Products > Test Equipment
FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
GregDunn:
I've been using my FY6800 pretty much as the generic test signal source for my troubleshooting and repair efforts; it's nice to be able to check gear with swept frequency and amplitude as well as single frequency input.
I use mine almost exclusively for audio. Running it into my HP331A I see that the distortion in the range under 100KHz is moderate - about 0.25% or so. Honestly I'm not interested in extending the bandwidth or output level of my generator per se; but has anyone seen or tested a mod which will reduce the distortion at audio frequencies into normal 10K-100KΩ loads? That's about the only thing which would be handy for the work I do.
JS:
--- Quote from: GregDunn on August 20, 2018, 03:26:28 am ---I've been using my FY6800 pretty much as the generic test signal source for my troubleshooting and repair efforts; it's nice to be able to check gear with swept frequency and amplitude as well as single frequency input.
I use mine almost exclusively for audio. Running it into my HP331A I see that the distortion in the range under 100KHz is moderate - about 0.25% or so. Honestly I'm not interested in extending the bandwidth or output level of my generator per se; but has anyone seen or tested a mod which will reduce the distortion at audio frequencies into normal 10K-100KΩ loads? That's about the only thing which would be handy for the work I do.
--- End quote ---
How low do you want? I guess your only option is filtering, if you are interested in a particular frequency a fixed filter would do. Otherwise, you are likely better to use a sound card or a dedicated sinewave generator but sweeping is hard-ish for an easy DIY project. The best option could be a tracking filter, which you could do. There is an article of a THD analyzer by Robert Cordell from '81 with a residual THD down to 0.0003% for a certain condition where you could find a few useful blocks. I don't attach it here as it weights about 5MB and I don't have a link but google will help you I guess.
JS
GregDunn:
I don't really want to kludge a filter or other device on the generator that isn't transparent to its basic operation. If I want low distortion at a single frequency, I guarantee my Heathkit will outperform most anything that isn't a professional series oscillator (somewhere around 0.01% over its operating range). I was just curious whether someone had investigated a mod which would improve the audio band distortion of the FY6x00 series. If no one has, that's OK; I just didn't want to overlook an easy mod.
bitseeker:
--- Quote from: DaveR on August 20, 2018, 02:19:58 am ---It was decided a while ago to keep the same thread going as the FY6600 and FY6800 are essentially the same item, and anything discussed about one applies to the other. A new thread for the FY6800 alone would potentially result in masses of accumulated information being missed by new searchers who aren't aware of the history of the two devices. Likewise, questions posted in an FY6800 thread would get missed by knowledgeable FY6600 owners who could otherwise provide help and answers.
--- End quote ---
Certainly, a new thread for the 6800 alone wouldn't make sense and that isn't being suggested here.
A common way to handle it is to have an active member create a new thread (correctly labeled for both models, unlike this one), link from this one to the new one (and vice versa so that people know where older info is located), and continue in the new thread (locking this one as archival).
Another option is if one of the primary contributors to this thread messages gnif or Dave to rename the thread so that it's more accurate. It's the most elegant solution.
soundtec:
Its a good plan to include the Fy6800 in the title somehow ,but now when I search FY6600 this post and this forum come up top everytime . I guess we dont want to loose top billing in browser search for our thread ,so how would we make sure our search priority wasnt affected by a thread namechange ,maybe leaving the main name of the thread unchanged and adding (including FY6800 model) in brackets ,really we need to find out the implications it might have before changing the name .
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 .
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