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Old 7th February 2010, 08:04 AM   #11
Frex is offline Frex  France
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Hello everyone,

I think now soon send Gerber files for pcb manufacturing.
I think use "pcbcart" service. It' offer cost effective solution and they job is very good.(145 for 2 boards including shipping).
I hope that my job doesn't yet contain many errors.


Frex
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Old 9th February 2010, 09:03 PM   #12
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ghg,

Thanks for the good tip, but that -168dB floor in your plot, is relative to what voltage?

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Originally Posted by ghg View Post
Hi Frex

Impressive pcb work, fine.

Maybe you are looking for something readymade, and possible unbeatable, take a look at TI's PCM4222EVM ( US $ 149,-- +shipping ).
You just need a dual 15V and single 5V powersupply.

Here a FFT; source Krohn-Hite 4400A, both units SLA battery driven, PC interface RME-PAD via AES/EBU.
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Old 10th February 2010, 04:35 AM   #13
Frex is offline Frex  France
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Ghg, I would also like to know the full setup of of your measurements.
A fully detailed explanation will be welcome

Frex
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Old 10th February 2010, 12:47 PM   #14
ghg is offline ghg  Austria
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Analog oscillator:
KROHN-HITE 4400A ( SLA battery driven ) unbalanced, 50 Ohm output

ADC:
PCM4222EVM ( SLA Battery driven ) AES/EBU-output

PC interface:
RME-Digi96/8-PAD AES/EBU input

FFT software:
Spectraplus 5.0 demo (download at SpectraPLUS - Audio Spectrum Analyzer)
fs=44.1kHz, 1048576 points, Blackman, 24 bit.

What additional info do you need ?

Gary
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Old 10th February 2010, 04:04 PM   #15
Frex is offline Frex  France
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ghg,

What is the rms level of the analyzed signal ?
The spectrum analyzer is it calibrated in real dBv ?
It will be interesting to make measurements with higher sampling rate,
because noise increase.
Do you use weighting filter ?

Can you post more pictures ?


Frex
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Old 23rd February 2010, 04:06 PM   #16
Frex is offline Frex  France
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I have ordered 2 PCB at pcbcart.
I wait them in about 18 days.
of course, i will post a picture as soon it arrived.


Frex
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Old 3rd March 2010, 01:47 AM   #17
grenert is offline grenert  United States
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One concern I have with using ADC designs for testing is that it is too easy to blow up the front end with too much voltage. What do you think about adding a voltage divider and/or diode clamps before the first opamp stage? The DIY oscilloscope mentioned elsewhere here and detailed at:
DPScope - A Low-Cost PC-Based Oscilloscope
uses both.
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Old 3rd March 2010, 03:38 PM   #18
Frex is offline Frex  France
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Hello grenert,

I essentially test audio devices. In my many tests, with my first ADC design using AKM5394, i have never damaged the input stage.
Of course, if you test an audio amplifier outputs, the voltage can be higher than tens volts, and you need to add a divider to fit to the input scale of the ADC.
But i agree, about the need to protect inputs if the device is intended for high voltage measurements.
If your are interested by the ADC, you can easily add your own attenuator (maybe internal..).

The adding resistors ladder network for the input attenuator and a protection diodes at OPAMP inputs, it degrade noise performance and can cause non-linearity and distortion (leakage current).

Frex.

(For the next version of the pcb design, i will add protection diodes which could be solder only if necessary) :-)
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Old 6th March 2010, 12:24 AM   #19
iko is offline iko  Canada
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Nice project Frex, found this just as I was thinking about the same thing. Any updates?
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Old 6th March 2010, 06:24 AM   #20
Frex is offline Frex  France
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As i have already wrote, the PCB was sent to manufacturer, and i wait it for the next week. I will post pictures of the PCB as soon i will receive it.
I must be patient now...
Fortunately, i can work on others audio projects pending.

Frex.

final schematics :AA5381v1sch
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