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Old 16th November 2012, 11:08 AM   #671
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I was thinking about noise and not PSRR per se. The regs you use are relatively noisy, and my question was how much total RMS uV noise they have in a given BW, say 20 - 20kHz. My concern is that a IV converter of your caliber need a super low noise PS.

/S

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Originally Posted by smms73 View Post
To measure power supply rejection ratio one inject a signal in the power rail , then measure the amplitude at the rails and then in output, the psrr is the difference between the two . I have already done that and post the results somewhere in this thread, if I remember it is 80db at 50 Hz .

That buffer that I present is intend to distort , is not to be use in this project. Is for a test that I am preparing, to understand the influence of harmonics in the sound , more of a psychoacoustics test.

Just by looking to the fft graph you can see that the buffer is in class a , class b produce lots of high order harmonics.

If you take a good look to the tagus schematic you will find a suitable buffer .
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Old 16th November 2012, 12:55 PM   #672
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In post #662 I only post the noise of a power supply based on 7915/7815 for comparation i will not use that power supply .
The noise measurements from the power supply that I am going to use are the second and third images , the noise is really very low (I was surprised by such a low noise)
basically is the same as the emu1212m .
Or as you say a super low noise PS.

Edit: I use this type of power supply for a long time but this was the first time I test them. I will post a schematic of it , when I have finish all the alterations that I want to do.
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Old 16th November 2012, 02:42 PM   #673
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by staccatiss View Post
my question was how much total RMS uV noise they have in a given BW, say 20 - 20kHz.
/S
The 0 dbfs of emu1212m is 2 Vrms so looking at the graphic we see the hight noise is at 20Hz is -127 db and that is 950nV rms, at 1Khz is 120nV rms.
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Old 16th November 2012, 03:27 PM   #674
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OK, then it is only to integrate the squares of all voltage levels between 20-20kHz and then take the sqaure root of that integral (sum) to get the total noise 20-20kHz....I thought that the software could do that but maybe Arta cannot.

BTW, the caps are correct across the constant current diodes and the caps are not for stability.


/S

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Originally Posted by smms73 View Post
The 0 dbfs of emu1212m is 2 Vrms so looking at the graphic we see the hight noise is at 20Hz is -127 db and that is 950nV rms, at 1Khz is 120nV rms.
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Old 16th November 2012, 03:37 PM   #675
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Quote:
Originally Posted by smms73 View Post
Yesterday I have been working in the power supply for this circuit.
First is the power supply based on 7915/7815, second is the modifications at the power supply, as you can see the noise and ripple is extremly low, and almost the noise floor of the EMU1212m.

One tip: Use ferrite beads in your power supply, there are some high frequency spikes that only ferrite beads can supress.

first 7915 , second positive w/mod, last negative w/mod.

measurements made in the power rails , with 40ma load.
So, you recommend ferrite beads between the regulator and the circuit to reduce noise? I should try this, thanks. I can see the noise from the 7815/7915 in my power supplies on my scope, but wasn't sure what to do about it.
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Old 16th November 2012, 06:40 PM   #676
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The circuit has rather high(ish) PSU noise suppression, as it's fed by current sources from both rails..and there's an option to add a large(ish) cap between the current rails.
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Old 16th November 2012, 07:35 PM   #677
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I have a good solution for the buffer, i am working on the circuit, and it will have to be tested,
do you guys think that the pcb should have a buffer in it. or the buffer should be in another board so we can try different buffers?
For me personally , i think i will not need the buffer on the pcb.
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Old 16th November 2012, 07:54 PM   #678
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I would like it included, as you can imagine myself and my customers are driving into a low impedance Lightspeed Attenuator. Why not have the board with a jumper bypass option and no buffer components installed for those that don't need it?

Cheers George
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Old 16th November 2012, 10:08 PM   #679
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I would like the buffer on the same pcb but draw in a way that it can be omitted just not soldering the components there (so kind of double output point). Simple enough? If alex_mm will do the pcb should be easy cake for him.
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Old 17th November 2012, 08:16 AM   #680
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Telstar, I will be the one that makes the pcb.
.
This is my contribution to the diy community.
Everyone can make a pcb for personal use. please, just do not sell it.

These last note is not for anyone in particular.
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