Interesting G-120 amp design...

Mixedgas:
"LM3886 is just a big inverting opamp"

LM3886 is just a big opamp. Inverting or non-inverting option depends on external components. At this moment my drivers use them as non-inverting power opamps.

"test with a speaker or wire wround resistor before you go galvo"

I prefer high-power resistors as active load. Speaker costs much more than resistor.

"but here:..."

Wow! Special cases of the bridge connection... It seems that what I need. Thank you Steve!

LesioQ:
"to my opinion the best way to go with fast & universal galvo drive is DSP"

Compare cost of signal processor (or FPGA as that) and cost of three chips with 12 opamps. Most of all I dont need the highest precision and the fastest speed. I only want to accelerate my current galvo drivers.


Sergey

[QUOTE=Sergey;68069]Mixedgas:
"LM3886 is just a big inverting opamp"

LM3886 is just a big opamp. Inverting or non-inverting option depends on external components. At this moment my drivers use them as non-inverting power opamps.

"test with a speaker or wire wround resistor before you go galvo"

I prefer high-power resistors as active load. Speaker costs much more than resistor.

A speaker at my local electronics place is 5-8$ for a decent power level. Wire wound ceramic "fireproof" resistor is 3$ for 2-3 watts, speaker, in terms of mass/per financial unit, is better deal.

Strange , but true.

I too, would use the resistive load.

Steve

So, all that being said, the question comes back up. Is this a decent amp? Bill doesn't seem to like it and I am inclined to listen to the man becuase of his vast experience, but then again, even Einstien had to revise a few of his theories after they were published. I need something though because I am barely getting 15K out of my G120s at 8 degrees and I can't seem to find a Turbo Track either. Unless someone has a couple of Minisax amps they want to part with, this is my next option. I am hoping for 20K at 10 to 15 degrees. If this amp can't do that, or may damage my galvos' torsion bars, then I don't want to attempt it.

I had almost half of it's large step time with MiniSAX. MiniSAXes have bridged output, though they lack hf-damping (current dev.)
I'll count my MiniSaxes over weekend and check if have too many.

This design appears OK, nothing suprising.... ok, except it's claimed speed :D
Piotr.K

As I can see from that drivers schematic diagram HF-damping is not used(R10 and C39). In my drivers which are 9K max I cant get any effect from HF-damping. Is it limiting by galvos frequency range?

HF damping helps to reduce the oscillative nature of galvo response during breaking after large jump. If Your acceleration and deceleration peak current is not high enough this may be true that HF won't do any visible good. Are You suffering from the dip after fast slope command like square wave ? This becoms visible when tuned for highest speed only. If not - Youur amp is probably not able to push G120 really hard, so HF-damping wont be of use. Are You sure You're running G120 coils in parallel, not in series (as LaserFX suggest as I remember ?).
I've heared that there's also a limit of G120 rotor magnetic saturation ...
Piotr.K

Quote:

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Originally Posted by drlava

Definitely worth considering building and tweaking if there were a glut of amp-less galvos available.

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Well, I don't know if I'd call it a glut, but Aron Bacs sells refurbished G-120's for around $100 a pop. At the last FLEM he brought a box of about 50 or so!

He's going to be at FLEM on Saturday; maybe I'll plant a bug in his ear to check out this thread. Might be a few folks interested in picking up a pair or two.

Adam

Magnetic saturation? I heard Bill speak of this. Is this a permanant effect due to too strong a field or is it the theoratical limit of the magnetic properties that can be exerted on a G120 rotor?

Quote:

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Originally Posted by absolom7691

Magnetic saturation? I heard Bill speak of this. Is this a permanant effect due to too strong a field or is it the theoratical limit of the magnetic properties that can be exerted on a G120 rotor?

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That would be a short-term effect, I think. It would manifest as " no more rotational force with increased magnetizing coil drive current".
Piotr.K

Quote:

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Originally Posted by LesioQ

Are You sure You're running G120 coils in parallel, not in series

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Well, my galvos are not G-120. They are home-made, but principles of work are the same, as I guess.
Probably I cant achieve the highest acceleration because of my PSU - It cant supply more than 2-3A RMS to each driver(5-6A total). And galvos coils have low active resistance - about 0.5 Ohms for each galvo.