KH Oscillator circuit
I looked at the circuit closely and realized that it wouldn't work. I then pulled out my copy of the 6800 manual (pre-release) and saw the same mistake, plus other missing connections.
I then pulled out my 6880 manual (again prerelease, did they ever actually publish a manual?) and it has the correct circuit.
The changes are +/- on the level detector opamp are reversed and R11 goes to ground. They have a trim cap on C3 to fine adjust the frequency if thats important. They only claim .005% THD for the oscillator. Its dependent on the time constant of the photocell to work.
The AGC circuit is the most difficult part of a low distortion oscillator. It can cause distortion from its rectification and affect the settling time dramatically. I don't think this circuit would work as is much below 1 KHz. But adding an active rectifier and switchable time constants could change all of that.
I looked at the circuit closely and realized that it wouldn't work. I then pulled out my copy of the 6800 manual (pre-release) and saw the same mistake, plus other missing connections.
I then pulled out my 6880 manual (again prerelease, did they ever actually publish a manual?) and it has the correct circuit.
The changes are +/- on the level detector opamp are reversed and R11 goes to ground. They have a trim cap on C3 to fine adjust the frequency if thats important. They only claim .005% THD for the oscillator. Its dependent on the time constant of the photocell to work.
The AGC circuit is the most difficult part of a low distortion oscillator. It can cause distortion from its rectification and affect the settling time dramatically. I don't think this circuit would work as is much below 1 KHz. But adding an active rectifier and switchable time constants could change all of that.
Hi all,
I have looked around and decided to order the DSO-2150 that has been advertised on the 'net and also on Ebay. There is a vendor close to me that had them on sale. They do FFT.
These are 150 msamples / sec., 8 bit. Most DSOs are 8 bit, although the Agilent 6000 series has a 12 bit mode. My plan is to feed the residual from my THD meter into this device. It runs off the USB port, so with any luck there will not be too much noise.
I'll start a thread once I figure it out and let you all know what I think of it.
If any of you are interested, I have a link for the Canadian rep. that I can give you.
-Chris
I have looked around and decided to order the DSO-2150 that has been advertised on the 'net and also on Ebay. There is a vendor close to me that had them on sale. They do FFT.
These are 150 msamples / sec., 8 bit. Most DSOs are 8 bit, although the Agilent 6000 series has a 12 bit mode. My plan is to feed the residual from my THD meter into this device. It runs off the USB port, so with any luck there will not be too much noise.
I'll start a thread once I figure it out and let you all know what I think of it.
If any of you are interested, I have a link for the Canadian rep. that I can give you.
-Chris
I have used the Picoscope on the output of an AP with good success. 8 bits are more than enough after the preprocessing of the analyzer. The THD meter should have a differential input and the source should be floating, not grounded. If both of these are OK then the scope shouldn't introduce noise into the measurements. But you never know until you try it.
Hi Demian,
Well, there is noise.
Then there is the software and how easy it is to operate.
This unit is supposed to be good to 60 MHz. I don't think it's that useful up there, but you never know.
With any luck, I should have it by Monday. Then I have to set it up and play a little before I can report on it.
-Chris
Well, there is noise.
Then there is the software and how easy it is to operate.
This unit is supposed to be good to 60 MHz. I don't think it's that useful up there, but you never know.
With any luck, I should have it by Monday. Then I have to set it up and play a little before I can report on it.
-Chris
When I got the Picoscope 8 years ago I tred all of the ones on the market then. We retruned all of the others. Most were really mickymouse. Its much better now and that one I posted a link to earlier is a good Chinese copy of a Tek interface. But looking good and working well are two very different things. Let us know how yours works out. My Picoscope has a parallel interface and new PC's are losing that interface. The Pico adapter to USB is expensive and the normal ones won't work.
Hi Demian,
To be honest with you, you would be further ahead to simply buy another model as long as it works well. These run about $220 USD at full list. Some sound cards cost more.
Mind you, for me $220 is $220 that I have to scrape up from somewhere when my credit card bill comes in.
-Chris
To be honest with you, you would be further ahead to simply buy another model as long as it works well. These run about $220 USD at full list. Some sound cards cost more.
Mind you, for me $220 is $220 that I have to scrape up from somewhere when my credit card bill comes in.
-Chris
I looked at the software for the scope you referred to and while its useable the Picoscope has more utility for me. I also have a THS720 so I'm well covered but the spectrum analyzer in the picoscope is very good. They have an audio range 16 bit scope that pretty impressive, but speed limited.
Hi Demian,
I have you beat there.
I own a working Norland Prowler. It has one 8 bit channel and one 12 bit channel. Slow? Oh yeah.
I'll see how this coming USB thing works. I hope it does a good job, because I own it now. Sight unseen. I haven't even been able to find someone who has tried one out.
The vendor has said that he may be able to work on a 12 bit version of that unit for audio use. Faster than a sound card and higher resolution than most digital oscilloscopes. An interesting prospect, but years in the future I'm guessing.
-Chris
I have you beat there.
I own a working Norland Prowler. It has one 8 bit channel and one 12 bit channel. Slow? Oh yeah.
I'll see how this coming USB thing works. I hope it does a good job, because I own it now. Sight unseen. I haven't even been able to find someone who has tried one out.
The vendor has said that he may be able to work on a 12 bit version of that unit for audio use. Faster than a sound card and higher resolution than most digital oscilloscopes. An interesting prospect, but years in the future I'm guessing.
