Products > Test Equipment
FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
DaveR:
Soundtec - are you getting the values of R45 and R54 from the schematic, which shows them as 499 ohms? On my two boards, and in the high res photos posted in May, the values are 68 ohms, which would give a gain of 23, not 4. Either the schematic values are wrong, or there was a redesign carried out by Feeltech in late 2017. I was thinking I might change R74 and R83 to 1k to give a more conservative gain of around 16 if I put 3491s in (or do one channel to see if there's any real difference).
Dave
soundtec:
I didnt measure them on my board ,but just relied on the schematic ,
with either standard output stage or upgraded op amps Im getting more or less the same from both units within 10 to 20 mV, . A buddy just explained to me the gain is very little to do with the opamps themselves and more to do with the proportions of the feedback and other resistor than goes to ground . Id still like to see a pot on the feedback path to the final op amp ,just for fine tuning .
DPA31:
Hi Sountech, Hi Dave,
I verified R45 & R54 resistors on the SB: they are coded 68A that is 499 ohms.
just in case : http://www.resistorguide.com/resistor-smd-code/
@Sountech
Yes trimmer footprints are compatible with the pads on the PCB. see attached picture.
Can you describe the measure you would like me to do : 5V sine both channels, frequency ? You measure mV on both channels with ?
Cheers.
Dom.
soundtec:
They fit in nice Dom , I'll have to do that mod myself for extra tweekage.
What you could try is dial in 5.1 p-p (sine)on the unit ,now with your RMS multimeter measure the output voltage , it should read approx 1.803 v rms.
Now if you repeat the same test but with an output voltage of .51 volts ,this will mean only the opa686 is engaged ,now measure again your rms volts at the output ,you should be seeing .1803 volts rms . On the lower output range you could tweek the adjust pots on the opa686 to get exactly .1803 volts ac ,but this inevitably means your high range (over 5 volts output) will be off by a margin . Having adjust pots on the final high level output stage would allow an extra measure of accuracy to be tweeked in . So it looks like our feedback network on the high level output stage uses 1% tollerance components ,maybe upping these to .1% would be a worthwhile exercise .
DaveR:
Thanks for that info and link, Dom - I thought it was 68R I was seeing, so just assumed it was 68 ohms. You live and learn!! :)
Regards,
Dave
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