drive repair tips?

Tony Duell ard at
Mon Aug 22 16:53:13 CDT 2005

[ELektor GBDSO]

> My thoughts exactly. I don't usually build stuff when the firmware sources
> are unavailable. It also seems to be quite limited - high AF at best, not
> much good for anything other than debugging audio gear.

Actually, a low-bandwidth scope is still useful for looking for power 
supply ripple, looking at motor drive signals, SMPSU waveforms, etc. This 
one, like the Velleman LCD 'scope that I have, has the advantage that 
it's not connected to the mains, so it can be 'floated' (taking great care!) 
for looking at signals on the mains side of an SMPSU.


> I'm also toying with the idea of building a 40MHz version of the GBDSO. The
> hard bit is finding amplifiers that are fast enough, and learning about the
> analogue side of things - I've never really done any analogue design.

>From what I rememebr, Burr-Brown did some nice ones, Analogue Devices did 
some with very misleading data sheets.

Be warned that hogh-speed analogue design is not easy. 'Strays' (PCB 
inductance nad capacitance) matter even more than for high speed digital 
design. Op-amps misbehave, it's not at all uncommon for there to be 
significant phase shift at high frequencies -- enough to turn -ve 
freedback into +ve. If you're trying to get a low gain out of an op-amp 
-- that is, you've applied a lot of -ve feedback -- it's likely the darn 
thing will turn into a nice RF oscillator.


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