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Old 15th December 2012, 02:19 AM   #1151
davada is offline davada  Canada
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Default Difference of 339a range

Rick have a look at this.

The green is 1KHz in the 1K range and the yellow is 1KHz in the x100 range.
The noise floor and notch shoulders are lower in the x100 range.
The padding resistors and filter resistors are lower in value and the caps are larger in the x100 range.
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File Type: png range.PNG (451.7 KB, 178 views)
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Old 15th December 2012, 04:10 PM   #1152
RNMarsh is online now RNMarsh  United States
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hmmm. about 3dB increase. that number sounds familiar.... keeps popping up in electronics. Not worth changing anything around for- IMO. But interesting. For now... Its one of those "oh well' things.

Last edited by RNMarsh; 15th December 2012 at 04:15 PM.
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Old 15th December 2012, 04:31 PM   #1153
RNMarsh is online now RNMarsh  United States
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Default Drinks are on me !

Take the week off! Drinks are on me ! The ShibaSoku AD725D has arrived. .0003 full scale. I'll check the 339A source today. [Now if I just had a schematic] -RNMarsh
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Old 15th December 2012, 04:49 PM   #1154
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Congrats on that. They are quite rare. We need to see how different yours is from my much older one.
There is someone on the web with a rentable manual.
You will now need the matching oscillator. I can lend you one for a while.

Sent from my myTouch_4G_Slide using Tapatalk 2
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Old 15th December 2012, 05:05 PM   #1155
dimitri is offline dimitri  United States
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Quote:
The ShibaSoku AD725D has arrived.

Now you can search for the mate: AG15C
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Old 15th December 2012, 05:12 PM   #1156
RNMarsh is online now RNMarsh  United States
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I understand there is also a AG16_. I hope one turns up - a 15 or a 16 before long. Or, I will borrow Demian's to get some work done. Thx- Richard
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Old 15th December 2012, 07:30 PM   #1157
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
Take the week off! Drinks are on me ! The ShibaSoku AD725D has arrived. .0003 full scale. I'll check the 339A source today. [Now if I just had a schematic] -RNMarsh

Hi Rick,

Here is something to compare it too.

This is the 339A oscillator, with mods and a tight calibration, at it best.
1KHz, 1Vrms. The notch filter in the 339a is seeing 1Vrms from the buffer amp.

Cheers,
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File Type: png 339a best 1KHz 1Vrms.PNG (446.9 KB, 151 views)
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Old 15th December 2012, 07:40 PM   #1158
dimitri is offline dimitri  United States
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Very good. David, where 1/f noise is originated: oscillator, input att/amplifier, notch amp/capacitance neutralizer, etc?
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Old 15th December 2012, 08:35 PM   #1159
davada is offline davada  Canada
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Quote:
Originally Posted by dimitri View Post
Very good. David, where 1/f noise is originated: oscillator, input att/amplifier, notch amp/capacitance neutralizer, etc?
Hi Dimitri,

I'm not sure I can put my finger on it. It looks like it's a bit of all of the above mentioned.
Some of the answers can come from calculation and the rest has to be measured.
Resistor noise we can calculate or just say we have a 100K input impedance and so that is a source. But this is in parallel resistance with the source resistance which is 600 ohms. This impedance changes with input attenuation as seem by the input of the amplifier. At 0dB attenuation we have the source but as we change input attenuation we have something different at the amplifier input. This effect can be seen by reducing the oscillator output level and changing the input sensitivity. The 339a meter rises for the same voltage seen by the amplifier's input. We also have a gain change on this amplifier as the input sensitivity is changed.

I would say the most noise is generated by the notch filter control elements. The LDR's. Another source is the auto set level. The auto set level maintains a constant output level within a 10dB range of the input range selector. it also has an LDR. At unity it's resistance is very high and is reduced as needed to a max of 10dB increase.

Then there is just the normal contribution of the amplifier noise at what ever gain.
What matters most is the noise at the output of the notch filter. After that it is amplified 80dB, 10000 times. That's a lot. This gain is distributed over the distortion amplifier 30dB, the auto set level 10dB and the meter amplifier just before the RMS detector 40dB.

We can see from the plot in the last post the SW is reporting a total noise power of -94.6dB at the output of the notch filter. -95dB + 80dB is -15dB (0.178mVrms) of noise in a 20KHz of bandwidth. Out of 1Vrms this is 17.78% of noise out of the FS and with all filter, in that's a 29.6KHz bandwidth seen by the meter. 17.78% of 0.01% FS is 0.001778 residual which is exactly what HP states for the 339a.

My answer then is the majority of the noise is from the input stage, the notch filter and or the oscillator /attenuator. I don't think it's the oscillator but it might be. I'm at my measurement noise floor.

Here is a clue. The residual of the level meter with all filters in, on a good day with no signal and input loaded to 600 ohms is about 5uVrms with a 339a option 001.
In level mode the distortion amplifier is bypassed. The chain in level mode is input amplifier + level amplifier + meter amplifier with a maximum gain of 80dB FS. Plus a bit more for option 001.

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Old 15th December 2012, 08:39 PM   #1160
davada is offline davada  Canada
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Quote:
Originally Posted by dimitri View Post
Very good. David, where 1/f noise is originated: oscillator, input att/amplifier, notch amp/capacitance neutralizer, etc?

The capacitance neutralizer doesn't seem to contribute much noise which I find surprising for a circuit using positive feedback, negative impedance.

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