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Boonton 1121 Audio Analyzer: some questions
Boonton 1121 Audio Analyzer: some questions
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Old 14th September 2021, 08:16 PM   #21
krais23 is offline krais23
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Join Date: May 2015
Quote:
Originally Posted by 1audio View Post
I just checked one of mine for the same signals to get a baseline.
Conditions- loopback BNC to BNC, input and output floating, 1 KHz, level 14V 50 Ohms source (spl 75), TP 2 out output board clip lead to chassis. (do not connect before boot is complete).
Thanks so much Demian for all the effort and guidance. I'll try to replicate these baseline measurements and will report back.

A few new player's questions if you don't mind (you might be overestimating my skill level):
- You mean putting the 1121 in special function 75 when doing the measurements, correct?
- "TP5 ac coupled at high gain": do you mean setting the probe in 1:1 mode?
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Old 15th September 2021, 12:02 AM   #22
1audio is offline 1audio  United States
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Boonton 1121 Audio Analyzer: some questions
Special 75 sets the output impedance to 50 Ohms. That reduces its sensitivity to external noises. TP5- AC coupled with high gain to see the noise. I did use 1:1 on the probe for more sensitivity. And 20 MHz band limit to lower the noise of the scope re: input. There isn't anything that's liable to oscillate at 100 MHz in a stock unit. The 5534's won't get there. Is there a radio station near you?
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Old 15th September 2021, 07:42 PM   #23
krais23 is offline krais23
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Hmm... yes I do think there is a FM radio transmission tower within half a mile from my house but not 100% sure if it's still in use.
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Old 19th September 2021, 06:39 PM   #24
krais23 is offline krais23
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Today I tried to reproduce the baseline measurements (loopback BNC to BNC, input and output floating, 1 KHz, level 14V 50 Ohms source (spl 75), TP 2 out output board clip lead to chassis). Distortion measured was around 0.0025%.

I didn't know how to get a scaled output of the input signal so measured TP1 on the source board instead.

First picture: source TP1 (yellow) vs. TP5 on source board (green) (AC coupled, 20MHz bandwidth).
Second picture: source TP1 (yellow) vs. Monitor out (green).
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File Type: png SCR21.PNG (90.0 KB, 19 views)
File Type: png SCR23.PNG (122.3 KB, 19 views)
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Old 19th September 2021, 06:51 PM   #25
krais23 is offline krais23
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Btw, I noticed some random glitches to the signal at TP5 (source), see video capture below.
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File Type: mp4 TP5.mp4 (3.20 MB, 5 views)
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Old 19th September 2021, 07:42 PM   #26
1audio is offline 1audio  United States
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Boonton 1121 Audio Analyzer: some questions
That all looks typical for a stock unit. The second harmonic is the dominant and can be addressed on both source and analyzer. I think its mostly from the analog multipliers.

You can see the sample pulse on TP5 but its mostly lost in all the RF noise you are getting.

I have noticed that there can be some noise across the grounds in these which is annoying. The balanced to balanced is an effort to reduce it. I get those random glitches as well. It may simply be random noise from something getting it.

I hope Tuesday I'll be able to post some simple upgrades as a first step. I'll be gone for a week after Tuesday so any more documentation will need to wait until I return.
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Old 20th September 2021, 05:52 PM   #27
krais23 is offline krais23
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Thanks Demian! Looking forward to any tips you could share on upgrades. No rush...

One additional note: besides the glitches on TP5, I noticed several glitches in the monitor out signal as well (see att.), not sure if that's expected for a stock unit.
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File Type: jpg Screenshot 2021-09-20 at 19.45.14.jpg (171.4 KB, 9 views)
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