Have a look at the Max038 signal generator chip. I once started a design together with a student, using two of these chips and a 4-channel DAC along with a few other things to produce a dual-channel signal generator up to 20 MHz with all the features that I previously described. There's a lot of stuff about this chip on the www, so that could provide you with some amusement. I wanted to use the DAC's in place of some of the pot's but in parallel with them, so the instrument could be driven by software if desired, but could also be hand-operated. That's important for things that require you control both channels with the display. Sometimes it's handy to phase-lock two signals that are of related but widely separated frequency, while other times you want to use the system as a synthesizer.

That'll keep you busy.

If your 475 is misbehaving, you could probably do well with a replacement from eBay, provided, of course, that you shop carefully. I note that there are several of them on the eBay site even now. One major advantage that thse offer is that you're already familiar with that model. Another, of course, is that it's NOT computer-controlled, hence, doesn't suffer from "creeping featurism" as do many modern instruments.

The problem you describe seems as though it's a power supply problem. Could it be that you suffer from widely fluctuating input (mains) voltage? I have constant voltage transformers, rated at about 15 amperes, that I can use to power my instruments if need be. I seldom need 'em, which is good, as they're very heavy, but if I have to, I can haul 'em to a site where I'm working.

I'm still curious why you feel you need such high-speed digital signals. I'd worry a lot more about doing the same thing an order of magnitude (or two) slower. The problem's the same, of course.

RE