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Old 1st December 2012, 03:48 AM   #941
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
400K across 3.48K wouldnt change the amp gain at all. With full LED current, the LDR value will be lowest.
Hi Rick,

This was the LDR for the phase detector not the amplitude detector.
The impedance is much higher in the phase leg. If you look at the drivers for the LDRs you may notice they are biased differently. I will know better once I have an LDR out and test it proper.
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Old 1st December 2012, 04:48 AM   #942
davada is offline davada  Canada
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Default 339a LDR

Here is the LDR curve and data

Cheers,
Attached Images
File Type: png LDR R vs I.PNG (62.0 KB, 156 views)
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Old 1st December 2012, 05:35 AM   #943
davada is offline davada  Canada
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Default 339a LDR

I tried subbing a Vactrols VTL5C6 which looks like a fairly close match.
The cal is out of range and I'm not able to get more than a -80dB notch depth.
This was placed in the E1 position for the phase error detector.
There is not much change in distortion.
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Old 1st December 2012, 05:47 AM   #944
davada is offline davada  Canada
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Quote:
Originally Posted by Frex View Post
Hello davada,

Could you say what FFT software do you use for your screenshot ?
Regards.
Frex
Hi Flex,

Yes QuantAsylum is fine with me saying who they are.
You can check out there web pages here.

QA Blog - QuantAsylum Home Page

There are some videos there you can watch on the QA400 software and hardware.

Cheers,
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Old 1st December 2012, 05:56 AM   #945
1audio is offline 1audio  United States
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I hope that curve is in milliamperes. . .
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Old 1st December 2012, 06:34 AM   #946
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
I hope that curve is in milliamperes. . .
Okay, Okay, I fix it.

The data columb says milliamperes.

I was wondering what that bad smell was.

Cheers,
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Last edited by davada; 1st December 2012 at 06:41 AM.
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Old 1st December 2012, 06:41 AM   #947
davada is offline davada  Canada
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Default 339a LDR

This better?
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File Type: png LDR R vs I.PNG (62.1 KB, 177 views)
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Old 1st December 2012, 07:32 AM   #948
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by davada View Post
This better?
so we shouldnt use it below 60K Ohms?? Adjust/scale it to be so??

is Q of the notch high enough? More gain needed?

Can also measure THD of the LDR at different LED currents -- out of the box --- not in 339A circuit.

Thx... excellent detective work. -RNMarsh
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Old 1st December 2012, 07:57 AM   #949
1audio is offline 1audio  United States
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If you check Nelson Pass's work he has already done that for the Silonex parts. Starts here:Lightspeed Attenuator a new passive preamp

All you will ever need to know. The Vactrol pdf (attached) has similar info as well. Also suggests that some DC will cause 2nd harmonic and pure AC 3rd harmonic. Very much a high voltage coefficient resistor.
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File Type: pdf VT500.pdf (969.0 KB, 28 views)
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Old 1st December 2012, 04:36 PM   #950
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
If you check Nelson Pass's work he has already done that for the Silonex parts. Starts here:Lightspeed Attenuator a new passive preamp

All you will ever need to know. The Vactrol pdf (attached) has similar info as well. Also suggests that some DC will cause 2nd harmonic and pure AC 3rd harmonic. Very much a high voltage coefficient resistor.
Hi Demian,

This all stands to reason then with my findings that the least amount of distortion, when operated as a series element, is when the LDR is near saturation or at least the LED current limit. The AC voltage across the LDR is at minimum.

Can some numbers be put to the DC influence? Are we talking uV, mV etc. I know you've made reference but I am lazy on the weekends.

Cheers,
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