the jellybeaning in your current laser you might want to live with it for now. (At least until you can afford a better laser.)

Robin's driver for your red should not exhibit this jellybeaning problem, BTW. It's controlling a direct injection diode (your red laser), so the modulation response should be very fast and very clean. If you have problems with your red, post the results here.

Adam

[badger1666]

robins driver back in and working great had to dial in the tec again beacause i am driving a higher current ,its funny few more milliamps on the diode and the beans come back another tweak on the tec and they go,
them crystals are very sensetive. but alls good now but would like to see the lasers as bright as they were when i had a ttl dac next job buy a blue laser nearly have enough saved

[buffo]

Chris;

You may never get the same performance, even with all the tweaking you've done to the TEC circuit. Reason is that TTL modulation is easier to deal with than analog modulation. With TTL you can predict in advance what the temperature is going to do when the blanking signal changes, because there are only 2 states. (Off, and on at full power)

But with analog blanking, the laser can be at any power level between full off and full on. So it's hard to predict what will happen to the crystals. Especially when you consider that the temperature effects are non-linear. So you may not need any feed-forward control until you reach a certain power level, and then all of the sudden you need lots of it! That's a tricky circuit to design, and an even harder one to tweak for maximum performance across the whole operating range. This is one of the reasons why we're still suffering with this problem *years* after they invented DPSS lasers...

Of course, the trade off is that with TTL color, you only get 7 possible colors, but with analog color you get millions of combinations. Most people agree that the increased color palette is worth it, but if you have a laser that *really* has a bad jellybeaning problem, then you might want to upgrade it to one that better supports analog blanking.

Take heart though - some of the brightest minds in the market are actually looking at this very problem right now. Maybe in a year or so we'll have a possible solution. (For sure we'll understand a lot more about the problem, anyway.)

Adam

[stanwax]

One other thing that helps is having a biased diode ie when its off the pump diode is still on just simmering below the DPSS threshold. This can help stability - again as adam says its down to the design of the laser - but has secondary benefits too as the analogue range is much improved. To achieve this you need a mod to your driver or a replacement driver altogether.

Rob

[norty303]

That sounds a bit like the pre-heat function on some lighting dimmers. They pass a small voltage into the coil to warm it, so that when you require a fast flash, the light responds much quicker and also prolongs the lamp life as it's not such a huge temperature differential from fully off to fully on.

[stanwax]

I guess so - obviously there is quite a difference in power dissipation between a diode producing a handfull of mW to full power and a few watts but it certainly helps the stability - which is why I have a little idea up my sleeve for stabilising the temp of a modulated pump diode with a TEC and a magic ingredient - More will follow when I have experimented with the concept. All the diodes in my rgb are driven this way with threshold control.

Rob