QuantAsylum QA400 and QA401

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#2,222
We should move the autoranger into its own thread.

Meanwhile I think the max matches the QA100 pretty well.

I have not checked a couple of AK5394A implementations and the optimim seems to be between -15 dBFS and -20 dBFS. So scaling the autoranger to match seems like a good idea.

I'll be reworking an EMU 1010 analog card this weekend to see if i can maximize its performance. Right now I get -120 dB 2nd and -120 dB 3rd at -18 dBFS. On a selected Emu 1616m I'm get -128 dB 2nd and 3rd so I know more is possible.

(And there goes any chance of getting more EMU1212m's cheap.)
 
#2,226
Mark Johnson said:
How about using the pin to select between two different values of hysteresis? Zero hysteresis and 15% hysteresis, for example.

Then if the input amplitude wanders a few percent AND if, at the same time, it's right at a range switching boundary, the autorange won't oscillate.
Click to expand...

Actually, the hysteresis should be more than the minimum gain step which is 4dB, otherwise it will continue to switch up and down.

Jan
 
#2,227
DualTriode said:
Hello Jan,


When I read the question about “threshold” I went off track in the direction of, how low of an input voltage will output “about” 1 Volt. I recall reading on you page somewhere around 0.1 V to 0.15 V. (16 dB gain)

Is there any ability to use that extra pin to increase the AR gain to 40 dB to resolve low level distortion and noise. MerlinB used a 100X preamplifier to study tube noise vs frequency.

Thanks

DT
Click to expand...

It is an interesting idea. There are some implications that have to be considered though. Increasing the gain necessarily also increases distortion and you don't want the AR to become the limiting factor. I will think about it but right off the cuff I'd think an external preamp can be optimised for the task and is probably a better solution.

Jan
 
#2,228
This is the ranging board. I am putting three together for beta-testing, first one just tested OK.

Of course what you don't see is the front panel PCB that contains the display and all the intelligence 😉

Jan
 

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#2,239
Put it in a cage!

Hello,

Interesting to me.

I connected the generator output of this QA401 to the input and ran the FFT. I am impressed with the performance per dollar. One funny, odd, thing popped out at me. This one meter long BNC cable leaks 60Hz and harmonics. Sitting the QA401 on the desk there is no apparent 60Hz in the FFT plot. However set the QA401 on the PC and let the cable hang around the PC power supply then the power supply noise raises its head. Yeah I know, don’t do that. I also known that cable leakage is a matter of degree.

Last winter I went to a Keysight seminar they had a testing accessory, a small shielded enclosure sporting triaxial inerconnects for the transistor sized DUT inside.

I am thinking of using a large NEMA 1 enclosure to shield the entire bench test setup, amplifier (DUT) and QA401.

Any thoughts or war stories about shielding DUT’s, test equipment and cables?

DT :hohoho:
 
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