-Chris
And I have a Data Precision waveform analyzer Boat Anchor that does a million things but after firing it up once, I realized my 7854 will do what I want better.
I need to clear out my store room (museum of analog technology) of things I really don't need or use. Perhaps I should post a list for those close enough to come by to pick the excess up.
I need to clear out my store room (museum of analog technology) of things I really don't need or use. Perhaps I should post a list for those close enough to come by to pick the excess up.
Does anyone have experience comparing a high quality sound card to the new PicoScope 3224 kit?
The total cost is about $850usd. High precision and accuracy
would be nice, but is +-20mv with 1% accuracy enough for our measurement purposes here?
It would be great to find a tool to measure room acoustics as well.
http://www.picotech.com/pc-scope.html
Your thoughts are appreciated.
-David
The total cost is about $850usd. High precision and accuracy
would be nice, but is +-20mv with 1% accuracy enough for our measurement purposes here?
It would be great to find a tool to measure room acoustics as well.
http://www.picotech.com/pc-scope.html
Your thoughts are appreciated.
-David
dw8083,
The PS3224 is nice for what it is I'd say but its no match of course for a pro type sound card.. or even the better budget ones either. But the sound cards only go so far up in frequency range.
I have a Echo Audio Audiofire4 and also bought a PS3224 for the ultra sonic stuff. The ability to capture transients with the large memmory of the PS3224 seems like a nice function.
I'm a newbie when it comes to scopes and measurements but it seems like these two items will do most of the mesurements I might need to do. A digital scope with higher resolution and bandwith would be way to costly for me. Should I feel the need to see what is going on really high up I might get a used 200-300MHz analog Tektronix.
I do like the PS3224 a lot even though I might lack knowledge to really give it a rating.
edit: the PS3224 will let you see signals down to 4-5mV if I remember correct. Togehter with attenuators and low distortion preamps the range of use for this scope will broaden.
/Peter
The PS3224 is nice for what it is I'd say but its no match of course for a pro type sound card.. or even the better budget ones either. But the sound cards only go so far up in frequency range.
I have a Echo Audio Audiofire4 and also bought a PS3224 for the ultra sonic stuff. The ability to capture transients with the large memmory of the PS3224 seems like a nice function.
I'm a newbie when it comes to scopes and measurements but it seems like these two items will do most of the mesurements I might need to do. A digital scope with higher resolution and bandwith would be way to costly for me. Should I feel the need to see what is going on really high up I might get a used 200-300MHz analog Tektronix.
I do like the PS3224 a lot even though I might lack knowledge to really give it a rating.
edit: the PS3224 will let you see signals down to 4-5mV if I remember correct. Togehter with attenuators and low distortion preamps the range of use for this scope will broaden.
/Peter
dw8083 said:
I am also looking into that. The 1% accuracy means it is probably an 8 or 10 bit unit. That means if you want to do spectrum analysis to see THD you are limited to a noise floor of about 60-70dB, not too great.
I am looking at a unit slightly more expensive from TiePie Engineering, the HS3 series here:
http://www.tiepie.nl/uk/products/External_Instruments/USB_Oscilloscope/Handyscope_HS3.html .
The HS3 has two input channel and a useful arbitrary waveform generator as output that can function as a signal generator. The resolution can be as high as 16 bits at 100kHz which gives 96dB dynamic range, good for THD to 0.005 or something like that.
For higher frequencies the dynamic range is lower but you can use it as a scope up to 2.5-50MHz depending on how much you want to spend.
Jan Didden
Jan,
I have a TiePie HS3 and never regreted spending the money.
For one it is hard to get any scope with better than 10 bit resolution. With the HS3, you get 12 bit at least, 16 bit if you restrict freq. Yes you can argue how many of the last bits are noise. Still. The bit I like most is the built-in functions generator. Just makes life a lot easier.
The only thing against is that you need to boot your computer every time when you connect the HS-3 to it. Otherwise the TiePie software won't link to the scope.
I am sure you can get better funcgens and scopes stand alone, but not at that price combined. And it is a cute little thing.
Patrick
I have a TiePie HS3 and never regreted spending the money.
For one it is hard to get any scope with better than 10 bit resolution. With the HS3, you get 12 bit at least, 16 bit if you restrict freq. Yes you can argue how many of the last bits are noise. Still. The bit I like most is the built-in functions generator. Just makes life a lot easier.
The only thing against is that you need to boot your computer every time when you connect the HS-3 to it. Otherwise the TiePie software won't link to the scope.
I am sure you can get better funcgens and scopes stand alone, but not at that price combined. And it is a cute little thing.
Patrick
PS3224 is a 12bit unit with the possibility to use oversampling for increased resolution on static signals (or so they say).
The self noise on my unit is around 0.2mV peak and maximum input is 20V. A sinewave fed to the input becomes visible at 2mV RMS.
Seems like 80dB range to me and I have not changed any files in the software in order to maximise oversampling. Possibly the unit is set for maximum dynamic range, don't know.
/Peter
The self noise on my unit is around 0.2mV peak and maximum input is 20V. A sinewave fed to the input becomes visible at 2mV RMS.
Seems like 80dB range to me and I have not changed any files in the software in order to maximise oversampling. Possibly the unit is set for maximum dynamic range, don't know.
/Peter
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