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Old 29th December 2010, 03:43 PM   #1
PGDO is offline PGDO  Netherlands
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Join Date: Dec 2010
Location: Zuidhorn
Default Audio signal generator and (FFT)scope

Hi all,
I am planning to design and build my first tube amplifier in 2011, probably with an EMS 300B-XLS tube.
I think that before I start this project I should first have the necessary test equipment. I currently own an old Fluke scopemeter (PM93).
What I think I need is a audio signal generator (distortion <= 0.05% ??) and a scope with FFT analyzing capabilities.
It should not be to difficult to buy a secondhand function generator online on one of the auction sites.

I am just not sure what the minimum requirements for a scope should be to be useful and still affordable.
Does anybody know if a TiePie Handyscope HS3 (5MHz) is sufficient, it has a build in function generator. USB oscilloscoop - Handyscope HS3 - TiePie engineering
Or the PicoScope 4226? PicoScope Precision USB Oscilloscopes from Pico
Would the AWG of above mentioned PC scopes be suitable for distortion measurements?
regards,
Peter
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Old 29th December 2010, 08:51 PM   #2
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Scope fft's are useful, but a 12bit scope has about 72 db range, which is not so good for distortion measurements. I personally use a 96 khz sampling onboard sound card. The noise floor is at about -120, so distortion is easy to see.

Also found RMAA (http://audio.rightmark.org/download.shtml) very useful.
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Old 29th December 2010, 10:53 PM   #3
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Check the free Visual Analyzer software at Visual Analyser 2011, combined with an E-MU0404 USB soundcard and a Behringer ECM8000 microphone (calibrated by Cross·Spectrum Labs - Sound | Vibration | Engineering) will get you a lot for little money! E
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Old 29th December 2010, 10:58 PM   #4
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Most scopes that have FFT capabilities, are not very good FFT analyzers. They will show basic spectra, but usually detailed measurements are not available. A good FFT analyzer will give you THD and accurate response data. As you noted, to go along, you will need a good audio generator with low distortion. Typically function generators are not good enough, so look for a good audio generator.

paul
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Old 29th December 2010, 11:07 PM   #5
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Hi Peter,

The world is small. I have lived in Zuidhorn for 15 years, now in Groningen since 2008.
Do you know Pete Millet's kit? Look at his website and see what you can do with it; I have the complete kit here unbuild (too busy winding transformers). When you're interested and have the skill you are kindly invited to assemble the unit, and use it of course.

Verslik je niet in de oliebollen!!
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Old 30th December 2010, 01:58 PM   #6
PGDO is offline PGDO  Netherlands
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Join Date: Dec 2010
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Quote:
Originally Posted by nevermind View Post
Scope fft's are useful, but a 12bit scope has about 72 db range, which is not so good for distortion measurements. I personally use a 96 khz sampling onboard sound card. The noise floor is at about -120, so distortion is easy to see.

Also found RMAA (http://audio.rightmark.org/download.shtml) very useful.
Hi Nevermind,

TiePie claims 16 bit measurements (95db) which should be sufficient (have a look at their application note)

The thing with soundcards is that I don't thrust them that much as they are working in a noisy environment. Besides I read somewhere that their sampling rate is to low?

Also an concern is the high voltages used in tubeamps and the possibility of damaging the soundcard.

Thanks,
Peter
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Old 30th December 2010, 02:06 PM   #7
PGDO is offline PGDO  Netherlands
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Join Date: Dec 2010
Location: Zuidhorn
Quote:
Originally Posted by mickeymoose View Post
Check the free Visual Analyzer software at Visual Analyser 2011, combined with an E-MU0404 USB soundcard and a Behringer ECM8000 microphone (calibrated by Cross·Spectrum Labs - Sound | Vibration | Engineering) will get you a lot for little money! E
Hi Mickymoose,

I had already installed the Visual anlyser software, nice program. Used it as an signal generator via the soundcard which is working for simple tests but not for serious distortion measurements.

As for the soundcard option, see my comments on the previous post from Nevermind.

I do already have an Behringer ECM 8000 mic with pre-amp but I want to be able to take measurements directly from various points in the amplifier..

Thanks,
Peter
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Old 30th December 2010, 02:23 PM   #8
PGDO is offline PGDO  Netherlands
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Join Date: Dec 2010
Location: Zuidhorn
Quote:
Originally Posted by phaselag View Post
Most scopes that have FFT capabilities, are not very good FFT analyzers. They will show basic spectra, but usually detailed measurements are not available. A good FFT analyzer will give you THD and accurate response data. As you noted, to go along, you will need a good audio generator with low distortion. Typically function generators are not good enough, so look for a good audio generator.

paul
Hi Paul,

You're talking about a dedicated FFT analyzer, although probably the best solution it will likely be above my budget. I was hoping that a PC-scope with the right (FFT) software would suffice.

Thanks,
Peter
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Old 30th December 2010, 03:23 PM   #9
PGDO is offline PGDO  Netherlands
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Join Date: Dec 2010
Location: Zuidhorn
Quote:
Originally Posted by pieter t View Post
Hi Peter,

The world is small. I have lived in Zuidhorn for 15 years, now in Groningen since 2008.
Do you know Pete Millet's kit? Look at his website and see what you can do with it; I have the complete kit here unbuild (too busy winding transformers). When you're interested and have the skill you are kindly invited to assemble the unit, and use it of course.

Verslik je niet in de oliebollen!!
Hoi Pieter,

Indeed a small world.
I had a look at Pete Millit's site and the thread about it on this forum, it sure looks interesting.

Please mail or PM me so that we can communicate more directly.

Jij ook voorzichtig met de oliebollen en vuurwerk, alvast een gelukkig nieuwjaar gewenst.

Peter
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Old 30th December 2010, 09:43 PM   #10
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PGDO:
The E-MU0404 is a 24-bit/192kHz device, stereo mic (ph power) or line in. And, beeing a USB device, outside of the computer box and portable. Mine is not powered by the computer to avoid noise problems. As I said: check it out!
E
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