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Old 29th November 2012, 01:01 PM   #921
davada is offline davada  Canada
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Quote:
Originally Posted by coluke View Post
Wow - recognized it! Seen a few demo videos a couple of days ago, and discovered myself wondering about release date. It looks great (particularly the H/W), and seems very promising indeed (although I'd add a few more FFT windows...) - need another beta tester?

L.
Hi coluke,

Just send a request to support@ tell them about yourself and what you do.
They want to clear up a few software problems before taking on more beta testers. But it's always good to get your name in.
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Old 30th November 2012, 03:32 AM   #922
RNMarsh is online now RNMarsh  United States
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Default Osc thd -

Quote:
Originally Posted by 1audio View Post
It seems unlikely that those signals could be causing the distortion in the output. But their presence at all suggests the distortion is hiding under some rock nearby.

I would next try making the integrating caps on the level detectors larger and see if the harmonics increase or decrease. Those are the obvious nonlinear stage and driving them harder will show if they are coupling into the rest of the circuit.

The other candidate would be the LDR's themselves. Reading this thread DIYHiFi.org • View topic - LDR as a volume control suggests the LDR's in the 339 would be in the 2% THD generation. The Silonex parts would be substantially better. Looking at Nelson Pass's measurements you should keep the voltage across the LDR's below .2V or less. If they are the cause then a 20 dB improvement would be immediately visible. Perhaps you can look differentially across the LDR's in the 339?
Another obvious place to look is the oscillator and the osc's buffer IC themselves. These IC were probably sota at the time but now we have much lower thd opamps that could be used in their place. The oscillator op-amp is running pretty hard at 20 volts p-p output. And, the buffer takes that and has to drive 600 ohm loads? That asking a lot of opamps of the era. I think we can drop the thd with those changes. Might also change the osc output to 10 v p-p and change the Buffer to a X2 gain stage. Even with stock opamp it would help. But that is harder with the agc and all there, too. So just changing to lower thd opamp on osc and its buffer; A1U1 and A1U3. - Thx RNMarsh [btw - who is your source for the opamps?)

Last edited by RNMarsh; 30th November 2012 at 03:37 AM.
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Old 30th November 2012, 03:46 AM   #923
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
Another obvious place to look is the oscillator and the osc's buffer IC themselves. These IC were probably sota at the time but now we have much lower thd opamps that could be used in their place. The oscillator op-amp is running pretty hard at 20 volts p-p output. And, the buffer takes that and has to drive 600 ohm loads? That asking a lot of opamps of the era. I think we can drop the thd with those changes. Might also change the osc output to 10 v p-p and change the Buffer to a X2 gain stage. Even with stock opamp it would help. But that is harder with the agc and all there, too. So just changing to lower thd opamp on osc and its buffer; A1U1 and A1U3. - Thx RNMarsh [btw - who is your source for the opamps?)
Hi Rick,

The distortion we see from the 339A analyzer is about 20dB higher than the oscillator itself.
Yes the oscillator can be improved a bit but not that much more.

See Dick Moore's web page for details of tweaking the the 339A oscillator and you'll see what I mean.

Cheers,
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Last edited by davada; 30th November 2012 at 03:54 AM.
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Old 30th November 2012, 03:52 AM   #924
davada is offline davada  Canada
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Default More on the 339A

Further investigation of the 339A's elevated distortion from the analyzer revealed these results.

First I bypassed the E2 LDR with a trim pot. The distortion 2nd and 3rd H dropped about 5dB but I could only get the notch to -80dB with a pot. No surprise there. I re-soldered the LDR back in.

Demian suggested increasing the feedback cap of the integrator on the output of the amplitude error detector balanced modulator. I increased the cap from 47uF to 1000uF. This had no effect on the distortion. The notch would not settle to less than -95dB and took over 1 minute to do this. So I changed the cap to 10uF with no change in distortion level.

It stands to reason that the distortion is not produced by the phase detector or amplitude detector but by the LDR's.

Cheers,
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Last edited by davada; 30th November 2012 at 04:01 AM. Reason: oops, had the scale wrong
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Old 30th November 2012, 04:27 AM   #925
davada is offline davada  Canada
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This is as far as I'm going with he 339A Analyzer.

In conclusion the remarkable notch depth is only obtainable with a lot of calibration effort.
It does not hold very well changing with level and frequency. I don't see an easy way of dealing with the elevated analyzer distortion and I don't think it's worth the money or time to try. I agree with the assessment of boat anchor as far as the analyzer is concerned.
The oscillator is very good and worth the improvement. The 339A works very well as a level meter and if you have the 001 option it can go right down to 10uV or better.

Cheers,

David.
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Old 30th November 2012, 04:28 AM   #926
RNMarsh is online now RNMarsh  United States
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Quote:
Originally Posted by davada View Post
Further investigation of the 339A's elevated distortion from the analyzer revealed these results.

First I bypassed the E2 LDR with a trim pot. The distortion 2nd and 3rd H dropped about 5dB but I could only get the notch to -80dB with a pot. No surprise there. I re-soldered the LDR back in.

It stands to reason that the distortion is not produced by the phase detector or amplitude detector but by the LDR's.

Cheers,
But you said the LDR only affected the thd by 5dB Which LDR?
-RNM

Last edited by RNMarsh; 30th November 2012 at 04:41 AM.
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Old 30th November 2012, 05:04 AM   #927
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
But you said the LDR only affected the thd by 5dB Which LDR?
-RNM
E2 is the LDR for the amplitude control of the notch filter.
E1 is for the phase detector.

My aim was to identify the main source of the distortion and I am convinced it is the LDRs.
I think with both LDRs bypassed there would be reasonable drop in distortion but there is still the notch amp and feedback amp which contribute as well. Add in the input amp and buffer.

The Twin T is a better option since it is a passive notch filter. I would rather focus on an auto tune circuit for that than to modify the 339A.

Cheers,

David.
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Old 30th November 2012, 06:39 AM   #928
1audio is offline 1audio  United States
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It looks like you did find the real distortion limiter. It would be interesting to know the voltage across the LDR in operation.

I agree that you may have hit a wall in the box. Its architectural. Unfortunately, even if you had the correct Silonex LDR's the distortion still may be limited unless its possible to get the voltage across the LDR's small. However my experience with the ST1700 suggests that the LDR's do age and may need replacement do to age.

If the opamps are LM318's and 5534's etc. they aren't a major limiter. They are in the KH4400 and it can get to less than -120 dB harmonics.

Modding it to use JFETs seems difficult, analog multipliers harder still and the lowest distortion option, servo pots, impractical in the extreme.
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Old 30th November 2012, 07:08 AM   #929
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If the LDR is the primary distortion source, you can reduce its contribution by replacing it with a series-parallel combination of four LDRs. The combo has the same control law, but much lower distortion because each resistor element sees just half the AC voltage.

Samuel
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Old 30th November 2012, 08:45 AM   #930
RNMarsh is online now RNMarsh  United States
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Quote:
Originally Posted by Samuel Groner View Post
If the LDR is the primary distortion source, you can reduce its contribution by replacing it with a series-parallel combination of four LDRs. The combo has the same control law, but much lower distortion because each resistor element sees just half the AC voltage.

Samuel
Well since it is the LDR... where do I get some to use in a ser/par fashion? Who makes them? make and model to buy??

Thx - Richard
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