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Old 7th December 2012, 05:32 PM   #8001
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That is the challenge or we are back at the Paradise topology, the most simple solution that works so far.
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Old 7th December 2012, 06:17 PM   #8002
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Quote:
Originally Posted by Joachim Gerhard View Post
That is the challenge or we are back at the Paradise topology, the most simple solution that works so far.
True but I don't understand why you are not keeping in consideration the solution I suggested.
That will work for sure and calibrating the impedance of the current source it can have a high precision RIAA using same caps used on Paradise and noise down to 0.55uV/rtHz which I believe is as low as the paradise.
Diffderence on the CCS will deeply impac noise performance and DC and also low frequency response of the gainstage.
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Old 7th December 2012, 06:22 PM   #8003
GaryB is offline GaryB  United States
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Originally Posted by FdW View Post
It will not work for the purpose, due to the small SOA and 150mW maximum dissipation. At 30mA and Vcc 35V the device to be used must be able to dissipate at the least 20 * 30m = 600mW (and that is not even considering any margin/SOA concerns).
Well how about the 5LP01C, which is slightly higher power at 0.25W. It's ZTC is about 22ma, so that a couple of current sources in parallel could provide 45ma. Just run the input FETs a bit harder and you're there. You still need to cascode the 5LP01Cm to limit the voltage across them to stay within the power limit, which starts getting a bit more complicated.
http://www.onsemi.com/pub_link/Collateral/EN6619-D.PDF

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Old 7th December 2012, 06:28 PM   #8004
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Stefano, i thought you will build your version yourself. I just do not like to intrude.
I will work my way up from the downright simple to the more complex if the simple does not work.
" Make everything as simple as possible but not simpler " Albert Einstein
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Old 7th December 2012, 06:40 PM   #8005
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Quote:
Originally Posted by Joachim Gerhard View Post
Stefano, i thought you will build your version yourself. I just do not like to intrude.
I will work my way up from the downright simple to the more complex if the simple does not work.
" Make everything as simple as possible but not simpler " Albert Einstein
yeah the concept is correct.
I was going to do it but I got caught like I said by other things and then I was too tired to do that.
I mean have you tried with the simple cascoded IRF9610 CCS? It might not be as bad as we think and you should be able to get 61dB of gain out of the thing.
If you will try that I will consider sending you on private email the circuit with the values for evaluation and if it works it can be posted as well.
Just let me know.
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Old 7th December 2012, 06:48 PM   #8006
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A little something off record.
Maybe someone has an idea as how to fix it.

Yesterday I was listening to the modified version of the paradise without Elcap and bass response improved noteacebly and due to that I can now hear some very low frequency buzz. Probably on the 25-30 Hz range.
I thought at first it was the air pump broken or something transmitting vibration to the needle.
So I turned it off and nothing changed (I can still track a quite track for noise evaluation).
It sounds like vibration picked up from the motor or soemthing.
Any idea as how to fix it?

Thanks
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Old 7th December 2012, 08:45 PM   #8007
MiiB is offline MiiB  Denmark
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Did you use trans-diodes instead of the caps...?? you know the caps reduce noise primarily in the base.. so what you hear could also be increased noise levels in the base..??

For the new concept.. I believe the temp-co of the CCS is only half the story..
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Old 7th December 2012, 08:49 PM   #8008
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Did you use trans-diodes instead of the caps...?? you know the caps reduce noise primarily in the base.. so what you hear could also be increased noise levels in the base..??

For the new concept.. I believe the temp-co of the CCS is only half the story..
no I didn't use trans-diodes in place of the cap I used the simplest resistor.
The noise I hear disappears if I lifr the pick up from the record so IMHO has nothing to do with the phono.
Increased noise is only a wite distribution with higher density noise.
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Old 7th December 2012, 08:54 PM   #8009
MiiB is offline MiiB  Denmark
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how much gain did you loose with the resistor..??
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Old 7th December 2012, 08:54 PM   #8010
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why would you think thhink that the Temp-Co would be only half of the story?

Regarding Tempco what I think is that cancelling Tempco on the CCS still doesn't completely solve the non zero tempco of the Jfet (unless the If3601 have a temp-co point).
I mean ideally when the CCS pumps a fixed amount of current indipendent from the Temperature, the temperature contribute of the input device should be negligeble.
However I think that in practice even the jfet swill give a wide contribute to the Thermal drifting.

I also noticed that using the opamp solution to compensate for the CCS increases output spectra noise quite a bit.
Basically anything done to the CCS will deeply affect noise performance as well so that will be the culprit for stability noise and gain.
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