You're the one making the claims. You're a very good troll I will give you that. You have a talent for pseudoscientific explanations of non-existent phenomena. You could make a lot of money writing books on quack medicine.
After graduating, I almost went to work for a company in New Jersey that manufactured military analog computers.
Guess that was quite a while ago.
So the demo card is new? The part has been around it looks like for 13 years.I just got a full demo card of our AD1955 DAC our ESS 9018 "equivalent". In their infinite wisdom it was laid out to facilitate op-amp rolling. So I'm ready to pick open the sores on alternative DAC filtering.
Does the 1955 have a spec on preserving performance requiring a maximum "current" output voltage burden? (lazy here).
Well I guess it was a popular use of the things for calculating trajectories and figuring out how to lob leaden death at targets. I liked the mechanical ones, that one would see in surplus.
Yeah. I remember Barrie Gilbert's polemical discussion of how bad conventional op amps should be for I-V conversion. Nelson says some like passive even when it may entail non-monotonic behavior. The one I saw that raised my eyebrows had, I recall, a 10 ohm terminating resistor, followed by a tube stage.No output compliance spec that I've been able to spot in the DS - just an injunction against using passive I/V
I thought it was cool to see the differential equations unfolding in real time.
In terms of audibility I reckon its because their OPSs aren't pure class A over the range of DAC output currents (8mA or so swing for the 1955). So perhaps a current source bias on the OPS would help. I've tried that on my own DACs (not AD1955 any longer but I was using one of Barrie's chips), not completely certain it made an improvement but I left it in anyway.
I was a fan of passive for many years, gone back to active again now - the PSRR benefits of active won the day. Better monotonicity can't but help though.
I agree. I simulated an oscillator circuit (differential equations) on the Heathkit analog computer back in 1962. I thought it really elegant to be able to do so. They were still using them full time at Lockheed in 1963, but I only ran the digital mainframes at the time. Somewhere, along the line, I was told that a digital program virtually replaced the analog computer, even with an IBM 1401 computer, and I guess they faded away from there.
The elephant in the living room is How much does the output Z of this so-called current source change as a function of code? I don't know any manufacturer who bothers to mention it. There are some lower-priced DACs that really do have rather high-Z outputs, but they don't seem to be very popular.
I think EUVL's simple JFET common-gate designs with floating power supplies are pointing the way to a more suitable approach. Making the input still lower Z with an added amplifier can manage very good performance. You're starting with low Z to begin with and just making things lower, rather than starting with high Z and using a lot of feedback to make it low Z.
But op amps are very convenient. And probably quite adequate.
I worry more (coming from a SQ pov) about the magnitude of the Zout because lower Zout means poorer PSRR in my simple logic. Some very popular DACs have surprisingly low Zout (PCM1704 springs to mind @1kohm) and yeah, no mention of the degree of variation over code.
Schitt just released another DAC using a multiplying part (AD5547) - the DS says Zout is code dependent but leaves it to the reader to work out what it'll be from the internal schematic
The 200pF output capacitance is also code dependent.Which are the cheap DACs you've found with high Z outputs?
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