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Old 24th April 2008, 01:07 PM   #11
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I built the Cordell analyzer way back when I knew even less than I know now, if that's possible. It's really not that hard, except for the rotary switches, which have to be made up from many sections and joined together. Probably expensive today. I often recommend building just the signal generator board, if one needs a very good low distortion sine generator.

Another possibility for a nice programmable waveform generator are the Analog Devices DDS chips. Maybe a AD9953 or similar, though I don't know how good the distortion is.
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Old 24th April 2008, 01:11 PM   #12
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Default Re: Homebrew Digital Sampling Audio spectrum analyser.

Quote:
Originally posted by G.Kleinschmidt
(an Analog Devices part, canít remember the part number ATM)

AD8307 perhaps?

Quote:
Originally posted by Bonsai
Glen,


I looked at Bob Cordells distortion analyzer but it would be a bitch to build - too many boards/interconnects etc and a lot of the componenets are unavailable now.

Everything from Cordell's article is still available (including the LM1496 balanced modulator/demodulator-- this oscillator is the basis of the Tektronix SG505 -- i agree that it would be a real PIA to build the thing.
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Old 24th April 2008, 01:22 PM   #13
GK is offline GK  Australia
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Default Re: Re: Homebrew Digital Sampling Audio spectrum analyser.

Quote:
Originally posted by Bonsai
Glen,

take a look at this

http://uk.geocities.com/cyrilb2@btinternet.com/

Might give you some inspiration/ideas with your project.

Bottom line is most people on the forum would love an easy to build, dedicated distortion analyzer with a 80KHz bandwidth i.e. a poor mans AP.

I looked at Bob Cordells distortion analyzer but it would be a bitch to build - too many boards/interconnects etc and a lot of th e componenets are unavailable now.

Some kind of pre-processor that fed into a PC or scope is probably the right way to go in '08.

Hi Bonsai.

I should note that a spectrum analyzer is a rather different beast to a THD analyzer. However, my design would mate nicely to Bob's unit to examine the spectral content of the extracted distortion residual.



Quote:
Originally posted by jackinnj


AD8307 perhaps?

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Old 24th April 2008, 01:42 PM   #14
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Default Re: Homebrew Digital Sampling Audio spectrum analyser.

Quote:
[
G.Kleinschmidt]

All I have to do now is to find a decent low phase noise VCO IC to cover the relatively low frequency range of 800,000 Hz Ė 999,980 Hz.


Any suggestions? [/B]

What about the older synthesizer chips from CURTIS ELECTROMUSIC ? ONE VCO CEM3340/3345 PDF or DUAL VCO CEM3374 --> PDF
Well used also for example in the Roland's Flagship Jupiter-8

They are old but you can find still of them. Maybee in e-bay
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Old 24th April 2008, 01:59 PM   #15
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Please count me in. It is very interesting for me. I was using my PC audio card as frequency analyzer but I am not satisfied with the accuracy especially if I have to measure noise and distortion.

Dimitar
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Old 24th April 2008, 02:36 PM   #16
Corax is offline Corax  Germany
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Hi folks,

what do you think about this project with an ATmega and a graphic LCD with 122x32 pixel:

http://elm-chan.org/works/akilcd/report_e.html


Of course it won't be possible to measure distortion with that beast but it could replace the standard PA spectrum analyzer if you add a (digital) pink noise generator and a microphon preamp.
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Old 24th April 2008, 06:13 PM   #17
jcx is online now jcx  United States
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wouldn't an eval board for a 18 or 24 bit Msample monolithic ADC from Analog or TI be a lot more capable? and no 'scope needed for display - 2+ GHz 64 bit PCs should be quite adequate for dsp and display



http://www.analog.com/en/prod/0%2C28...7760%2C00.html

http://focus.ti.com/docs/prod/folder...t/ads8484.html
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Old 24th April 2008, 06:56 PM   #18
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those starter kits and dev modules run $300 to $400+ once you figure in the additional stuff you need to get them to go.

i have the TI ADS1271 -- the devkit is $50, but the "PAK" and MPS430 tools were multiples of this
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Old 24th April 2008, 07:20 PM   #19
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See here:
200 MSPS acquisition board with ADC08200 should be enough
http://www.knjn.com/ShopFlashy.html
And in order to do FFT & DSP you will need FPGA:
http://www.knjn.com/board_Xylo.html
http://www.knjn.com/ShopBoards_USB2.html

In total it will come up for around $250 for freq analyzer + programming/configuring the FPGA.

D.
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Old 24th April 2008, 11:54 PM   #20
GK is offline GK  Australia
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Quote:
Originally posted by jcx
[B]wouldn't an eval board for a 18 or 24 bit Msample monolithic ADC from Analog or TI be a lot more capable? and no 'scope needed for display - 2+ GHz 64 bit PCs should be quite adequate for dsp and display

I already have ~20 oscilloscopes in my workshop, and no room for another PC.

I pledge to work my nuts off over the next few weeks of evenings to get the display driver / sampling and double buffered screen memory board circuit design simplified with a little PIC here and there, using non-obsolete parts, layed out, operational and tested.

After that I will work on converting the <10Hz resolution ~90dB dynamic range analogue end and hybrid PLL working at 20-200,000Hz.

Cheers,
Glen
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