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Old 9th February 2013, 05:33 PM   #1731
1audio is online now 1audio  United States
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Quote:
Originally Posted by davada View Post
No. A small dc offset on a loud speaker has absolutely no effect on the sound.
Actually it can. Cone drivers are not that linear and a small DC offset can move the voice coil enough to reduce/increase the distortion some. If you look at a Klippel plot you can see the source of the issue.

A small DC offset can saturate the transformer of a electrostatic speaker increasing the distortion a lot.
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Old 9th February 2013, 08:22 PM   #1732
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The problems with the state variable filter used that way is the intrinsic distortion of the amplifiers and the tuning. That is the core of the analyzer in several analyzers, the Boonton and the Amber are two examples. The passive notch, like the B&K, are better. You could modify the B&K with active circuitry to make a tuneable high q notch with it. We just need to reverse engineer its circuitry, not a small task.
It's that complex?
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Old 9th February 2013, 08:28 PM   #1733
davada is offline davada  Canada
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Actually it can. Cone drivers are not that linear and a small DC offset can move the voice coil enough to reduce/increase the distortion some. If you look at a Klippel plot you can see the source of the issue.

A small DC offset can saturate the transformer of a electrostatic speaker increasing the distortion a lot.
I meant smaller offset than that. Less than 1Vdc.

Electrostatics are another matter.
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Old 9th February 2013, 08:37 PM   #1734
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Originally Posted by davada View Post
It's that complex?
I did not think so until I pulled the cover off. The tuning element is a pot with switched caps and some other circuitry but its not real easy to follow in the box.

I'll post some pictures later.
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Old 9th February 2013, 09:23 PM   #1735
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The K-H 4400 has a very low-Q filter, with not much notch depth. Not a good candidate i my opinion. Most oscillators use relatively low-Q filters for tuning. The 339 and 239 probably have the highest Q filters, but even so their notch depth would not be much over 30dB. None of the commercial oscillators I've seen use a Twin-T for tuning -- most use a Wien or bridged-T -- inherently low-Q.
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Old 10th February 2013, 12:08 AM   #1736
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None of the commercial oscillators I've seen use a Twin-T for tuning -- most use a Wien or bridged-T -- inherently low-Q.
Hi Dick,
I found a commercial Twin-T oscillator for you - the Radford LDO3 from 1975:
http://www.stancurtis.com/Soundtech/...%20Series3.pdf
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Old 10th February 2013, 12:30 AM   #1737
davada is offline davada  Canada
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Hi Dick,
I found a commercial Twin-T oscillator for you - the Radford LDO3 from 1975:
http://www.stancurtis.com/Soundtech/...%20Series3.pdf
Cool.
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Old 10th February 2013, 12:35 AM   #1738
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.. but not so cool looking, more info at
Radford Low Distortion Tee-Twin Sine Oscillator
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Old 10th February 2013, 12:43 AM   #1739
davada is offline davada  Canada
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.. but not so cool looking, more info at
Radford Low Distortion Tee-Twin Sine Oscillator
That one looks like it's been through a middle Eastern war.
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Old 10th February 2013, 12:46 AM   #1740
davada is offline davada  Canada
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Default Twin T osc

It looks like there is a few of them out there.

Art's Theremin Page: Twin-T Audio Sine Wave Oscillator
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