Products > Test Equipment
FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
DaveR:
--- Quote from: Mr. Scram on August 20, 2018, 03:25:55 am ---
We can decide all we want, but the thread isn't going to be found by people interested in the FY6800 very quickly if they weren't already familiar with the thread.
--- End quote ---
Eh??? Just try typnig "FY6800" in the search box and see how many hits to this thread come up!
--- Quote from: bitseeker on August 20, 2018, 06:20:28 am ---It's the most elegant solution.
--- End quote ---
Solution to which problem, exactly?
GregDunn:
--- Quote from: soundtec on August 20, 2018, 10:16:40 am ---
Im wondering is the limits in terms of distortion in the FY 66/6800 due to the dac/filter and the bits , in which case Im not sure if theres much benefit in distortion terms from changing out the op amps , surely though if you wanted the highest quality signal from the unit ,say for audio testing which often will require smaller signal voltages ,you'd be better off using the sig gen to make a large amplitude signal ,then using a passive attenuator network to attenuate that to a level suitable for your purpose , in otherwords does producing a smaller output voltage in the FY limit the bit rate of the output signal ?. Could a specially made switched attenuator, optimised for 50 ohms, used after the generator allow an improvement in distortion ? I know that in the case of using a sound card for audio testing a couple of the smarter people in another forum I visit made up a special attenuator allowing attenuation in Db ,the signal generator is then run at 0db Fs digital for minimum digital artifacts. If at higher levels in the 66/6800distortion of the output stage is the limiting factor then power supply and op amp upgrades are worthwhile. For most audio testing the small distortion in the output signal of this unit is of no consequence ,it only comes into play really if its distortion your trying to measure . I guess a computer and high quality dac /attenuator is a better option for producing signals in the audio range with very low distortion in any case .
--- End quote ---
That's right, the DAC is used to generate the output and it's just buffered by the op amps; using it to generate a lower level signal will effectively use fewer bits. Running the output at max level and putting a post attenuator on the FY6800 ought to lower the distortion quite a bit due to (1) reduced quantization errors and (2) linear scaling of the signal. I should have thought of that, and I will try it.
bitseeker:
I just did a search in the forum for "FY6800" and none of the top six results are this thread, five of which have "FY6800" in the thread title.
Anyway, that's all. Carry on.
GregDunn:
OK, that worked well. I maxed out the FY6800 at 20V, ran it into the 331A through the attenuator, and measured a THD+N of approximately .03% - close to the theoretical limit for a 12-bit system. That's more than sufficient for anything I'm doing, and not far from my IG5218. Color me suitably impressed.
soundtec:
I like the filter approach suggested by JS ,you needen't butcher the internals of the 66/6800 ,it could easlity be made into a passive box and placed on the output of the sig gen with a known amount of attenuation of signal .into a given load impedence ,maybe with switchable centre frequencies , Bruel & Kjaer make some very nice passive attenuators/filters for audio measurement work ,I wonder if one of these would be a good off the shelf add on to a sig gen setup , the units themselves seem to be for interface with certain other B&K gear ,but adding some BNC's would surely be an option .
https://www.ebay.de/itm/Bruel-Kjaer-1616-1-3-Octave-Filter-Set/123213621878
https://www.ebay.de/itm/Bruel-Kjaer-Logarithmic-Potentiometer-ZR-0003-92C-3/140942018492
Im not sure about the impedences these B&K units are designed for .
Maybe an even simpler solution would be a series of inline filters with set frequencies, a bnc female to male adapter could be used to house the components ,no switches no pots ,a handfull of preset values might have you covered .We know that at certain whole mulptiples or divisors of the clock frequency the performance of this generator is better ,so why not create a set of filters that corresponds to these sweet spots on the 66/6800, ensuring best possible performance from each range .
Is there software that would help calculate component values for audio filters with defined requirements in terms of impedence and insertion loss in db etc? Ive seen a few of these type programs but never got the hang of them ,or they were not dedicated to audio specifically. Im also not MSoffice aware so I didnt try spread sheets
From what I can gather the 3491 is capable of swinging a handfull more volts at the output for a given rail-rail supply than 3091/95 , all the better if we need to drive passive filters with attendant losses . With the stock switcher psu and the stock output ic ,I see around 600millivolts drop across the rails at full output into 50 ohms both channels driven , thats pretty bad regulation by anyones standards ,simply bolting on the extra horsepower of the 3491 will cause an even larger modulation of the powersupply rails . Peak current of two 3491's is likely to be in the region of 1A and to get best performance your going to want good voltage regulation right through the current range .
I know someone who designed an attenuator specifically for sound measurement ,designed to be placed on the output of the soundcard ,therefore completely avoiding digital attenuation of any kind ,digital out is always hitting 0db fs ,you then have a coarse and fine resistor attenuation network say 5 coarse steps of 10db and fine scale of +/-5db ,using selected or hi-stability resistors very close tollerance attenuation can achieved over a wide range. I'll look up the post and make a link to it
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