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Old 2nd December 2012, 10:54 PM   #991
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Quote:
Originally Posted by davada View Post
Okay so what's slowing it down then? 100 32k would appear to be real time.
I wasn't referring to the hardware. It's the OS that's being blamed.

Cheer,
The OS has nothing to do with it a 32K double precision FFT takes a few mSec just try it in Matlab or Mathcad or Octave (free). Even Cooledit 1998 will do 8K FFT's real time. You have to refine what you mean by real time, do you mean visible on screen latency or doing an entire FFT between audio samples (this is another matter).
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Last edited by scott wurcer; 2nd December 2012 at 10:59 PM.
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Old 2nd December 2012, 11:40 PM   #992
davada is offline davada  Canada
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Quote:
Originally Posted by scott wurcer View Post
The OS has nothing to do with it a 32K double precision FFT takes a few mSec just try it in Matlab or Mathcad or Octave (free). Even Cooledit 1998 will do 8K FFT's real time. You have to refine what you mean by real time, do you mean visible on screen latency or doing an entire FFT between audio samples (this is another matter).
Hi Scott,

I mean visually. The user experience.
I thought that was what Demiam was asking about.

Cheers,
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Old 3rd December 2012, 12:00 AM   #993
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Quote:
Originally Posted by davada View Post
Hi Scott,

I mean visually. The user experience.
I thought that was what Demiam was asking about.

Cheers,
OK that has to do with your GUI API, they are all over the place some have horrible overhead just so they are easy to program. The actual behind the scenes computation is lost in the round off.
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Old 3rd December 2012, 02:00 AM   #994
davada is offline davada  Canada
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Default The milk is getting creamy 5dB at a time

I replaced U1 on the oscillator board with an LT1468, removed C45 and C48.
Not wanting to remove any more components or cut a trace I clipped pin 8 off the IC.
Pin 8 is not used but has rail voltage on it. I wish I could use at 1468 in the buffer stage but they don't do well with a 600 ohm load.

The feedback in the notch amp should stay as it is. As it is it's down 1dB at 2n H.

Cheers,

David
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Old 3rd December 2012, 02:24 AM   #995
davada is offline davada  Canada
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Even the switches contribute.
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Old 3rd December 2012, 03:19 AM   #996
davada is offline davada  Canada
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Default What's been done so far

Here's the summery of what been done so far.

Oscillator:

Replaced A1U1 with LT1468 compensated version.
Clipped pin 8 off the 1468. It has power on it.
Removed A1C45 and A1C48.
Replaced A1U2 quad op amp with low noise Jfet type.
Changed A1R50 to 2,49K and paralleled a 20K trim. This is the 2nd H trim at 1KHz.
Optional is to replace A1C47 with 640pF to 1000 pF. This need to be experimented with.
It trims the distortion balance with 1KHz and 10KHz - 20KHz.
Clean and calibrate oscillator.

Analyzer:

Replaced A3U3 and A3U4 with OPA1641.
Removed A3C27 ans A3C26.
Replaced A4U1 with LT1468 uncomp.
Changed A4R1 to 200 ohm. Increases signal gain to 1000 for balanced multipliers.
Added 10pF feedback capacitor to A4U1 (1468)
Changed A4C47 to 1uF tan. Speeds up error signal to amplitude control of notch filter.

Connect FFT to TP3. Set input for 1KHz at 1Vrms on TP4. Calibrate notch level and phase roughly. Put FFT on A4 TP1. Set input balance trim for least amount of hash and harmonics. Repeat notch calibration.

Connect TP3 to AM input connector with mini coax. Find the best grounding point for AM (now output) which has least amount of hash and distortion.

I suggest isolating the ground of the BNC connector with extruded nylon washers. Then you get to choose.

There is still more to come. Lots more to do.

Cheers,
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Old 3rd December 2012, 05:23 AM   #997
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Default THD of parts -

Your on a roll.

I noticed there are electrolytic caps and trimmer controls that are not part of any feedback... for example the trim controls dropped thd by 6 db when replaced by better parts. Now, I see a pair of tantalum caps back to back as coupling caps. Well, that configuration reduces the cap distortion BUT we are after thd levels below what tant caps back to back provide.... I replaced the two tantalum back to backs (A3 C206,207) with a small 50v film cap and the third harmonic dropped another 6dB. No opamps have been changed, yet... waiting for adapters for the IC's to be mounted.

The THD (source plus analyzer) is now already 25 db below the -80db Full Scale, so we need a meter switch for X10 or -100dB F.S. range. When the opamps are changed, this will be more feasable (with the lower noise and distortion). Just need to trim the 2H down to much lower level. -Thx RNMarsh
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File Type: jpg film cap.jpg (682.4 KB, 185 views)
File Type: jpg THD meter.jpg (727.1 KB, 182 views)

Last edited by RNMarsh; 3rd December 2012 at 05:46 AM. Reason: Don't forget Parts distortion -
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Old 3rd December 2012, 06:40 AM   #998
1audio is offline 1audio  United States
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Quote:
Originally Posted by scott wurcer View Post
OK that has to do with your GUI API, they are all over the place some have horrible overhead just so they are easy to program. The actual behind the scenes computation is lost in the round off.
My ancient Wavetek plugin for a Tek 7K frame uses something like an intel 8008 processor. A zoomed view so i can see the harmonics or fundamental as I'm tuning with some averaging is slow.

The QA400 may be a good replacement. I emailed them and hope to hear back.

It looks like major progress on the venerable HP339. The work will help highlight the sensitivity and where to focus efforts in improving other analyzers.
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Old 3rd December 2012, 02:24 PM   #999
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
My ancient Wavetek plugin for a Tek 7K frame uses something like an intel 8008 processor. A zoomed view so i can see the harmonics or fundamental as I'm tuning with some averaging is slow.

The QA400 may be a good replacement. I emailed them and hope to hear back.

It looks like major progress on the venerable HP339. The work will help highlight the sensitivity and where to focus efforts in improving other analyzers.
Hi Demian,

It could be a week or so before you get an answer or maybe right away.

Was it the hardware, software or user experience you were asking about earlier?

Cheers,
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Last edited by davada; 3rd December 2012 at 02:28 PM.
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Old 3rd December 2012, 07:02 PM   #1000
davada is offline davada  Canada
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Default Oscillator.

I've got some weirdness going on with the oscillator.
The IC change may not have had the effect seen in the plots.

If the level range is switched range lower and the level brought up by the level pot the distortion drops 5dB on the 2nd H. It's the same level into the analyzer. The dial is broken off on this knob and I hadn't notice the range change. Now I have to figure out this odd behavior. The pot is between the oscillator and buffer amps.
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