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Old 2nd April 2009, 10:32 PM   #11
anatech is offline anatech  Canada
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Hi Brad,
Quote:
DDS from the PCM1704 could be paired with analog-to-digital conversion from a PCM1804 to provide a flexible analysis tool, instead of just generating pure tones... though it's basically a novelty soundcard now
Hardly!
Now you are beginning to chase an Audio Precision type system. The generator and A/D sections are two completely different projects that could be included in the same case. Note I didn't mention "card", as in "installed in a computer".

To get the low noise and THD you want, plus input and output signal conditioning, you would need a larger box free from switching power supply noise. It would help to ventilate some of the components that would run warm. That's a side effect of chasing the low noise figures. It's no mistake that AP used an external box for all the analog signal processing. It's all done for a very good reason.

My X-fi Extreme music is a sound card. This is an instrument.

-Chris
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Old 3rd April 2009, 05:02 PM   #12
EC8010 is offline EC8010  United Kingdom
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Square waves are best generated in the analogue domain. Since (for audio) we're concerned mostly with the rise time or the flatness across the top, there's a very good way of generating suitable waves. Use a mercury-wetted relay switched at mains frequency to direct a floating DC supply to the output terminals. You can now use a 10 turn wirewound pot (with dial) to adjust the DC voltage of the (regulated supply), giving you a very accurately calibrated square wave with a rise time in ps (picoseconds). Definitely good enough for audio. The fact that it can only repeat at mains frequency isn't a problem because we look at the edge for HF and the top for LF.
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Old 3rd April 2009, 05:35 PM   #13
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Scott Wurcer chimed in on this thread:

Can we improve this low distortion sine oscillator ?

there's a link to an EDN article to be found.

I built the "Eager Oscillator" (paen to Dale Eagar who wrote the Linear Tech Application Note) -- aka "Uber Oscillator" and describe it here:

http://www.tech-diy.com/TestEquipmen...oscillator.htm


Click the image to open in full size.

For ease of application, I wouldn't recommend the uberoscillator -- instead look for Bob Cordell's version of the SG-505 on his website.
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Old 3rd April 2009, 08:40 PM   #14
anatech is offline anatech  Canada
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Hi EC8010,
I have to agree with both your points on square waves. I must admit that I'm lazy and either use my generator output, or an HP pulse generator I bought for that purpose. Your relays may in fact do a better job of creating a square wave.

The buzz let's you know it's on!

Hi Jack,
Completely forgot about the SG-505 clone, I'll have t read up on the "Eager Oscillator".

Thank you for the links!

-Chris
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Old 8th September 2011, 10:51 AM   #15
mome is offline mome  Thailand
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Quote:
Originally Posted by geekysuavo View Post
i would have to agree with that. DDS from the PCM1704 could be paired with analog-to-digital conversion from a PCM1804 to provide a flexible analysis tool, instead of just generating pure tones... though it's basically a novelty soundcard now, lol! i'll look into it, most definitely.

~ brad.
Hi Brad,
I want you to look at this circuit.
Perhaps it is useful to you?.

Click the image to open in full size.

Low-distortion Audio-range Oscillator using NE5532
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Old 24th March 2013, 05:13 PM   #16
RNMarsh is online now RNMarsh  United States
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You might enjoy not reinventing the wheel as this has been started already over in another section.... been going on awhile and in various stages... oscillators and analyzers. I am modifying existing oscillators at this time and am down to reading my osc at -140db 2H and 3H so far. ... modified KH4402B.

Thx-RNMarsh

Last edited by RNMarsh; 24th March 2013 at 05:16 PM.
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Old 26th March 2013, 03:04 PM   #17
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Hey all,

Thanks for the insights! I may come back to this later on, but it's a shelved idea for me for now. The DAC/DDS route is something I'll probably play with soon, but at higher (4-6 m band) frequencies...

~ Brad.
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