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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 6th May 2016, 02:44 PM   #11
Evenharmonics is offline Evenharmonics  United States
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Quote:
Originally Posted by acceler8 View Post
Here is a screen cap from the QA400:
Click the image to open in full size.
What's going on with those peaks at the lower half?
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Old 6th May 2016, 09:30 PM   #12
acceler8 is offline acceler8  United States
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Ugh, I never seem to pick the right link to images in the gallery. Here is the full-size:
TSE 300b Frequency Response - My Photo Gallery

I assumed the peaks were 60Hz hum (and harmonics). I've never really got a clean test without them.
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Old 7th May 2016, 04:40 AM   #13
gcom is offline gcom  Ireland
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That is also an fft.

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Old 7th May 2016, 05:44 PM   #14
acceler8 is offline acceler8  United States
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I'll freely admit that I am unsure of the differences between an FFT and a Frequency Response graph. I assumed the the 'FR' mode of the QA400 referred to 'Frequency Response'. Can you (and/or TomChr) explain the difference? I (think) I know that FFT implies a mathematical conversion from a time domain to a frequency domain. But at the end of the day, doesn't that conversion imply a close relation to the frequency of a device under test?
Thanks for making me ask questions!
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Old 7th May 2016, 07:31 PM   #15
gcom is offline gcom  Ireland
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My understanding of it. Wide open to correction or improvement:
That analysis is of a single pure tone (in this case 1Khz) that is played through your amp.
The FFT then runs a spectrum analysis on what comes out to see it the amp has added other tones or harmonics. So you see the 60hz hum and some harmonics that have been added.
A freqeuncy response analysis plays a sweep of all the frequencies from low to high and graphs the level of what comes out to tell you if it is playing all frequencies equally or some frequencies louder or quieter than others.
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Old 8th May 2016, 02:32 AM   #16
Evenharmonics is offline Evenharmonics  United States
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FFT here. Frequency response here.

What amp FFT measurement typically looks like.
Click the image to open in full size.

What amp frequency response typically looks like.
Click the image to open in full size.
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Old 13th May 2016, 10:09 PM   #17
Francis Jansz is offline Francis Jansz  Australia
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Dear Audio specs.
I need to know what resistor values and the Capacitor values . Ņeeded to build a tube active 2 way ćrossover and change the filter to 600Hz low pass at 24 db i recently bought a pete millett 2 way tube crossover PCB and would like to get the filter working to low pass 600 hz cut out frequency at 24 db slope and would like my high pass filter to start from 600 hz to infinity please help me to achive this i need to know as to the values of the caps and the resusters to do this. So that i can order the right parts.
Kind Regards
Francis Jsnsz
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