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Old 3rd December 2012, 03:35 PM   #7861
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As far as i can see you get too little gain. One reason may be that the output impedance of
this alternative input stage is not high enough and the other is that the RIAA is much lower impedance then the one simulated by Sampler.
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Old 3rd December 2012, 03:56 PM   #7862
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Quote:
Originally Posted by Joachim Gerhard View Post
As far as i can see you get too little gain. One reason may be that the output impedance of
this alternative input stage is not high enough and the other is that the RIAA is much lower impedance then the one simulated by Sampler.
no matte what RIAA I put on it gives pretty much same results.
I personally think that this circuit doesn not work like this, but I am wondering how come sampler was getting 60dB gain with his simulator.
What simulator does he use?
Which result is correct though?

If the voltage drops and everything looks alright I can try to build this but usually I don't like to build something that doesn't even show the minumum functionalities on the simulator though.
Any thought on this?
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Old 3rd December 2012, 04:35 PM   #7863
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I will make more experiments today if i can make an input stage based on the proposed topology that has enough gain.
Two years ago i made a parallel symmetric version of it that worked very well.
I designed a very high output impedance, low noise CCS but i forgot exactly how that was designed. I will try to find it in my files but i may need some hours.
There is a ton of circuits i made the last 5 years.
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Old 3rd December 2012, 04:43 PM   #7864
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Quote:
Originally Posted by Joachim Gerhard View Post
I will make more experiments today if i can make an input stage based on the proposed topology that has enough gain.
Two years ago i made a parallel symmetric version of it that worked very well.
I designed a very high output impedance, low noise CCS but i forgot exactly how that was designed. I will try to find it in my files but i may need some hours.
There is a ton of circuits i made the last 5 years.
why is the current source here a concern?
I mean the cascade current source with LEDs is very low noise and high impedance as well.
My main concerns would be whether the topology works properly or not, in other words, if it puts out the gain is supposed to and is not inverting and has decent noise and distortion performance.
For some strange reason the proposed topology doesn't work on the LTSpice simulator.
Is there any volonteer that wants to check that out as well?
I can share my project file.
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Old 3rd December 2012, 04:45 PM   #7865
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Quote:
Originally Posted by Stefanoo View Post
why is the current source here a concern?
I mean the cascade current source with LEDs is very low noise and high impedance as well.
My main concerns would be whether the topology works properly or not, in other words, if it puts out the gain is supposed to and is not inverting and has decent noise and distortion performance.
For some strange reason the proposed topology doesn't work on the LTSpice simulator.
Is there any volonteer that wants to check that out as well?
I can share my project file.
Like this? Does not work (for now).
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File Type: png CroMagnon.PNG (28.0 KB, 134 views)
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Old 3rd December 2012, 05:04 PM   #7866
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Well, Sampler made it work. How, i do not know. Maybe he comes back on this.
In my book the gain is Gm x RIAA / output impedance of the input stage
I also though to add a folded cascode but then we have the problem that this amount of current ( say we run the folded cascode also on 50mA ) drops too much voltage over the
bass resistor of the RIAA. Say the bass resistor is 100kOhm, then we have 0,05 x 100000 = 5000 V !

Last edited by Joachim Gerhard; 3rd December 2012 at 05:07 PM.
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Old 3rd December 2012, 05:05 PM   #7867
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Like this? Does not work (for now).
yep it is the same model I have and sampler has simulated.
I agree with you that it doesn't work and I would be astounded to see that such a simple circuit boosts 80dB with relatively low distortion, it would be the MOST minimal circuit you can ever think.
I would rave to try such a topology if it was working.

However I still don't understand why Sampler got that result.
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Old 3rd December 2012, 05:06 PM   #7868
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Frans, your circuit does not work because there is only ca. 25mA idle in the input stage and your CCS delivers 50mA. That makes the voltage over the CCS break down.
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Old 3rd December 2012, 05:20 PM   #7869
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Quote:
Originally Posted by Joachim Gerhard View Post
Frans, your circuit does not work because there is only ca. 25mA idle in the input stage and your CCS delivers 50mA. That makes the voltage over the CCS break down.
Good hint.
I got it to work on the basic idea. It is a matter of having the right amount of current droving on the top current source of the cascade.
Here is a screnshot.

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File Type: jpg Sim-2.JPG (97.5 KB, 130 views)
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Old 3rd December 2012, 05:24 PM   #7870
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However on dynamic behaviour, it is pretty odd.

Take a look at this:
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File Type: jpg Sim-3.JPG (79.1 KB, 126 views)
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